Final answer:
Cysteine is an amino acid with a sulfhydryl group, crucial for forming disulfide bonds that stabilize protein structure, notably in insulin. Its genetic codons are UGU and UGC, and it is related to selenocysteine, encoded exceptionally by UGA in certain contexts.
Step-by-step explanation:
The amino acid cysteine (abbreviated as Cys or C) is notable for its sulfur-containing side-chain, known as a sulfhydryl group (SH).
Cysteine plays a crucial role in protein structure and stability.
When two cysteine residues come into proximity within a protein or between different protein chains, they can undergo oxidation to form a disulfide bond (R-S-S-R) by linking their sulfur atoms.
This bond, often referred to as a cystine when considering the dimeric form, significantly contributes to the tertiary and quaternary structures of proteins.
One key example of cysteine's function is seen in insulin, where disulfide bonds both connect the A and B chains and help the A chain to fold properly, which is essential for the hormone's activity.
The genetic code for cysteine is represented by the codons UGU and UGC.
Additionally, selenocysteine, a related amino acid, is encoded by the UGA codon, typically a stop signal, but through a specific mRNA sequence structure, becomes encoded for this distinct 21st amino acid.