AP BIOLOGY

Detailed explanation-1: -DNA is always synthesized in the 5’-to-3’ direction, meaning that nucleotides are added only to the 3’ end of the growing strand.

Detailed explanation-2: -DNA polymerase is able to add nucleotides only in the 5’ to 3’ direction (a new DNA strand can be only extended in this direction). It also requires a free 3’-OH group to which it can add nucleotides by forming a phosphodiester bond between the 3’-OH end and the 5’ phosphate of the next nucleotide.

Detailed explanation-3: -The need for accuracy probably explains why DNA replication occurs only in the 5′-to-3′ direction. If there were a DNA polymerase that added deoxyribonucleoside triphosphates in the 3′-to-5′ direction, the growing 5′-chain end, rather than the incoming mononucleotide, would carry the activating triphosphate.

Detailed explanation-4: -The 3′ finish of the DNA harbors an OH bunch which can cooperate with the approaching nucleotide’s phosphate situated at its 5′ ends to bring the nucleotide into the developing DNA chains by a phosphodiesterase enzyme.

Detailed explanation-5: -So, the correct option is ‘DNA polymerases can only add nucleotides to the 3′ end of a polynucleotide strand’.