Question

Question 78 Which of the following statements about the cytoskeleton is TRUE? All eukaryotic cells have actin, microtubules, and intermediate filaments in their cytoplasm The cytoskeleton provides a rigid and unchangeable structure important for the shape of the cell. The three cytoskeletal filaments perform distinct tasks in the cell and act completely independently of one another Actin filaments and microtubules have an inherent polarity, with a plus end that grows more quickly than the minus end С. D

Answer 1

Answer:

78. The correct statement is: D. Actin filaments and microtubules have an inherent polarity with a plus end that grows more quickly than the minus end.

Explanation: Actin filaments and microtubules are polar in nature with two distinct ends i.e. a plus end and a minus end. The microtubules grow or shrink at the plus end because the tubulin molecules polymerise (growth) or depolymerise (shrink) at the plus end of the microtubules whereas the minus end is attached to the centrosome. High concentration of tubulin bound GTP attach to the plus end (i.e. polymerise) and growth continues. However, if the GTP bound to plus end hydrolysed to GDP then rate of polymerization decreases and rate of depolymerisation increases which results in dissociation of GDP bound tubulin from the plus end and shrinkage of microtubules.

Therefore the plus end grows more quickly than minus end.

79. Cyclin D is the cyclin of S phase: False

Explanation: Cyclin D is synthesized during G1 phase, accumulates to the maximun level and promote the cell cycle progression from G1 to S phase.

80. The correct statement is: C. Chaperone proteins in the mitochondria facilitates the movement of proteins across the outer and inner mitochondrial membrane.

Explanation: Normally chaperone proteins help in protein folding by preventing non specific aggregation thus provides cellular resistance to various stress conditions. But mitochondrial chaperone Hsp 70 or mtHsp 70 helps in translocation (coupled with ATP hydrolysis) of cytoplasmic presursure protein across the inner and outer mitochondrial membrane.

81. N linked modifications is more complex than O linked: True

Explanation: The O linked glycosilation is shorter and have simple O linked glycans where the sugar chains are added to the hydroxyl oxygen of side chain of hydroxylysine, hydroxyproline, serine and threonine.

N linked glycosilation is attachment of oligosaccharides to the amide nitrogen of the side chain of asparagine. The N glycans have very complex structure with different combinations of mannose, N acetylglucosamine, N acetylgalactosamine, fucose, sialic acid residues etc. Therefore N linked glycosilation is more complex than O linked.