Quick questions on Protein structure: primary, secondary, tertiary and quaternary (VCE Biology Unit 3)

Every amino acid has the same core:

Primary structure. The linear sequence of amino acids in the polypeptide, read from the N-terminus to the C-terminus. It is determined directly by the order of codons in mRNA. The primary sequence dictates all higher levels of folding.

The linear sequence of amino acids in the polypeptide, read from the N-terminus to the C-terminus. It is determined directly by the order of codons in mRNA. The primary sequence dictates all higher levels of folding.

Local repeating folds stabilised by hydrogen bonds between backbone N-H and C=O groups (not between R groups). The two main motifs are:

The full three-dimensional fold of a single polypeptide, stabilised by interactions between R groups:

Two or more polypeptide chains (subunits) assembled into a functional complex, held together by the same kinds of R-group interactions as tertiary structure. Examples include haemoglobin (four subunits: two alpha, two beta, each with a haem group) and insulin (two chains held by disulfide bridges).

Name the four levels of protein structure and identify the bond responsible for each. [4 marks]

Insulin contains two polypeptide chains held together by disulfide bridges. (a) Identify the level of structure represented by the two-chain arrangement. (b) State which amino acid contributes to disulfide bonds.

Refer to a protein denatured by boiling. (a) State which levels of structure are disrupted. (b) Explain why the primary structure usually survives.