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The Sarcomere
The span from one Z-line to
the next is known as the
During contraction the Z-lines
become close together as
the I-band and H-zone
reduce in length.
The A-band remains the
same length during
contraction.…read more

Slide 3

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Protein Filaments
There are two types of protein filaments found in the
muscle cells:
Thin filament is made up of two strands of F-actin
coiled together. Each strand is composed of a G-
actin subunit. Tropomyosin molecules coil around the
F-actin which has a troponin molecule attached.
The troponin has 3 binding sites, one to the actin,
one to tropomyosin and the last to calcium ions.
Thick filament are bundles of the protein myosin.
Each myosin molecule consists of a tail and two
protruding heads ­ called myosin heads.…read more

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The Power Stroke
1. Calcium ions are released from the sarcoplasmic
reticulum at the neuromuscular junction and bind to
the troponin molecules. This moves the
tropomyosin away from the binding site on the
2. The actin-myosin binding sites are uncovered and
the myosin head attaches to the surrounding actin
filament. This forms a cross bridge.
3. The head group bends causing thin filament to be
pulled and overlap with the thick filament. This is
the power stroke.
4. ADP and Pi are released.…read more

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5) ATP is required to break the cross bridge as it is
stable. The ATP attaches to the myosin head and
the cross bridge is broken.
6) The myosin head moves backwards and resets as
ATP is hydrolysed to ADP and Pi.
7) The myosin head can now form a new cross bridge
further along the thin filament.…read more

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Maintenance of ATP Levels
There is little levels of ATP readily within the muscle
There is a store of creatine phosphate (CP) within
the sarcoplasm. An enzyme transfers phosphate to
ADP that can be re-synthesised to ATP. This only
supplies enough energy for 6-8 seconds of exercise.
ATP must then be synthesised from aerobic
respiration in the mitochondria of muscle cells. The
level of ATP depends of the level of oxygen and
respiratory substrates available.
The rest comes from anaerobic respiration when
lactate is produced.…read more


Bethany Cunningham

Great resource. It has really helped me with my revision.

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