1. DNA Replication

3. Complementary Strands
DNA arranged in double helix (Rosalind Franklin’s work)
Antiparallel –on 1 strand run phosphate to sugar and opposite on other strand
2 strands are complementary; ie
AGTAC
TCATG

5. DNA Replication is semiconservative
Confirmed by Messelson-Stahl:

6. Steps in DNA Replication
Begins at specific sites called origins of replication
DNA helicase unwinds double helix by breaking H-bonds – forms replication forks
Single-stranded binding proteins hold strands open

7. DNA polymerase adds nucleotides to 3’-end of growing DNA strand
Synthesis is always in’ one direction
Requires a RNA primer to build off of
DNA primase synthesizes a short complementary RNA strand for DNA polymerase to build on to

8. DNA Replication occurs on both strands at the same time
Strands run in opposite directions
DNA only replicates in one direction
Therefore, only 1 strand can replicate toward the replication fork: leading strand
Strand replicating away from the fork is called the lagging strand
Can only synthesize short pieces at a time
Okazaki fragments

10. Synthesis on leading strand is continuous
Synthesis on lagging strand requires multiple primers
When RNA primer of previous Okazaki fragment is reached, DNA polymerase breaks it down
DNA ligase seals Okazaki fragments together

11. Proofreading
DNA polymerase proofreads new nucleotides against template
If mistake made, DNA polymerase repairs mistake
If mistake not corrected, mutation has occurred

12. Pro vs. Eukaryotes Prokaryotes have 1 origin of replication
DNA synthesis proceeds in both directions around the circular chromosome until 2 replication forks meet
Eukaryotic chromosomes have multiple origins of replication
Replication bubbles eventually meet and merge
Speeds up process