DNA Replication- PowerPoint Flashcards
What is the template strand?
parent strand, what the daughter strand replicates from
What is the daughter strand?
new strand
Watson and Crick proposed what type of model?
semi-conservative model
What is the Conservative replication model?
The two strands of the original molecule serve as templates for the two strands of a new DNA molecule; then, they rewind into an all “old” molecule.
What is a the Dispersive replication model?
Neither parental strand is conserved, and both chains of each replicated molecule contain old and new segments.
What is semi-conservative model?
2 daughter stands both have a parent strand for first round of replication
Which mode of replication would require the most amount of energy?
dispersive model
Which mode of replication does DNA actually follow?
semi-conservative model
What happened in Meselson and Stahl experiment?
- Bacterial cells were grown in a heavy isotope of nitrogen, 15N
- All the DNA incorporated 15N
- Cells were switched to media containing lighter 14N
- DNA was extracted from the cells at various time intervals
- DNA Molecules with different densities were separated by centrifugation
How did they band the density gradient in Meselson and Stahl experiment?
cesium chloride
Something with a higher density will band where?
bottom of tube
Where were the location of the 15N and 14N in the tube?
15N on bottom bc higher density and 14N in the top of the tube
How does the density gradient separate a sample?
the sample will band with the density band that matches it
How long does it take for a bacteria to replicate? (binary fission)
20 minutes
What do the peaks correspond to?
the number of bands
During the first round where the sample had 0 rounds of replication what nitrogen was found in it?
15N
During the first round where the sample had 1 rounds of replication what nitrogen was found in it?
15N and 14N
During the first round where the sample had 2 rounds of replication what nitrogen was found in it?
15N and 14N hybrid and a pure 14N
DNA with 15N and 14N will have what type of density?
hybrid
Which replication models did the first sample where 0 rounds of replication occurred?
all
Which replication models did the second sample where 1 rounds of replication occurred?
semi-conservative and dispersive
Which replication models did the third sample where 2 rounds of replication occurred?
only semi-conservative
What are DNA polymerases?
assemble complementary polynucleotide chains from
individual deoxyribonucleotides
What are the 4 deoxyribonucleotide triphosphates?
dATP, dGTP, dCTP, and dTTP
Where does DNA polymerases add nucleotides?
only to the 3′ end of an existing chain
What are the rules of DNA polymerase? (3)
1) 5’ —–> 3’
2) nucleotides added to 3’ end
3) new and old strand are anti-parallel
What provides energy for DNA chain elongation reaction?
hydrolysis of Pyrophosphate
What do they use for banding densities now?
sucrose
What is the gel that DNA is run on?
auger gel
How long does the auger gel need to solidify?
10 mins
What is used for intercalation (inbetween) between base pairs?
ethridium bromide
How do you see the DNA after you have run the gel?
UV light
What does ethridium bromide color the DNA?
pink
What is used to make wells in the gel?
comb
If one sample has 80 base pairs and the other sample has 120 base pairs which sample moves faster in the sample?
80 base pair sample
What is the control in the gel?
molecular weight marker
How many base pairs is 1kb?
1000kb
What 3 things does DNA replication require?
1) Parental DNA molecule—template
2) Enzymes – DNA Polymerases
3) Nucleotide triphosphates – four different dATP, dTTP, dCTP, and dGTP
What do DNA polymerases assemble?
complementary polynucleotide chains from individual
deoxyribonucleotides
What is a sliding clamp and what is its shape?
protein, doubt shape
Is the sliding clamp behind or ahead of the DNA polymerase?
behind
Whats the role of the sliding clamp?
make sure DNA polymerase doesn’t fall off the template strand
What is the result of the sliding clamp?
increases efficiency
How is the sliding clamp loaded and unloaded onto replicating DNA in humans?
clamp loader, The efficient unloading of sliding clamps by clamp loaders once DNA polymerase has dissociated from DNA is probably important for the overall efficiency of DNA replication
How does a new strand of DNA begin if there is no existing chain?
A new strand begins with a short chain of RNA (primer), synthesized by the enzyme primase
What does primase do?
Primase leaves the template, and DNA polymerase takes over, extending the RNA primer with DNA nucleotides as it synthesizes the new DNA chain
What are RNA primers are replaced with later in replication?
DNA
What is ori? and what happens?
origin of replication, In the bacterial chromosome, unwinding of DNA for replication occurs here bidirectionally
What unwinds DNA?
DNA helicase
What does DNA helicase produce?
Y-shaped replication fork
What do Single-stranded binding proteins (SSBs) do?
coat the exposed single-stranded DNA segments, keeping them from pairing.
What does Topoisomerase do?
cuts and rejoins DNA to prevent twisting in circular
bacterial chromosomes.
What direction is the template strand read in?
3′→5′ direction
What is torsional strain?
the strain caused by the twisting of DNA
What relieves torsional strain?
topoisomerase
What does DNA helicase get its energy from?
ATP hydrolysis
What is a leading strand?
the new DNA strand is synthesized in the direction of DNA unwinding. This is a single priming event.
Which strand is Synthesized on the leading strand template?
leading strand
What is the lagging strand?
strand synthesized discontinuously in the direction opposite DNA unwinding
How many priming events does the leading strand need?
1
How many priming events does the lagging strand need?
multiple
Which strand is Synthesized on the lagging strand template?
lagging stand
What are Okazaki fragments? how long are they?
fragments of DNA, 100 – 200 base pairs long
Which strand replicates away from the fork?
lagging strand
Which strand replicates towards the fork?
leading strand
