AP BIOLOGY

Detailed explanation-1: -DNA polymerases can only make DNA in the 5’ to 3’ direction, and this poses a problem during replication. A DNA double helix is always anti-parallel; in other words, one strand runs in the 5’ to 3’ direction, while the other runs in the 3’ to 5’ direction.

Detailed explanation-2: -Since DNA polymerase requires a free 3’ OH group for initiation of synthesis, it can synthesize in only one direction by extending the 3’ end of the preexisting nucleotide chain. Hence, DNA polymerase moves along the template strand in a 3’–5’ direction, and the daughter strand is formed in a 5’–3’ direction.

Detailed explanation-3: -DNA is always synthesized in the 5’-to-3’ direction, meaning that nucleotides are added only to the 3’ end of the growing strand. As shown in Figure 2, the 5’-phosphate group of the new nucleotide binds to the 3’-OH group of the last nucleotide of the growing strand.

Detailed explanation-4: -DNA polymerase builds DNA in the 5 prime to 3 prime direction and works on the 3 prime to 5 prime original DNA strands. Now let’s look at the lagging strand. When the replication fork is open, its 3’ end lies at the base of the fork, and the 5’ end lies at the opposite end.

Detailed explanation-5: -coli polymerase I has 3′ to 5′ as well as 5′ to 3′ exonuclease activity. The 5′ to 3′ exonuclease operates in the direction of DNA synthesis and helps remove RNA primers from Okazaki fragments.