BI203 Lecture 19: Cytoskeleton - Muscle Contraction

Question 1

_____ _____ - Actin filaments associate with myosin, a molecular motor, to convert ATP to mechanical energy, generating force and movement.

Answer 1

muscle contraction

Question 2

Muscle contraction: Actin filaments associate with _____, a molecular motor, to convert ATP to mechanical energy, generating force and movement.

Answer 2

myosin

Question 3

Muscles are composed of bundles of _____ _____ - Elongated cells created by cell fusion during development.

Answer 3

muscle fibers

Question 4

Muscle fibers:

Most of the cytoplasm - _____.

1) _____ filaments of _____.
2) _____ filaments of _____.

Answer 4

myofibrils, thick, myosin, thin, actin

Question 5

Thick filaments of myosin and thin filaments of actin are organized in tandem contractile units: _____.

Answer 5

sarcomeres

Question 6

_____ regions are discernible by electron microscopy.
The bands correspond to presence or absence of _____ filaments.
_____ filaments are attached at the barbed ends to the Z disc, which includes the cross-linking protein _____.

Answer 6

sarcomere, myosin, actin, a-actinin

Question 7

The _____ _____ _____ of muscle contraction was proposed in 1954.

During contraction, each sarcomere _____, bringing the _____ closer together.

There is _____ change in the width of the A band, but the _____ _____ and _____ _____ almost disappear.

Answer 7

sliding filament model, shortens, Z discs, no, I bands, H zone

Question 8

Ends of each sarcomere defined by _____ _____.

Answer 8

Z discs

Question 9

_____ _____ are attached to Z discs by their barbed ends.

Answer 9

actin filaments

Question 10

Middle of each sarcomere defined by the _____ _____.

Answer 10

M line

Question 11

_____ _____ are anchored to the M line & project out in both directions.

Answer 11

myosin filaments

Question 12

KEY: _____ & _____ _____ filaments overlap on either side of the M line.

Answer 12

actin, myosin II

Question 13

Muscle contraction entails the sliding of _____ & _____ filaments past each other.

Answer 13

actin, myosin

Question 14

During muscle contraction, the actin and myosin filaments slide past one another so that the actin filaments move into the _____ _____ and _____ _____.

Answer 14

A band, H zone

Question 15

The molecular basis for muscle contraction is the binding of _____ to actin filaments, allowing it to function as the _____ that drives filament _____.

Answer 15

myosin, motor, sliding

Question 16

_____ _____ = A motor protein with 2 domains, which drives filament sliding.

Answer 16

myosin II

Question 17

Myosin II (the type in muscle) has _____ heavy chains and _____ pairs of light chains.

The heavy chains have a _____ _____ _____ and a long _____ _____.

The tails twist around each other in a coil.

Answer 17

2, 2, globular head region, a-helical tail

Question 18

_____ _____: Several hundred myosin molecules in a parallel staggered array.

Answer 18

thick filaments

Question 19

The globular heads bind _____, forming cross-bridges between thick and thin filaments.

The orientation of myosin and polarity of actin filaments _____ at the M-line.

Answer 19

actin, reverses

Question 20

_____ _____ hydrolyze ATP, providing energy to drive filament sliding.

Answer 20

myosin heads

Question 21

Myosin changes shape during repeated cycles of interaction between myosin heads and actin.
The conformational changes in myosin result in _____ of myosin heads along actin filaments.

Answer 21

movement

Question 22

_____-binding & hydrolysis drives myosin-mediated filament sliding.

Answer 22

ATP

Question 23

Hundreds of _____ contract a sarcomere.

Hundreds of _____ contract a skeletal muscle.

Answer 23

myosins, sarcomeres

Question 24

Binding of _____ dissociates myosin from actin.

ATP hydrolysis induces a conformational change that displaces the myosin _____ group.

The myosin head binds to a new position on the actin filament and _____ is released.

_____ _____: myosin head returns to its original conformation, which drives actin filament sliding, and ADP is released.

Answer 24

ATP, head, Pi, power stroke

Question 25

The cycle of myosin head/actin filament sliding/sarcomere shortening/muscle contraction is regulated by the ion _____.

Answer 25

Ca2+

Question 26

Presence of Ca2+ -> _____.

Absence of Ca2+ -> _____ _____.

Answer 26

contraction, no contraction

Question 27

Nerve impulses increase Ca2+ amount _____.

Answer 27

100-fold

Question 28

_____ _____ increase Ca2+ amount 100-fold.

Answer 28

nerve impulses

Question 29

Muscle contraction is triggered by nerve impulses which stimulate release of Ca2+ from the _____ _____.

Answer 29

sarcoplasmic reticulum

Question 30

The increased Ca2+ concentration in the cytosol affects two actin filament binding proteins: _____ and _____.

Answer 30

tropomyosin, troponin

Question 31

Tropomyosin binds lengthwise along actin filaments, and is also bound to _____.

Answer 31

troponins

Question 32

The _____ _____ blocks the binding of myosin to actin.

Binding of Ca2+ to _____ _____ shifts the n complex, and allows contraction to proceed.

Answer 32

n complex, troponin C

Question 33

Cytokinesis:

A _____ _____ of actin and myosin II is assembled by membrane-bound myosin just beneath the plasma membrane.
Contraction of the ring pinches the cell in two.

Answer 33

contractile ring

Question 34

Unconventional myosins which don’t form filaments: myosin _____ and _____ move along actin filaments and help move vesicles and organelles around the cell.

Answer 34

I, V

Question 35

_____ _____ - Globular head groups which can act as molecular motors.
Short tails bind to other structures. Movement of _____ _____ along an actin filament can transport its attached cargo, such as a vesicle.

Answer 35

myosin I

Question 36

_____ _____ - Two-headed dimer that transports vesicles and other cargo along actin filaments; important in neurons.

Answer 36

myosin V