Question

Which one among the following is a peptide linkage?
A)
 

B)

C)

D)

Answer 1

Hint: Peptides are short chains of amino acids that are linked by peptide bonds. A peptide bond is an amide-type covalent bond present between two alpha-amino acids groups. It is also known as the eupeptide bond, to make it different from the isopeptide bond which is also a type of amide bond between two amino acids.

Complete answer:
There are various types of peptides present, less than ten or fifteen amino acids are known as oligopeptides, they include dipeptide, tripeptides, and tetrapeptides.
A peptide between two alpha-amino acids is present between $C_1$ of one amino acid and $N_2$ of the other amino acid along with a peptide or protein bond. Let us review each and every option given to us.
A) The structure is given to us is similar to the DNA molecule, in this molecule the 3’ carbon is attached to the other 5’ carbon. The highlighted bond is known as a phosphodiester bond which connects two nucleotides. These phosphodiester bonds are largely found in DNA and RNA.
B) The reaction given to us is between carboxylic acid and amines. Though the bond formed is very similar to the peptide bond, but the given bond is an amide bond and not a peptide bond. The bond is formed between the Hydroxyl group of the carboxylic acid and the Amine group of the primary amine.
C) This bond is a peptide bond. A peptide bond is primarily formed between two amino acids group. This bond is formed by the dehydration condensation process. A water molecule is formed as a residue. Option C is the correct answer.
D) Given to us are two molecules of sugar or carbohydrates. Two molecules of carbohydrates are joined together by a glycosidic bond. It is not necessary that the other molecule should also be a carbohydrate.

Note:
Peptide bond and amide bond look very similar as both of them are $-CO-NH-$. Remember that the amide bond is formed between carboxylic acid and amines. A peptide is also a type of amide bond, but the reactants are two amino acids only.