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: -3’ to 5’ polymerases would never work because the energy required would be way too high. Normal DNA polymerases are 5’-to-3’ polymerases. DNA polymerases extend the 3’ tail of the DNA molecule but it synthesizes 5’-to-3’. 3’ to 5’ polymerases would never work because the energy required would be way too high.

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 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-5: -RNA polymerase synthesizes an RNA strand complementary to a template DNA strand. It synthesizes the RNA strand in the 5’ to 3’ direction, while reading the template DNA strand in the 3’ to 5’ direction. The template DNA strand and RNA strand are antiparallel.