Chapter 35. Molecular Motors

Question 1

Substances, such as glucose, that, when present in the form of a gr adient, cause bacteria to swim toward the source of the gradient.

Answer 1

Chemoattractant

Question 2

The process of moving in specific directions in response to environmental cues.

Answer 2

Chemotaxis

Question 3

Proteolytic digestion products of myosin that are the force-generating units of the intact myosin molecule; the S1 fragment contains the ATPase and actin-binding sites.

Answer 3

S1 fragment

Question 4

A bundle of microtubules which is composed of a peripheral group of nine microtubule pairs surrounding two singlet microtubules.

Answer 4

axoneme

Question 5

The ability of the immune system to respond more rapidly and effectively to pathogens that have been encountered previously.

Answer 5

Immunological memory

Question 6

Internal scaffolding of cells, made up of microfilaments, intermediate filaments, and microtubules, which enables cells to transport vesicles, change shape, and migrate.

Answer 6

Cytoskeleton

Question 7

A bacterial flagellar protein that is part of the MS (membrane and supramembrane) ring; FliG, in combination with flagellar proteins MotA/MotB, forms a proton channel that drives the rotation of the flagellum.

Answer 7

FliG

Question 8

A highly conserved protein found in all eukaryotes; in striated muscle, it forms the thin filaments of the sarcomere and activates the ATPase of myosin.

Answer 8

Actin

Question 9

Actin monomers that come together to form filaments called F-actin.

Answer 9

G-actin

Question 10

A property of microtubules such that some microtubules in a population lengthen while other simultaneously shorten; a result of the random fluctuations in the number of GTP- tubulin subunits or GDP-tubulin subunits at the ends of the microtubule. GTP-tubulin polymerizes more readily.

Answer 10

Dynamic instability

Question 11

A short segment of kinesin that binds to the head domain of kinesin when ATP is bound and is released when the nucleotide-binding site is vacant or occupied by ADP.

Answer 11

Neck linker

Question 12

A filament of G-actin monomers that is a polar, self-assembling, dynamic polymer.

Answer 12

F-actin

Question 13

Vaccines that contain pathogens that have been rendered harmless by treatment with chemicals or high heat.

Answer 13

Killed, or inactivate, vaccines

Question 14

A protein that forms the thick filaments of striated muscle; displays ATPase activity at its globular head, which, in conjunction with the ability to reversibly bind actin at its fibrous region, provides the power stroke of muscle contraction.

Answer 14

Myosin

Question 15

A long helix that connects the switch regions of the S1 fragment to the lever arm; the nature of the nucleotide in the S1 fragment (ATP or ADP) allows the relay helix to change position, resulting in a reorientation of the lever arm.

Answer 15

Relay helix

Question 16

A large protein with ATPase activity that is a component of microtubules; the ATPase activity provides the power for the movement of cilia and flagella. In cytoplasm, a motor protein that is related to the dynein in flagella and cilia and powers retrograde transport

Answer 16

Dynein

Question 17

Potentially harmful substances, such phenol, that, when present in the form of a gradient, cause bacteria to swim away from the source of the gradient.

Answer 17

Chemorepellant

Question 18

Located in the thin filaments of a sarcomere, a protein that plays a role in the regulation of muscle contraction by blocking the interaction of myosin with actin at low Ca2+ concentrations; regulated by troponin.

Answer 18

Tropomyosin

Question 19

A motor protein, built around a P-loop NTPase core, that has several structural features in common with myosin; conventional kinesin moves toward the plus end of microtubules.

Answer 19

Conventional kinesin

Question 20

A long helix that protrudes from the S1 fragment of myosin to bind the light chains; amplifies small structural changes at the nucleotide-binding site of myosin to achieve 110-Å movement along an actin filament.

Answer 20

Lever arm

Question 21

The conformational change in myosin heads powered by phosphate release as myosin binds to actin and pulls the actin filament, with the resulting displacement of the myosin heads.

Answer 21

Power stroke

Question 22

The concentration of G-actin monomers above which polymerization occurs and below which depolymerization occurs. The critical concentration is equal to the dissociation constant (Kd) of an actin monomer from a filament.

Answer 22

Critical concentration

Question 23

The functional unit of a myofibril; its distinct repeating structure is due to the overlapping of thick protein filaments, composed of myosin, and thin filaments, composed of actin and other proteins, which contract through the use of a sliding-filament method.

Answer 23

Sarcomere

Question 24

One of the two protein filaments present in a myofibril, which have diameters of about 15 nm and consist primarily of myosin.

Answer 24

thick filaments

Question 25

A cytoskeleton element that is a major component of cilia, eukaryotic flagella, and the mitotic spindle; composed primarily of alpha- and beta-tubulin; capable of rapid assembly and disassembly.

Answer 25

Microtubule

Question 26

One of the two protein filaments present in a myofibril, which have diameters of approximately 8nm and consist of actin as well as tropomyosin and the troponin complex.

Answer 26

thin filaments

Question 27

A pair of bacterial proteins that form a ring around the base of the flagellum and, in conjunction with FliG, form a proton channel that drives the rotation of the flagellum.

Answer 27

MotA-MotB pair

Question 28

The protein component of bacterial flagella.

Answer 28

Flagellin

Question 29

A protein in the bacterial chemotaxis signaling pathway that, when phosphorylated, leads to clockwise rotation of the flagellum, causing tumbling, and that, when dephosphorylated, leads to counterclockwise rotation and smooth swimming.

Answer 29

CheY

Question 30

A means of measuring the force exerted by a single myosin molecule on an actin filament.

Answer 30

Optical trap

Question 31

A protein with ATPase activity that moves cellular organelles along microtubule tracks in anterograde transport.

Answer 31

Kinesin

Question 32

Fibrils inside the cytosol of vertebrate muscle cells that give such cells their striated appearance; the functional unit of a myofibril is a sarcomere.

Answer 32

Myofibril

Question 33

Vaccines that contains live pathogens that have accumulated mutations so that they are no longer virulent to human cells.

Answer 33

Live attenuated vaccines

Question 34

Vaccines that contain a purified protein component of a pathogen.

Answer 34

Subunit vaccines

Question 35

Vaccines that are used against pathogens that employ an extracellular toxin to cause disease. These vaccines contain a form of the toxin that has been inactivated by treatment with chemicals or high heat.

Answer 35

Toxoid vaccines

Question 36

The major microtubule protein component that exists in two forms, alpha- and beta-tubulin; tubulins display GTPase activity that is vital for the assembly and disassembly of microtubules.

Answer 36

Tubulin

Question 37

Located in the thin filaments of the sarcomeres, that regulate muscle contraction through allosteric interactions with tropomyosin in response to changes in Ca2+ concentrations.

Answer 37

Troponin complex