2 - DNA and chromosome replication Flashcards
How is the DNA double helix opened
H bonds cleaved by helicase. Requires ATP
How does replication start
Replication forks. Y shaped DNA structures
Direction of replication
5’ –> 3’ direction
Leading strand
5’–>3’ direction, made continously
Leading strand
5’–>3’ direction, made continuously
Lagging strand
3’ –> 5’ direction, made discontinuously (Okazaki fragments) in opposite direction to replication fork unzipping
DNA pol epsilon
Leading strand (adds nts 5’ –> 3’)
DNA pol delta
Lagging strand (adds nts 5’ –>3’)
DNA pol proofreading
3’–>5’ exonuclease activity allows DNA pol to ‘chew back’ to remove the error (only gamma, delta and epsilon
How is DNA pol held onto DNA
Sliding clamp and clamp loader
Clamp loader
Replication factor C, acts like screw nut (threads matching grooves of DNA)
Sliding clamp
Proliferating cell nuclear antigen. Locks DNA pol to DNA
DNA Ligase
Seals DNA strands by forming phosphodiester bonds between adjacent fragments
Origin recognition complex
Multi protein complex that binds origin and separates DNA strands. Recruits replication proteins
Proteins involved in initiation
- Origin recognition complex
- Cell divison cycle 6 (S phase)
- Minochromosome maintenance (helicase)
- CDC-dependent transcript 1
Chromosome end replication problem
At end of newly synthesised lagging strand, no template for RNA primer to base pair with. chromosomes get shorter evert replication round
Solution to chromosome end replication problem
Telomerase Reverse Transcriptase enzyme (TERT) completes the chromosome end and maintains chromosome length
T loop
The ssDNA at end of 3’ DNA forms T loop which interacts with a complex of proteins to protect chromosome ends.
Which histone subunits aren’t removed during replication
H3 and H4. Allow nucleosomes to be rebuilt
