DNA Replication 1 Flashcards
What are the three rules of DNA replication?
- It is semiconservative
- replication beings at an origin and proceeds bidirectionally
- Synthesis proceeds in a 5’—>3’ direction and is semidiscontinuous
What does semiconservative replication mean?
Each daughter duplex consists of one parental strand and one newly synthesized strand.
The parental strand is used as a template for the synthesis of the new strand.
What are origins of replication?
Unique sites at which replication begins that are rich in AT base pairs.
What initiates DNA synthesis?
An RNA primer
What is the name of the strand that is synthesized continuously? Discontinuously?
Leading strand is continuous
Lagging strand is discontinuous
What is the function of AAA+ ATPase (DnaA)?
Binds to the origin of replication and dissociates the strands utilizing ATP hydrolyzation.
What is the function of DNA Ligase?
Creates phosphodiester bonds utilizing ATP, seals “nicks” in the DNA strand
What is the role of DNA polymerase?
Group of enzymes that are responsible for strand elongation, require a ssDNA for a template and an RNA primer
What is the function of helicase?
Unwinds the double helix utilizing ATP
What is the function of nucleases?
Sever phosphodiester bonds of the DNA backbone, can be endo- or exo-
What is the function of primase?
Synthesizes short stretches of RNA complementary to the template DNA strand that serve as a primer for DNA polymerase
What is the function of topoisomerase?
Adjust the supercoiling of DNA double helices to alleviate supercoiling stress and introduce negative supercoiling.
Contain both endonuclease and ligase function
What are the three steps of DNA synthesis?
Initiation
Elongation
Termination
What happens during initiation?
DNAa binds the origin of replication
Helicase dissociates the double helix
SsDNA binding proteins protect DNA and maintains dissociation
How is the leading strand synthesized?
DNA polymerase III synthesizes the strand in the 5’—>3’ direction, starting at the 3’ end of an RNA primer.
Synthesized continuously
How is the lagging strand synthesized?
Discontinuously as a series of small fragments (Okazaki fragments) by DNA polymerase III.
Still made in the 5’—>3’ direction
What is DNA gyrase and what is its function?
A type II topoisomerase that alleviates positive supercoiling imposed by strand unwinding
How are mismatches identified in DNA proofreading and how are they corrected?
The number of rings and the hydrogen bonding pattern.
If these aren’t correct, DNA polymerase uses its 3’—>5’ exonuclease activity to excise the mismatched nucleotide
What happens during termination?
DNA gyrase resolves the two newly formed chromosomes
What are the three mechanisms that ensure replication fidelity?
Geometry of the active site of DNA polymerase
Proofreading: 3’—>5’ exonuclease activity
Mismatch repair and DNA methylation
How does DNA methylation ensure replication fidelity?
The parent strand is methylated so that the cell can tell which strand should be used to correct mistakes
What is the function of DNA polymerase I?
DNA repair and removes RNA primers during replication
Function of DNA Pol II?
DNA repair
Function of DNA pol III?
Synthesizes most of the DNA on both leading and lagging strands
Function of DNA pol IV and V?
DNA repair functions
