The diagram represents a protein molecule. Two long polypeptides each adopt $\alpha$-helices over most of their length, and these wind around one another to make a fibre. At one end, each polypeptide folds into a globular head. Two short polypeptides attach to each head. What describes the protein structure of this molecule?
- Aquaternary structure because each molecule consists of six polypeptides
- Bsecondary structure because the long polypeptides form $\alpha$-helices
- Ctertiary structure because the $\alpha$-helices form a fibre
- Dtertiary structure because the heads form globular proteins