1. DNA REPLICATION

4. DNA gyrase: the bacterial enzyme that relieves the tension produced by the unwinding of DNA
DNA helicase: enzyme that unwinds double-helical DNA by disrupting hydrogen bonds
DNA polymerase I: enzyme that removes RNA primers and replaces them with the appropriate deoxyribonucleotides
DNA polymerase III: enzyme responsible for synthesizing complementary strands of DNA
DNA ligase: enzyme that joins DNA fragments together by catalyzing the formation of a bond between the 3’ hydroxyl and a 5’ phosphate group on the sugar-phosphate backbone
Primase: enzyme that builds RNA primers

6. Leading strand Lagging strand
Complementary strand is built toward replication fork
Built continuously
Primase needs to add only 1 RNA primer that DNA polymerase will use to build toward the replication fork
Lagging strand
Complementary strand is built away from replication fork
Built discontinuously in small sections (Okazaki fragments)
Primase continuously adds primers as replication fork travels along DNA molecule
Gaps between Okazaki fragments are joined by DNA ligase

8. Replication fork
Where the enzymes replicating a DNA molecule are bound to the untwisted, single-stranded DNA
Replication bubble
Formed when two replication forks are in close proximity to each other, resulting in a bubble of single-stranded DNA between them.

9. Why eukaryotic DNA has multiple replication origin sites…
Due to its size…
It would take too long for DNA replication to occur if replication started at one end of a DNA molecule and proceeded to the other end.
The speed of DNA replication for the humans is about 50 nucleotides per second per replication fork. But the human Genome can be copied only in a few hours because because many replication forks take place at the same time (multiple initiation sites).

11. DNA polymerase III, and DNA pol I act as quality control by proof reading the new strands. When mistakes occur either enzyme can function as an exonuclease.