Question

Calculate the number of disulfide bond arrangements possible for each of the polypeptides listed below, assuming that each of the cysteine residues forms a disulfide bridge. Also assume that all disulfide bridges are intramolecular, not intermolecular.

a. a polypeptide with four cysteines

b. a polypeptide with six cysteines

c. a polypeptide with 8 cysteines

d. a polypeptide with 10 cysteines

Answer 1

Disulfide bridges stabilize the tertiary structure of proteins. The number of possible arrangements of disulfide bonds depends on the number of cysteines in the polypeptide.

Step-by-step explanation:

Disulfide bridges play a crucial role in stabilizing the tertiary structure of proteins. Each disulfide bond is formed between two cysteine residues, and the number of possible arrangements depends on the number of cysteines present in the polypeptide.

a. For a polypeptide with four cysteines, there are two possible disulfide bond arrangements.

b. For a polypeptide with six cysteines, there are 15 possible disulfide bond arrangements.

c. For a polypeptide with eight cysteines, there are 105 possible disulfide bond arrangements.

d. For a polypeptide with ten cysteines, there are 945 possible disulfide bond arrangements.

Answer 2

a. a polypeptide with four cysteines has two disulfide bonds

b. a polypeptide with six cysteines has three disulfide bonds

c. a polypeptide with 8 cysteines has four disulfide bonds

d. a polypeptide with 10 cysteines has five disulfide bonds

Step-by-step explanation:

A disulfide bond is formed by two sulphur atoms linked covalently. Since it specifically require two linked sulphur atoms, and cysteine contains just one sulphur atom, then a polypeptide with an even number of cysteine molecules will have disulfide bonds halved the number of cysteine molecules.

Therefore, a polypeptide with even numbers of cysteine molecules like:

4 has 2 disulfide bonds;

6 has 3 disulfide bonds:

8 has 4 disulfide bonds;

10 has 5 disulfide bonds