Muscles

Question 1

Describe the structure of a myosin protein

Answer 1

Bulbous head
Tail
Quaternary structure - two proteins held together

Question 2

What do the two binding site on the myosin head bind to ?

Answer 2

Actin
ATP

Question 3

Name the ion that binds to troponin

Answer 3

Calcium ions

Question 4

Name the protein that covers the myosin binding sites when the muscle is not contracting

Answer 4

Tropomyosin

Question 5

What is the name of the theory that explain muscle contraction?

Answer 5

Sliding filament theory

Question 6

Name the two types of filament involved in the sliding filament theory

Answer 6

Myosin and actin

Question 7

Describe the role of ATP in muscle contraction

Answer 7

Attachment of ATP on myosin head causes myosin to detach from actin. Causes the actinomycin cross bridge to break
Hydrolysis of ATP (on myosin head) causes myosin to re-cock

Question 8

Describe the role of calcium ions in muscle contraction

Answer 8

Calcium ions diffuse into myofibrils from sarcoplasmic reticulum
Bind to troponin
Tropomyosin moves to reveal myosin binding sites
Myosin heads attach to binding sites on actin

Question 9

Describe the role of glycogen in skeletal muscle

Answer 9

Hydrolysed to form glucose
Respired to release ATP

Question 10

Name the connection that forms when myosin binds to actin

Answer 10

Actinomyosin bridge

Question 11

Name three types of muscle found in the body and state where they are located.

Answer 11

Cardiac - exclusively in the heart
Smooth- walls of blood vessels and intestine
Skeletal - attached to bones by tendons

Question 12

What does the term ‘antagonistic pair’ means in terms of muscles?

Answer 12

Muscles act in pairs to pull joint n opposite directions

Question 13

Describe the gross structure of the skeletal muscle

Answer 13

Muscle cells fused together to form bundles of parallel muscle fibres (myofibrils)

Question 14

Describe the microscopic structure of skeletal muscle

Answer 14

Myofibrils - site of contraction
Sarcoplasm - shared nuclei and cytoplasm with lots of mitochondria and endoplasmic reticulum
Sarcolemma - cell membrane folds inwards to form T tubules

Question 15

Describe how an action potential is transmitted to the muscle cells at a neuromuscular junction

Answer 15

Action potential arrives at junction.
Calcium ion channels open and calcium ions diffuse into the pre-synaptic knob
Vesicles move towards and fuse with pre-synaptic membrane
Acetylcholine released and diffuses across synapse.
Acetylcholine binds to rector site on the muscle cell membrane (sarcolemma).
Sodium ions channels open causing depolarisation.

Question 16

Outline the sliding filament theory

Answer 16

Myosin head with ADP attached forms a cross bridge with actin
Power stroke - myosin head changes shape and loses ADP, pulling actin over myosin
ATP attaches to myosin head, causing it to detach from actin
ATP hydrolase so myosin head can return to original position
Myosin head re-attaches to actin further along the filament

Question 17

How does the sliding filament action cause a myofibril to shorten?

Answer 17

Myosin heads cause actin filaments to be pulled towards each other.
Distance between adjacent z lines shortens
Repeated up to 100 times per second to shorten the myofibril

Question 18

What happens during muscle relaxation?

Answer 18

Calcium ions actively transported back into the endoplasmic reticulum
Troponin changes shape
Causes tropomyosin to move and block actin binding sites.

Question 19

Explain the role of phosphocreatine in muscle contraction

Answer 19

Phosphorylates ADP directly to ATP when oxygen is in short supply due to vigorous exercise.

Question 20

Where are slow and fast twitch muscle fibres found in the body?

Answer 20

Slow twitch - sites of sustained contraction
Fast twitch - site of short term, rapid, powerful contractions

Question 21

Explain the role of slow and fast twitch muscle fibres

Answer 21

Slow twitch - long duration contraction, adapted to aerobic conditions to prevent lactate build-up
Fat twitch - powerful short term contraction, adapted for anaerobic respiration

Question 22

Explain the structure and properties of slow twitch muscles

Answer 22

Glycogen store - hydrolysed to release glucose for respiration
Contain myoglobin - higher affinity for oxygen at lower partial pressure
Many mitochondria - aerobic respiration needed to supply ATP
Surrounded by many blood capillaries to supply oxygen and glucose.

Question 23

Explain the structure and properties of fast twitch muscles

Answer 23

Large store of phosphocreatine
High concentration of enzymes for anaerobic respiration
Extensive endoplasmic reticulum to allow rapid uptake and release of calcium ions.