Lecture 3.2a - Protein and amino acid metabolism

Proteins

• Proteins have multiple functions, including: cell signalling receptors, structural members of membranes, enzymes, ion pumps, ion channels, and transporters (e.g. haemoglobin)
• Excess proteins can serve as a metabolic fuel source and be converted into glucose or triglycerides for energy or energy reserves
• Proteins are synthesised from amino acids, and essential amino acids must be obtained from the diet

Protein Metabolism

• Protein anabolism is the process by which proteins are formed from amino acids
• There are 20 amino acids involved in protein synthesis

Protein Catabolism

• Stage 1 of protein catabolism occurs in the GI tract:
  • Stomach: pepsin and HCl denature proteins at low pH
  • Small intestine: digestive enzymes (secretin and CCK) break down polypeptide chains into smaller peptides
  • Pancreas: digestive enzymes further break down peptides
• Protein catabolism is also called proteolysis and can lead to further amino acid degradation

Catabolism of Amino Acids

• Stage 2 of protein catabolism involves the catabolism of amino acids:
  • Removal or exchange of functional groups
  • Release of excess nitrogen in the form of ammonium (NH4+)
  • Catabolism of the remaining carbon skeleton, which participates in different routes in the body

Nitrogen Metabolism

• Nitrogen metabolism refers to the metabolic processes related to the metabolism of all nitrogen-containing compounds (N-compounds)
• The human body (70kg male) contains approximately 2.0kg of nitrogen, accounting for ~3% of body weight

Nitrogen Balance

• Nitrogen balance is the measure of nitrogen output subtracted from nitrogen input
• A negative nitrogen balance is associated with malnourishment and/or overtraining, indicating that catabolic processes are overriding anabolic ones
• A positive nitrogen balance is often found during periods of over nutrition

This quiz covers the functions and synthesis of proteins, as well as protein metabolism including anabolism and catabolism. Learn about the importance of amino acids and protein's role in the body.