BIOMOLECULES AND ENZYMES

Detailed explanation-1: -In the Watson–Crick model, the DNA double helices are formed from the coiling of two strands of purine and pyrimidine bases. Guanine pairs with cytosine, and adenine pairs with thymine in DNA. Interstrand hydrogen bonds are responsible for this pairing.

Detailed explanation-2: -The Adenine-Thymine base pair is held together by 2 hydrogen bonds while the Guanine-Cytosine base pair is held together by 3 hydrogen bonds.

Detailed explanation-3: -Each nucleotide base can hydrogen-bond with a specific partner base in a process known as complementary base pairing: Cytosine forms three hydrogen bonds with guanine, and adenine forms two hydrogen bonds with thymine. These hydrogen-bonded nitrogenous bases are often referred to as base pairs.

Detailed explanation-4: -The chemical structures of Thymine and Cytosine are smaller, while those of Adenine and Guanine are larger. Size and structure of the specific nucleotides cause Adenine and Thymine to always pair together while Cytosine and Guanine always pair together.

Detailed explanation-5: -The two strands are held together by hydrogen bonds between pairs of bases: adenine pairs with thymine, and cytosine pairs with guanine.