Break down of carbon skeleton (R): Catabolism of carbon skeleton leading to formation of one or more of the following products:pyruvate, fumarate, α-ketoglutarate, succinyl CoA, oxaloacetate, acetyl CoA and acetoacetate. 1- Amino acids whose catabolism yields:pyruvate, fumarate, α- ketoglutarate, succinyl CoA or oxaloacetate are known to be glucogenic amino acids. These products are substrates for gluconeogenesis and lead to glucose production. 2- Amino acids whose catabolism yields acetoacetate (ketone body) or its precursor; acetyl CoA or acetoacetyl CoA are known to be ketogenic e.g. Leucine and Lysine are pure ketogenic. 3- Some amino acids are catabolized into both substrates of gluconeogenesis (i.e. give glucose) and acetoacetate so they are called: mixed ketogenic and glucogenic e.g phenylalanine, tyrosine, tryptophan and isoleucine.

Remember: Nutritional classification of amino acids: 1- Essential amino acids: These amino acids can’t be formed in the body and so, it is essential to be taken in diet. Their deficiency affects growth, health and protein synthesis. 2- Semiessential amino acids: These are formed in the body but not in sufficient amount for body requirements especially in children. Summary of essential and semiessential amino acids: Villa HM = Ten Thousands Pound V= valine i= isoleucine l= lysine l= leucine A = arginine* H= histidine* M= methionine T= tryptophan Th= threonine P= phenyl alanine *= arginine and histidine are semiessential 3- Non essential amino acids: These are the rest of amino acids that are formed in the body in amount enough for adults and children. They are the remai ning 10 amino acids.

Glycine amino acid: I- Non essential amino acid: as it is synthesized in the body from serine or threonine Serine ↔ glycine +CHO Threonine → glycine +CH 3 CHO II- glucogenic : Being converted into serine which is converted into pyruvate by the enzyme Serine dehydratase.

Functions of glycine: 1- Synthesis of heme: Glycine + Succinyl CoA → → → → → →Heme 2- Bile salt formation: Cholic acid (bile acid) +glycine + Na + or K + → Na or K glycocholate

3-Purines: C 4, C 5 and N 7 of purines are derived from glycine Serine: Glycine is converted into serine by the enzyme serine hydroxymethyl transferase. Serine is then converted into pyruvate so both glycine and serine are glucogenic ↔

5- Creatine: - Creatine is formed of glycine + arginine + methionine amino acid

Creatine is present in blood in the free form, while in muscles it is gained phosphate group from ATP by creatine kinase (CK) to give creatine phosphate (creatine ~ p) or called phospho creatine (PCr.) and ATP is converted into ADP. creatine ~ p is the main storage form of energy in muscles and used during muscle contraction. During intense physical exertion, ATP is rapidly recreated from ADP by the donation of a phosphate group from Phosphocreatine (PCr).

Creatinine: Is the anhydrous form of creatine and formed in muscles by nonenzymatic dehydration of creatine - Creatinine is excreted in urine. It is one of the kidney function tests. - Elevated creatinine levels in blood than normal indicates renal disease. -Normal creatinine levels: mg/dl. -II- Glycine participates in detoxification reactions in the body. It detoxify aromatic acids such as benzoic acid (toxic) converting it into hippuric acid (less toxic) which is excreted in urine.