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Role of ATP in mammals- muscle contraction and sodium
potassium pumps
Adenosine triphosphate, also known as ATP, is a molecule that carries energy within
cells
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All living things use ATP
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Structure of ATP as shown in the
diagram
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6Kj of energy
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One of the key metabolic processes in the body that utilises ATP is muscle
contraction or locomotion
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Firstly, skeletal muscles are
attached to bones by bundles of collagen fibres known as tendons
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The 2nd type of muscle is cardiac muscle
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Its main function is to pump blood
around the heart
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The 3rd type of muscle in the
body is smooth muscle; it consists of myocytes which are muscle cells common in
every muscle found in the body
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Smooth muscle is generally found in tubular structures like vessels and
ducts to transport fluid or molecules around the body
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Myofibrils consist of myofilaments actin and
myosin
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Actin: A thin, contractile
protein filament, containing 'active' or 'binding' sites
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To further go into the structure of the 2 myofilaments; actin and myosin an electron
microscope can be utilised to show the functional unit of a myofilament
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They consist of long, fibrous
proteins that slide pst each other as muscle contraction occurs
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This is the protein
band to which actin is linked
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The myosin,
being thicker, shows up as a dark band
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This is a band found in
the middle of the sarcomere which
are formed from cross bridges of the
cytoskeleton
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At each twist there is a binding
site for myosin
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Myosin:
The filament consists of many myosin molecules
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The head attaches to the myosin binding sites on the actin where the actin and
myosin filaments overlap
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The heads contain ATPase enzyme which
releases energy from ATP to power muscle contraction
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The
impulse at this stage is an electrical one
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Contraction occurs when an impulse from a motor neurone reaches the synapse at
the junction with the muscle
To bring about a response the neurone cell membranes become depolarised which
will involve the sodium- potassium pumps, sodium channels and potassium
channels
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When a stimulus occurs, the neurone cell membrane is excited, which causes
the sodium ion channels to open
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So, sodium diffuses down an electrochemical gradient, which will
make the inside of the neurone less negative
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If the potential difference reaches the threshold, ( -55mv) voltage-hated
sodium channels open
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This is
depolarisation
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Around +30mv, sodium ion channels close, and potassium ion channels open
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Which gets the membrane back to its resting potential
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4
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The potential difference becomes more negative than the
resting potential ( -70 mv)
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To maintain the resting potential, the ion-channels are reset, the sodiumpotassium pumps move sodium ions out of the membrane (3 Na+ ions)
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This creates an
electrochemical gradient
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The sodium-potassium pumps also move potassium ions into the neurone (2
k+)
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This makes the outside of the cell positively charged compared to the inside
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The pumps use active transport to move three sodium ions out of the neurone
and 2 potassium ions into the neurone
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With
muscle contraction, synapses are involved at the junction of the muscle
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1
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2
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Calcium diffuses into sarcoplasmic reticulum
4
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5
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6
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This energy causes the myosin heads to rotate
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7
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