Lecture 6: Genome Replication
What is your DNA doing?
- 3 billion base pairs
- Mistake: researchers defined functional as anything that looks like it can
o Belief that 80% of the genome is “functional”
However, junk DNA = helpful evidence for evolution
- How does DNA get replicated?
- What is a fork?
- What is a replication bubble?
- What to do with the ends of the DNA strands?
Double helical structure of DNA with two antiparallel backbones DNA Structure
- A distinct 3’ and 5’ end confers “polarity” on each of the DNA backbones.
- 3’ has free hydroxyl (OH)
- 5’ has free phosphate
- Two strands of double helix run “antiparallel”
Replication is semi-conservative
- Replication fork
- Know of Meselson and Stahl experiment – DNA replication is semi-conservative
- New chain added on 3’ end leading strand
- Original 5’ end lagging strand
- Every DNA polymerase only does one form of elongation and elongates 3’ ends
DNA polymerase adds to a free 3’OH Replisomes (proteins together) replicate one strand continuously, one discontinuously
- REPLISOMES – active at the replication fork
- Contains 2 molecules of DNA polymerase – 2 replisomes working simultaneously
- Can only extend 3’ end
- Parent strands are anti-parallel
- Replication starts from the sole origin
- Sends replication forks on either sides
- RESULT: replication bubble
Replication bubble is just two forks
- Primers provide 3’ polymerase to the chains
- Prokaryote genomes are usually small
- Can replicate from one replication bubble
- Humans way more complex – need many more origins
- Replication “bubble” arises from two “forks” created at one “origin”
Large, linear, eukaryotic chromosomes fire several origi