Download Main Concepts Muscle structure, Oxidation of fats, Muscle types

Main Concepts Muscle structure, Oxidation of fats, Muscle types
1. The body has three different types of muscle tissue: skeletal (responsible for voluntary movement), cardiac and
smooth.
2. Skeletal muscle is composed of bundles of fibres, long thin multi-nucleated cells, each made from a bundle of
about one thousand fibrils. These fibrils consist of alternating sections of thick and thin filaments.
3. Thick filaments consist primarily of myosin, a large protein molecule consisting of three pairs of polypeptide
chains.
4. The major constituent of thin filaments is the protein actin, with smaller quantities of tropomyosin and
troponin.
5. Tropomyosin and troponin play an important role in muscle physiology by preventing the interaction between
myosin and actin when the muscle is in a relaxed state.
6. The repeating structural unit of a muscle fibril is called a sarcomere.
7. In muscle fibres the globular heads of the thick filaments project to form crosslinks with the thin filaments.
8. The mechanism for muscle contraction is explained by the ‘sliding filament model’, which proposes that the
thin actin filaments and the thick myosin filaments slide past each other and the area of overlap is extended as
a muscle contracts.
9. Muscle contraction requires the presence of both calcium ions (Ca2+) and ATP.
10. Skeletal muscle is composed of two types of muscle cells:
Type 1 (slow twitch) muscle cells which gain their energy from aerobic respiration
Type 2 (fast twitch) muscle cells which gain their energy from anaerobic respiration.
11. Glycogen is stored in small granules in muscle tissue. This can readily be broken down to glucose which is
available for glycolysis.
12. Anaerobic respiration generates lactate ion. The accompanying decrease in pH causes muscle fatigue and
cramps.
13. The tissues of the human body are able to utilise a variety of food compounds as fuels to supply their energy
needs. These fuel molecules include glucose, amino acids and fatty acids. All of these molecules can be
converted to acetyl–CoA by a variety of biochemical pathways.
14. The brain relies mainly on a constant supply of blood glucose to provide its energy needs. The inability of the
brain to use fatty acids as a fuel is due to the absence of the enzymes required for fatty acid oxidation and the
inability of the protein albumin to move from the blood into the brain.
15. Triacylglycerols (fats) provide considerably more energy per gram than carbohydrates and are the major form
of energy storage in humans.
16. To utilise the stored energy of triacylglycerols they must first be broken down into their components, glycerol
and fatty acids.
17. Fatty acids bind to albumin in the blood allowing them to be transported in a soluble form. These fatty acids
are converted to activated fatty acyl–CoA by the action of ATP and, two carbon atoms at a time, to acetyl–
CoA which then enters the TCA cycle in aerobic respiration.
18. The oxidation of fatty acids produces large quantities of energy in the form of ATP.
19. Fatty acid oxidation is in direct competition with glucose metabolism, competing for coenzyme A (CoA)
which converts pyruvate to acetyl–CoA.
20. Coenzyme A (CoA) is a carrier molecule which attaches to acetyl and acyl groups.
21. The body tends to use:
anaerobic respiration when short bursts of intensive exercise are involved;
aerobic respiration for extended periods of less intensive exercise.
22. In glycolysis, stored glycogen is converted to glucose. This process can provide energy at a much greater rate
than oxidation in the TCA cycle and accompanying oxidative phosphorylation.
23. Anaerobic glycolysis leads to the production of lactic acid (2-hydroxypropanoic acid) or lactate ion. The
overall reaction is:
glucose + 2ADP + 2Pi

2lactate + 2ATP + 2H2O
24. Much of the resulting lactate is transported to the liver where it is converted to glucose
25. Lactate production is accompanied by a build-up of hydrogen ion concentration in muscles, resulting in a
lowering of the tissue pH. This lowering of pH is the cause of muscle fatigue and cramps.