1 Amino Acid Metabolism .pdf

Amino Acid Metabolism 1 POLYMER OF AMINO ACIDS Protein Structure 2 Objectives list the function and role of amino acids. describe briefly the process of protein digestion and amino acids absorption. explain the importance of transamination, deamination and decarboxylat...

Amino Acid Metabolism 1 POLYMER OF AMINO ACIDS Protein Structure 2 Objectives list the function and role of amino acids. describe briefly the process of protein digestion and amino acids absorption. explain the importance of transamination, deamination and decarboxylation in the removal of nitrogen and carbon from amino acids. describe briefly essential and non essential amino acid metabolism. explain the concept of nitrogen balance. explain the concept of nitrogen metabolism in the body in times of dietary surplus and depletion of the pool of amino acids. describe the importance of glucogenic and ketogenic amino acids.  Digestion of Proteins During Fed State  Absorption of Amino Acid Secondary active Na+ dependent transport system Facilitated transporter  Structure of Amino Acid Peptide bond Side chain Amino group Carboxyl group  Amino Acids Functions Serves as the building blocks for protein synthesis Precursors for the nitrogen-containing compounds of the body Neurotransmitters and hormones Heme Purine and pyrimidine bases source of energy in starvation  Nitrogen balance Difference between the amount of nitrogen taken into the body each day and the amount of nitrogen-containing compounds lost in urine, sweat, feces and dead cells Healthy adult, Nitrogen balance =0 More is lost than obtained from diet, Nitrogen balance = negative ✓Inadequate dietary protein ✓Lack of any essential amino acids ✓During physiologic stress – trauma, burns, illness, surgery More ingested than excreted, Nitrogen balance = positive ✓Required for growth of children, pregnancy & recovery from illness Fate of Amino Acids  Removal of Nitrogen from Amino Acids Transamination & Deamination are crucial process for protein turnover and amino acid degradation Alanine & Glutamine are major carriers of nitrogen from amino acid degradation in muscle and peripheral tissues to the liver for urea cycle  Transamination Process of removing amine group from amino acids. Nitrogen is transferred from amino acid to α-ketoglutarate to form glutamate. Catalysed by transaminase or aminotransferase Cofactor involved is pyridoxal phosphate (vit B6) Reversible reaction All amino acids except lysine & threonine can undergo transamination. ALT AST  Diagnostic Value Alanine aminotransferase Aspartate aminotransferase Elevated levels in plasma indicates damage to cells rich in these enzymes. Liver disease Plasma AST and ALT are elevated Non-hepatic disease Myocardial infarction Muscle disorders  Deamination removal of nitrogen from amino acids such as glutamate, histidine, serine, threonine, glutamine & asparagine as ammonia or ammonium source of ammonia/ammonium for urea cycle occur in cells and gut bacteria  Breakdown of Amino Acids Carbon Skeletons Catabolism of amino acids involves removal of amino groups and breakdown of carbon skeletons to form intermediates for storage and energy metabolism Glucogenic amino acids ✓ yields pyruvate or intermediates of TCA cycle or substrates for gluconeogenesis Ketogenic amino acids ✓yields acetoacetate, acetyl CoA or acetoacetyl CoA ✓leucine and lysine are exclusively ketogenic  Glucogenic Both Ketogenic Nonessential Alanine Tyrosine *Arginine Asparagine Aspartate Cysteine Glutamate Glycine Proline Serine Essential Histidine Isoleucine Leucine Methionine Phenylalanine Lysine Threonine Tryptophan Valine  Essential amino acids must be obtained in the diet Non-essential amino acids can be synthesized in the body carbon skeletons come from intermediates of glycolytic pathway & Kreb’s Cycle. amino group is added by transamination of preexisting amino acids. can be formed from 3- phosphoglycerate, pyruvate, oxaloacetate and α-ketoglutarate.