Question

QUESTION 37

1. The dynamic instability of microtubules ____________________.

   a		reflects a balance between the rate of GTP hydrolysis by tubulin dimers and the addition of new GTP-bound dimers at the plus end
   b		reflects a balance between the rates of GTP-bound tubulin dimer addition at the plus and and proteolytic degradation of the microtubule
   c		reflects a balance between the rates of GDP-bound tubulin dissociation at the plus and addition of GTP-bound dimers at the minus end
   d		reflects a balance between the rates of GTP-bound tubulin dimer addition at the plus end and GDP-bound dimer loss at the minus end

QUESTION 38

1. Depolarization of a skeletal muscle cell plasma membrane begins ____________________.

   	a	when potassium (K+) exit through leak channels triggers opening of voltage-gated sodium (Na+) channels
   	b	when calmodulin binding triggers the opening of ligand-gated calcium (Ca2+) channels
   	c	when acetylcholine binding triggers the opening of ligand-gated sodium (Na+) channels
   	d	when acetylcholine binding triggers the opening of T tubule calcium (Ca2+) release channels

QUESTION 39

1. Match each type of intermediate filament with the correct description.

   -       A.       B.       C.       D.    Nuclear lamins       -       A.       B.       C.       D.    Keratin filaments       -       A.       B.       C.       D.    Neurofilaments       -       A.       B.       C.       D.    Vimentin and vimentin-related filaments

   A. Assembly and disassembly is regulated by phosphorylation B. Found in connective tissue cells and glial cells C. Most diverse class of intermediate filament D. Found only in nerve cells

Answer 1

37)

The dynamic instability of microtubules ____________________.

a) reflects a balance between the rate of GTP hydrolysis by tubulin dimers and the addition of new GTP-bound dimers at the plus end. This is because microtubule's growth or shrinkage is determined by the rate of tubulin addition relative to the rate of GTP hydrolysis. when i) GTP-bound tubulin molecules are added more rapidly than GTP is hydrolyzed, a GTP cap is retained at the plus end and microtubule grows. ii)but when the GTP bound to tubulin at the plus end of the microtubule is hydrolyzed to GDP. the GDP-bound tubulin dissociates, and results in rapid depolymerization and shrinkage of the microtubule rest options are not true as they don't fit the exact scenario of the tubular growth

38).

Depolarization of a skeletal muscle cell plasma membrane begins ____________________

c)

when acetylcholine binding triggers the opening of ligand-gated sodium (Na+) channels. this binding of Ach molecules with the AchR receptors in neuromuscular junction leads to opening up of the ligand-gated ion channel which depolarizes the sarcolemma and triggers muscle contraction.

39).

nuclear lamins	Found in connective tissue cells and glial cells
keratin filament	Most diverse class of intermediate filament
neurofilaments	Found only in nerve cells
Vimentin and vimentin-related filaments	Assembly and disassembly is regulated by phosphorylation