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Question 1
Incorrect
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Intermediate filaments achieve cell to cell contact via:
Your Answer: Gap junctions
Correct 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 2
Incorrect
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Which of the following statements is most suitable to describe necrosis?
Your Answer: Shrinking of cytoplasm and condensation of nucleus.
Correct 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
- Medicine
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Question 3
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 4
Incorrect
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The formation of superoxide is catalysed by which enzyme?
Your Answer: Oxide reductase
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 5
Incorrect
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In blistering dermatological disorders e.g.. Pemphigus, which junctions are attacked by autoantibodies?
Your Answer: Hemidesmosomes
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
- Medicine
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Question 6
Incorrect
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Cyclic AMP activates the following enzyme
Your Answer: Adenylyl cyclase
Correct 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
- Medicine
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Question 7
Correct
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The Cellular Theory of Ageing involves?
Your 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 8
Incorrect
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With regards to the Na+/K+ ATPase, which one of the following is correct?
Your Answer:
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 9
Incorrect
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What is the function of gap junctions?
Your Answer:
Correct 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
- Medicine
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Question 10
Incorrect
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With regard to the cell membrane:
Your Answer:
Correct 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
- Medicine
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Question 11
Incorrect
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Microtubule disassembly:
Your Answer:
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 12
Incorrect
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Question 13
Incorrect
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Regarding oxidative deamination of amino acids, which of the following is true?
Your Answer:
Correct 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
- Medicine
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Question 14
Incorrect
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What is the function of the pro-apoptotic Bcl-2 family of proteins, Bax and Bak?
Your Answer:
Correct 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
- Medicine
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Question 15
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:
Correct 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
- Medicine
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Question 16
Incorrect
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Question 17
Incorrect
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In the body what are fatty acids broken down to?
Your Answer:
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
- Medicine
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Question 18
Incorrect
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Question 19
Incorrect
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The free radical most abundantly formed by the immune system is:
Your Answer:
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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Question 20
Incorrect
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The cell membrane:
Your Answer:
Correct 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 21
Incorrect
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Question 22
Incorrect
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Cell membrane proteins may act as:
Your Answer:
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 23
Incorrect
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In the presence of oxygen , lactate that was produced under anaerobic conditions is converted to:
Your Answer:
Correct 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 24
Incorrect
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The complete oxidation of 1 molecule of glucose to CO2 and H20 produces a total of __ATP.
Your Answer:
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
- Medicine
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Question 25
Incorrect
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In which organelle is the intrinsic apoptotic pathway initiated?
Your Answer:
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
- Medicine
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Question 26
Incorrect
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Hydroxyl radicals are broken down by which of the following substance?
Your Answer:
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 27
Incorrect
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Which one of the following is able to move across cell membranes by passive diffusion?
Your Answer:
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
- Medicine
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Question 28
Incorrect
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What is the function of secondary messengers?
Your Answer:
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 29
Incorrect
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Regarding integrins, which option is false?
Your Answer:
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 30
Incorrect
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The processing of NH3 to urea occurs in:
Your Answer:
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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SESSION STATS - PERFORMANCE PER SPECIALTY
