Amino Acid Metabolism

• TCA cycle

  Metabolic pathway that converts pyruvate into energy in the form of ATP
• ETC


  Electron transport chain, a series of protein complexes that transfer electrons to produce ATP
• Energy molecules in food

  • Sugars
  • Fatty acids
  • Protein
  • Amino acids
• Excess amino acids aren't stored and aren't simply excreted
• What are the three main destinations for amino acids in the amino acid pool?

  1. Protein synthesis
  2. Direct use or minor modification
  3. Breakdown and redeployment
• Direct use of amino acids in pool:

  
  

  Neurotransmitters:

  • Glutamate, Aspartate and Glycine
  • Glutamate -> GABA
  • Tyrosine -> Dopamine, Noradrenaline, Adrenaline
  • Tryptophan -> Serotonin
  • Arginine -> NO

  Hormones:

  • Tyrosine -> Thyroxine
  • Tryptophan -> Melatonin
• Deamination


  Removal of the amino group from an amino acid, producing ammonia
• Urea synthesis

  1. CO2 + NH4+ + H2O + 2ATP -> Carbamoyl phosphate

  2. Carbamoyl phosphate -> Urea cycle
• Urea cycle

  Arginine -> Ornithine -> Argininosuccinate -> Citrulline -> Urea
• Carbon skeletons from amino acid breakdown as one of:

  • Pyruvate
  • Acetyl CoA
  • Acetoacetyl CoA
  • Succinyl CoA
  • Fumarate
  • α-ketoglutarate
  • Oxaloacetate
• Sulphurous amino acids

  Methionine and Cysteine
• Disposal of sulfur from sulphurous amino acids


  Methionine -> Adenosine + Vitamin B6 -> Cysteine -> Cysteine sulphinate -> β-sulphinylpyruvate -> β-mercaptopyruvate -> Sulfate -> Hydrogen sulfide
• What is de novo synthesis in amino acid metabolism?

  Synthesis from basic precursors, not from other amino acids
• Other biosynthesis from amino acid precursors

  • Pyrimidines
  • Purines
• What neurotransmitter is synthesized from Glutamate?


  GABA (gamma-aminobutyric acid)
• Which amino acid is a precursor for Dopamine, Noradrenaline, and Adrenaline?


  Tyrosine
• What are the products of amino acid breakdown in terms of their carbon skeleton and amino group?

  • Carbon skeleton: CO2 + H2O (energy production) or other biosynthetic pathways (e.g., purines, pyrimidines, haem)
  • Amino group: Ammonia (NH3)
• What is the primary enzyme involved in transamination reactions and what cofactor does it use?

  Aminotransferase; it uses Pyridoxal phosphate (PLP) derived from Vitamin B6
• What are the two main amino acids involved in transamination with α-ketoglutarate?


  • Glutamate
  • Aspartate
• What is the overall energy cost of the urea cycle per molecule of urea produced?

  4 ATP molecules
• What is the role of Glutamate Dehydrogenase in amino acid metabolism?


  It catalyzes the deamination of Glutamate to produce α-ketoglutarate and ammonia (NH4+), with NAD+ being reduced to NADH
• Name two amino acids that are directly used for the synthesis of neurotransmitters and their respective products


  • Glutamate → GABA
  • Tryptophan → Serotonin
• What is the function of Carbamoyl phosphate synthetase I in the urea cycle?


  It catalyzes the synthesis of carbamoyl phosphate from CO2, NH4+, and ATP
• How is ammonia transported to the liver for detoxification?


  As Glutamine (Gln) or Alanine (Ala), which are transported in the blood to the liver where the amino groups are released as ammonia for conversion to urea
• What enzyme in the urea cycle converts Arginine into Urea and Ornithine?

  Arginase
• Which amino acids are involved in purine biosynthesis?


  • Glycine (Gly)
  • Glutamine (Gln)
  • Aspartate (Asp)
• What is the fate of the carbon skeletons of amino acids after deamination?


  They are used in synthetic pathways or for ATP production via the TCA cycle
• What is the role of aminotransferases in amino acid metabolism?


  Aminotransferases catalyze the transfer of amino groups from amino acids to α-ketoglutarate, forming glutamate and α-keto acids. They use Pyridoxal phosphate (PLP) as a cofactor
• How is ammonia detoxified in the liver?

  Ammonia is detoxified by converting it into urea through the urea cycle, which takes place in the liver
• What are the primary products of amino acid deamination?

  The primary products of amino acid deamination are ammonia (NH4+) and α-keto acids
• Which enzyme catalyzes the conversion of glutamate to α-ketoglutarate and NH4+?

  Glutamate dehydrogenase catalyzes the conversion of glutamate to α-ketoglutarate and NH4+
• What is the function of carbamoyl phosphate synthetase I in the urea cycle?

  Carbamoyl phosphate synthetase I catalyzes the synthesis of carbamoyl phosphate from CO2, NH4+, and ATP, initiating the urea cycle
• What are the key intermediates in the urea cycle?

  Key intermediates in the urea cycle include carbamoyl phosphate, citrulline, argininosuccinate, arginine, and ornithine
• How are the amino groups from extra-hepatic tissues transported to the liver?

  Amino groups from extra-hepatic tissues are transported to the liver as glutamine (Gln) or alanine (Ala)
• What are the six final products of amino acid carbon skeleton catabolism?

  The final products of amino acid carbon skeleton catabolism are pyruvate, acetyl CoA, acetoacetyl CoA, succinyl CoA, fumarate, and α-ketoglutarate
• What is the role of transamination in amino acid metabolism?


  Transamination transfers amino groups between amino acids and α-keto acids, facilitating the interconversion of amino acids and their corresponding α-keto acids
• What are the end products of the urea cycle and how are they excreted?

  The end products of the urea cycle are urea and fumarate. Urea is excreted in the urine
• Which amino acids are directly involved in neurotransmitter synthesis and their corresponding neurotransmitters?

  • Glutamate → GABA
  • Tryptophan → Serotonin
  • Tyrosine → Dopamine, Noradrenaline, Adrenaline
• What inhibits and activates glutamate dehydrogenase?

  Glutamate dehydrogenase is inhibited by GTP and activated by ADP
• How does the body maintain nitrogen balance through amino acid metabolism?

  The body maintains nitrogen balance by ensuring that the intake and breakdown of proteins are equal, with 100g/day of protein being synthesized and degraded