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. 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-2: -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-3: -DNA replication goes in the 5’ to 3’ direction because DNA polymerase acts on the 3’-OH of the existing strand for adding free nucleotides.

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: -Strand elongation Once RNA polymerase and its related transcription factors are in place, the single-stranded DNA is exposed and ready for transcription. At this point, RNA polymerase begins moving down the DNA template strand in the 3’ to 5’ direction, and as it does so, it strings together complementary nucleotides.