When in the cell cycle does DNA replication occur?
S phase
Requirements for DNA replication
DNA Polymerase
Mg +2
Template
dNTP
Primer
Direction of DNA replication
5' to 3'
Complimentary characteristic of DNA replication
for each A of the template strand, a T is added to teh new strand, and for each G a C is added
DNA Polymerase
enzymes that replicate DNA by catalyzing nucleotide polymerization
DNA Replication Proofreading
3'-5' exonuclease activity excises mixmatches
Magnesium
it is a cofactor required for replication
De Nova Strand
New DNA strand
Primer
free 3' OH on a previously existing strand
A strand with a 3' OH is often reffered to as a primer
Bidirectional
replication in both directions from central origins of replication
discontinuous
lagging strand replicated in short stretches
Okazaki fragments
Proofreading
3' to 5' exonuclease activity that double checks for mistakes
dNTPs
Deoxyribonucleotides
Building blocks of DNA
All four are required for replication
complimentary
Every A is paired with a T and every G with a C
Matching, mirror image sequences are called complimentary sequences
How many charges do A and T have?
Two specific charges
How many charges do G and C have?
Three
Semiconservative
One strand of a daughter chromosome is newly synthesized, the other template strand is inherited intact from teh parental chromosome
Overview of DNA Replication
Initiation
Extension
What is the ori?
Origins of replication
sequences where DNA replication begins.
What is a replicon?
Region of a eukaryotic chromosome that is replicated as a unit, from one central ori.
Where does replication begin?
At teh ori in teh center of a replicon and extends.
How does replication move from the replicon?
Extends in both directions until it reaches the end of an adjacent replicon
What is a helicase
An enzyme that unwinds DNA
One of the first factors to bind to an ori
What are single stranded Binding Proteins?
SSB
Factors that stabilize single stranded DNA by preventing it from winding back into a double helix.
What is a DNA Replication Apparatus?
a cluster of factors that assemble around helicase to replicate DNA.
What are the most important factors of DNA replication apparatus?
helicase
DNA Polymerase
Pol alpha
Beta clamp
primase
Beta clamp
Ring like protein that wraps aroudn DNA to stabilize the association of teh replication apparatus
Required for Pol processivity
Allows for greater extension
Leading Strand Replication
One strand is continuously synthesized in teh normal 5' - 3' direction
DNA Polymerase
enzyme that replicates the leading strand.
It reads the template one base at a time incorporating complementary nucleotides, ligating their 5' phosphate to the 3' OH of the growing leading strand
Pol
DNA Polymerase
Discontinuous Replication of the Lagging Strand
Other strand is replicated discontinuously with okazaki fragments because the overall direction of lagging strand synthesis is in the opposite direction
Primase
enzyme binds the unwound lagging strand template and transcribes a short stretch of RNA.
Is a primer, providing 3' OH group required by Pol alpha
DNA polymerase alpha
Pol alpha
This enzyme uses the RNA primer to synthesize an okazaki fragment
How many Okazaki fragments does Pol alpha synthesize?
one
How long does Pol alpha replicate the okazaki fragment?
until it reaches the primer at the end of the previous fragment.
What happens to the primase when the lagging strand is released?
Primase makes the next primer at th eend of the new single stranded region and the process is repeated
What is a consequence of unwinding by helicase?
Supercoiling increases
What do Topoisomerase do?
restores the DNA to the proper level of supercoiling
How is RNA primers removed from the lagging strand?
RNAse
DNA polymerase beta
DNA Ligase
RNAase
This enzyme digests any RNA
DNA Polymerase beta
This polymerase fills in gaps in DNA.
It fills in the gaps left after the RNA primers are removed.
Leaves nicks in teh DNA
DNA ligase
Binds any free 3' hydroxyls and 5' phosphates of DNA.
It seals the nicks between the okazaki fragments left by the Pol beta.
Telomerase
Reverse transcriptase
Uses RNA as a template to make DNA
Fills in the gap from overhang that can't be filled in by the DNA polymerase.
It also extends the length of the DNA
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