Muscles

Question 1

Myofibril

Answer 1

Made up of fused cells that
share nuclei/cytoplasm
(sarcoplasm) and many
mitochondria
millions of muscle fibres make
myofibrils - bringing about
movement

Question 2

Role of Ca in the
sliding filament
theory

Answer 2

When an action potential reaches the
muscle fibre, calcium ions are released
from the sarcoplasmic reticulum and
diffuse into the myofibrils.
calcium ions cause tropomyosin to
move and expose the binding sites on
the actin filament.
with these sites now accessible, the
myosin heads attach to actin, forming
actin moyosin cross-bridges.

Question 3

Role of
tropomyosin in
sliding filament
theory

Answer 3

Tropomyosin covers the myosin
binding site on the actin filament
Ca causes tropomyosin to move
and expose the binding site
2+
allows myosin to bind to actin,
forming cross-bridge

Question 4

Role of ATP in
myofibril
contraction

Answer 4

Hydrolysis of ATP -> ADP + Pi releases
energy
to break actinomyosin bridges (detach
or attach myosin and actin).
to move/bend the myosin head (the
powerstroke or recocking movement) so
that action filaments are moved
inwards.
for active transport of calcium ions
back into the sarcoplasmic reticulum
when nerve stimulation stops.

Question 5

Role of myosin
in myofibril
contraction

Answer 5

Myosin heads (with ADP attached)
attach to binding sites on actin.
form actinomyosin cross-bridge
power stroke - myosin heads move,
pulling actin
requires ATP to release energy
ATP binds to the myosin head to
break cross-bridge so myosin heads
can move further along actin

Question 6

Phosphocreatine

Answer 6

A chemical which is stored in muscles
If ATP levels are low, muscle contraction
cannot proceed efficiently.
Phosphocreatine (PCr) acts as a rapid
ATP source in muscle cells by donating
a phosphate group to ADP to make ATP,
ensuring ATP availability during short
bursts of intense activity.

Question 7

Slow-twitch
muscle fibres

Answer 7

Specialised for slow, sustained
contractions (endurance)
lots of myoglobin
many mitochondria - high rate
aerobic respiration to release ATP
many capillaries - supply high
concentrations of glucose/O2 &
prevent build-up of lactic acid
e.g. calf

Question 8

Fast-twitch
muscle fibres

Answer 8

Specialised in producing rapid,
intense contractions for short
duration
large glycogen store -> hydrolysed
to glucose -> glycolysis
higher concentration of enzymes
involved in anaerobic respiration -
fast glycolysis
phosphocreatine store
e.g. biceps

Question 9

Describe the
gross structure of
skeletal muscle

Answer 9

• Made up of bundles of muscle fibres
• muscle fibre is a long, cylindrical,
  multinucleate cell
• contain myofibrils, made up of
  repeating units called sarcomeres
• sarcoplasm is the cytoplasm of the
  muscle fibre
• sarcoplasmic reticulum stores and
  releases Ca2+ ions needed for muscle
  contraction

Question 10

Describe the
microscopic
structure of skeletal
muscle

Answer 10

• contain many myofibrils, made up of
  repeating sarcomeres
• Each sarcomere contains:
• → Actin (thin filament) and myosin
  (thick filament)
• → A-band: dark band (overlap of actin
  and myosin)
• → I-band: light band (only actin)
• → H-zone: only myosin
• → Z-lines: mark the ends of a sarcomere

Question 11

What is the role
of glycogen in
muscles?

Answer 11

• Glycogen is a stored form of glucose in
  muscle cells
• Acts as an energy reserve for aerobic and
  anaerobic respiration
• Hydrolysed into glucose for respiration
  to produce ATP
• → Ensures a rapid and local supply of
  glucose for muscle contraction