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A&P Lecture Unit 3 > Cross Bridge Cycle > Flashcards

Flashcards in Cross Bridge Cycle Deck (41)
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1
Q

Myosin cross bridges are the __ ___ sites.

A

force generating

2
Q

Contraction does not necessarily cause ___ of fiber.

A

Shortening

3
Q

Contraction is defined as

A

generation of force

4
Q

In the relaxed state, thin and thick filaments overlap only at

A

ends of A band

5
Q

Sliding filament model of contraction 1: During contraction, thin filaments slide past ___ filaments so that actin and myosin filaments overlap to a greater degree.

A

thick

6
Q

Sliding filament model of contraction: When does sliding begin?

A

When the myosin heads on the thick filaments latch onto myosin-binding sites on actin in the thin filaments.

7
Q

Sliding filament model of contraction: For sliding to begin, the ___ heads on the thick filaments latch onto __ __ ___ on actin in the thin filaments.

A

myosin,

myosin-binding sites

8
Q

Sliding filament model of contraction 2: These cross bridge attachments form and break several times during a contraction, acting like tiny ratchets to generate tension and propel the thin filaments toward the ___ of the sarcomere.

A

center

9
Q

Sliding filament model of contraction: What happens when cross bridge attachments form and break several times during a contraction?

A

It generate tension and propels the thin filaments toward the center of the sarcomere.

10
Q

Sliding filament model of contraction 3: What is the end result of the generated tension that propels the thin filaments toward the center of the sarcomere?

A

Causes the muscles to shorten

11
Q

Sliding filament model of contraction: Notice that as the thin filaments slide centrally, the Z discs to which they attach are pulled __ the M line.

A

toward

12
Q

Overall, as a muscle cell shortens, what are the 4 things that occur?

A

1- I bands shorten
2-Distance between Z discs shorten
3-H zones disappear
4-A bands move closer together; length does not change

13
Q

Cross bridges occur when

A

myosin heads bind to actin

14
Q

Overall, as a muscle cell shortens, what are the 4 things that occur?

A

1- I bands shorten
2-Distance between Z discs shorten
3-H zones disappear
4-A bands move closer together; length does not change

15
Q

During muscle shortening, the ___ is pulled toward the M line.

A

Z discs

16
Q

Contraction ends when the ___ ___ become inactive, ___ declines, and the muscle fiber ___.

A

cross bridges
tension
relaxes

17
Q

A contraction is triggered by a series of molecular events known as the

A

Cross bridge cycle

18
Q

The formation of a cross bridge is initiated when ___ ___ released from the sarcoplasmic reticulum bind to troponin.

A

Calcium ions

19
Q

The formation of a cross bridge is initiated when calcium ions released from the sarcoplasmic reticulum bind to ___. This binding causes ___ to change shape.

A

troponin, troponin

20
Q

____ moves away from the myosin binding sites on actin allowing the myosin to bind actin and form a cross bridge.

A

Tropomyosin

21
Q

The myosin head must be activated before cross bridge cycle can begin. This occurs when ___ binds to the head and is hydrolyzed to ADP and inorganic phosphate.

A

ATP

22
Q

The myosin head must be activated before cross bridge cycle can begin. This occurs when ATP binds to the head and is hydrolyzed to _________.

A

ADP and inorganic phosphate.

23
Q

The energy liberated from the __ _ __ activates the myosin head, forcing it into the cocked position.

A

hydrolysis of ATP

24
Q

Cross bridge cycle maybe divided into four steps.

Step 1: __ __

A

Crossbridge formation

25
Q

Step 1: Cross bridge formation
The activated myosin head binds to actin, forming a cross bridge. ___ ___ is released and the bond between myosin and actin become stronger.

A

Inorganic phosphate

26
Q

What is released to cause the bond between myosin and actin become stronger?

A

Inorganic phosphate

27
Q

What is Step 2?

A

Step 2: The power stroke

28
Q

Step 2: The power stroke

__ is released and the activated myosin head pivots, sliding the thin myofilament toward the center of the sarcomere.

A

ADP

29
Q

What is Step 3?

A

Step 3: Cross bridge detachment

30
Q

Step 3: Cross bridge detachment

When another ___ binds to the Myosin head, the link between the myosin head and actin __ and the myosin head detaches.

A

ATP, weakens

31
Q

What is Step 4?

A

Step 4: Reactivation of myosin head

32
Q

Step 4: Reactivation of myosin head

ATP is hydrolyzed to __ __ ___ __. The energy released during hydrolysis reactivates the myosin head, returning it to the cocked position.

A

ADP and inorganic phosphate

33
Q

As long as the binding sites on __ remain exposed, the cross bridge cycle will repeat.

A

actin

34
Q

And as the cycle repeats, the thin myofilaments are pulled ___ each other and the sarcomere ___. This shortening causes the whole muscle to contract.

A

Toward, shortens

35
Q

Cross bridge cycling ends when calcium ions are actively transported back into the ___ ___.

A

sarcoplasmic reticulum

36
Q

___ returns to its original shape allowing tropomyosin to glide over and cover the myosin binding site on actin.

A

Troponin

37
Q

Polypeptide strand which is a rod-shaped protein and spirals about the actin core to help stiffen and stabilize it.

A

Tropomyosin

38
Q

Successive tropomyosin molecules are arranges end to end along the actin filaments, and in a relaxed muscle fiber, block __ __ __ __ __ so that myosin heads on the thick filaments cannot bind to thin filaments.

A

myosin-binding sites on actin

39
Q

Troponin is a globular 3-polypeptide complex. One of its polypeptides is an inhibitory subunit that binds to

A

actin

40
Q

Another type of troponin binds to tropomyosin and helps position it on

A

actin

41
Q

The third type of troponin binds

A

calcium ions