Contraction of Skeletal Muscle

Question 1

Describe the part played by tropomyosin in myofibril contraction

Answer 1

Moves out of the way when Ca2+ bind

Allowing myosin to bind to actin

Question 2

Describe the part played by Myosin in myofibril contraction

Answer 2

Head bind to actin and moves
Mysoin detaches from actin and resets
which uses ATP

Question 3

Describe the role played by ca2+ in muscle contractions

Answer 3

Ca2+ changes position of tropomyosin

Question 4

Explain how the muscle cell contracts

Answer 4

Myosin head changes shape

moving (actin and myosin) filaments between / past / along/over each other; [

Question 5

Describe how ATP is used in muscle contraction

Answer 5

hydrolysis of ATP releases energy for the power stroke

AT of Ca ions

Question 6

Endurance athletes, such as marathon runners, nearly always have a high proportion of slow fibres in their muscles. Explain the benefit of this.

Answer 6

Endurance athletes exercise for long periods of time; Respire / release energy aerobically; Or too much lactate would accumulate; Slow twitch fibres adapted to aerobic metabolism; As have many mitochondria; Site of Krebs’ cycle; And electron transport chain; Much ATP formed; Also are resistant to fatigue;

Question 7

Give three differences in structure between a muscle fibre and an epithelial cell from the lining of the small intestine.

Answer 7

multi-nucleate; striations / sarcomeres / banding; actin / myosin / contractile protein; no microvilli / surface not folded; more mitochondria; contain myoglobin;

Question 8

Describe the mechanism that brings about the change in position of the filaments when the myofibril contracts.

Answer 8

myosin filaments; form cross bridges to actin / bind to actin; move actin filaments / actin filaments move; ratchet mechanism described; allow relevant reference to ATP as energy source;

Question 9

Explain how a resting potential is maintained in a neurone.

Answer 9

membrane relatively impermeable / less permeable to sodium ions / gated ion channels are closed / fewer channels; sodium ions pumped / actively transported out; by sodium ion carrier / intrinsic proteins; higher concentration of sodium ions outside the neurone; inside negative compared to outside / 3 sodium ions out for two potassium ions in;

Question 10

Describe the roles of calcium ions and ATP in the contraction of a myofibril.

Answer 10

1. Calcium ions diffuse into myofibrils from
   (sarcoplasmic) reticulum;
2. (Calcium ions) cause movement of tropomyosin
   (on actin);
3. (This movement causes) exposure of the
   binding sites on the actin;
4. Myosin heads attach to binding sites on actin;
5. Hydrolysis of ATP (on myosin heads) causes
   myosin heads to bend;
6. (Bending) pulling actin molecules;
7. Attachment of a new ATP molecule to each
   myosin head causes my

Question 11

Give two ways in which ATP

is a suitable energy source for cells to use

Answer 11

1. Releases relatively small amount of energy /
   little energy lost as heat;
2. Releases energy instantaneously;
3. Phosphorylates other compounds, making them
   more reactive;
4. Can be rapidly re-synthesised;
5. Is not lost from/does not leave cells;

Question 12

Name the three types of muscle

Answer 12

Cardiac, Smooth and skeletal

Question 13

Muscle fibres are made up of ______

Muscle fibres share _____ and ______

Answer 13

Muscle fibres are made up of myofibrils

Muscle fibres share nuclei and sarcoplasm

Question 14

Sacoplasm has a large concentration of _____ and ___

Answer 14

Sacoplasm has a large concentration of Mitochondrion and endoplasmic reticulum

Question 15

What two materials are myofibrils made up of?

Answer 15

Actin and myosin

Question 16

Describe the structure of an actin

Answer 16

2 thinner twisted stands

Question 17

Describe the structure of a myosin

Answer 17

Thicker long rod-shaped tails with a bulbous head that project 2 the side

Question 18

Name the parts of a zoomed up fibril

Answer 18

I band 
Z line
H zone 
A band 
Sarcomere

Question 19

What does the I band stand for?

Answer 19

Isotropic band

Question 20

What does the A band stand for?

Answer 20

Anisotropic band

Question 21

Describe the structure of the I band

Answer 21

Light as a thick and thin filament that don’t overlap

Question 22

Describe the structure of the A band

Answer 22

Dark as filaments overlap

Question 23

Where is the H-zone?

Answer 23

At the centre of the A-band

Question 24

Where is the Z-line?

Answer 24

At the centre of the I-band

Question 25

Where is the sarcomere?

Answer 25

Distance between adjacent Z lines