Nature of Bonds Linking Monomers in Biomolecules
Proteins, carbohydrates, nucleic acids, and certain important biomolecules are collectively referred to as macromolecules. These macromolecules consist of polymers whose monomers are linked through specific bonds. We would be discussing some of these bonds like peptide bond, glycosidic bond, etc in this article in order to gain a better understanding.
Proteins consist of polypeptides as they are polymers of amino acids. The amino acids are linked through peptide bonds. An amino acid has two functional groups, the amine (-NH2) group, and the carboxylic acid (-COOH) group. A peptide bond is an amide bond (-CONH) between the –NH2 group and the –COOH group of adjacent amino acids. A water molecule is eliminated when a peptide bond is formed.
A glycosidic bond is a bond present in disaccharides and polysaccharides. This is a bond formed between two adjacent monosaccharides. Like peptide bond, elimination of a water molecule accompanies the formation of a glycosidic bond as well. In other words, it is a dehydration reaction.
The above figure shows the formation of a 1,4-glycosidic bond between carbon 1 and carbon 4 of adjacent glucose molecules. A water molecule is eliminated from the two hydroxyl (-OH) groups of carbon 1 of the first glucose molecule and carbon 4 of the second glucose molecule.
In DNA double helix, the backbone of the strands consists of deoxyribose sugar and phosphate groups. They are linked by phosphodiester bonds.
An ester group is formed by dehydration of an acid and an alcohol group. In a phosphodiester linkage, two acidic groups of phosphate radical form ester linkages with OH groups of adjacent ribose molecules.
Base pairing in DNA
The two strands of a DNA double helix are held together by hydrogen bonds between nitrogenous bases of the opposite strands. These hydrogen bonds are very specific. Adenine only bonds with thymine in the opposite strand by forming 2 hydrogen bonds. Guanine forms 3 hydrogen bonds when it pairs with cytosine. Two bonded nitrogenous bases from opposite strands constitute a base pair. The length of a DNA molecule is often denoted by the number of the base pairs.
This was just an introduction to the different types of chemical bonds that exist in biomolecules. To know more about this topic, visit Byju’s.