Function of Brown

The amount of brown fat in the body is greatest at the time of birth. Brown fat is the major site for thermogenesis (heat production) in the newborn, and is especially prominent around the kidneys and adrenal glands. Smaller amounts are also found around the blood vessels of the chest and neck. In response to regulation by thyroid hormone (see chapter 11) and norepinephrine from sympathetic nerves (see chapter 9), brown fat produces a unique

Fat Beta Oxidation

■ Figure 5.13 Beta-oxidation of a fatty acid. After the attachment of coenzyme A to the carboxyl group (step 1), a pair of hydrogens is removed from the fatty acid and used to reduce one molecule of FAD (step 2). When this electron pair is donated to the cytochrome chain, 1.5 ATP are produced. The addition of a hydroxyl group from water (step 3), followed by the oxidation of the P-carbon (step 4), results in the production of 2.5 ATP from the electron pair donated by NADH. The bond between the a and P carbons in the fatty acid is broken (step 5), releasing acetyl coenzyme A and a fatty acid chain that is two carbons shorter than the original. With the addition of a new coenzyme A to the shorter fatty acid, the process begins again (step 2), as acetyl CoA enters the Krebs cycle and generates ten ATP.

■ Figure 5.13 Beta-oxidation of a fatty acid. After the attachment of coenzyme A to the carboxyl group (step 1), a pair of hydrogens is removed from the fatty acid and used to reduce one molecule of FAD (step 2). When this electron pair is donated to the cytochrome chain, 1.5 ATP are produced. The addition of a hydroxyl group from water (step 3), followed by the oxidation of the P-carbon (step 4), results in the production of 2.5 ATP from the electron pair donated by NADH. The bond between the a and P carbons in the fatty acid is broken (step 5), releasing acetyl coenzyme A and a fatty acid chain that is two carbons shorter than the original. With the addition of a new coenzyme A to the shorter fatty acid, the process begins again (step 2), as acetyl CoA enters the Krebs cycle and generates ten ATP.

uncoupling protein. This protein causes H+ to leak out of the inner mitochondrial membrane, so that less H+ is available to pass through the respiratory assemblies and drive ATP synthase activity. Therefore, less ATP is made by the electron-transport system than would otherwise be the case. Lower ATP concentrations cause the electron-transport system to be more active and generate more heat from the respiration of fatty acids. This extra heat may be needed to prevent hypothermia (low body temperature) in newborns.

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