F215:04:09 The sliding filament model Flashcards Preview

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Flashcards in F215:04:09 The sliding filament model Deck (33)
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1
Q

Where are sarcomeres?

A

they are the span between one Z-line to the next

2
Q

How long is the sarcomere in a relaxed state?

A

2.5um

3
Q

Why are Z lines close together when a muscle is contracted?

A

because the lengths of the I-band and H-zone are reduced

But the A band does not change in length during contraction

4
Q

Describe how the different zones change in the sarcomere when muscles contract

A

the lengths of the I-band and H-zone are reduced

But the A band does not change in length during contraction

5
Q

What are the 2 types of filament involved in contraction?

A

actin and myosin

6
Q

Describe actin

A

Two strands coiled around each other like a twisted double string of beads
Each strand is composed of of G-actin subunits
Then Tropoyosin molecules coil round the F actin to reinforce it

7
Q

What is the purpose of Tropomyosin and where is it found?

A

Found coiled round actin

Acts as a reinforcement

8
Q

What is tropomyosin?

A

a rod shaped protein found coiled round actin

It has a troponin complex attached to each tropomyosin molecule

9
Q

What is troponin made up of?

A

3 polypeptides, one binds to actin, one to tropomyosin and the other to calcium ions

10
Q

Why is it important that troponin binds to tropomyosin and actin?

A

Ti keep the tropomyosin in place around the actin

11
Q

What are thick filaments bundles of?

A

the protein myosin, whose heads stick out from opposite ends of the filament

12
Q

What does each myosin molecule consist of?

A

a tail and 2 protruding heads

13
Q

what is the power stroke?

A

When the head groups bend causing the thin filament to be pulled along and so overlap with more thick filament.
Its part of muscle contractions and ADP and Pi are released

14
Q

What are the 4 stages of muscle contraction?

A
  1. Myosin head groups attach to the surrounding actin filaments forming a cross-bridge
  2. The head group then bends, causing the thin filament to be pulled along and so overlap more with the thick filament (power stroke) ADp and Pi are released
  3. The cross bridge is then broken as new ATP attaches to the myosin head
  4. The head group moves backwards as the ATP is hydrolysed to ADP and Pi. It can then for a cross bridge with the thin filament further along and start again
15
Q

What is a cross bridge?

A

When the myosin head groups attach to the surrounding actin filaments forming the cross bridge

16
Q

How is the whole muscle shortened during the contraction of a muscle?

A

several million cross bridges are being continuously made and broken causing the thin filaments to slide past the thick filaments to shorten the sarcomere, which then shortens the whole muscle

17
Q

How is calcium involved in muscle contraction

A

As binding sites for the myosin head group on the actin fibre are covered by tropomyosin subunits, they cannot attach to myosin head groups.
When an action potential arrives, calcium ions are released from the sarcoplasmic reticulum and bind to the troponin molecules, which changes it shape and uncovers the binding sites for actin-myosin

18
Q

when happens when the nervous stimulation stops in terms of calcium?

A

The calcium ions are actively transported back into the sarcoplasmic reticulum by carrier proteins on the membrane which leads to muscle relaxation

19
Q

Why is ATP needed in the power stroke/.

A

As when myosin head groups have attached to the actin binding site and bends, the molecules are in their most stable form, so ATP is needed to break this and reset the myosin head forwards

20
Q

Is a muscle fibre a cell or an organelle?

A

A cell

21
Q

Are myofibrils cells or organelles?

A

organelles

22
Q

How much ATP is available in a muscle fibre at any one time?

A

Enough to support 1-2 seconds of contraction

23
Q

How is continued contraction maintained?

A

ATP must be generated as quickly as it is used up, this is carried out by 3 mechanisms:

  • aerobic respiration
  • Anaerobic respiration
  • Transfer from creatine phosphase in the muscle cell sarcoplasm
24
Q

How does aerobic respiration produce ATP to allow contraction to be maintained?

A

Aerobic respiration takes place in muscle cell mitochondria
The level at which this process can regenerate ATP is dependent on the supply of oxygen to the muscles and the availability of respiratory substrates

25
Q

How does anaerobic respiration produce ATP to allow contraction to be maintained?

A

It takes place in the muscle cell of the sarcoplasm
Its quite a quick process but leads to a build up on lactic acid which is toxic
The lactic acid enters the blood and stimulated an increase in blood supply to the blood

26
Q

What are the pros and cons of using anaerobic respiration to maintain muscle contraction

A
Pros: 
quick
The lactic acid enters the blood and stimulated an increase in blood supply to the blood 
Cons: 
Lactic acid is toxic
27
Q

How does the transfer from creatine phosphase in the muscle cell sarcoplasm produce ATP to allow contraction to be maintained?

A

As the phosphate group from creatine phosphate can be transferred to ADP to form ATP very quickly by the action of the enzyme creatine phosphotransferase
The supply of creatine phosphate is sufficient to support muscular contraction for a further 2-4 seconds

28
Q

How long will the supply of creatine phosphate is sufficient to support muscular contraction for?

A

a further 2-4 seconds

29
Q

What enzyme ensures the phosphate group from creatine phosphate is transferred to ADP to form ATP very quickly?

A

creatine phosphotransferase

30
Q

List 3 uses of ATP in muscle cells

A

Contraction of sarcomeres in the power stroke

Protein synthesis

31
Q

Suggest why anaerobic exercise such as weight lifting does not help weight loss

A

As it leads to the production of lactate during explosive exercise
On completion of exercise, most of the lactate is converted back into pyruvate.
Anaerobic respiration is carried out during anaerobic exercise which can only use glucose as a respiratory substrate, to respire fat/fatty acids, aerobic respiration and exercise must be carried out

32
Q

Suggest which process for ATP regeneration is most important for a marathon runner

A

Aerobic respiration

33
Q

Suggest which process for ATP regeneration is most important for a 100m sprinter

A

creatine phosphate regeneration of ATP