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Question 1
Incorrect
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With regard to cell membrane proteins:
Your Answer: Ion channels when inactivated permit the passage of ions into & out of the cells
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
- Medicine
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Question 2
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
- Medicine
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Question 3
Incorrect
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The function of the Golgi apparatus is
Your Answer: Transport of nuclear material around the cytoplasm
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
- Medicine
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Question 4
Incorrect
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The Cellular Theory of Ageing involves?
Your Answer: Gene regulation
Correct Answer: Loss of telomeres
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. Telomeres are bits of DNA on the ends of chromosomes that protect chromosomes from sticking to each other or tangling, which could cause DNA to abnormally function. As cells replicate, telomeres shorten at the end of chromosomes, and this process correlates to senescence or cellular aging.
Other theories include:
- The Free Radical Theory: Implicates the gradual accumulation of oxidative cellular damage as a fundamental driver of cellular aging. This theory has evolved over time to emphasize the role of free radical induced mitochondrial DNA (mtDNA) mutations and the accumulation of mtDNA deletions. Given the proximity of mtDNA to the electron transport chain, a primary producer of free radicals, it postulates that the mutations would promote mitochondrial dysfunction and concomitantly increase free radical production in a positive feedback loop. It is known that diet, lifestyle, drugs (e.g. tobacco and alcohol) and radiation etc., are all accelerators of free radical production within the body.
- Error theory: based on the idea that errors can occur in the transcription of the synthesis of DNA. These errors are perpetuated and eventually lead to systems that do not function at the optimum level. The organism’s aging and death are attributable to these events (Sonneborn, 1979).
- The Cross-Linking Theory: also referred to as the Glycosylation Theory of Aging. In this theory it is the binding of glucose (simple sugars) to protein, (a process that occurs under the presence of oxygen) that causes various problems. Once this binding has occurred the protein becomes impaired and is unable to perform as efficiently. Living a longer life is going to lead to the increased possibility of oxygen meeting glucose and protein and known cross-linking disorders include senile cataract and the appearance of tough, leathery and yellow skin.
- The Neuroendocrine Theory First proposed by Professor Vladimir Dilman and Ward Dean MD, this theory elaborates on wear and tear by focusing on the neuroendocrine system. This system is a complicated network of biochemicals that govern the release of hormones which are altered by the walnut sized gland called the hypothalamus located in the brain. The hypothalamus controls various chain-reactions to instruct other organs and glands to release their hormones etc. The hypothalamus also responds to the body hormone levels as a guide to the overall hormonal activity. But as we grow older the hypothalamus loses it precision regulatory ability and the receptors which uptake individual hormones become less sensitive to them. Accordingly, as we age the secretion of many hormones declines and their effectiveness (compared unit to unit) is also reduced due to the receptors down-grading
- The Membrane Theory of Aging: According to this theory it is the age-related changes of the cell’s ability to transfer chemicals, heat and electrical processes that impair it. As we grow older the cell membrane becomes less lipid (less watery and more solid). This impedes its efficiency to conduct normal function and in particular there is a toxic accumulation
- The Decline Theory: The mitochondria are the power producing organelles found in every cell of every organ. Their primary job is to create Adenosine Triphosphate (ATP) and they do so in the various energy cycles that involve nutrients such as Acetyl-L-Carnitine, CoQ10 (Idebenone), NADH and some B vitamins etc. Enhancement and protection of the mitochondria is an essential part of preventing and slowing aging. Enhancement can be achieved with the above mention nutrients, as well as ATP supplements themselves.
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This question is part of the following fields:
- Cell Biology
- Medicine
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Question 5
Incorrect
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With regards to the Na+/K+ ATPase, which one of the following is correct?
Your Answer: 2 K+ 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
- Medicine
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Question 6
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
- Medicine
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Question 7
Incorrect
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Inhibition of cell division at the end of G1 occurs through:
Your Answer: p53
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
- Medicine
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Question 8
Incorrect
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The formation of superoxide is catalysed by which enzyme?
Your Answer: Superoxide dismutase
Correct 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
- Medicine
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Question 9
Correct
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Which caspase is part of both the intrinsic and extrinsic apoptotic pathways?
Your 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
- Medicine
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Question 10
Correct
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In the body what are fatty acids broken down to?
Your 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
- Medicine
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Question 11
Incorrect
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Which intercellular connections are responsible for fastening the cells to one another?
Your Answer: Connexons & gap junctions
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
- Medicine
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Question 12
Incorrect
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Regarding integrins, which option is false?
Your Answer: All of the options are true
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
- Medicine
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Question 13
Incorrect
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What is the function of secondary messengers?
Your Answer: Communication from intracellular to extracellular signalling pathways
Correct 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
- Medicine
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Question 14
Correct
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The breakdown of superoxide is catalysed by which enzyme?
Your 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
- Medicine
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Question 15
Incorrect
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Cell membrane proteins may act as:
Your Answer: Cell adhesion molecules
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
- Medicine
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Question 16
Correct
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In which organelle is the intrinsic apoptotic pathway initiated?
Your 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, also known as the mitochondrial pathway, is primarily initiated within the mitochondria. This pathway is activated in response to various internal stimuli, such as DNA damage, oxidative stress, and other cellular stresses.
When the intrinsic pathway is triggered, several events occur in the mitochondria:
- Release of cytochrome c: Cytochrome c is released from the mitochondrial intermembrane space into the cytoplasm.
- Formation of the apoptosome: Cytochrome c in the cytoplasm binds to apoptotic protease activating factor-1 (Apaf-1) and procaspase-9, forming a complex known as the apoptosome.
- Activation of caspase-9: The apoptosome activates caspase-9, an initiator caspase.
- Caspase cascade: Activated caspase-9 then activates executioner caspases, such as caspase-3, leading to the execution phase of apoptosis, which results in the orderly dismantling of the cell.
The mitochondria play a crucial role in this pathway by regulating the release of pro-apoptotic factors that are essential for the activation of downstream apoptotic processes.
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This question is part of the following fields:
- Cell Biology
- Medicine
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Question 17
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
- Medicine
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Question 18
Correct
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Intermediate filaments achieve cell to cell contact via:
Your Answer: Desmosomes
Explanation:At the plasma membrane, some keratins interact with desmosomes (cell-cell adhesion) and hemidesmosomes (cell-matrix adhesion) via adapter proteins.
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This question is part of the following fields:
- Cell Biology
- Medicine
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Question 19
Correct
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Which one of the following is able to move across cell membranes by passive diffusion?
Your 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
- Medicine
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Question 20
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
- Medicine
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Question 21
Incorrect
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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: Mutations in this protein may slow down the cell cycle causing mutations to persist
Correct Answer: It permits repair of mutations and other defects in RNA
Explanation:The p53 protein is a crucial tumor suppressor and plays several key roles in maintaining cellular integrity:
- Nuclear transcription factor: p53 is a nuclear transcription factor that regulates the expression of various genes involved in cell cycle control, DNA repair, apoptosis, and senescence.
- DNA repair: p53 permits repair of mutations and other defects in DNA (not RNA). It activates the transcription of genes involved in DNA repair mechanisms, allowing the cell to correct errors before proceeding with the cell cycle.
- Cell cycle regulation: p53 can induce the expression of p21, a protein that inhibits cyclin-dependent kinases, thereby halting the cell cycle at the G1/S checkpoint to allow time for DNA repair or to trigger apoptosis if the damage is irreparable. Mutations in p53 may fail to halt the cell cycle, allowing mutations to persist and potentially leading to cancer.
- Apoptosis: If DNA damage is extensive and cannot be repaired, p53 triggers apoptosis to prevent the propagation of damaged cells.
- Suppression of proto-oncogenes: p53 indirectly contributes to the suppression of proto-oncogenes by preventing the proliferation of cells with damaged DNA, thereby reducing the risk of oncogenic transformation.
Given these functions, the statement that p53 “permits repair of mutations and other defects in RNA” is incorrect, as p53 is primarily involved in the repair of DNA, not RNA.
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This question is part of the following fields:
- Cell Biology
- Medicine
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Question 22
Incorrect
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Hydroxyl radicals are broken down by which of the following substance?
Your Answer: Catalase
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
- Medicine
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Question 23
Correct
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Mitosis is the process of cell division which culminates in cell chromosomes which are:
Your 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
- Medicine
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Question 24
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
- Medicine
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Question 25
Incorrect
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Changes in cadherin expression are associated with
Your Answer: All of the above
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
- Medicine
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Question 26
Incorrect
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Which ion channel is a dimer?
Your Answer: K+ 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
- Medicine
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Question 27
Incorrect
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The processing of NH3 to urea occurs in:
Your Answer: Mitochondria alone
Correct 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
- Medicine
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Question 28
Correct
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Cyclic AMP is formed from ATP via which enzyme
Your 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
- Medicine
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Question 29
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
- Medicine
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Question 30
Incorrect
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The free radical most abundantly formed by the immune system is:
Your Answer: Superoxide
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
- Medicine
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SESSION STATS - PERFORMANCE PER SPECIALTY
