Protein metabolism

Protein metabolism denotes the various biochemical processes responsible for the synthesis of proteins and amino acids, and the breakdown of proteins (and other large molecules, too) by catabolism.

Dietary proteins are first broken down to individual amino acids by various enzymes and hydrochloric acid present in the gastro-intestinal tract.^[1] These amino acids are further broken down to α-keto acids which can be recycled in the body for generation of energy, and production of glucose or fat or other amino acids. This break-down of amino acids to α-keto acids occurs in the liver by a process known as transamination, which follows a bimolecular ping pong mechanism.^[2]

Protein synthesis

Protein biosynthesis relies on four processes:

• amino acid synthesis
• RNA synthesis
• transcription
• translation

Protein anabolism is the process by which protein are formed from amino acids (aka anabolic amino acid synthesis).

Protein breakdown

Protein catabolism is the process by which proteins are broken down to their amino acids. This is also called proteolysis.

This can be followed by further amino acid degradation.

Amino acid metabolism

The following list contains links to information about the metabolism of individual amino acids.

• Positively charged side chains
  • Arginine
  • Histidine
  • Lysine
• Negatively charged side chains
  • Aspartic acid
  • Glutamic acid
• Polar uncharged side chains
  • Serine
  • Threonine
  • Asparagine
  • Glutamine
• Special cases
  • Cysteine
  • Selenocysteine
  • Glycine
  • Proline
• Hydrophobic side chains
  • Alanine
  • Valine
  • Isoleucine
  • Leucine
  • Methionine
  • Phenylalanine
  • Tyrosine
  • Tryptophan

References

1. ↑ Mehta, S. Digestion of Dietary Proteins
2. ↑ Mehta, S. Metabolism of amino acids- bimolecular ping pong mechanism of transamination.

Metabolism map
Carbon Fixation Photo- respiration Pentose Phosphate Pathway Citric Acid Cycle Glyoxylate Cycle Urea Cycle Fatty Acid Synthesis Fatty Acid Elongation Beta Oxidation Peroxisomal Beta Oxidation Glyco- genolysis Glyco- genesis Glyco- lysis Gluconeo- genesis Decarb- oxylation Fermentation Keto- lysis Keto- genesis feeders to Gluconeo- genesis Direct / C4 / CAM Carbon Intake Light Reaction Oxidative Phosphorylation Amino Acid Deamination Citrate Shuttle Lipogenesis Lipolysis Steroidogenesis MVA Pathway MEP Pathway Shikimate Pathway Transcription & Replication Translation Proteolysis Glycosy- lation Sugar Acids Double/Multiple Sugars & Glycans Simple Sugars Inositol-P Amino Sugars & Sialic Acids Nucleotide Sugars Hexose-P Triose-P Glycerol P-glycerates Pentose-P Tetrose-P Propionyl -CoA Succinate Acetyl -CoA Pentose-P P-glycerates Glyoxylate Photosystems Pyruvate Lactate Acetyl -CoA Citrate Oxalo- acetate Malate Succinyl -CoA α-Keto- glutarate Ketone Bodies Respiratory Chain Serine Group Alanine Branched-chain Amino Acids Aspartate Group Homoserine Group & Lysine Glutamate Group & Proline Arginine Creatine & Polyamines Ketogenic & Glucogenic Amino Acids Amino Acids Shikimate Aromatic Amino Acids & Histidine Ascorbate (Vitamin C) δ-ALA Bile Pigments Hemes Cobalamins (Vitamin B12) Various Vitamin B's Calciferols (Vitamin D) Retinoids (Vitamin A) Quinones (Vitamin K) & Carotenoids (Vitamin E) Cofactors Vitamins & Minerals Antioxidants PRPP Nucleotides Nucleic Acids Proteins Glycoproteins & Proteoglycans Chlorophylls MEP MVA Acetyl -CoA Polyketides Terpenoid Backbones Terpenoids & Carotenoids (Vitamin A) Cholesterol Bile Acids Glycero- phospholipids Glycerolipids Acyl-CoA Fatty Acids Glyco- sphingolipids Sphingolipids Waxes Polyunsaturated Fatty Acids Neurotransmitters & Thyroid Hormones Steroids Endo- cannabinoids Eicosanoids Major metabolic pathways in metro-style map. Click any text (name of pathway or metabolites) to link to the corresponding article. Single lines: pathways common to most lifeforms. Double lines: pathways not in humans (occurs in e.g. plants, fungi, prokaryotes). Orange nodes: carbohydrate metabolism. Violet nodes: photosynthesis. Red nodes: cellular respiration. Pink nodes: cell signaling. Blue nodes: amino acid metabolism. Grey nodes: vitamin and cofactor metabolism. Brown nodes: nucleotide and protein metabolism. Green nodes: lipid metabolism.