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Question 1
Correct
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Free radicals are best defined by which of the following statements.
Your Answer: Atoms or molecules with unpaired electrons
Explanation:Free radicals form when one of weak bond between electrons is broken and an uneven number of electrons remain. This means the electron is unpaired, making it chemically reactive and attempt to steal an electron from a neighbouring molecule to stabilize itself.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 2
Correct
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A 24-year-old athlete drinks a 500 ml hypertonic sports drink before an endurance event he participates in. Which of the following effects will this cause?
Your Answer: The interstitial fluid becomes more concentrated
Explanation:Osmosis is the passive movement of water across a semipermeable membrane from a region of low solute concentration to a region of higher solute concentration. When hypertonic fluid is ingested: The plasma becomes CONCENTRATED. The cells lose water and shrink The intracellular fluid becomes more concentrated. Water and ions move freely from the plasma into the interstitial fluid and the interstitial fluid becomes more concentrated. The increased osmotic potential draws water out of the cells.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 3
Correct
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What are the major motor proteins that interact with microtubules?
Your Answer: Kinesin and dynein
Explanation:The major motor proteins that interact with microtubules are kinesin, which usually moves toward the (+) end of the microtubule, and dynein, which moves toward the (−) end.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 4
Correct
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The movement of molecules across the cell membrane relies greatly on active transport. Which of the following statements about active transport is correct?
Your Answer: Active transport occurs in glucose absorption from the gut
Explanation:The movement of a material against a concentration gradient, i.e. from a low to a high concentration, is known as active transport. Primary active transport is defined as active transport that involves the use of chemical energy, such as adenosine triphosphate (ATP). Secondary active transport occurs when an electrochemical gradient is used. The sodium-potassium pump, calcium ATPase pump, and proton pump are all key active transport systems that use ATP. An electrochemical gradient is used by the sodium-calcium co-transporter, which is an example of secondary active transport. The sodium-dependent hexose transporter SGLUT-1 transports glucose and galactose into enterocytes. Secondary active transport is exemplified here.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 5
Correct
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Which of the following statements is correct regarding the neuronal action potential?
Your Answer: Initial depolarisation occurs as a result of a Na + influx.
Explanation:The resting potential in most neurons has a value of approximately -70 mV. The threshold potential is generally around -55 mV. Initial depolarisation when there is Na+influx through ligand-gated Na+channels. Action potential is an all or nothing response. The size of the action potential is constant and so, the intensity of the stimulus is coded by the frequency of firing of a neuron. K+efflux is responsible for repolarisation.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 6
Correct
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The role of the hemidesmosome is?
Your Answer: Attaches cells to underlying basal lamina
Explanation:Hemidesmosomes connect the basal surface of epithelial cells via intermediate filaments to the underlying basal lamina. The transmembrane proteins of hemidesmosomes are not cadherins, but another type of protein called integrin.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 7
Correct
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A patient presents with a history of excessive thirst, urination and high fluid intake. His blood sugar is normal. You estimate his osmolarity as part of his work-up. Which of these equations can be used to estimate osmolarity?
Your Answer: 2 (Na + ) + 2 (K + ) + Glucose + Urea
Explanation:Osmolality and osmolarity are measurements of the solute concentration of a solution. Although the two terms are often used interchangeably, there are differences in the definitions, how they are calculated and the units of measurement used. Osmolarity, expressed as mmol/L, is an estimation of the osmolar concentration of plasma. It is proportional to the number of particles per litre of solution. Measured Na+, K+, urea and glucose concentrations are used to calculate the value indirectly. It is unreliable in pseudohyponatremia and hyperproteinaemia. The equations used to calculate osmolarity are: Osmolarity = 2 (Na+) + 2 (K+) + Glucose + Urea (all in mmol/L) OR Osmolarity = 2 (Na+) + Glucose + Urea (all in mmol/L) Doubling of sodium accounts for the negative ions associated with sodium, and the exclusion of potassium approximately allows for the incomplete dissociation of sodium chloride.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 8
Correct
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Question 9
Correct
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The processing of NH3 to urea occurs in:
Your Answer: Mitochondria and cytoplasm
Explanation:The urea cycle (also known as the ornithine cycle) is a cycle of biochemical reactions that produces urea ((NH2)2CO) from ammonia (NH3). The urea cycle consists of four enzymatic reactions: one mitochondrial and three cytosolic.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 10
Correct
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Which of the following pathology terms refers to programmed cell death?
Your Answer: Apoptosis
Explanation:Apoptosis is described as programmed cell death. The cell release certain proapoptotic mediators that regulate this cell death.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 11
Correct
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Question 12
Correct
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In the presence of oxygen , lactate that was produced under anaerobic conditions is converted to:
Your Answer: Pyruvate
Explanation:Lactate can be used in two ways:Oxidation back to pyruvate by well-oxygenated muscle cells, heart cells, and brain cells. Pyruvate is then directly used to fuel the Krebs cycle orConversion to glucose via gluconeogenesis in the liver and release back into circulation.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 13
Correct
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Pressure across the wall of a flexible tube (the transmural pressure) increases wall tension and extends it. Which law best describes transmural pressure?
Your Answer: Laplace’s law
Explanation:The transmural pressure (pressure across the wall of a flexible tube) can be described by Laplace’s law which states that: Transmural pressure = (Tw) / r Where: T = Wall tension w = Wall thickness r = The radius A small bubble with the same wall tension as a larger bubble will contain higher pressure and will collapse into the larger bubble if the two meet and join. Fick’s law describes the rate of diffusion in a solution Poiseuille’s law is used to calculate volume of flow rate in laminar flow Darcy’s law describes the flow of a fluid through a porous medium. Starling’s law describes cardiac haemodynamics as it relates to myocyte contractility and stretch.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 14
Correct
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With regard to the cell cycle. In what phase do chromatids get cleaved into chromosomes and pulled apart?
Your Answer: Anaphase
Explanation:Mitosis is the process during which cell division occurs. It is divided into 4 stages:- The first stage is the prophase during which the chromosomes condense, mitotic spindles form and the chromosomes pair which each other. – The second stage is the metaphase during which the chromatids align at the equatorial plane. – The third stage is the anaphase during which the chromatids are separated into 2 daughter chromosomes. – The fourth phase is the telophase during which the chromatids decondense and a new nuclear envelop forms around the each of the daughter chromosomes. Cytokinesis is the process during which the cell cytoplasm divides.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 15
Correct
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Which of the following statements is most suitable to describe necrosis?
Your Answer: Significant inflammatory response
Explanation:Necrosis is the death of most or all of the cells in an organ or tissue due to disease, injury, or failure of the blood supply. Cellular death due to necrosis does not follow the (regulated) apoptotic signal transduction pathway, but rather various receptors are activated, and result in the loss of cell membrane integrity and an uncontrolled release of products of cell death into the extracellular space. This initiates in the surrounding tissue an inflammatory response which attracts leukocytes and nearby phagocytes which eliminate the dead cells by phagocytosis.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 16
Incorrect
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Hydroxyl radicals are broken down by which of the following substance?
Your Answer: Superoxide dismutase
Correct Answer: Antioxidants
Explanation:Unlike superoxide, which can be detoxified by superoxide dismutase, the hydroxyl radical cannot be eliminated by an enzymatic reaction but it is believed can be counteracted by antioxidants.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 17
Correct
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Cyclic AMP activates the following enzyme
Your Answer: Protein Kinase A
Explanation:Cyclic AMP works by activating protein kinase A (PKA, or cAMP-dependent protein kinase). Protein kinase A can also phosphorylate specific proteins that bind to promoter regions of DNA, causing increases in transcription.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 18
Correct
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The interior of lysosomes is kept at a pH of around 5 by the action of:
Your Answer: H+ ATPase
Explanation:The lysosome maintains its pH differential by pumping in protons (H+ ions) from the cytosol across the membrane via proton pumps and chloride ion channels. Vacuolar H+-ATPases are responsible for transport of protons, while the counter transport of chloride ions is performed by ClC-7 Cl−/H+ antiporter.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 19
Correct
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What is the function of secondary messengers?
Your Answer: Communication from extracellular to intracellular signalling pathways
Explanation:First messengers may not physically cross the phospholipid bilayer to initiate changes within the cell directly. This functional limitation necessitates the cell to devise signal transduction mechanisms to transduce first messenger into second messengers, so that the extracellular signal may be propagated intracellularly. Second messengers are intracellular signalling molecules released by the cell to trigger physiological changes such as proliferation, differentiation, migration, survival, and apoptosis. Secondary messengers are therefore one of the initiating components of intracellular signal transduction cascades.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 20
Correct
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What is the function of the pro-apoptotic Bcl-2 family of proteins, Bax and Bak?
Your Answer: Form permissive pores in the mitochondrial membrane
Explanation:The pro-apoptotic proteins in the BCL-2 family, including Bax and Bak, normally act on the mitochondrial membrane to promote permeabilization and release of cytochrome C and ROS, that are important signals in the apoptosis cascade. Growing evidence suggests that activated BAX and/or Bak form an oligomeric pore, MAC in the mitochondrial outer membrane. This results in the release of cytochrome c and other pro-apoptotic factors from the mitochondria, often referred to as mitochondrial outer membrane permeabilization, leading to activation of caspases.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 21
Correct
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Which of the following prolongs Prothrombin time?
Your Answer: Factor V deficiency
Explanation:Prothrombin time is increased in:- Factor V deficiency- Vitamin K deficiency (which affects factors 2,7 and 10)- Warfarin therapy- Severe liver failureProtein C is an anticoagulant and deficiency results in a hyper-coagulable state with tendency towards thrombosis.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 22
Correct
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You see a patient on the ward who is acutely short of breath and perform an ABG. The results are as follows
Your Answer: Respiratory Acidosis
Explanation:This patient has acidosis as the pH is low <7.35 The pO2 is irrelevant. The pCO2 is raised i.e. the respiratory system is causing acidosis. The patient is acidotic so this is a respiratory acidosis The Base Excess is normal. You would typically expect the base excess to rise but metabolic compensation is slower than respiratory compensation so this picture may be seen acutely.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 23
Correct
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Regarding oxidative deamination of amino acids, which of the following is true?
Your Answer: Occurs in the kidney & liver
Explanation:Oxidative deamination is a form of deamination that generates α-keto acids and other oxidized products from amine-containing compounds, and occurs largely in the liver and kidney. Oxidative deamination is an important step in the catabolism of amino acids, generating a more metabolizable form of the amino acid, and also generating ammonia as a toxic by-product. The addition of ubiquitin to a substrate protein is called ubiquitination.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 24
Correct
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What is the function of gap junctions?
Your Answer: Diffusion of small molecules between neighbouring cells
Explanation:Gap junctions are a specialized intercellular connection between a multitude of cell-types. They directly connect the cytoplasm of two cells, which allows various molecules, ions and electrical impulses to directly pass through a regulated gate between cells.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 25
Correct
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The formation of superoxide is catalysed by which enzyme?
Your Answer: NADPH oxidase
Explanation:Superoxide is biologically toxic and is deployed by the immune system to kill invading microorganisms. In phagocytes, superoxide is produced in large quantities by the enzyme NADPH oxidase for use in oxygen-dependent killing mechanisms of invading pathogens.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 26
Incorrect
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The flow of ions across a cell membrane causes electrical activity in biological tissues. Excitable tissues are specialized tissues that may generate a significant electrical signal called an action potential, which is followed by a refractory period. Which set of ion channels is responsible for the refractory period?
Your Answer: Non-selective cation channels
Correct Answer: Sodium channels
Explanation:A refractory period follows each action potential. The absolute refractory time and the relative refractory period are two divisions of refractory periods. Because the sodium channels seal after an AP, they enter an inactive state during which they cannot be reopened regardless of membrane potential, this time occurs. The sodium channels slowly come out of inactivation during the relative refractory period that follows. During this time, a stronger stimulus than that required to initiate an action potential can excite the cell. The strength of the stimulus required early in the relative refractory period is relatively high, and it steadily decreases as more sodium channels recover from the inactivation of the refractory period. Nodes of Ranvier are periodic holes in a myelinate axon when there is no myelin and the axonal membrane is exposed. There are no gated ion channels in the portion of the axon covered by the myelin sheath, but there is a high density of ion channels in the Nodes of Ranvier. Action potentials can only occur at the nodes as a result of this.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 27
Incorrect
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Which caspase is part of both the intrinsic and extrinsic apoptotic pathways?
Your Answer: Caspase-4
Correct Answer: Caspase-3
Explanation:Once initiator caspases are activated in both the intrinsic and extrinsic pathway, they produce a chain reaction, activating several other executioner caspases (Caspase 3, Caspase 6 and Caspase 7).
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 28
Incorrect
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You examine a patient's blood tests and discover that her electrolyte levels are abnormal. Which of the following is the major extracellular cation?
Your Answer: Chloride
Correct Answer: Sodium
Explanation:Electrolytes are compounds that may conduct an electrical current and dissociate in solution. Extracellular and intracellular fluids contain these chemicals. The predominant cation in extracellular fluid is sodium, whereas the major anion is chloride. Potassium is the most abundant cation in the intracellular fluid, while phosphate is the most abundant anion. These electrolytes are necessary for homeostasis to be maintained.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 29
Incorrect
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A 34-year-old woman was diagnosed with multiple sclerosis two years ago. Her symptoms have been steadily deteriorating, with no intervals of remission in sight. Which of the following aspects of nerve conduction is disrupted by multiple sclerosis?
Your Answer: The refractory period
Correct Answer: Saltatory conduction
Explanation:Local currents propagate action potentials down the axons of neurons. This local current flow following depolarisation results in the depolarisation of the neighbouring axonal membrane, and when this region approaches the threshold, more action potentials are generated and so forth. Due to the refractory period, portions of the membrane that have recently depolarized will not depolarize again, resulting in the action potential only being able to go in one direction. The square root of axonal diameter determines the velocity of the action potential; the axons with the biggest diameter have the quickest conduction velocities. When a neuron is myelinated, the speed of the action potential rises as well. The myelin sheath is an insulating coating that surrounds certain neural axons. By increasing membrane resistance and decreasing membrane capacitance, the myelin sheath improves conduction. This enables faster electrical signal transmission via a neuron, making them more energy-efficient than non-myelinated neuronal axons. Electrical impulses are quickly transmitted from one node to the next, causing depolarization of the membrane above the threshold and triggering another action potential, which is then transmitted to the next node. An action potential is rapidly conducted down a neuron in this manner. Saltatory conduction is the term for this. Multiple sclerosis is an example of a clinical disorder in which the myelin sheath is affected. It is an immune-mediated disorder in which certain nerve cells in the brain and spinal cord become demyelinated. The ability of some areas of the nervous system to properly transmit action potentials is disrupted by demyelination, resulting in a variety of neurological symptoms and indications.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 30
Incorrect
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Which one of the following is able to move across cell membranes by passive diffusion?
Your Answer: K+
Correct Answer: CO2
Explanation:The cell membrane is permeable to water molecules and a few other small, uncharged, molecules like oxygen (O2) and carbon dioxide (CO2). Larger molecules like glucose or charged ions are unable to cross passively.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 31
Incorrect
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With regard to cell membrane proteins:
Your Answer: All tend to traverse the whole membrane
Correct Answer: Carriers are involved in facilitated diffusion
Explanation:Pumps use a source of free energy such as ATP to transport ions against a gradient and is an example of active transport. Unlike channel proteins which only transport substances through membranes passively, carrier proteins can transport ions and molecules either passively through facilitated diffusion, or via secondary active transport. Channels are either in open state or closed state. When a channel is opened, it is open to both extracellular and intracellular. Pores are continuously open to both environments, because they do not undergo conformational changes. They are always open and active.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 32
Correct
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With regard to the cell membrane:
Your Answer: It consists of an outer hydrophilic & an inner hydrophobic layer
Explanation:The cell membrane consists primarily of a thin layer of amphipathic phospholipids that spontaneously arrange with the hydrophobic tail regions on the inside and the hydrophilic head regions outside. Membranes typically have a large content of proteins, around 50% of membrane volume.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 33
Incorrect
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Selectins
Your Answer: Allow the passage of solute between 2 adjacent cells
Correct Answer: Interact with carbohydrate ligands or mucin complexes on leucocytes and endothelial cells
Explanation:Selectins are involved in constitutive lymphocyte homing, and in chronic and acute inflammation processes, including post-ischemic inflammation. Each selectin has a carbohydrate recognition domain that mediates binding to specific glycans on apposing cells.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 34
Incorrect
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Cyclic AMP is formed from ATP via which enzyme
Your Answer: Protein Kinase A
Correct Answer: Adenylate cyclase
Explanation:Cyclic AMP is synthesized from ATP by adenylate cyclase located on the inner side of the plasma membrane and anchored at various locations in the interior of the cell.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 35
Incorrect
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Cellular Theory of Ageing
Your Answer: Loss of telomeres
Correct Answer: Gene regulation
Explanation:Cellular theories of aging propose that human aging is the result of cellular aging, whereby an increasing proportion of cells reach senescence, a terminal stage at which cells will cease to divide. This will limit the body’s ability to regenerate and to respond to injury or stress.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 36
Incorrect
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You've been asked to give a discussion to a group of medical students about skeletal muscle physiology and its use in clinical medicine. They pose a series of difficult questions to you. Which of the following definitions for the A-band of the sarcomere is correct?
Your Answer: The segment between two neighbouring Z-lines
Correct Answer: A band that contains the entire length of a single thick filament (myosin)
Explanation:Myofibrils, which are around 1 m in diameter, make up each myofiber. The cytoplasm separates them and arranges them in a parallel pattern along the cell’s long axis. These myofibrils are made up of actin and myosin filaments that are repeated in sarcomeres, which are the myofiber’s basic functional units. Myofilaments are the filaments that make up myofibrils, and they’re made mostly of proteins. Myofilaments are divided into three categories: Myosin filaments are thick filaments made up mostly of the protein myosin. Actin filaments are thin filaments made up mostly of the protein actin. Elastic filaments are mostly made up of the protein titin. The sarcomere is a Z-line segment that connects two adjacent Z-lines. The I-bands are thin filament zones that run from either side of the Z-lines to the thick filament’s beginning. Between the I-bands is the A-band, which spans the length of a single thick filament. The H-zone is a zone of thick filaments that is not overlaid by thin filaments in the sarcomere’s centre. The H-zone keeps the myosin filaments in place by surrounding them with six actin filaments each. The M-band (or M-line) is a disc of cross-connecting cytoskeleton elements in the centre of the H-zone. The thick filament is primarily made up of myosin. The thin filament is primarily made up of actin. Actin, tropomyosin, and troponin are found in a 7:1:1 ratio in thin filaments.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 37
Correct
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With regards to the cell cycle, which phase represents period of cell growth that divides the end of DNA synthesis and the beginning of somatic cell division?
Your Answer: Gap 2
Explanation:Interphase is divided into three phases: G1 (first gap), S (synthesis), and G2 (second gap). During all three parts of interphase, the cell grows by producing proteins and cytoplasmic organelles. However, chromosomes are replicated only during the S phase. Thus, a cell grows (G1), continues to grow as it duplicates its chromosomes (S), grows more and prepares for mitosis (G2), and finally divides (M) before restarting the cycle.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 38
Incorrect
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Question 39
Incorrect
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The complete oxidation of 1 molecule of glucose to CO2 and H20 produces a total of __ATP.
Your Answer: 16
Correct Answer: 38
Explanation:Textbooks often state that 38 ATP molecules can be made per oxidised glucose molecule during cellular respiration (2 from glycolysis, 2 from the Krebs cycle, and about 34 from the electron transport system). However, this maximum yield is never quite reached because of losses due to leaky membranes as well as the cost of moving pyruvate and ADP into the mitochondrial matrix, and current estimates range around 29 to 30 ATP per glucose.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 40
Incorrect
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Which of the following organelles form lysosomes?
Your Answer: The nucleus
Correct Answer: The Golgi apparatus
Explanation:Lysosomes are formed by the Golgi apparatus or the endoplasmic reticulum. Lysosome releases its enzymes and digests the cell when the cell dies.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 41
Incorrect
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Microtubule disassembly:
Your Answer: Does not occur simultaneously with microtubule assembly.
Correct Answer: Occurs at the positive and negative end
Explanation:Dynamic instability refers to the coexistence of assembly and disassembly at the ends of a microtubule. The microtubule can dynamically switch between growing and shrinking phases in this region. Although both assembly and disassembly occur at both ends they occur preferentially at the (+) end.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 42
Incorrect
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Question 43
Correct
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Which of these structures is the smallest and deepest component of muscle connective tissue?
Your Answer: Endomysium
Explanation:There are three types of muscle: Skeletal muscle Cardiac muscle Smooth muscle Individual muscle is enveloped in a layer of dense irregular connective tissue called the epimysium. The epimysium protects the muscles from friction against bones and other muscles. Skeletal muscle is composed of muscle fibres, referred to as myofibers which is ensheathed by a wispy layer of areolar connective tissue called the endomysium. The endomysium is the smallest and deepest component of muscle connective tissue. Myofibers grouped together in bundles form fascicles, or fasciculi. These are surrounded by a type of connective tissue called the perimysium. Beneath the endomysium lies the sarcolemma, an elastic sheath with infoldings that invaginate the interior of the myofibers, particularly at the motor endplate of the neuromuscular junction.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 44
Incorrect
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The fluid in contact with a tube is dragged by frictional forces to the tube's sidewalls. This creates a velocity gradient in which the fluid flow is greatest in the tube's centre. Which of the following terms most accurately characterizes this flow pattern?
Your Answer: Turbulent flow
Correct Answer: Laminar flow
Explanation:The fluid in contact with a tube is dragged by frictional forces at the tube’s sidewalls. This creates a velocity gradient in which the fluid flow is greatest in the tube’s centre. This is known as laminar flow, and it characterizes the flow in most circulatory and respiratory systems when they are at rest. The velocity of the fluid flow can fluctuate erratically at high velocities, particularly within big arteries and airways, disrupting laminar flow. As a result, resistance increases significantly. This is known as turbulent flow, and symptoms include heart murmurs and asthmatic wheeze.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 45
Incorrect
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Inhibition of cell division at the end of G1 occurs through:
Your Answer: p54
Correct Answer: Unphosphorolated retinoblastoma protein (uRb)
Explanation:A cell’s decision to enter, or re-enter, the cell cycle is made before S-phase in G1 at what is known as the restriction point, and is determined by the combination of promotional and inhibitory extracellular signals that are received and processed. Ultimately unphosphorylated Rb acts as an inhibitor of G1.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 46
Incorrect
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In the body what are fatty acids broken down to?
Your Answer: Galactose
Correct Answer: Acetyl Co A
Explanation:Fatty acids are broken down into acetyl Co A. The acetyl-CoA produced by beta oxidation enters the citric acid cycle in the mitochondrion by combining with oxaloacetate to form citrate.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 47
Incorrect
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Which of the following statements is correct regarding flow through the cardiovascular system?
Your Answer: If the vessel diameter is suddenly reduced, flow rate will increase.
Correct Answer: Turbulent blood flow may be caused by increased cardiac output.
Explanation:Frictional forces at the sides of a vessel cause a drag force on the fluid touching them in laminar blood flow, which creates a velocity gradient where the flow is greatest at the centre. Laminar blood flow may become disrupted and flow may become turbulent at high velocities, especially in large arteries or where the velocity increases sharply at points of sudden narrowing in the vessels, or across valves. There is increased tendency for thrombi formation when there is turbulent blood flow. Clinically, turbulence may be heard as a murmur or a bruit. As a result of elevated cardiac output, there may be turbulent blood flow, even when the cardiac valves are anatomically normal, and as a result, a physiological murmur can be heard. One such example is pregnancy.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 48
Incorrect
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What will the destruction of endoplasmic reticulum stop?
Your Answer: Synthesis of lipids
Correct Answer: Synthesis of proteins
Explanation:The rough endoplasmic reticulum is the factory for the manufacturing of proteins. It contains ribosomes attached to it and transports proteins that are destined for membranes and secretions. The rough ER is connected to the nuclear envelope and to the cisternae of the Golgi apparatus by vesicles that shuttle between the two compartments.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 49
Incorrect
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The myocardium is responsible for creating the force with which the atrial and ventricular muscles contract. It is made up of myocytes, which are heart muscle cells. Which of the following statements about cardiac muscle anatomy is correct?
Your Answer: The nucleus is peripherally located within the myocyte
Correct Answer: Cardiac myocytes have intercalated discs
Explanation:Typically, granuloma has Langerhan’s cells (large multinucleated cells ) surrounded by epithelioid cell aggregates, T lymphocytes and fibroblasts. Antigen presenting monocytic cells found in the skin are known as Langerhan’s cells.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 50
Incorrect
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In blistering dermatological disorders e.g.. Pemphigus, which junctions are attacked by autoantibodies?
Your Answer: Zonula adherens
Correct Answer: Desmosomes
Explanation:Pemphigus is an autoimmune disease caused by antibodies directed against both desmoglein 1 and desmoglein 3 present in desmosomes. Loss of desmosomes results in loss of cohesion between keratinocytes in the epidermis, and a disruption of the barrier function served by intact skin. The process is classified as a type II hypersensitivity reaction
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 51
Correct
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How does an action potential in the motor end plate rapidly spread to the central portions of the muscle cells?
Your Answer: Transverse tubules
Explanation:When the concentration of intracellular Ca2+rises, muscle contraction occurs. The pathway of an action potential is down tube-shaped invaginations of the sarcolemma called T-tubules (transverse tubules). These penetrate throughout the muscle fibre and lie adjacent to the terminal cisternae of the sarcoplasmic reticulum. The voltage changes in the T-tubules result in the opening of sarcoplasmic reticulum Ca2+channels and there is there is release of stored Ca2+into the sarcoplasm. Thus muscle contraction occurs via excitation-contraction coupling (ECC) mechanism.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 52
Correct
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Cardiac myocytes contract by excitation-contraction coupling, very much like skeletal myocytes. On the other hand, calcium-induced calcium release (CICR) is a mechanism that is unique to Cardiac myocytes. The influx of calcium ions (Ca 2+) into the cell causes a 'calcium spark,' which causes more ions to be released into the cytoplasm. In CICR, which membrane protein in the sarcoplasmic reticulum is involved?
Your Answer: Ryanodine receptor
Explanation:Cardiac myocytes contract by excitation-contraction coupling, just like skeletal myocytes. Heart myocytes, on the other hand, utilise a calcium-induced calcium release mechanism that is unique to cardiac muscle (CICR). The influx of calcium ions (Ca2+) into the cell causes a ‘calcium spark,’ which causes more ions to be released into the cytoplasm. An influx of sodium ions induces an initial depolarisation, much as it does in skeletal muscle; however, in cardiac muscle, the inflow of Ca2+ sustains the depolarisation, allowing it to remain longer. Due to potassium ion (K+) inflow, CICR causes a plateau phase in which the cells remain depolarized for a short time before repolarizing. Skeletal muscle, on the other hand, repolarizes almost instantly. The release of Ca2+ from the sarcoplasmic reticulum is required for calcium-induced calcium release (CICR). This is mostly accomplished by ryanodine receptors (RyR) on the sarcoplasmic reticulum membrane; Ca2+ binds to RyR, causing additional Ca2+ to be released.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 53
Incorrect
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The free radical most abundantly formed by the immune system is:
Your Answer: Myeloperoxidase
Correct Answer: Hydroxyl radical
Explanation:Neutrophil and macrophage phagocytosis stimulates various cellular processes including the respiratory burst whereby increased cellular oxygen uptake results in the production of the potent oxidant bactericidal agents, hypochlorous acid and hydroxyl radical.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 54
Incorrect
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Which of the following statements is correct regarding homeostasis?
Your Answer: Negative feedback mechanisms are seen in the release of oxytocin in childbirth.
Correct Answer: In negative feedback mechanisms, effectors always act to move the variable in the opposite direction to the change that was originally detected.
Explanation:The vast majority of systems within the body work by negative feedback mechanisms. This negative feedback refers to the way that effectors act to move the variable in the opposite direction to the change that was originally detected. Because there is an inherent time delay between detecting a change in a variable and effecting a response, the negative feedback mechanisms cause oscillations in the variable they control. There is a narrow range of values within which a normal physiological function occurs and this is called the ‘set point’. The release of oxytocin in childbirth is an example of positive feedback.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 55
Incorrect
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Which ONE statement about homeostasis is true?
Your Answer: The two body systems that regulate homeostasis are the cardiovascular and endocrine systems
Correct Answer: Negative feedback occurs via receptors, comparators and effectors
Explanation:Homeostasis is the property of a system in which variables are regulated so that internal conditions remain relatively constant and stable. Homeostasis is achieved by a negative feedback mechanism. Negative feedback occurs based upon a set point through receptors, comparators and effectors. The ‘set point’ is a NARROW range of values within which normal function occurs. The two body systems that regulate homeostasis are the Nervous system and the Endocrine system. The smooth muscle of the uterus becomes more active towards the end of pregnancy. This is a POSITIVE feedback.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 56
Incorrect
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Mitosis is the process of cell division which culminates in cell chromosomes which are:
Your Answer: Tetraploid
Correct Answer: Diploid
Explanation:Mitosis is a part of the cell cycle when replicated chromosomes are separated into two new diploid nuclei.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 57
Incorrect
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From which of the following cell types are platelets derived?
Your Answer: Promyelocytes
Correct Answer: Megakaryocytes
Explanation:Synthesis of platelets occurs in the bone marrow by fragmentation of megakaryocytes cytoplasm, derived from the common myeloid progenitor cell. The average time for differentiation of the human stem cell to the production of platelets is about 10 days. The major regulator of platelet formation is thrombopoietin and 95% of this is produced by the liver. Normal platelet count is 150 – 450 x 109/L and the normal lifespan of a platelet is about 10 days. Usually about one-third of the marrow output of platelets may be trapped at any one time in the normal spleen.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 58
Incorrect
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What is the primary function of the mitochondria?
Your Answer: The transcription of ribosomal RNA
Correct Answer: The production of the cell's supply of chemical energy
Explanation:The mitochondria is responsible for the production of the cell’s supply of chemical energy. It does this by using molecular oxygen, sugar and small fatty acid molecules to generate adenosine triphosphate (ATP) by a process ss known as oxidative phosphorylation. An enzyme called ATP synthase is required. Transcription of ribosomal RNA occurs in the nucleolus Production of messenger RNA occur in the nucleus Production of lysosome occurs in the Golgi apparatus The post-translational processing of newly made proteins occurs in the endoplasmic reticulum
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 59
Incorrect
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With regard to the cell cycle. In which part of the cycle does DNA replication occur?
Your Answer: Cytokinesis
Correct Answer: Interphase
Explanation:DNA replication occurs during S phase but that isn’t one of the options. Remember Interphase comprises G1,S and G2 phases!
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 60
Incorrect
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In which organelle is the intrinsic apoptotic pathway initiated?
Your Answer: Nucleus
Correct Answer: Mitochondria
Explanation:Apoptosis is a programmed form of cell death involving the degradation of cellular constituents by a group of cysteine proteases called caspases. The caspases can be activated through either the intrinsic (mitochondrial mediated) or extrinsic (death receptor mediated) apoptotic pathways. The intrinsic apoptotic pathway is characterized by permeabilization of the mitochondria and release of cytochrome c into the cytoplasm.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 61
Incorrect
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Which is true of the citric acid cycle?
Your Answer: Acetyl-CoA is the only entry point
Correct Answer: Involves a series of reactions where oxaloacetate is regenerated
Explanation:The cycle consumes acetate (in the form of acetyl-CoA) and water, reduces NAD+ to NADH, and produces carbon dioxide as a waste by-product. The NADH generated by the citric acid cycle is fed into the oxidative phosphorylation (electron transport) pathway. At the end of each cycle, the four-carbon oxaloacetate has been regenerated, and the cycle continues. The net result of these two closely linked pathways is the oxidation of nutrients to produce usable chemical energy in the form of ATP. Acetyl-CoA, is the starting point for the citric acid cycle and in eukaryotic cells, the citric acid cycle occurs in the matrix of the mitochondrion. Though the Krebs cycle does not directly require oxygen, it can only take place when oxygen is present because it relies on by-products and is therefore an aerobic process.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 62
Incorrect
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On review of a patient's serum and urine osmolality test result, you note that both osmolarities are decreased. There urine osmolality does not increase with fluid ingestion. What is the most likely cause?
Your Answer: Syndrome of inappropriate antidiuresis
Correct Answer: Hyponatraemia
Explanation:As part of the investigation of hyponatraemia, serum osmolality is commonly requested in combination with urine osmolality to aid diagnosis. When: Serum osmolality is decreased and urine osmolality is decreased with no intake of fluid, the causes are Hyponatraemia Overhydration Adrenocortical insufficiency Sodium loss (diuretic or a low-salt diet) Serum osmolality is normal or increased and urine osmolality is increased the causes include: Dehydration Hyperkalaemia Hyperglycaemia Hyponatremia Mannitol therapy Diabetes mellitus Alcohol ingestion Congestive heart failure Renal disease and uraemia Serum osmolality is normal or increased and urine osmolality is decreased the usual cause is diabetes insipidus Serum osmolality is decreased and urine osmolality is increased the usual cause is syndrome of inappropriate antidiuresis (SIAD)
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 63
Incorrect
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Which statement regarding skeletal muscle is true?
Your Answer: Actin is the major constituent of the thick filament
Correct Answer: Myosin is the major constituent of the thick filament
Explanation:Myosin is the major constituent of the thick filament. Actin is the major constituent of the THIN filament. Thin filaments consist of actin, tropomyosin and troponin in the ratio 7:1:1.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 64
Incorrect
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Cardiac muscle and skeletal muscle are alike, but there are a few key variations. Which of the following is NOT a characteristic of skeletal muscle but is a characteristic of cardiac muscle?
Your Answer: Contraction by excitation-contraction coupling
Correct Answer: The presence of intercalated discs
Explanation:Cardiac muscle is striated, and the sarcomere is the contractile unit, similar to skeletal muscle. Contracture is mediated by the interaction of calcium, troponins, and myofilaments, much as it occurs in skeletal muscle. Cardiac muscle, on the other hand, differs from skeletal muscle in a number of ways. In contrast to skeletal muscle cells, cardiac myocytes have a nucleus in the middle of the cell and sometimes two nuclei. The cells are striated because the thick and thin filaments are arranged in an orderly fashion, although the arrangement is less well-organized than in skeletal muscle. Intercalated discs, which work similarly to the Z band in skeletal muscle in defining where one cardiac muscle cell joins the next, are a very significant component of cardiac muscle. Adherens junctions and desmosomes, which are specialized structures that hold the cardiac myocytes together, are formed by the transverse sections. The lateral sections produce gap junctions, which join the cytoplasm of two cells directly, allowing for rapid action potential conduction. These critical properties allow the heart to contract in a coordinated manner, allowing for more efficient blood pumping. Cardiac myocytes have the ability to create their own action potentials, which is referred to as myogenic’. They can depolarize spontaneously to initiate a cardiac action potential. Pacemaker cells, as well as the sino-atrial (SA) and atrioventricular (AV) nodes, control this. The Purkinje cells and the cells of the bundle of His are likewise capable of spontaneous depolarization. While the bundle of His is made up of specialized myocytes, it’s vital to remember that Purkinje cells are not myocytes and have distinct characteristics. They are larger than myocytes, with fewer filaments and more gap junctions than myocytes. They conduct action potentials more quickly, allowing the ventricles to contract synchronously. Cardiac myocytes contract by excitation-contraction coupling, just like skeletal myocytes. Heart myocytes, on the other hand, utilise a calcium-induced calcium release mechanism that is unique to cardiac muscle (CICR). The influx of calcium ions (Ca2+) into the cell causes a ‘calcium spark,’ which causes more ions to be released into the cytoplasm. An influx of sodium ions induces an initial depolarisation, much as it does in skeletal muscle; however, in cardiac muscle, the inflow of Ca2+ sustains the depolarisation, allowing it to remain longer. Due to potassium ion (K+) inflow, CICR causes a plateau phase in which the cells remain depolarized for a short time before repolarizing. Skeletal muscle, on the other hand, repolarizes almost instantly. Comparison of skeletal and cardiac muscle: Skeletal muscle Cardiac muscle Striation Striated but arrangement less organised Multiple nuclei located peripherally Usually single nucleus (but can be two), located centrally Discs None Intercalated discs No Gap junctions Gap junctions No Pacemaker Pacemaker Electrical stimulation: Nervous system (excitation) Pacemaker (excitation)
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 65
Incorrect
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Which ion channel is a dimer?
Your Answer: Na+ channel
Correct Answer: Cl- channel
Explanation:A dimer is a chemical structure formed from two similar sub-units. Chloride channels or exchangers are composed of two similar subunits—a dimer—each subunit containing one pore.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 66
Incorrect
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Changes in cadherin expression are associated with
Your Answer: Activation of apoptosis in the cell.
Correct Answer: Tumour metastatic potential
Explanation:Cadherins play a role in maintaining cell and tissue structure, and in cellular movement. The E-cadherin–catenin complex plays a key role in cellular adhesion; loss of this function has been associated with greater tumour metastasis.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 67
Incorrect
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With regards to the Na+/K+ ATPase, which one of the following is correct?
Your Answer: 2 Na+ released into the extracellular fluid
Correct Answer: 3 Na+ released into the extracellular fluid
Explanation:Na+/K+ pump or sodium–potassium pump is an enzyme found in the plasma membrane. This pumping is active (i.e. it uses energy from ATP) and is important for cell physiology. Its simple function is to pump 3 sodium ions out for every 2 potassium ions taken in and since they both have equal ionic charges, this creates a electrochemical gradient between a cell and its exterior.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 68
Incorrect
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The breakdown of superoxide is catalysed by which enzyme?
Your Answer: Oxide reductase
Correct Answer: Superoxide dismutase
Explanation:As superoxide is toxic, nearly all organisms living in the presence of oxygen contain isoforms of the superoxide-scavenging enzyme superoxide dismutase, or SOD. SOD is an extremely efficient enzyme; it catalyses the neutralization of superoxide nearly as quickly as the two can diffuse together spontaneously in solution.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 69
Incorrect
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Regarding integrins, which option is false?:
Your Answer: Can bind to ligands and stimulate secondary signals resulting in endocytosis, proliferation and apoptosis
Correct Answer: Play no role in cell signalling.
Explanation:Integrins are transmembrane receptors that facilitate cell-extracellular matrix (ECM) adhesion. Upon ligand binding, integrins activate signal transduction pathways that mediate cellular signals such as regulation of the cell cycle, organization of the intracellular cytoskeleton, and movement of new receptors to the cell membrane. Integrins are obligate heterodimers, meaning that they have two subunits: α (alpha) and β (beta). Integrins play an important role in cell signalling by modulating the cell signalling pathways of transmembrane protein kinases such as receptor tyrosine kinases (RTK).
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 70
Incorrect
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The function of the Golgi apparatus is
Your Answer: Control of the process of apoptosis
Correct Answer: Maturation of peptides secreted by the rER into functional proteins by glycosylation
Explanation:Steroidogenesis is a multi-step process that occurs in two organelles, the endoplasmic reticulum (ER) and the mitochondrion. The Golgi apparatus is a major collection and dispatch station of protein products received from the endoplasmic reticulum (ER). Proteins synthesized in the ER are packaged into vesicles, which then fuse with the Golgi apparatus. The majority of proteins synthesized in the rough ER undergo glycosylation which occurs in the Golgi apparatus. Glycosylation mainly refers in particular to the enzymatic process that attaches glycans to proteins, lipids, or other organic molecules. These cargo proteins are modified and destined for secretion via exocytosis or for use in the cell. The Golgi apparatus is also involved in lipid transport and lysosome formation.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 71
Correct
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Question 72
Correct
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With regards to the function of the p53 protein produced by the p53 gene, which of the following statements is incorrect?
Your Answer: It permits repair of mutations and other defects in RNA
Explanation:P53 has many mechanisms of anticancer function and plays a role in apoptosis, genomic stability, and inhibition of angiogenesis. In its anti-cancer role, p53 works through several mechanisms:It can activate DNA repair proteins when DNA has sustained damage. Thus, it may be an important factor in aging.It can arrest growth by holding the cell cycle at the G1/S regulation point on DNA damage recognitionIt can initiate apoptosis (i.e., programmed cell death) if DNA damage proves to be irreparable.It is essential for the senescence response to short telomeres.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 73
Correct
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Which of the following statements is not true regarding ion channels?
Your Answer: Ion channels provide a charged, hydrophobic pore through which ions can diffuse across the lipid bilayer.
Explanation:Ion channels are pore-forming protein complexes that facilitate the flow of ions across the hydrophobic core of cell membranes. They are present in the plasma membrane and membranes of intracellular organelles of all cells, and perform essential physiological functions. They provide a charged, hydrophilic pore through which ions can move across the lipid bilayer. They are selective for particular ions and their pores may be opened or closed. Because of this ability to open and close, ion channels allow the cell to have the ability to closely control the movement of ions across the membrane. Gating refers to the transition between an open and closed ion channel state, and is brought about by a conformationational change in the protein subunits that open or close the ion-permeable pore. Ion channels can be: 1. voltage-gated these are regulated according to the potential difference across the cell membrane or 2. ligand-gated – these are regulated by the presence of a specific signal molecule.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 74
Correct
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The cell membrane:
Your Answer: Is a bilayer of amphipathic lipids
Explanation:The cell membrane consists of a bilayer of amphipathic lipids with embedded proteins. The basic function of the cell membrane is to protect the cell from its surroundings. It is selectively permeable to ions and organic molecules. The entire membrane is held together via non-covalent interaction of hydrophobic tails, however the structure is quite fluid and not fixed rigidly in place. Membranes are typically 7.5–10 nm in thickness and typically have a large content of proteins, around 50% of membrane volume.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 75
Incorrect
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What type of pump is the Na+/K+ATPase pump?
Your Answer: A uniporter
Correct Answer: An antiporter
Explanation:In order for primary active transport to pump ions against their electrochemical gradient, chemical energy is used in the form of ATP. This is facilitated by the Na+/K+-ATPase antiporter pump, which uses metabolic energy to move 3 Na+ions out of the cell for every 2 K+ions that come in, against their respective electrochemical gradients. As a result, the cell the maintains a high intracellular concentration of K+ions and a low concentration of Na+ions.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 76
Incorrect
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The action potential is generated by excitable tissues, which are specialized tissues that can generate a meaningful electrical signal. Local currents transport action potentials down the axons of neurons. Which of the following claims about the action potential's conduction is correct?
Your Answer: Axons with the largest diameter have the slowest conduction velocities
Correct Answer: The areas of the membrane that have recently depolarised will not depolarise again due to the refractory period
Explanation:Local currents propagate action potentials down the axons of neurons. Following depolarization, this local current flow depolarizes the next axonal membrane, and when this region crosses the threshold, more action potentials are formed, and so on. Due to the refractory period, portions of the membrane that have recently depolarized will not depolarize again, resulting in the action potential only being able to go in one direction. The square root of axonal diameter determines the velocity of the action potential; the axons with the biggest diameter have the quickest conduction velocities. When a neuron is myelinated, the speed of the action potential rises as well. The myelin sheath is an insulating coating that surrounds certain neural axons. By increasing membrane resistance and decreasing membrane capacitance, the myelin coating increases conduction. This enables faster electrical signal transmission via a neuron, making them more energy-efficient than non-myelinated neuronal axons. Nodes of Ranvier are periodic holes in a myelinate axon when there is no myelin and the axonal membrane is exposed. There are no gated ion channels in the portion of the axon covered by the myelin sheath, but there is a high density of ion channels in the Nodes of Ranvier. Action potentials can only arise at the nodes as a result of this. Electrical impulses are quickly transmitted from one node to the next, causing depolarization of the membrane above the threshold and triggering another action potential, which is then transmitted to the next node. An action potential is rapidly conducted down a neuron in this manner. Saltatory conduction is the term for this.
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 77
Incorrect
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Which law describes the rate of diffusion in a solution?
Your Answer: Starling’s law
Correct Answer: Fick’s law
Explanation:Fick’s law describes the rate of diffusion in a solution. Fick’s law states that: Jx = -D A (ΔC / Δx) Where: Jx = The amount of substance transferred per unit time D = Diffusion coefficient of that particular substance A = Surface area over which diffusion occurs ΔC = Concentration difference across the membrane Δx = Distance over which diffusion occurs The negative sign reflects movement down the concentration gradient
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 78
Incorrect
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Cell membrane proteins may act as:
Your Answer: Ionic channels
Correct Answer: All of the options
Explanation:Membrane proteins perform a variety of functions including:Membrane receptor proteins relay or carry signals between the cell’s internal and external environments.Transport proteins move molecules and ions (ionic channels) across the membrane. Membrane enzymes may have many activities, such as oxidoreductase, transferase or hydrolase andCell adhesion molecules
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 79
Incorrect
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Which intercellular connections are responsible for fastening the cells to one another?
Your Answer:
Correct Answer: Hemidesmosomes, zonula adherens & desmosomes
Explanation:There are three major types of cell junction:Adherens junctions, desmosomes and hemidesmosomes (anchoring junctions),Gap junctions (communicating junction) &Tight junctions (occluding junctions)
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This question is part of the following fields:
- Cell Biology
- Physiology
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Question 80
Incorrect
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The neurotransmitter in the synaptic cleft is either eliminated or deactivated after the postsynaptic cell responds to the neurotransmitter. Which of the following enzymes catalyses the breakdown of noradrenaline?
Your Answer:
Correct Answer: Catechol-O-methyltransferase (COMT)
Explanation:The neurotransmitter in the synaptic cleft is either eliminated or deactivated after the post-synaptic cell responds to the neurotransmitter. This can be accomplished in a variety of ways: Re-uptake Breakdown Diffusion Serotonin is an example of a neurotransmitter that is uptake. Serotonin is absorbed back into the presynaptic neuron via the serotonin transporter (SERT), which is found in the presynaptic membrane. Re-uptake neurotransmitters are either recycled by repackaging into vesicles or broken down by enzymes. Specific enzymes found in the synaptic cleft can also break down neurotransmitters. The following enzymes are examples of these enzymes: Acetylcholinesterase (AChE) catalyses the acetylcholine breakdown (ACh) The enzyme catechol-O-methyltransferase (COMT) catalyses the breakdown of catecholamines like adrenaline , dopamine and noradrenaline. The breakdown of catecholamines, as well as other monoamines like serotonin, tyramine, and tryptamine, is catalysed by monoamine oxidases (MOA). Diffusion of neurotransmitters into nearby locations can also be used to eliminate them.
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This question is part of the following fields:
- Cell Biology
- Physiology
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SESSION STATS - PERFORMANCE PER SPECIALTY
