Replication Flashcards
(24 cards)
What is replication?
The making of a copy of the DNA molecule
Why is DNA replication called semi-conservative?
Because each strand from the “old” strand serves a a template for a new strand, leading to after replication each molecule contains one old (conserved) strand and one new.
What is the meaning of replication being bidirectional?
That the strand are simultaneously unwound and replicated in both directions, using 2 replication forks.
Always starts at an unique point called the origin
What does it mean that replication is semidiscontinous?
The both strands are replicated at the same time but the leading strand is being replicated without interruption (continuous) while the lagging strand is replicated in smaller Okazaki fragment (discontinuous)
In which direction is DNA syntethis?
Always 5’ to 3’
In which direction is the template read?
It’s read from 3’ to 5’
What is the continous strand called?
The leading strand
What is the discontinuous strand called?
The lagging strand
What is a DNA polymerase?
Enzyme that synthesize DNA molecules, by creating identical DNA strand from a original strand
What is a primer?
A strand segment that is added to the template strand to enable polymerization.
Has a free 3’ hydroxyl group
What is the replisome?
The DNA copy-machine
Contains helicases, polymerases, nucleases and ligases
Processes the discontinuous stretches of the lagging strand
Describe the process of a replisome in replication
Replisome accesses to DHA strand
Helicases separates the two parent strands
SSB DNA binding proteins are stabilizing the separated strands
Primers are synthesized by primase to enable the DNA syntezining
DNA polymerase 1 remove primers and replace them by DNA
The remaining nick is sealed by ligases
What are the three stages of replication?
Initiation
Elongation
Termination
Describe the initiation phase
Regulated so that it only occurs once/cycle
Starts at the OriC where the strand is unwound by helicases
A primer is syntezised by primase to create a free 3’ end
Describe the elongation phase
The leading strand synthesis:
Starts with DNA primase DnaG, proceeds continuously. DNA helicase DnaB moves along the strand and the nucleotides are added by DNA polymerase III
The lagging strand synthesis:
RNA primer is synthesized by primase
The strand is replicated in short sequences called Okazaki fragments, which all requires a new primer to initiate
DNA polymerase adds nucleotides
All primers are removed by DNA polymerase I, creating a nick
DNA ligase seals the nicks
Describe the three domains of DNA polymerase I
DNA polymerase 5’-3’
3’ to 5’ exonuclease
5’ to 3’ exonuclease
Describe the action of DNA polymerase I
Can promote nick translation, where a break/nick in DNA is moved along with the enzyme
This process is used in DNA repair and removal of RNA primers during replication
What are the differences in replication between eukaryotes and procaryotes?
Procariotes: has only one OriC DNA polymerase III termination by TusTer-complexes Eucarytotes: Multiple origins DNA polymerase (delta) Termination by telomere synthesis (Telomerase)
What is a telomere?
Many tandem copies of a short T-G sequence
The ends of a linear chromosome are not readily replicated by cellular DNA polymerase she due to no template available
What is telomerase and its function?
It’s a reverse transcriptase containing proteins and RNA
It’s RNA acts as template to DNA synthesis
After extension the complementary strand is synthesized by cellular DNA polymerases
Mostly sequestered by T-loop
What could be the reasons for DNA damage?
Abnormal bases
Mismatch
DNA lesions
What is a silent mutation?
A mutation in nonessential DNA or if it has negligible effects
What is proofreading?
Error correcting processes
DNA polymerases has a 3’-5’ exonuclease activity that double-checks each nucleotide after its been added.
What are the different types of repair?
Mismatch repair
Base-excision repair
Nucleotide-excision repair
Direct repair
