Protein and Amino Acid Metabolism Lecture Notes PDF
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Aston University
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These lecture notes explain protein and amino acid metabolism, including synthesis, breakdown, and the nitrogen cycle. The document details stages of protein catabolism and emphasizes the role of amino acids and nitrogen balance.
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Proteins: ◦Cell signalling receptors, structural members of membranes, enzymes, ion pumps, ion channels, transporters (e.g. haemoglobin) ◦Potential to serve as a metabolic fuel source ◦Excess proteins must be converted into glucose or triglycerides, and used to supply...
Proteins: ◦Cell signalling receptors, structural members of membranes, enzymes, ion pumps, ion channels, transporters (e.g. haemoglobin) ◦Potential to serve as a metabolic fuel source ◦Excess proteins must be converted into glucose or triglycerides, and used to supply energy or build energy reserves ◦Proteins are synthesised from amino acids ◦Essential amino acids obtained from diet Protein metabolism - synthesis: ◦Protein anabolism is the process by which proteins are formed from amino acids ◦20 amino acids Stages of catabolism: Protein metabolism - breakdown: ◦Stage 1 - GI tract: ‣ Stomach - pepsin and HCl ‣ Low pH denatures proteins ‣ Small intestine - secretin and CCK (digestive enzymes that break down long polypeptide chains into smaller peptides) ‣ Pancreas - digestive enzymes Catabolism of proteins - stage 1: ◦Protein catabolism is the process by which proteins are broken down to their amino acids ◦This is also called proteolysis and can be followed by further amino acid degradation. Catabolism of proteins - stage 2: ◦Stage 2 - catabolism of amino acids: ‣ Removal or exchange of functional groups ‣ Releases excess nitrogen in the form of ammonium (NH4+) ‣ Catabolism of the remaining carbon skeleton - participates in different routes in the body Nitrogen metabolism: ◦Metabolic processes that relate to the metabolism of all nitrogen-containing compounds (N- compounds) ◦Nitrogen in the body (70kg male) is ~2.0kg (~3% of the body weight) Nitrogen balance: ◦Measure of nitrogen output subtracted from nitrogen input ◦A negative nitrogen balance is associated with malnourishment and/or overtraining i.e. catabolic processes are overriding anabolic ones ◦A positive value is often found during periods of over nutrition (e.g. pregnancy and childhood) Amino acids - pool: ◦The 9 essential amino acids are - histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine Catabolism of amino acids: ◦Transamination - removal of the NH2 group ◦Alanine aminotransferase (ALT) (also called glutamate-pyruvate transaminase (GPT)) ‣ Alanine + alpha-ketoglutarate pyruvate + glutamate ◦Aspartate aminotransferase (AST) (also called glutamate-oxaloacetate transaminase (GOT)) ‣ Aspartate + alpha-ketoglutarate oxaloacetate + glutamate ◦Deamination - removal of the NH2 group as free ammonia, then converted to urea (urea cycle) ◦Most (98.5%) of the ammonia in the body (pH 7.4) is in the form of the ammonium ion: ‣ NH3 + H2O NH4 + OH- (NH3 is toxic)
