protein metabolism

• AAs are not stored by the body and are present in cells, blood, and the extracellular fluids.
• AAs must be acquired from the diet (essential amino acids), de novo synthesis (nonessential amino acids), and protein degradation.
• AAs are depleted through body protein synthesis, biosynthesis of essential nitrogen-containing small molecules, and catabolism to glucose, glycogen, fatty acids, ketone bodies, or CO2 + H2O.
• In the glucogenic pathway, aspartate and asparagine are converted to oxaloacetate.
• Succinyl CoA is produced in the major glucogenic pathway and is converted to CoA via glycine.
• In the degradation of aspartate, the major product is oxaloacetate.
• In the degradation of aspartate, the minor product is fumarate.
• In the glucogenic pathway, phenylalanine and tyrosine are converted to fumarate.
• In the fed state, amino acids are used for the synthesis of proteins in the liver and in other tissues, with the excess used to produce glucose or triacylglycerol.
• In the fasting state, muscle protein is cleaved to amino acids, with some of the amino acids oxidized to produce energy.
• Phenylalanine and tyrosine are amino acids that yield fumarate in the ketogenic pathway.
• Aspartate and asparagine are amino acids that yield OAA in the ketogenic pathway.
• Protein turnover results from the simultaneous synthesis and degradation of protein molecules.
• Uremia is a biochemical abnormality that includes S/ Sx.
• In the fasting state, the carbon skeletons of the amino acids produce glucose, ketone bodies, and CO2 + H2O.
• The carbon skeletons of the amino acids produce six major products: Pyruvate, Acetyl-CoA, α-ketoglutarate, Succinyl-CoA, Fumarate.
• Hyperammonemia is a rise in ammonia level due to defects in urea cycle, which is a medical emergency due to neurotoxic effects on the CNS.
• In the well-fed state, the liver can convert intermediates of amino acid metabolism to glycogen and triacylglycerols.
• Protein is a fuel, with almost all amino acids generating NADH during degradation, which can enter the ETC for oxidative phosphorylation.
• Metabolism of the carbon skeleton parallels metabolism of glucose and fatty acids.
• Azotemia is a biochemical abnormality characterized by a high level of nitrogenous products in the blood, including BUN, creatinine, and urea.
• Protein synthesis and protein degradation occur in the cell.
• Lysosomal degradation primarily degrades extracellular proteins.
• Ubiquitin-Proteasome Pathway primarily degrades intracellular proteins.
• In the Ubiquitin-Proteasome Pathway, proteins attach covalently to ubiquitin, a small (76 AA), globular, non-enzymic protein.
• The linkage of the α-carboxyl group of the C-terminal Gly of ubiquitin to the ε-amino group of a Lys on the protein substrate is a three-step, enzyme-catalyzed, ATP-dependent process.
• Glutamate, Glutamine, Proline, Arginine, Histidine are degraded to α-KG.
• Glucogenic amino acids degradation leads to pyruvate, while ketogenic amino acids degradation leads to acetyl CoA.
• Serine, Glycine, Cysteine, Alanine, Tryptophan, Threonine are degraded to pyruvate.
• Glucogenic amino acids include Serine, Glycine, Cysteine, Alanine, Tryptophan, Threonine.
• Methionine, Valine, Isoleucine, Threonine are degraded to succinyl CoA.
• Ketogenic amino acids include Acetyl CoA, Tryptophan, Isoleucine, Threonine, Lysine.
• Glucogenic amino acids yield pyruvate or TCA intermediates such as α-KG, succinyl CoA, fumarate, OAA.
• Ketogenic amino acids yield ketone bodies or their precursors such as acetyl CoA or acetoacetyl CoA.
• Leucine, Lysine, Tryptophan, Isoleucine, Threonine are degraded to acetyl CoA.
• Polyubiquitinated proteins are recognized by proteasomes, a protease complex.
• The proteasome unfolds, deubiquitinates, and cuts the target protein into fragments that are then further degraded to amino acids, which enter the amino acid pool.
• Amino acid pool is in a steady state - the input to the amino acid pool is balanced by the output.
• The amount of nitrogen ingested each day, mainly in the form of dietary protein, is equal to the amount of nitrogen excreted.
• Cytosolic and mitochondrial fumarase and malate dehydrogenase communicate in the urea cycle.