NEET BIOLOGY

Detailed explanation-1: -DNA base pair. Under normal circumstances, the nitrogen-containing bases adenine (A) and thymine (T) pair together, and cytosine (C) and guanine (G) pair together. The binding of these base pairs forms the structure of DNA .

Detailed explanation-2: -Guanine pairs with cytosine, and adenine pairs with thymine in DNA. Interstrand hydrogen bonds are responsible for this pairing.

Detailed explanation-3: -Guanine has two tautomeric forms, the major keto form (see figures) and rare enol form. It binds to cytosine through three hydrogen bonds.

Detailed explanation-4: -A always pairs with T and G always pairs with C because these are the only combinations that allow for hydrogen bonding to occur, given the spatial constraints of the double helix, which requires there to be one purine and one pyrimidine in each base pair.

Detailed explanation-5: -The purines form hydrogen bonds with pyrimidines, in which adenine bonds only to thymine in two hydrogen bonds, and cytosine bonds only to the guanine in three hydrogen bonds. This arrangement of two nucleotides binding together across the double helix is known as a base pair.