alleryStart learning →How are the A and B chains of insulin held together?
ABy hydrogen bonds between their carbonyl groups
BBy ionic bonds between oppositely charged R groups
CBy peptide bonds joining the two chains end to end
DBy disulfide bonds formed between cysteine residues
Answer & Solution
Correct answer: D. By disulfide bonds formed between cysteine residues
1. Insulin, the pancreatic hormone, has two polypeptide chains, A and B.
2. The two chains are linked together by disulfide bonds.
3. Those bonds form when two sulfhydryl groups on cysteine side chains react in the presence of oxygen.
4. Peptide bonds join amino acids within a chain, so they cannot be what holds two separate chains side by side.
5. Insulin also uses hydrogen bonds in its folded ball shape, but the link between the chains is the disulfide bond.
_Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 3 "Biological Macromolecules", section 3.4 Proteins_
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