Question

What is a peptide bond?

Answer 1

The peptide bond is formed between the two organic molecules. Peptide bond is connected with proteins. When the carboxyl group of one molecule reacts with the amino group of other molecules a chemical bond is formed between them with the release of water molecules.

Complete step by step answer:
Proteins are the polymers of ${{\alpha - amino\; acid}}$ and they are connected to each other by peptide bond or peptide linkage. Peptide linkage is an amide formed between ${{ - COOH}}$ group and ${{ - N}}{{{H}}_{{2}}}$ group. The reaction between two molecules of similar or different amino acids proceeds through the combination of the amino group of one molecule with the carboxyl group of another. This results in the elimination of water molecules and formation of peptide bond ${{ - CO - NH}}$. This product of the reaction is called dipeptide because it is made up of two amino acids.
Eg: When carboxyl group of glycine combines with the amino group of alanine dipeptide, glycyl alanine is formed.
If a dipeptide is combined with a third amino acid, the product is a tripeptide. A tripeptide has three amino acids which are linked by two peptide linkages. Similarly linkage of four, five or six amino acids results in the formation of products which are known as tetrapeptide, pentapeptide or hexapeptide, respectively. When the number of amino acids linked is more than ten, and then the products are called as polypeptides. A polypeptide having more than hundred amino acid residues with molecular weight higher than 10,000u is called a protein. Whereas the difference between polypeptide and a protein is not very high. Polypeptides having fewer amino acids are called to be proteins if they ordinarily have a well-defined conformation of a protein such as insulin which contains 51 amino acids.

Note: Amino acids which have been introduced into the peptide are known as residues. Also, each peptide has a nitrogen terminus and carbon terminus residue at the ends of the peptide. Peptides are classified into dipeptides, tripeptides, tetrapeptides etc. based on the number of peptide bonds.