Question

A protein containing several proline residues is:

a. not likely to form quarternary structures.
b. likely to be found in beta turns.
c. not likely to form alpha helices.
d. likely to be an integral membrane protein.

Answer 1

A protein with several proline residues is likely to be found in beta turns and is not likely to form long stretches of alpha helices. Proline can be present in integral membrane proteins, but its presence does not necessarily mean that the protein will be an integral membrane protein. So the correct option is b.

Step-by-step explanation:

The presence of several proline residues in a protein suggests certain structural characteristics. Proline is a unique amino acid, as its side chain is cyclized to the backbone, which restricts its ability to fit within certain secondary structures, particularly the alpha helix. Because of this restriction, a protein with multiple proline residues is:

• likely to be found in beta turns, which are short turns or loops in proteins that often contain proline due to their ability to induce a bend in the peptide chain.
• not likely to form long stretches of alpha helices, which are a common type of secondary structure that proline often disrupts.

Regarding the options provided, integral membrane proteins often have alpha-helices or beta-sheets that span the membrane, consisting mostly of non-polar and hydrophobic amino acids. Although proline is non-polar, its structure can disrupt the alpha-helical domains within the membrane. Consequently, proteins with several proline residues may still be integral membrane proteins, but their presence does not inherently predict this.

Answer 2

The correct answer is b. likely to be found in beta turns.

Step-by-step explanation:

Proline is the amino acid which is unique from other amino acids as the side chain of proline is connected which gives it a cyclic structure. Beta turns are the secondary structure found in proteins that helps in the changing of direction of polypeptide chain in the protein.

The amino -acid proline is commonly found in beta turns because the unique cyclic structure of proline suits the beta-turn organization. Glycine is another amino acid that is abundant in beta turn because of its small size.

Therefore the correct answer is b. likely to be found in beta turns.