(a)[2]
Outline what the terms primary structure and tertiary structure of a protein mean.
(b(i))[2]
Use a diagram to show how the disulfide cross-links are formed. The amino acid that produces this cross-linking is cysteine, $\text{H}_2\text{NCH}(\text{CH}_2\text{SH})\text{CO}_2\text{H}$.
(b(ii))[1]
Which type of reaction is this?
(b(iii))[4]
State three additional interactions that stabilise the tertiary structure of proteins.
(c(i))[1]
Which type of bonding is responsible for stabilising the $\beta$-pleated sheet in silk?
(c(ii))[3]
In the diagram below, add a second polypeptide strand and show how bonds would form to stabilise this $\beta$-pleated sheet.
(d)[1]
Suggest why the $\beta$-pleated sheet in $\beta$-keratin is so much less flexible than the $\beta$-pleated sheet in silk.