DNA Replication Flashcards
Watson and Crick’s model of DNA allowed for replication, and thus transfer of genetic information.
- Conservative
- Semiconservative
- Dispersive
Replication Models
One parent double helix and one new double helix
Conservative Model
One strand is from the parent and one is the novel strand from the new molecules, forming the double helix
Semiconservative Model
Amounts of the parent strand are dispersed in the novel strand, forming a mixed double helix
Dispersive Model
- DNA polymerase
- Helicase
- Ligase
- dNTP
- Primers
- Primase
- Protein binding complex
- Topoisomerase
- Telomerase
- SSb
- Okazaki fragments
Molecules involved in replication
Catalyzes phosphodiester bond formation
-polymerization of dNTPs,
DNA polymerase
Breaks hydrogen bonds between the nitrogenous bases
“unzips genes”
Helicase
Connects DNA strands
Ligase
deoxynucleosidetriphosphate
-“nucleotide”
dNTP
RNA fragments
Primer
Synthesizes the RNA primer
-Can only add nucleotides to the existing strand of DNA.
Primase
Untwist DNA to relieve pressure ahead of replication fork
Topoisomerase
Synthesizes telomeres
Telomerase
Single stranded binding protein
stabilize newly single stranded regions
SSb
Discontinuous lagging strand
Okazaki Fragments
- Replicator sequence is denatured by initiator proteins to form a replication bubble
- new strand is made in accordance with complementary basepairing rules - Helicase loaded onto the DNA
- breaks H bonds, requires ATP - Helicase recruits Primase
- change in shape when helicase binds to DNA is recognized by Primase - Primase synthesizes a short primer
- RNA: 5-10 nucleotides long, annealed to template DNA strand according to complementary base pairing rules
Initiation of Replication Process
- SSB proteins bind to the single stranded DNA
- Polymerase III adds nucleotides ONLY in the 5’ to 3’ direction
- DNA gyrase relaxes the tension ahead of the replication fork
- Polymerase I activity
- DNA ligase activity
Semidiscontinuous Replication
Displaced by polymerase prevents reannealing
SSB proteins binding to the single stranded DNA in the fork
- synthesizes off of RNA primer for both leading & lagging strand
- catalyzes 5’ to 3’ polymerization of dNTPs
- reads template 3’ to 5’
DNA Polymerase III
Synthesis from 5’ to 3’ direction
All polymerases synthesize this way
-Introduces supercoiling in order to relieve stress
DNA Gyrase
- Joining of the Okazaki fragments
- Digests RNA primer ahead of it using its 5’ to 3’ exonuclease activity.
- Replaces RNA primer with dNTPs using its 5’ to 3’ polymerase activity
DNA Polymerase I
Degrades sequence at the ends
Exonucleases
- Joining of Okazaki Fragments
- Seals the nick between adjacent fragments
DNA Ligase
All known DNA polymerases:
a. can initiate DNA chain synthesis
b. have 5’ to 3’ polymerization activity
c. have 5’ to 3’ exonuclease activity
d. have 3’ to 5’ polymerization activity
e. all of the above
b. have 5’ to 3’ polymerization activity
What is the primer for DNA pol. I?
a. RNA synthesized by primase
b. DNA synthesized by primase
c. Okazaki fragment
d. It doesn’t need a primer
c. Okazaki fragment
Accuracy of polymerase
Fidelity
How long DNA polymerase can stay on the strand
Procesicivity
- More mistakes to correct, less time to add nucleotides
- Almost always adds the correct complementary bp.
Polymerase’s proofreading activity
Have 3’ to 5’ exonuclease activity
Both DNA Pol. I and DNA Pol. III
Remove incorrect 3’ nucleotide, insert correct base, and keep synthesizing
DNA Polymerase
DNA Polymerase ______ has 5’ to 3’ and 3’ to 5’ exonuclease activity.
a. I
b. III
a. I - only DNA Pol. I will chew up Okazaki primer.
- a complex molecular machine that carries out replication of DNA.
- first unwinds double stranded DNA into two single strands.
- For each of the resulting single strands, a new complementary sequence of DNA is synthesized.
The Replisome
-Replication process similar to prokaryotes, but chromosomes are bigger and linear
-Contains multiple origins per chromosome
ex. autonomously replicating sequences in yeast.
-15 polymerases
not all participate in replication, many participate in DNA repair
-DNA is packed as it is synthesized
DNA Replication in Eukaryotes
Area where one origin of replication to where 2 origins of replication fuse
Replicon
Multiple Origins: Many start at the same time
Replication in Eukaryotes
- Tandemly repeated
- added by enzyme telomerase
Telomeres
Is a reverse transcriptase
complex of protein (does the synthesizing) and RNA (template)
Telomerase
Makes DNA from RNA template
Reverse transcriptase
Telomerase_____
a. contains its own RNA template
b. is a reverse transcriptase
c. extends one strand of the telomere
d. is responsible for helping to maintain chromosome size
e. all of the above are true
e. all of the above are true
Type of supercoiling that relieves stress
Think of DNA Gyrase and what it does
Positive supercoiling
