Amino Acid Metabolism Quiz

Study Notes

Amino Acid Metabolism

Glycine:
- Non-essential, glucogenic amino acid
- Important in purine base synthesis (carbon atoms 4, 5, and nitrogen atom 7 derived from glycine)
- Component of glutathione (a tripeptide with glutamate and cysteine), acting as a hydrogen carrier
- Used in creatine synthesis (combining with arginine and methionine)
- Used in heme synthesis (reacting with succinyl CoA)
- Involved in collagen synthesis (present in every third position in the triple helix)
- Used in bile salt formation (conjugated with primary bile acids, e.g., cholic acid, to form glycocholic acid)
- Involved in hippuric acid formation (conjugates with toxic benzoate)
- Acts as an inhibitory neurotransmitter in the spinal cord
- Involved in glyoxylic acid formation
Phenylalanine:
- Essential, mixed glucogenic and ketogenic amino acid
- Important in body protein structure
- Precursor for tyrosine synthesis primarily in the liver
- Deficiency in the enzymes of the phenylalanine hydroxylase pathway leads to phenylketonuria.
- The reaction is irreversible
Tyrosine:
- Non-essential amino acid
- Derived from phenylalanine
- Mixed glucogenic and ketogenic
- Important in catecholamine synthesis (precursor to dopamine, noradrenaline, and adrenaline)
- Precursor to thyroid hormones (T3 and T4)
- Forms melanin pigment in tissues, particularly in the eye, hair, and skin
- Involved in the formation of phenol, cresol, and tyramine (putrefactive substances from bacterial action)
Tryptophan:
- Essential amino acid
- Mixed glucogenic and ketogenic
- Important in tryptophan derivatives:
  - Biosynthesis of alanine and acetoacetyl CoA
  - Biosynthesis of niacin (vitamin B complex)
  - Biosynthesis of serotonin (5-hydroxytryptamine, a neurotransmitter)
  - Biosynthesis of melatonin (a hormone from the pineal gland)
  - Synthesis of indol and skatole
Arginine:
- Semi-essential, glucogenic amino acid
- Microorganisms can synthesize it
- Important in a-ketoglutarate synthesis
- Involved in creatine synthesis
- Part of streptomycin synthesis, ornithine conversion to other compounds, urea synthesis, and arginine phosphate synthesis in invertebrates
- Involved in nitric acid synthesis
Serine:
- Non-essential, glucogenic amino acid
- Involved in glycine synthesis
- Part of cysteine and ethanolamine/choline synthesis
- Involved in sphingosine synthesis
- Involved in the formation of purine and pyrimidine bases (methyl group source)
- Involved in phosphoprotein synthesis (e.g., casein)
Methionine:
- Essential, glucogenic amino acid
- Involved in methyl donor function (as S-adenosylmethionine, SAM)
- Crucial in creatine, noradrenaline/adrenaline, ethanolamine/choline, carnosine, and anserine synthesis
- Important in glucose, cysteine, and polyamine synthesis (spermine/spermidine)
Glutamic Acid:
- Non-essential, glucogenic amino acid
- Synthesized from a-ketoglutarate
- Involved in a-ketoglutarate synthesis for glucose production
- Crucial in glutamine, proline, hydroxyproline, ornithine, glutathione, and GABA (inhibitory neurotransmitter) synthesis
Aspartic Acid:
- Non-essential, glucogenic amino acid
- Synthesized from oxaloacetate through transamination
- Important in purine and pyrimidine synthesis (source of N1, C4, C5, and C6)
- Plays a role in urea synthesis
- Involved in beta-alanine and asparagine synthesis