AP BIOLOGY

Detailed explanation-1: -New DNA is made by enzymes called DNA polymerases, which require a template and a primer (starter) and synthesize DNA in the 5’ to 3’ direction. During DNA replication, one new strand (the leading strand) is made as a continuous piece.

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: -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.

Detailed explanation-4: -Which way’s which? When we look at a sequence of DNA, we read it in the 5′-3′ direction. The relative positions of genes or other sites along a DNA strand can be described as upstream (towards the 5′ end) or downstream (towards the 3′ end).

Detailed explanation-5: -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.