Physiology 2130 Study Guide - Midterm Guide: Globular Protein, Endoplasmic Reticulum, Muscle Fascicle

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2 Feb 2016
Skeletal muscle structure:
- Composed of bundles of multi-nucleated cells
- Number of muscle cells in a whole muscle depends on size of whole muscle
- Lengths very from 1mm to 12 cm
- Myofibril is made of a series of sarcomeres, the basic contractile unit of muscle
- Contain glycogen as form of energy store and myoglobin in store O2
Breakdown of muscle:
Whole muscle- fascicle- muscle cell/fiber- myofibril- myofilaments (thick and thin)
Sarcoplasmic reticulum: forms a sleeve like structure around each myfibril, at the end
of each fiber there is a lateral sac or terminal cisternae where calcium is stored. Also
wraps around myofibrils
Transverse t- tubules: are continuations of the cell membrane that travel into muscle and
wrap around myofibrils. They allow the AP to travel inside the muscle cell where
contractile proteins are located
Thin Myofilament: Made of 3 proteins
1) Actin- a globular protein forming a 2 strand chain, contains myosin binding sites
2) Tropomyosin- rod shaped protein composed of 2 protein chains wrapped to form
a super coil. Lies lengthwise on actin strands and each molecule is associated with
6-7 actin globular molecules. In relaxed muscle it is situated to partially cover the
myosin binding site
3) Troponin- in relaxed muscle it is attached to trophomyosin and actin so that it
holds the trophomyosin molecule over the myosin binding site on the actin
Thick Myofilament: made of many individual myosin molecules. Myosin is made of 2
polypeptide chains with an alphahelical head and a globular tail. Head has binding site
for actin
Sliding Filament Theory:
- when myosin binds to actin a cross bridge is formed
- myosin then changes shape and a power stroke occurs
- actin slides past myosin
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