84) All three types of fatty acids (long-chain, medium-chain and short-chain fat

Question

84) All three types of fatty acids (long-chain, medium-chain and short-chain fatty acids) are used for b-oxidation in mitochondria. However, they are processed differently. How different?

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85) Keton bodies are very important source for energy homeostasis. Where is it made and what is the source of keton body synthesis?

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86) Where is keton bodies used primarily?

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87) Protein is degraded during fasting. Where are amino acids used and for what purpose?

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88) During fasting, TAG is hydrolyzed to free fatty acids and glycerol. Is glycerol used for any purpose?

Explanation / Answer

The solutions to the above given problems are given below as,

84) Fatty acids yield energy by beta oxidation in the mitochondria of all cells, except those in the brain and kidney. They enter the mitochondria as specific acyl carnitine derivatives. Saturated short, medium, and long-chain fatty acids undergo the first step of beta-oxidation with different dehydrogenases. The process yields successive acetylCoA molecules which enter the tricarboxylic acid cycle or other metabolic pathways. Acetate is the eventual product from fatty acids with an even number of carbon atoms. Unsaturated fatty acids require two more enzymatic steps than saturated fatty acids to change cis double bonds to trans and to move them from the a to beta position. Even so, oxidation of unsaturated fatty acids, including linoleic acid is as fast or faster than that of palmitic acid. The initial oxidative reaction is carried out by a different enzyme from that in mitochondria; the fatty acyl CoA enters directly into this organelle. The process does not proceed to the complete production of acetate but a shortened fatty acid is transferred to the mitochondria for complete oxidation. Long chain (>20C) fatty acids are preferentially oxidized by peroxisomes; also fatty acids with less than 14C are oxidized by this system. Peroxisomal oxidation is energetically less efficient than mitochondrial oxidation and yields more heat.

85) Ketone bodies are synthesized in the liver from acetyl-CoA source.

86) Ketone bodies is primarily used as source of energy for the body in place of glucose during low intake of food or carbohydrate presence.

87) Proteins are degraded and synthesized within all tissues on a regular basis. When the body's energy sources are low, it begins to degrade proteins into amino acids for use as an alternative energy source. Amino acids can be classified as glucogenic or ketogenic. Glucogenic amino acids produce glucose under conditions of low glucose. This process is also known as gluconeogenesis, or the production of "new glucose." ketogenic amino acids on the ther hand produce ketones when energy sources are low. Some of these amino acids are degraded directly to ketone bodies such as acetoacetate. The other ketogenic amino acids can be converted to acetyl CoA. Acetyl CoA has several different fates, one of which is the conversion to acetoacetate. When energy sources are high, both glucogenic and ketogenic amino acids are converted to fatty acids through the intermediate acetyl CoA. Other amino acids that are degraded to intermediates in the Krebs Cycle are siphoned off into the production of urea, a nitrogenous carboxyl compound that is filtered through the kidneys and secreted in the urine.

88) Glycerol formed by the TAG hydrolysis is converted to the Glycolysis intermediate dihydroxyacetone phosphate.

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