Synthesis of amino acids

Question 1

Describe the synthesis of amino acids from phenylalanine

Answer 1

Question 2

What does epinephrine and norepinephrine break down into

Answer 2

VMA: vanillymandelic acid

Pheochromocytoma leads to increased VMA

Question 3

What does dopamine break down into

Answer 3

HMA: homovanillic acid

Question 4

Describe the synthesis of serotonin

Answer 4

• Serotonin is synthesized in the gut, platelets and CNS
• Synthesized from tryptophan
• Serotonin is metabolized to 5-HIAA by MAO

Question 5

Describe the steps of tryptophan to serotonin

Answer 5

Question 6

Describe carcinoid syndrome

Answer 6

• Tumor of serotonin producing cells in GIT (APUD cells)
• Cutaneous flushing, sweating, diarrhea, bronchospasm

Question 7

Describe tetrahydrobiopterin

Answer 7

• Reactions using THBP
  
  • Phenylalanine hydroxylase (converts Phe to Tyr)
  • Tyrosine hydroxylase (converts Tyr to DOPA)
  • Tryptophan hydroxylase (converts Trp to 5-hydroxy tryptophan)

Question 8

Describe tetrahydrobiopterin deficiency

Answer 8

• Results in hyperphenylalaninemia and decreased synthesis of neurotransmitters
  
  • Severe mental impairments and seizures

Question 9

Describe the steps in formation of thyroid hormone

Answer 9

• Trapping iodine in the thyroid cell
• Iodination of the thyroglobulin protein
• Coupling of the iodinated Tyrosine side chains
• Release of thyroid hormone
• De-iodination of T4 to the active T3 form

Example of post translational modification

Question 10

Describe the function of thyroperoxidase

Answer 10

• TPO fixes iodine to thyroglobulin
• Next TPO acts as a peroxidase
  
  • Objective is to link two iodo-tyrosine side chains together