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Biology A2: 5.5 > 5.5.11: Muscle contraction > Flashcards

5.5.11: Muscle contraction Flashcards

1
Q

What is creatine phosphate?

A

A compound in a muscle that acts as a store of phosphates and can supply phosphates to make ATP rapidly.

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2
Q

What are myofibrils and what do they contain?

A
  • They are the contractile units of skeletal muscle and contain two types of protein filament:
  • Thin filaments, which are aligned to make up the light band. These are held together by the z line.
  • Thick filaments, which make up the dark band.
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3
Q

How much overlap is there between the thick and thin filaments?

A
  • The thick and thin filaments overlap, but in the middle of the dark band there is no overlap.
  • This is called the H zone.
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4
Q

What is the distance between two Z lines called?

A

-A sarcomere.

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5
Q

What is the function and size of the sarcomere?

A
  • This is the functional unit of the muscle.

- At rest, a sarcomere is about 2.5 um long.

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6
Q

What are the thick and thin filaments surrounded by?

A

Sarcoplasmic reticulum.

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7
Q

What are the thin filaments made up of?

A
  • Actin
  • Each filament consists of two chains of actin subunits twisted around each other.
  • Wound around the actin is a molecule of tropomyocin to which are attached globular molecules of troponin.
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8
Q

What does each troponin complex consist of?

A
  • Three polypeptides.

- One binds to actin, one to tropomyosin and the third binds to calcium when it is available.

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9
Q

What is the function of tropomyosin and troponin?

A
  • Tropomyosin and troponin are part of the mechanism to control muscular contraction.
  • At rest, these molecules cover binding sites to which the thick filaments can bind.
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10
Q

What does each thick filament consist of?

A
  • A bundle of myosin molecules.
  • Each myosin molecule has two protruding heads, which stick out at each end of the molecule.
  • These heads are mobile and can bind to the actin when the binding sites are exposed.
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11
Q

Which observation led to the sliding filament hypothesis?

A
  • During contraction, the light band and the H zone get shorter.
  • Therefore, the Z lines move closer together and the sarcomere gets shorter.
  • During contraction, the thick and thin filaments slide past one another.
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12
Q

What is the sliding action in muscles caused by?

A
  • The movement of the myosin heads.
  • When the muscle is stimulated, the tropomyosin is moved aside, exposing the binding sites on the actin.
  • The myosin heads attach to the actin and move, causing the actin to slide past the myosin.
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13
Q

Describe the stages in the control of muscle contraction.

Step 1:

A
  1. When the muscle is stimulated, the action potential passes along the sarcolemma and down the transverse tubules into the muscle fibre.
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14
Q

Describe the stages in the control of muscle contraction.
Step 1: When the muscle is stimulated, the action potential passes along the sarcolemma and down the transverse tubules into the muscle fibre.
Step 2:

A
  1. The action potential is carried to the sarcoplasmic reticulum, which stores calcium ions, and causes the release of calcium ions into the sarcoplasm.
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15
Q

Describe the stages in the control of muscle contraction.
Step 2: The action potential is carried to the sarcoplasmic reticulum, which stores calcium ions, and causes the release of calcium ions into the sarcoplasm.
Step 3:

A
  1. The calcium ions bind to the troponin, which alters the shape pulling the tropomyosin aside. This exposes the binding sites on the actin.
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16
Q

Describe the stages in the control of muscle contraction.
Step 3: The calcium ions bind to the troponin, which alters the shape pulling the tropomyosin aside. This exposes the binding sites on the actin.
Step 4:

A
  1. Myosin heads bind to the actin, forming cross-bridges between the filaments.
17
Q

Describe the stages in the control of muscle contraction.
Step 4: Myosin heads bind to the actin, forming cross-bridges between the filaments.
Step 5:

A
  1. The myosin heads move, pulling the actin filament past the myosin filament.
18
Q

Describe the stages in the control of muscle contraction.
Step 5: The myosin heads move, pulling the actin filament past the myosin filament.
Step 6:

A
  1. The myosin heads detach from the actin and can bind again further up the actin filament.
19
Q

Millions of cross-bridges can be formed between the actin and the myosin filaments. What happens after the contraction has occurred?

A

-The calcium ions are rapidly pumped back into the sarcoplasmic reticulum, allowing the muscle to relax.

20
Q

What is the role of ATP in muscle contraction?

A

ATP supplies the energy for muscle contraction.

21
Q

How does a part of the myosin head act as ATPase?

A

It can hydrolyse the ATP into ADP and inorganic phosphate (Pi), releasing energy.

22
Q

How is ATP used during contractions?

Step 1:

A
  1. The myosin head attaches to the actin filament, forming a cross-bridge.
23
Q

How is ATP used during contractions?
Step 1: The myosin head attaches to the actin filament, forming a cross-bridge.
Step 2:

A
  1. The myosin head moves (tilts backwards), causing the thin filament to slide past the myosin filament. This is the power stroke. During the power stroke, ADP and Pi are released from the myosin head.
24
Q

How is ATP used during contractions?
Step 2: The myosin head moves (tilts backwards), causing the thin filament to slide past the myosin filament. This is the power stroke. During the power stroke, ADP and Pi are released from the myosin head.
Step 3:

A
  1. After the power stroke, a new ATP molecule attaches to the myosin head, breaking the cross-bridge.
25
Q

How is ATP used during contractions?
Step 3: After the power stroke, a new ATP molecule attaches to the myosin head, breaking the cross-bridge.
Step 4:

A
  1. The myosin head then returns to its original position (swings forward again) as the ATP is hydrolysed, releasing the energy to make this movement occur. The myosin head can now make a new cross-bridge further along the actin filament.
26
Q

Why is there a huge requirement for ATP?

A

Because there are millions of myosin heads involved in muscle contraction.

27
Q

Why does ATP need to be regenerated very quickly in order to allow continued contraction?

A

-The ATP available in muscle tissue is only enough to support at most 1-2 seconds’ worth of contraction.

28
Q

What are the three mechanisms involved in maintaining the supply of ATP?

A
  • Aerobic respiration in mitochondria.
  • Anaerobic respiration in the sarcoplasm of the muscle tissue.
  • Creatine phosphate.
29
Q

How does aerobic respiration in mitochondria maintain the supply of ATP and what is the drawback?

A
  • Muscle tissue contains a large number of mitochondria.
  • The Bohr effect helps to release more oxygen from the haemoglobin in the blood.
  • However, during intense activity, rate at which ATP produced limited by the delivery of oxygen to the muscle tissue.
30
Q

How does anaerobic respiration in the sarcoplasm of the muscle tissue maintain the supply of ATP and what is the drawback?

A
  • Anaerobic respiration releases a little more ATP from the respiratory substrates.
  • However, it leads to the production of lactate (lactic acid), which is toxic.
  • Anaerobic respiration can only last a few seconds before lactic acid build-up starts to cause fatigue.
31
Q

How does creatine phosphate in the sarcoplasm maintain the supply of ATP?

A
  • Creatine phosphate in the sarcoplasm acts as a reserve store of phosphate groups.
  • The phosphate can be transferred from the creatine phosphate to ADP molecules, creating ATP very rapidly.
32
Q

Which enzyme is involved in the production of ATP from creatine phosphate?

A

-The enzyme creatine phosphotransferase is involved.

33
Q

How long will the supply of creatine phosphate support muscular contraction?

A

-The supply of creatine phosphate is sufficient to support muscular contraction for a further 2-4 seconds.

Biology A2: 5.5 (11 decks)

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