6.5

Question 0

Several myosin molecules lie together in a thick bundle with their bases attached at a point called the

Answer 0

M-line

Question 1

2 kinds of myofilaments:

Answer 1

Thick = myosin (dark bands)
Thin = actin (light bands)

Question 2

The myosin molecules have hook-shaped ‘heads’ projecting from the

Answer 2

Bundle

Question 3

The actin molecules lie together in a long chain, and 2 chains f actin twist together to form a long

Answer 3

Thin filament

Question 4

The actin filaments attach to each other at a point called the

Answer 4

Z-line

Question 5

The actin and myosin filaments lie alongside each other and overlap, producing the striped appearance of the

Answer 5

Myofibril

Question 6

The darker areas are where the actin and myosin filaments

Answer 6

Overlap

Question 7

The distance between 2 Z-lines is called a

Answer 7

Sarcomere

Question 8

(Sliding filaments) when muscles contract, the sarcomeres in each Myofibril get

Answer 8

Shorter

Question 9

(Sliding filaments) the sarcomere gets shorter because the

Answer 9

Actin and myosin filaments slide over each other, pulling the Z-lines closer together

Question 10

(Sliding filaments) energy from the ATP is needed for

Answer 10

The filaments to slide over each other

Question 11

(Sliding filaments) this sequence of sarcomeres shortening happens several times, making the actin filament

Answer 11

Slide past the myosin ‘heads’

Question 12

(Sliding filaments) the 2 kinds of filaments overlap further, pulling the

Answer 12

Z-lines closer together

Question 13

Stage 1) tropomyosin molecule prevents myosin head from attaching to the

Answer 13

Binding site on the actin molecule

Question 14

Stage 2) calcium ions released from the endoplasmic reticulum cause the tropomyosin molecule to pull away from the

Answer 14

Binding sites on the actin molecule by entering the sarcoplasm and binding to troponin

Question 15

Stage 3) myosin head now attaches to the binding site on the

Answer 15

Actin filament

Question 16

Stage 4) head of myosin changes angle, moving the actin filament along as it does so (power stroke). The ADP molecule is

Answer 16

Released

Question 17

Stage 5) ATP molecule fixes to myosin head, causing it to

Answer 17

Detach from the actin filament

Question 18

Stage 6) hydrolysis of ATP to ADP by ATPase provides the energy for the

Answer 18

Myosin head to resume its normal position

Question 19

Stage 7) head of myosin reattached to a binding site further along the actin filament and the cycle is

Answer 19

Repeated

Question 20

(ROLE OF CALCIUM IONS) when ATP is present, muscle tissue

Answer 20

Contracts

Question 21

(ROLE OF CALCIUM IONS) the inhibitor to stop the tissue contracting all the time is called

Answer 21

Tropomyosin

Question 22

(ROLE OF CALCIUM IONS) tropomyosin fits into binding sites on the actin filaments -

Answer 22

Stopping myosin from binding

Question 23

(ROLE OF CALCIUM IONS) however, when a muscle contracts, calcium ions enter the sarcoplasm. These bind to the protein troponin which acts to pull the

Answer 23

Tropomyosin out of the way, allowing the myosin ‘heads’ to bind to the actin binding sites

Question 24

(ROLE OF CALCIUM IONS) in relaxed muscles, calcium ions are actively transported out of the sarcoplasm. They are collected together in the membranes of T-tubules in the

Answer 24

Muscle filaments

Question 25

(ROLE OF CALCIUM IONS) t-tubules are

Answer 25

Infoldings of membrane that run through the muscle fibres at intervals, close to the endoplasmic reticulum

Question 26

(STIMULATING A MUSCLE TO CONTRACT) muscles contract when they are stimulated by an

Answer 26

Action potential from a motor neurone

Question 27

(STIMULATING A MUSCLE TO CONTRACT) a motor neurone synapses with a muscle at a neuromuscular junction. When the transmitter substance fits into specific receptors in the postsynaptic membrane (sarcolemma), sodium ions enter the sarcoplasm -

Answer 27

Depolarising the membrane

Question 28

(STIMULATING A MUSCLE TO CONTRACT) depolarised membrane causes calcium ions from the T-tubules to enter the

Answer 28

Sarcoplasm and muscle contraction occurs