4. Metabolic classification of amino acids:according to metabolic fate or degradation products of amino acids

they may be:

Metabolic breakdown of amino acids

• Glucogenic amino acids-carbo n skeletons are broken down to

pyruvate, a-ketoglutarate, succinyl-CoA, fumarate, or oxaloacetate

(glucose precursors).

- TCA cycle intermediates or precursors to be metabolized to CO2, H2O,

or for use in gluconeogenesis.

• Ketogenic amino acids, are broken down to acetyl-CoA, beta hydroxy

butyrate or acetoacetate and therefore can be converted to fatty acids

Both glucogenic and ketogenic amino acids Yield α -ketoglutarate,

pyruvate, oxaloacetate, fumarate, or succinyl-CoA in addition to acetyl

CoA or acetoacetate Isoleucine ,Threonine,Tryptophan ,Phenylalanine

Tyrosine

Amino acid metabolism and central metabolic

pathways

Biomedical importance of amino acids• The amino acids fulfill vario us functions in the living organism: For

examples: Only the 20 proteinogenic amino acids are included in the

genetic code and therefore regularly found in proteins. The genetic code

is the set of rules by which information encoded within genetic material

(DNA or mRNA sequences) is translated into proteins by living cells.

DNA serves as the genetic blueprint of a cell

• Amino acids or their derivatives are also form components of lipidse. g.,

serine in phospholipids (cell membrane). The amino acid serine , which

has a hydroxyl group side chain provides the head group for the negative

phospholipid, phosphatidyl serine. .

• Several amino acids function as neurotransmitters themselves such as

glycine and glutamic acid, while others are precursors of

neurotransmitters, mediators.

Glycine acts as an inhibitory transmitter in spinal cord and medulla

(Adrenal gland).

• Glutamic acid is an excitatory neurotransmitter within the central

nervous system. That carries signals from one nerve to another.

Also glycine in bile salts, bile salts are

conjugated by the liver with glycine and are mainly responsible for the

emulsification of the fats.

Amino acids can be converted to biologically active nitrogenous products

such as creatine phosphate, dopamine, histamine and nitric oxide.

Phosphocreatine is formed from parts of three amino acids: arginine (Arg), glycine (Gly), and methionine (Met). Histamine is secreted by basophils and mast cells as part of a local immune response to the presence of invading bodies.The carbon chains of amino acids after deamination are a good

source of energy.

- Amino acid as a central metabolic pathways: specific amino acids form

precursors for other metabolites e. g., for glucose in gluconeogenesis, for

purine and pyrimidine bases in nucleic acid synthesis, heme in

hemoglobin, and for other molecules.