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PROTEIN METABOLISM

PROTEIN METABOLISM The liver and kidneys play important roles in what happens to that sandwich you eat Once in the bloodstream, the amino acids travel to the liver and other organs, such as skeletal muscles, that use them to make proteins for tissue creation or repair. Amino acids are also used to build important molecules such as enzymes and hormones. You eat a turkey sandwich. Two slices of turkey breast contain roughly 7 g of protein. Two slices of whole wheat bread contribute an additional 8 g. In the stomach, hydrochloric acid denatures the proteins, making them easier to digest. The HCl also triggers the release of pepsin, a stomach enzyme that attacks the proteins’ central peptide bonds. The action of pepsin results in smaller peptide molecules, such as proteoses and peptones, that enter the small intestine. In the small intestine, digestion occurs using three forms of the peptidase enzyme that break down the peptide molecules into amino acids. Then, two transport systems, made up of carrier proteins and glutathione, absorb the amino acids into the intestinal wall and push them out into the bloodstream. The liver removes amines from the amino acids, resulting in carbon skeletons called α-keto acids. It recombines the amines and α-keto acids to make different nonessential amino acids, depending on the body’s needs. The nine amino acids that the body cannot synthesize must be obtained from dietary intake, for example, by eating both beans and rice in the same day. Amines that are not converted into other amino acids can be used for nucleotide synthesis. What remains forms ammonia. The liver converts ammonia to less toxic urea. Leftover α-keto acids are transformed into glucose or fatty acid precursors, both of which can be used for energy or stored as fat. The kidneys filter urea and excrete it in the urine. Excess protein consumption triggers the kidneys to increase urea, water, and calcium in the urine.

The liver and kidneys play important roles in what happens to that sandwich you eat. Start the process by dragging the sandwich to the mouth and tapping. 

The liver and kidneys play important roles in what happens to that sandwich you eat.

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