Replication - Part 1 Flashcards
Prokaryotic genome organization
- Lower DNA content
- Main genome: single major DNA molecule (cccDNA)
- Operons
- Few repetitive sequences: no introns
- Other genes: plasmid
Eukaryotic genome organization
- Higher DNA content
- Enclosed in a nuclear membrane
- Several linear DNA, chromosome
- Organization of coding sequences
- With telomere
DNA replication is __
Semi-conservative
What is maintained inthe DNA
Specific base pairing
Needed for initiation of replication
Primer
Direction of newly synthesized DNA strand
5’-3’ direction
Replication of DNA is __
Semi-discontinuous
Grows continuously
Leading strand
Grows in segments
Lagging strand
Connects the okazaki fragments
DNA ligase
How are nucleotides become linked
Condensation reaction to form phosphodiester linkage
Where replication begins and proceeds
- begins at an origin
- proceeds bidirectionally
What is involved in DNA replication
Several enzymes and proteins (replisomes)
How are bacterial genes usually written
3 lowercase italicized letters
Example of how the gene and gene products are written
dnaA (gene) -> Dna A (protein)
Replication proteins
Replisome
What are the replisomes
- Initiation protein
- DNA helicase/ DNA unwinding proteins
- Helix destabilizing proteins or single-strand binding proteins (SSBP)
- Primase
- DNA polymerases
- DNA ligase
- Topoisomerases
Initiation protein of E.coli
dnaA protein
- recognizes the OriC
- binds to it (~20-30 dnaA)
dnaA protein
- local denaturation of DNA helix
- Requires ATP
- Binds ssDNA (not dsDNA)
DNA helicases/DNA unwinding proteins
2 helicases of E.coli
- Helicase II
- Rep protein
- attaches to template for lagging strand
- moves 5’–>3’
Helicase II
- attached to template for leading strand
- moves 3’–>5’
Rep protein
Bind to sites where template has been unwound but not yet duplicated
Helix Destabilizing Proteins or Single-strand Binding Proteins (SSBP)
Functions of Helix Destabilizing Proteins or Single-strand Binding Proteins (SSBP)
- prevent reannealing and tangling of ssDNA
- prevent formation of 2º structure
- protect ssDNA from nuclease degradation
Major SSB of eukaryotes
Replication protein A (RPA)
SSBPs are required to __ the unwound DNA
Iron out
Generate primers
Primases
- short RNA chain (4-12 nts)
- provides the 3’OH end needed by DNA polymerase during elongation
Primer
- monomeric or heteromultimeric
- 3 enzyme activities
DNA polymerase
3 enzymatic activities of DNA Polymerase
- 5’–>3’ polymerization activity
- 3’–>5’ exonuclease activity
- 5’–>3’ exonuclease activity
Add nucleotides onto the 3’OH end of a primer –> synthesize new DNA strands
5’–>3’ polymerization activity
property of DNA pol to remain attached to the template and incorporate nucleotides before detaching
Processivity
1 mistake per 10^9 or 10^10 nucs added
Fidelity
Proofreading
3’–>5’ exonuclease activity
- removes RNA primers at the 5’ end
- not present in eukaryotic DNA polymerase
5’–>3’ exonuclease activity
enzyme that perform 5’-3’ exonuclease activity in eukaryotes
- Rnase H
- Flap endonuclease 1 (FEN1)
- DNA pol delta
- remove RNA primers
- detects RNA-DNA hybrid in eukaryotes
Rnase H
removes remaining bits or RNA primer in eukaryotes
Flap endonuclease 1 (FEN1)
add/fill in the gaps from removal of primer in eukaryotes
DNA pol delta
3 main DNA polymerases for replication
- DNA pol I
- DNA pol II
- DNA pol III
Major repair enzyme
DNA pol I, II
Elongating enzyme
DNA pol III
Gene of DNA pol I
polA
Gene of DNA pol II
polB
Gene of DNA pol III
polC
SOS repair
DNA pol IV, V
Gene of DNA pol IV
dinB
Gene of DNA pol V
umuD’2C
- Replicates both strands simultaneously
- A dimer of 10 proteins
Bacterial DNA Polymerase III Holoenzyme
Core enzyme of Bacterial DNA Polymerase III Holoenzyme
- α – (5’->3’ polymerization)
ε - (3’->5’ exonuclease/proofreading) - θ stimulates ε
Sliding clamp of Bacterial DNA Polymerase III Holoenzyme
β2
purpose of sliding clamp β2
helps the holoenzyme
Clamp loader of Bacterial DNA Polymerase III Holoenzyme
(δδ’χΨ)2τ2γ2
Keeps DNA polymerase attached to the template to allow duplication of long stretches of DNA
Sliding clamp
Assembles the sliding clamp to the DNA
Clamp loader
E. coli sliding clamp = __
eukaryotic PCNA
Separates large fragment and 5’->3’ exonuclease
Subtilisin (proteolysis)
Used in in vitro synthesis of dsDNA from ssDNA
Klenow fragment
Eukaryotic DNA polymerases
α, β, γ, δ, ε, etc
(10 DNA polymerases)
Location of DNA pol α
Nuclear
Location of DNA pol β
Nuclear
Location of DNA pol γ
Mitochondrial
Location of DNA pol δ
Nuclear
Location of DNA pol ε
Nuclear
function of DNA pol α
priming and replication of lagging strand
function of DNA pol β
repair
function of DNA pol γ
mitochondrial
function of DNA pol δ
replication of leading strand
function of DNA pol ε
probably replication
relative activity of α
~80%
relative activity of DNA pol β
10-15%
relative activity of DNA pol γ
2-15%
MW of α
300,000
MW of β
40,000
MW of γ
180-300,000
MW of δ
170-230,000
MW of ε
255,000
No. of subunits of α
4 (several)
No. of subunits of β, γ, δ
1
DNA polymerases with 3’-5’ exonuclease activity
γ, δ, ε
seals nicks using ATP or NAD
DNA ligase
what does the DNA ligase use to seal nicks
ATP or NAD
- relaxes DNA
- removes negative supercoils
topoisomerases
topoisomerase that relax only one strand
topoisomerase I
topoisomerase that relax both strands
topoisomerase II
in E.coli, topoisomerase or gyrase is involved in what?
deconcatenation
process of releasing the final products of circular DNA replication
deconcatenation
what stage of the cell cycle does DNA replication happen
S phase
stages of replication
- initiation
- elongation
- termination
recognition of positions on a DNA molecule where replication will begin
initiation
copying of parent polynucleotide (template) at the replication fork
elongation
completion
termination