BIOMOLECULES AND ENZYMES

Detailed explanation-1: -In DNA, adenine always pairs with thymine, and guanine always pairs with cytosine. Therefore, purines always pair with pyrimidines. Purines do not pair with purines, and pyrimidines do not pair with pyrimidines.

Detailed explanation-2: -Introduction. Due to the presence of abundant hydrogen-bonding donors and acceptors, purine bases, especially guanine, can sometimes pair with another purine base to form purine·purine “mispair”.

Detailed explanation-3: -In naked unmodified nucleic acid duplexes, purines (guanine and adenine) pair up with pyrimidines (cytosine, thymine, and uracil) through complementary hydrogen bonds to form canonical G•C, A•T, and A•U Watson-Crick (WC) base-pairs (Figure 1A).

Detailed explanation-4: -Purines can’t combine with other purines due to double-ring structures. The higher the bond specificity higher the stability and the bond will be stronger. DNA hydrogen bond structures that cause only adenine to pair with thymine.

Detailed explanation-5: -Two purines can’t form a bond, and there is not enough space to sit in the double helix. Thus, adenine and guanine (purines) can’t form base pairs, and no hydrogen bonding is possible. b. Guanine and cytosine are stable hydrogen base pairs due to three hydrogen bonds.