Question

Regarding secondary structure of a protein, correct statement(s) is/are;
(A) Peptide bonds possess regional planarity.
(B) $C=O~$ and $-NH~$ of different peptide chains are held by Van der Waals attractions.
(C) They have a closely packed arrangement so as to minimize repulsion between R groups.
(a) Only C
(b) Only B
(c) A and B
(D) Only A

Answer 1

The three-dimensional arrangement of atoms in an amino acid chain molecule is the structure of proteins. Proteins are polymers formed from amino acid sequences, the monomers of the polymer, specifically polypeptides. By tradition, rather than a protein, a chain under $30$ amino acids is sometimes known as a peptide.

Complete step by step solution:
Proteins are the end products of the process of decoding that begins with cellular DNA information. Proteins form structural and motor components in the cell as workhorses of the cell, and they serve as catalysts for nearly every biochemical reaction that occurs in living things.
Conceptually, it is possible to understand protein structure at four stages. They are primary, secondary, quaternary and tertiary. All the covalent bonds between amino acids are included in the primary structure and are usually defined by the peptide-bonded amino acid sequence and disulphide bond locations. The relative spatial structure of the amino acids associated with it is unclear.
The secondary structure refers to recurrent repeated space structures in the polypeptide chain of neighboring amino acid residues. The tertiary structure refers to the spatial relationship in a polypeptide chain of all amino acids; it is a polypeptide’s entire three-dimensional structure.
Peptide bonds possess regional planarity. For the entire molecule, the long amino acid chain exists in a looped, coiled, stretched or folded structure. Thus, the statement A is correct. $C=O~$ and $-NH~$ of different peptide chains are held by intermolecular hydrogen bonds. Thus, the statement B is incorrect. Closely packed arrangement is due to hydrogen bonds. Thus, the statement C is incorrect.
Therefore, correct answer option D i.e. only A is correct.

Note:
Protein consisting of two or more similar or various polypeptide chains (subunits) occur in proteins. Since they have two or more subunits, these proteins are called oligomers. The quaternary structure describes the way in which the native protein is organized into subunits.