Question

Which of the following statements are true about protein domains?

I. Polypeptide chains longer than 200 amino acids in length have multiple domains.

II. Domains are tertiary structural components of proteins.

III. Different domains are encoded by different exons of a gene.

IV. Each domain in a protein has a specific function.

A. I, II, III, and IV

B. I, II, and III

C. II, III, and IV

D. II and IV

E. I and IV

Answer 1

A) A.1, 2, 3,and 4

A domain is an independent unit usually stable by itself it can comprise the whole protein or a part of the protein.

polypeptides with more than a few hundred amino acid residues often fold into two or more stable globular units called domains.

A domain retains its correct three dimensional structure even when it is separated( for example by proteolytic cleavage) from the remainder of the polypeptide chain .

A protein with multiple domains may appear to have a distant globular lobe for each domain but more commonly extensive contacts between domains make individual domains hard to discern.

Different domains often have distant functions such as the binding of small molecules or interaction with other proteins.

small proteins usually have one domain.(the domain is the protein).