OBLICZENIA BIOCHEMICZNE

do wykładu dr. hab. inż. P. Dobryszyckiego

LISTA ZADAŃ NR 13

MOTORY MOLEKULARNE

1. Match the proteins in the left column with their descriptions in the right column.

(a) myosin

(1) enormous protein

(b) kinesin

(2) helps separate chromosomes

(c) dynein

(3) important in muscle contraction.

2. Energy is required to drive the contraction of striated muscle, the beating of flagella or cilia, and the intracellular transport of vesicles along microtubules. Which of the following statements about energy transduction in these systems are correct?

(a) The proton-motive force across the plasma membrane surrounding the cell provides the energy for these movements.

(b) The binding of ATP to proteins, which then undergo a conformational change, provides the energy for these processes.

(c) The hydrolysis of ATP is coupled to the phosphorylation of tyrosine residues on the proteins of these systems to drive them.

(d) The hydrolysis of protein-bound ATP and the release of ADP + Pi lead to conformational transitions that complete a movement cycle.

(e) The binding of GTP to oriented proteins at the interface of the moving assemblies drives these processes.

3. Which of the following answers complete the sentence correctly? Actin (a) is formed from a 42-kd monomer (G-actin).

(b) monomers can exist with either ATP or ADP bound to themselves.

(c) exhibits an ATPase activity that helps power muscle contraction.

(d) in its F form binds myosin in an oriented manner.

(e) in its F form with myosin has a barbed and a pointed end.

4. Figure 1 is a schematic diagram of a longitudinal segment of a skeletal muscle myofibril.

Label the structures indicated in the figure by matching them with the listed choices.

(a) I band

(b) A band

(c) thin filaments

(d) M line

(e) H zone

(f) thick filaments

(g) Z line

Lista Zadań nr 13 – Motory molekularne

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5. Which of the following statements about myosin are true?

(a) Myosin binds to polymerized actin.

(b) In vitro, myosin assembles spontaneously into the thin filaments.

(c) Myosin is an ATPase.

(d) Myosin has domains that interact with one another to effect its physiological functions.

(e) Myosin is composed of two polypeptide chains, one of which forms an α-helical coiled coil and the other a globular head.

6. Which of the following statements concerning events related to the power stroke of muscle contraction are correct?

(a) The hydrolysis of ATP to ADP and Pi by myosin is fast relative to the release of the ADP

and Pi from the protein.

(b) The binding of actin to myosin stimulates the ATPase activity of myosin by facilitating the release of ADP and Pi.

(c) Actin and myosin are joined by cross-bridges that are stabilized by the binding of ATP

to the myosin head domains.

(d) Repeated cycles of ATP binding, ATP hydrolysis, and the resulting association and dissociation of cross-bridges and conformational changes in myosin contribute to the contractile process.

(e) In the region of overlapping thick and thin filaments of a sarcomere, the cross-bridges will either all be formed or all be dissociated, depending on the phase of the power stroke.

7. Considering only the power stroke of skeletal muscle contraction and the events that precede and follow it, place the following states or processes that occur in going from the resting state to the contracted state and back again in their proper order.

(a) The thick filament moves with respect to the thin filament.

(b) The Sl heads of myosin interact with actin, Pi is released, and myosin changes its conformation.

(c) ATP binds to myosin.

(d) The S1 heads of myosin are dissociated from the thin filament and contain bound ADP

and Pi.

(e) ATP is hydrolyzed to ADP and Pi and myosin undergoes a conformational change.

(f) ADP dissociates from the myosin to complete the power stroke.

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8. Which of the domains of myosin is primarily responsible for generating the force of skeletal muscle contraction?

(a) the hinge between the Sl and S2 domains

(b) the hinge between the S2 and the LMM domains

(c) the LMM domain

(d) the Sl globular head

(e) the S2 domain that connects the Sl domain to the α-helical coiled coil (f) the α-helical coiled coil.

9. Which of the following statements concerning microtubules are correct?

(a) Microtubules are filaments composed of α-helical coiled-coil polypeptide chains.

(b) Microtubules contain α-tubulin and β-tubulin protomers that are disposed in a helical array around a hollow core to form a cylindrical structure.

(c) The cilia and flagella of eukaryotic cells contain nine microtubule doublets that surround a pair of microtubule singlets.

(d) The outer microtubules in an axoneme are linked together and to an ATPase called dynein.

(e) The powered movements of dynein in an axoneme shorten the structure.

10. Match the major components of the chemotaxis system of E. coli in the left column with the appropriate descriptions from the right column.

(a) chemoreceptor

(1) contains several rings, a hook, and a rod

(b) processing system

(2) has binding sites for attractants or repellents

(c) flagellar motor

(3) includes cytosolic peripheral membrane proteins

(d) flagellum

(4) contains flagellin and adopts a helical configuration

11. The proposed model for the transduction of chemotactic signals via CheY, the tumble regulator, includes which of the following?

(a) Phosphorylated CheY promotes the counterclockwise rotation of the motor.

(b) The activation of CheY requires ATP.

(c) Attractants block the CheY pathway, and smooth swimming results.

12. Myosin, kinesin, and dynein all contain a globular head which harbors ATPase activity and a tail region which can be thought of as a protein-binding region. The specificity of these protein-binding domains changes the role of each of these three proteins in tissues.

What is the specificity of each of these three protein-binding domains, and how does it relate to the roles of myosin, kinesin, and dynein in tissues?

13. A neuron can move a vesicle approximately a meter from the central cell body to the end of an axon in a day. How are microtubules involved in this process, what provides the energy for the movement, and what protein is directly involved in the movement?

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