Write short notes on decarboxylation and transmethylation of amino acids.

How to lay out the answer. Follow the frame, then write it in your own words.

1 · Open in two lines. Decarboxylation removes CO₂ from an amino acid to form an amine. Transmethylation moves a methyl group from SAM to another molecule.
2 · Draw the methionine cycle. [Diagram: methionine → SAM → SAH → homocysteine → methionine, with ATP, methyltransferase, folate and B12 marked]
3 · Decarboxylation with examples.
- Enzyme: a decarboxylase with PLP.
- Histidine → histamine; glutamate → GABA; 5-hydroxytryptophan → serotonin; DOPA → dopamine.
4 · Transmethylation.
- Methionine + ATP → SAM.
- SAM gives CH₃ to make creatine, adrenaline, lecithin, and becomes SAH → homocysteine.
- Homocysteine → methionine with methyl-folate and B12.
5 · Significance. Forms hormones and brain signals, makes creatine and lecithin, and recycles methionine.
6 · Nutrition link. B6 for decarboxylases; folate and B12 for the methionine cycle; their lack raises homocysteine.
7 · Close in one line. Both reactions turn amino acids into small but vital molecules.

Scoring tip: For 5 marks, a small table of amines and the methionine cycle diagram are enough.

Write-up practice

Write your answer to “Write short notes on decarboxylation and transmethylation of amino acids.”, then compare it with the frame.

The check looks for key words only. It does not grade your answer and never writes it for you.