AQA A2 Biology Unit 5 - Muscle Contraction

Revision notes for AQA A2 Biology Unit 5 - Muscle Contraction, covering:

  • Structure of Skeletal Muscle
  • Muscle Fibres
  • Neuromuscular Junctions
  • Muscle contraction - sliding filament theory
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  • Created by: Alice
  • Created on: 16-06-12 14:15
Preview of AQA A2 Biology Unit 5 - Muscle Contraction

First 14 words of the document:

Muscle
Contractio
n
A2 Biology Unit 5
Alice Davies

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Structure of Skeletal Muscle
Muscles are effector organs that respond to nervous stimulation by contracting
and so bring about movement. There are three types of muscle in the body:
1. Cardiac Muscle ­ found exclusively in the heart, not under conscious
control
2. Smooth Muscle ­ found in the walls of blood vessels and the gut, not
under conscious control
3.…read more

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Microscopic Structure of Skeletal Muscle
Each muscle fibre is made up of myofibrils which are made up of two types of
protein filament:
Actin ­ thinner and consists of two strands twisted around one another
Myosin ­ thicker and consists of long rod-shaped fibres with bulbous
heads that project to the side
Arrangement of actin and myosin filaments
Myofibrils appear striped due to their alternating light-coloured and
dark-coloured bands.…read more

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Tropomyosin ­ forms a fibrous strand around the actin filament
Troponin ­ globular protein involved in muscle contraction
Types of Muscle Fibre
There are two types of muscle fibre, the proportions of which vary from muscle
to muscle and person to person.…read more

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There are many such junctions along the muscle. If there were only one junction
of this type it would take time for a wave of contraction to travel across the
muscle, in which case not all the fibres would contract simultaneously and the
movement would be slow.
As rapid muscle contraction is frequently essential for survival there are many
neuromuscular junctions spread throughout the muscle. This ensures that the
contraction of a muscle is rapid and powerful when it is simultaneously
stimulated by action potentials.…read more

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Contraction of Skeletal Muscles
The process of muscle contraction involves the actin and myosin
filaments sliding past one another and is therefore called the sliding
filament mechanism.
Evidence for the Sliding Filament Mechanism
Myofibrils appear darker in colour where the actin and myosin filaments
overlap and lighter where they do not. If the sliding filament mechanism is
correct, then there will be more overlap of actin and myosin in a contracted
muscle than in a relaxed one.…read more

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A globular protein formed in two bulbous structures at one end
(the head)
Actin ­ a globular protein whose molecules are arranged into long
chains that are twisted around one another to form a helical strand
Tropomyosin ­ forms long thin threads that are wound around actin
filaments
Sliding Filament Mechanism
Muscle Stimulation
An action potential reaches many neuromuscular junctions simultaneously,
causing calcium ion channels to open and calcium ions to move into the
synaptic knob.…read more

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Tropomyosin molecule prevents
myosin head from attaching to the
binding site on the actin molecule
2. Calcium ions released from the
endoplasmic reticulum cause the
tropomyosin molecule to pull away
from the binding sites on the actin
molecule.
3. Myosin head now attaches to the
binding site on the actin filament.
4. Head of myosin changes angle, moving
the actin filament along as it does so.
The ADP molecule is released.
5.…read more

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Muscle Relaxation
When nervous stimulation ceases, Ca2+ is actively transported back into
the endoplasmic reticulum using energy from the hydrolysis of ATP.
The reabsorption of Ca2+ allows tropomyosin to block the actin filament
again.
Myosin heads are now unable to bind to actin filaments and contraction
ceases, i.e. muscle relaxes.
Energy Supply during Muscle Contraction
Muscle contraction requires considerable energy which is supplied by the
hydrolysis of ATP to ADP and Pi.…read more

Comments

Pink Lipstick

Just copied out the textbook

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