Determine whether each of these statements is true or false and then explain why

Question

Determine whether each of these statements is true or false and then explain why?

a) Myosin II molecules have two motor domains and a rodlike tail that allows them to assemble into thick filaments with motor domains on either end, which is crucial for the efficient sliding of oppositely oriented actin filaments past each other.

b) When activated by Ca2+ binding, troponin C causes a conformation change in the troponin complex that allows tropomyosin molecules to shift their positions slightly so that the myosin heads can bind to the actin filaments.

c) In most animal cells, minus-end directed microtubule motors deliver their cargo to the periphery of the cell, whereas plus-end directed microtubule motors deliver their cargo to the interior of the cell. (Be sure to name these motors).

d) Both kinesin-1 and myosin II move processively making them suitably adapted for their biological functions.

e) Axonemal dyneins mediate the bending of cilia and eukaryotic flagella.

Explanation / Answer

a) Myosin II molecules contain two heavy chains and two light chains. The heavy chains contain globular head domain at its N terminus consisting of a force-generating machinery, followed by a very long amino acid sequence. This sequence forms an extended coiled-coil that mediates heavy-chain dimerization. Light chains bind at N - terminal head region and coiled tails bind with tails of other myosin molecule. The tail - tail interactions form thick filaments with several myosin heads, oriented in opposite directions at two ends of the thick filament. The statement is "true".

b)Tropomyosin molecule is bound to troponin and it is a complex of three polypeptides called troponin C meant for Ca2+-binding, troponin I (inhibitory), and troponin T (tropomyosin-binding). Binding of calcium ions causes a conformation change in the troponin complex that allows tropomyosin molecules to shift their positions slightly so that the myosin heads can bind to the actin filaments resulting in initiation of muscle contraction. The given statement is "true".

c) The Microtubules in most animal cells are established by the centrosome and centrosome nucleates microtubule growth at the minus end. Thus, the plus ends of the microtubules grow near the plasma membrane, and the minus ends are buried in the centrosome at the center of the cell. The orientation of the microtubule array requires that plus end-directed motors be used to transport cargo to the cell periphery and that minus end-directed motors be used for cargo delivery to the center of the cell. Thus, the given statement is "false".

d) Kinesin 1 is similar to myosin II instructure and contains two heavy chains per active motor. The two heavy chains form two globular head motors domains that are held together by an elongated coiled-coil tail that is responsible for heavy chain dimerization. The given statement is "true".

e) Axonemal dyneinscontain a second branch including monomers, heterodimers. The heterotrimers contain one, two, or three motor containing heavy chains, respectively. They are highly specialized for the rapid and efficient sliding movements of microtubules that drive the beating of cilia and flagella. The given statement is "true".

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