DNA replication Flashcards
DNA replication is ________ and __________
semi-conservative
bidirectional
Origin of replication
- sequence specific site recognized by replication proteins
- hundreds of origins per chromosome in euk (only 1 in prok)
Replication fork
where DNA helicases have unwound the double helix and the replication machinery sits and synthesizes complementary strands
Origin binding proteins
- Recognize replication origin
- Proteins bind to origin and become part of the complex, also recruits Polymerase
Helicase
enzymes that catalyze the breaking of H-bonds between base pairs and the subsequent ‘unwinding’ of the helix.
Single-Stranded Binding Proteins
bind to the melted strands of original DNA to prevent them from re-annealing or getting attacked by nucleases
Primase
Enzyme that catalyzes the addition of the RNA primer to begin replication
(RNA primer required for DNA pol)
DNA polymerase I (3 different activities)
Removes RNA primer, replace with DNA
1) 5’–>3’ exonuclease activity: removes RNA primer
2) 3’–>5’ exonuclease activity: proof-reading
3) 5’–>3’ DNA synthesis: fills gap once RNA is removed
_________ is distributive and falls on and off the DNA easily and _______ is processive
DNA polymerase I
DNA polymerase III
DNA Polymerase III (2 activities)
- Elongation of DNA from RNA primer
- uses sliding clamp (processive)
- multi-protein complex
1) 5’–>3’ DNA synthesis
2) 3’–>5’ Exonuclease activity (proofreading)
DNA polymerase III determines the correct base to input based on ________ and _________
H-bonds and geometry
DNA ligase
- enzyme responsible for sealing Okazaki fragments together once the RNA primers have been replaced by Pol I
- Uses cofactors (ATP-euk, NAD+ - prok)
Sliding clamp
- Holds on to DNA and allows DNA pol III to hold on to DNA strongly, but enables it to move
- PCNA (euk), Beta clamp (prok)
Telomere
- sequence at the ends of chromosomes, consisting of a large number of repeating segments
- gets consistently shorter with every chromosome replication
Dysteratosis congenita
telomere shortening syndrome