Which of the following is true about secondary structures of proteinsa)Alpha helix contains hollow core and side chains flanking out of helical baseb)Beta sheet can accommodate large amino acids such as tryptophan and isoleucinec)Antiparallel beta sheet is more stable than parallel beta sheetd)A beta turn must not contain a glycine or prolineCorrect answer is option 'A,C'. Can you explain this answer?

Question

Answer

Option (b) is incorrect
Unlike the α helix, side chains are squeezed close together in a β pleated sheet arrangement. As a result, very bulky side chains make the structure unstable.
Option (c) is correct
The parallel arrangement is less stable because the geometry of the individual amino acid molecules forces the hydrogen bonds to occur at an angle, making them longer and thus weaker. Contrarily. in the anti-parallel arrangement, the hydrogen bonds are aligned directly opposite each other, making for stronger and more stable bonds.
Option (d) is incorrect
Proline and glycine are frequently found in beta turns. Proline is present in beta turn because its cyclic structure is ideally suited for the beta turn. Glycine, with the smallest side chain, is most sterically flexible.

Answer

Option (b) is incorrect
Unlike the α helix, side chains are squeezed close together in a β pleated sheet arrangement. As a result, very bulky side chains make the structure unstable.
Option (c) is correct
The parallel arrangement is less stable because the geometry of the individual amino acid molecules forces the hydrogen bonds to occur at an angle, making them longer and thus weaker. Contrarily. in the anti-parallel arrangement, the hydrogen bonds are aligned directly opposite each other, making for stronger and more stable bonds.
Option (d) is incorrect
Proline and glycine are frequently found in beta turns. Proline is present in beta turn because its cyclic structure is ideally suited for the beta turn. Glycine, with the smallest side chain, is most sterically flexible.

Answer

The correct answers for this question are options A and C.

Explanation:

Primary Structure of Proteins:
The primary structure of a protein refers to the sequence of amino acids linked together by peptide bonds. It is the most basic level of protein structure.

Secondary Structure of Proteins:
The secondary structure of a protein refers to the local folding of the polypeptide chain into regular structures. The two most common types of secondary structures are the alpha helix and the beta sheet.

a) Alpha helix contains a hollow core and side chains flanking out of the helical base:
An alpha helix is a right-handed coil formed by a polypeptide chain. It is stabilized by hydrogen bonds between the carbonyl oxygen of one amino acid and the amide hydrogen of another amino acid, four residues ahead in the sequence. The alpha helix does not have a hollow core. The side chains of the amino acids are oriented outward from the helical base.

b) Beta sheet can accommodate large amino acids such as tryptophan and isoleucine:
A beta sheet is formed by hydrogen bonding between adjacent polypeptide chains or segments of the same chain, which are extended and aligned. The beta sheet can accommodate amino acids of various sizes, including large amino acids such as tryptophan and isoleucine.

c) Antiparallel beta sheet is more stable than parallel beta sheet:
In an antiparallel beta sheet, adjacent strands run in opposite directions, with the N-terminus of one strand aligned with the C-terminus of the adjacent strand. In a parallel beta sheet, adjacent strands run in the same direction. The antiparallel beta sheet is more stable than the parallel beta sheet because it allows for more favorable hydrogen bonding interactions between the strands.

d) A beta turn must not contain glycine or proline:
A beta turn is a type of secondary structure motif where the polypeptide chain reverses direction. It is often found connecting two adjacent strands in a beta sheet. A beta turn is characterized by four amino acids, with the second and third amino acids being adjacent in the primary sequence. Glycine and proline are commonly found in beta turns due to their unique structural properties that allow for the required conformational changes. Therefore, it is incorrect to say that a beta turn must not contain glycine or proline.

In summary, the correct answers are option A and option C.

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