Deck 15: Molecular Motors

Question 1

Which of the following is NOT correct regarding ciliary motion?

A)ATP-driven sliding or walking of dyneins occurs along microtubules.
B)Axonemes are surrounded by plasma membrane that is continuous with the plasma membrane of the cell.
C)Dynein molecules bridge between microtubules,alternating their "walking" along both bridging microtubules.
D)The result is a bending motion of the axoneme and subsequent bending of the cilia.

Answer 1

C

Question 2

Which best defines negative cooperativity of Rep helicase from E.coli?

A)When 1 subunit binds DNA,the other releases from the DNA.
B)When both subunits are bound to DNA,ATP hydrolysis promotes release of both subunits.
C)ATP hydrolysis promotes DNA binding of both subunits simultaneously.
D)Once it binds ssDNA,binding dsDNA is prohibited.

Answer 2

A

Question 3

How does intracellular movement of organelles in axons occur?

A)through axoneme motion through ATP-driven walking of dyneins along microtubules
B)through formation of ring-like structures around tubulin to move organelles
C)through progressive movement along DNA strands
D)through kinesin-mediated ATPase-driven movement along microtubules

Answer 3

D

Question 4

Which of the following is NOT a characteristic of microtubules?

A)They are made up of 2 repeating subunits.
B)They grow at one end and are degraded at the other end.
C)They are static,helical structures.
D)They are hollow,cylindrical structures.

Question 5

How does self-assembly of microtubules occur?

A)by helical twisting of strands of a-tubulin and b-tubulin
B)by intermolecular interactions of dimers of a-tubulin and b-tubulin
C)by polymerization of alternating a- and b-tubulin into a repeating a-b-a-b-.strand
D)by inter-subunit interaction to form a2b2-tetramers of tubulin

Question 6

From which structure are microtubules formed?

A)myosin
B)phospholipid
C)membrane
D)tubulin

Question 7

Which of the following does NOT occur during kinesin movement along a microtubule?

A)Leading head binds a new site on tubulin,with ADP dissociation.
B)The kinesin head with ADP is bound to tubulin,and the kinesin head with ATP is ready to move ahead.
C)Conformational changes in the neck linkers flip the trailing head to the next tubulin binding site.
D)ADP and Pi dissociate and ATP binds leading head.

Question 8

When would inhibition occur if the non-hydrolyzable ATP analog b,g-methylene-ATP were given to muscle cells?

A)during formation of the cross-bridge between actin and myosin
B)during the release of ADP and Pi
C)during the ATP binding step where actin and myosin dissociate
D)during the conformational change in the myosin head

Question 9

Which structural component houses a high concentration of Ca²⁺ and releases it to trigger muscle contraction?

A)sarcoplasmic reticulum
B)sarcomere
C)t-tubule
D)sarcolemma

Question 10

In the b-sheet of the -a-b-a-segment of myosin,a particular sequence likely binds ATP and is found in other nucleotide-binding proteins.Which of the following represents that sequence?

A)Cys-X-X-Cys-X-His
B)Arg-X-X-His-X-Gly
C)Gly-X-X-Gly-X-Gly
D)Lys-X-Gly-X-X-Ser

Question 11

Which protein component in the troponin complex shows 70% homology to calmodulin and is involved in Ca²⁺ binding?

A)TnT
B)TnC
C)TnI
D)TnA

Question 12

Which of the following features is a similarity between Rep helicase of E.coli and kinesin?

A)the capacity to move organelles
B)ring-like structures that encircle the substrate
C)2 subunits,1 of which is always bound to the polymer at any moment
D)tubulin binding heads that hydrolyze ATP

Question 13

Kinesins are proteins that exhibit ATPase activity.What are they involved with?

A)A-tubule and B-tubule movement within an axoneme
B)movement of cilia
C)movement of muscles
D)intracellular movement of organelles and vesicles from the minus end to the plus end of microtubules

Question 14

Which of the following does NOT affect microtubule polymerization and is NOT used in cancer chemotherapy?

A)taxol
B)colchicine
C)vinblastine
D)vincristine

Question 15

Which of the following is NOT a characteristic of molecular motors or motor proteins?

A)They must be able to associate irreversibly with a polymeric protein array,a surface,or substructure in the cell.
B)They use chemical energy (e.g.,ATP)to orchestrate movement.
C)They transfer ATP energy into mechanical energy.
D)ATP hydrolysis is presumed to drive and control protein conformational changes that result in sliding or walking movement of one molecule relative to another.

Question 16

Which of these actions is treadmilling,as carried out by microtubules?

A)ATP-hydrolysis-dependent movement over a plane
B)ATP-dependent addition of dimmers to the plus end
C)GTP-hydrolysis-dependent movement of a-tubulin over b-tubulin
D)GTP-dependent addition to the plus end and removal at the minus end

Question 17

Which of the following is NOT correct regarding the bands observed by electron microscopy of myofibrils?

A)I bands show a hexagonal array of thick filaments.
B)Thin filaments are composed mainly of actin,troponin,and tropomyosin.
C)H zones contain an array of thick filaments that are composed mainly of myosin.
D)Thick filaments are joined by cross-bridges.

Question 18

Myofibrils are the basic structural unit in the contraction of striated muscle.What is the linear array of cylindrical structures they made of?

A)t-tubules
B)sarcomeres
C)sarcolemmas
D)sarcoplasmic reticulum (SR)

Question 19

Which of the following is NOT a function of microtubules?

A)providing variations and maintenance of cell shape
B)forming the mitotic spindle during cell division
C)unwinding DNA to single-stranded DNA (ssDNA)
D)forming intracellular scaffolds

Question 20

Which component(s)of the 6 polypeptides that make up the thick filament contain(s)the ATPase activity?

A)LC1
B)LC2
C)myosin heavy chains
D)essential light chains

Question 21

Which of the following occurs during muscle contraction?

A)ATP is hydrolyzed.
B)The length of the thick filament is reduced.
C)The contraction produces an increased overlap of the actin and myosin filaments of the A band.
D)The length of the thin filaments remains constant.

Question 22

Which of the following is NOT a part of the reaction sequence for the involvement of free actin,free myosin,and ATPase activity on each other?

A)Actin binds and activates ATPase activity by stimulating the formation of Camp.
B)In the absence of actin,the addition of ATP to myosin produces a rapid release of H⁺.
C)New ATP is bound to the actomyosin complex.
D)Actomyosin dissociates into actin and myosin.

Question 23

Which of the following muscle protein components is responsible for ATP hydrolysis?

A)tropomyosin
B)myosin
C)troponin C
D)actin

Question 24

Which of these changes stimulates muscle contraction?

A)an increase in [Ca²⁺] in the vicinity of the muscle fibres
B)a decrease in the [Ca²⁺] in the mitochondria
C)an increase in [Ca²⁺] in the sarcolemma
D)a decrease in the [Ca²⁺] in the Golgi

Question 25

What is the power stroke in muscle contraction associated with?

A)the dissociation of ADP and Pi from the ATPase
B)binding of myosin to actin
C)addition of water for ATP hydrolysis
D)the hydrolysis of ATP

Question 26

Which of the following is NOT a characteristic exhibited by troponin C (TnC)?

A)TnC has 2 binding sites that are always complexed to Ca²⁺.
B)A conformational change in TnC occurs on Ca²⁺ binding.
C)Ca²⁺ binding to TnC decreases interaction between TnI and actin.
D)TnC has 4 equivalent Ca²⁺ binding sites

Question 27

In E.coli,which action powers the rotation of the flagella?

A)the hydrolysis of GTP by the flagella
B)phosphorylation of the motB protein by phosphoenolpyruvate
C)the hydrolysis of ATP by the motB protein
D)a proton gradient across the plasma membrane of the bacterium

Question 28

Which of the following troponin subunits is responsible for inhibiting actin-myosin binding?

A)troponin C
B)troponin M
C)troponin G
D)troponin I