1. Control of DNA Replication

2. Coolest DNA replication video ever!

3. Cell Cycle DNA synthesis take place in S
Cell cycle progress enables initiation of replication of the genome by providing Cdc6 and Cdt1

4. Eukaryotic initiation of replication
In yeast, 3 proteins needed to assemble the replisome
ORC, Cdt1 and Cdc6
All three recruit helicase
MCM complex
mini-chromosome maintenance

5. The replication problem at the end of chromosomes

6. Telomeres in Tetrahymena
Elizabeth Blackburn and Joe Gall, 1978
Single-celled ciliate
Micronucleus
Macronucleus
Fragmented chromosomes
40,000 telomeres
TTGGGG repeated sequence
Telomerase, adds the short
repeats to the 3’ ends of DNA

7. Telomere lengthening Telomerase = Protein + RNA
Lengthening of the 3’ overhang
Telomerase = Protein + RNA
Telomerase anneals to the 3’ overhang
Replication of complementary strand
Telomerase
Primer is synthesized
Primase
Elongation
Polymerase fills in the gap
DNA polymerase
Translocation
The primer is removed and ligase seals the gap
Elongation

8. Telomeric cap structure
Telomeres preserve chromosomal integrity by associating with proteins that form a protective cap
Without cap, the double stranded ends would be mistaken as a ds break
Can lead to apoptosis
telomeric repeat binding factor
WRN - helicase

9. Telomeres and Aging Somatic cells produce very little telomerase
Chromosomes get shorter with each cell division
Many Cancers have increased levels of telomerase
Telomeres the Secret of Life!!!
Dysfunctional telomeres and mutation in WRN gene
Werner Syndrome
Picture below same person
at 15 and 48

10. Concept question
The number of proteins in the prokaryotic replisome is 13, while the number in a eukaryotic cell is 27. What are the important protein components of the replisome in general? Why might a eukaryotic cell have more components?