Class 12th

This is a Long answer type Questions as classified in NCERT Exemplar

When DNA is fully degraded, a pentose sugar, phosphoric acid, and nitrogen-containing heterocyclic compounds known as bases are produced. Below is a diagram illustrating the structure of sugar and phosphoric acid.

DNA contains four bases adenine (A), guanine (G), cytosine (C) and thymine (T). The structures of all bases are shown below.

The attachment of a base to the 1'-position of sugar produces a nucleoside. When a nucleoside attaches to phosphoric acid at the sugar moiety's 5? position, a nucleotide is formed. Nucleotides are linked through the phosphodiester linkage between the 5' and 3' carbon atoms of the pentose sugar.

In DNA, two nucleic acid chains wrap around each other and are held together by hydrogen bonds between their bases.

This is a Long answer type Questions as classified in NCERT Exemplar

Proteins can have a single polypeptide chain or many polypeptide chains as their basic structure. A considerable number of α - amino acids are joined in a particular sequence in each polypeptide chain. The specific order in which the various α− amino acids found in a protein are linked to one another is the protein's primary structure. Any change to the main structure, i.e. the amino acid sequence, results in a different protein

Protein secondary structure: Secondary structure defines how polypeptide chains are folded or structured. As a result, the shape or conformation of the protein molecule is determined. This is explained by the planar geometry of the peptide bond and the hydrogen link between the and groups of separate peptide bonds.

An α - helix is a polypeptide chain that twists into a right-handed screw (helix), with the −NH group of each amino acid residue hydrogen bonded to the −C=O group of the next turn of the helix. The a-helix structure is also known as the 3.613 helix structure.

β- pleated sheet structure of proteins: The polypeptide chains are zigzagged side by side in this shape, with alternative R groups on the same side spaced at fixed intervals. The two nearby polypeptide chains are held together by intermolecular H-bonds. This type of interbounded chain can be used to make a sheet. These sheets are then stacked one on top of the other to create a three-dimensional structure, similar to the pages of this book.

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