19.What are all the different kinds of linkages that are formed between the two macromolecules, define and differentiate the same.

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 19.What are all the different kinds of linkages that are formed between the two macromolecules, define and differentiate the same. 

answers:

Macromolecules include proteins, nucleic acids, lipids, and carbohydrates. They are formed by polymerisation of smaller units called as monomers.  These monomeric units are held together by different kinds of bonds that depend upon the chemical nature of the monomeric unit.

Peptide Bond

Peptide bond

Peptide bond

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.

Glycosidic bond

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 hydroxyls (-OH) groups of carbon 1 of the first glucose molecule and carbon 4 of the second glucose molecule.

Phosphodiester bond

In DNA double helix, the backbone of the strands consists of deoxyribose sugar and phosphate groups. They are linked by phosphodiester bonds.

Phosphodiester bond

Phosphodiester bond

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.


Hydrogen Bonds

Once the nucleotides form nucleic acids, DNA and RNA formation occurs. DNA is double-stranded whereas RNA is single stranded. The two strands of the DNA are held together by weak hydrogen bonds that form between the nitrogen bases. The hydrogen bonds between the nitrogen bases are very specific. Adenine bonds only with thymine in the opposite strand by forming 2 hydrogen bonds,  guanine forms 3 hydrogen bonds when it pairs with cytosine of the opposite strand. Two bonded nitrogenous bases from opposite strands constitute a base pair.


 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.

Base pairing in DNA

Base pairing in DNA



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