Chapter 11- DNA Replication Flashcards
What is the correct model of DNA replication?
semiconservative model
Describe the semiconservative model
replicated DNA will have one old and one new strand of DNA
Describe the conservative model
the two parent strands rejoin
Describe the dispersive model
each strand is a mix of old and new
Describe origins of replication
where the two DNA strands are separated forming a “bubble”.
Describe the replication fork
the ends of the bubble where new DNA strands begin elongating.
Bacterial DNA is what shape?
circular
Describe helicases
enzymes that untwist the double helix at the replication forks
Describe topoisomerase
goes ahead of replication forks, cuts, unwinds, and rejoins DNA strands
Why is topoisomerase needed?
to keep the DNA strands from being too twisted
Describe single-strand binding protein
holds the DNA strand straight so it can be used as a template
What is a primer
a short strand of RNA that is laid down at the origin of replication
What is primase?
enzyme that lays down the primer
Describe DNA Polymerase III
adds DNA nucleotides to the 3’ end of the primer
The new strands grow in ________ directions.
opposite
DNA polymerases add nucleotides only to the __ ___of a strand
3’ end
a new DNA strand can elongate only in the __ to __ direction
5’ to 3’
Leading strand grows _______the origin of replication
in front of
Lagging strand grows _______ of the origin of replication
behind
Describe Okazaki fragments
a series of primers and new DNA segments
Describe DNA polymerase I
removes the RNA primers and replaces them with DNA nucleotides
Describe DNA ligase
connects the new DNA nucleotides
___ ___________ proofread DNA as it is added
DNA Polymerases
________ can repair __________ based pairs or ________ DNA
enzymes; mismatched; damaged
Describe nucleotide excision repair.
cutting out damaged DNA and replacing it with new DNA
Describe nuclease
an enzyme that cuts out damaged DNA
In nucleotide excision repair, what happens after DNA is cut out?
- DNA Polymerase adds new nucleotides2. Ligase seals the new nucleotides
Why is DNA cut short after every replication?
DNA can’t be added to 5’ end new strands
How is DNA code protected from being cut?
meaningless code protects the real code
Describe telomeres
repetitive nucleotide sequences at the end of DNA that do not contain genes
Describe telomerase
an enzyme that lengthens telomeres in gamete DNA
Why is telomerase needed?
so a zygote can start off with a full set of telomeres
If DNA replicated following the conservative model, what would the results of the Meselon-Stahl experiment look like?
There would be one 14N strand and one 15N strand
If DNA replicated following the dispersive model, what would the results of the Meselon-Stahl experiment look like?
Each band would be a mix of 15N and 14N
In prokaryotes, DNA replication is ___________ rather than ____________ (think direction)
bidrectional; unidirectional
In prokaryotes, DNA replication begins at a specific origin site called a _______.
replicon
DNA polymerase _, _, _, _ all repair damaged DNA.
I, II, IV, V
DNA polymerase _, _, _ have 5’-3’ polymerization and 3’ to 5’ exonuclease activity
I, II, III
3’ to 5’ exonuclease does what?
Proof-read synthesized base pairs
DNA polymerase _ has 5’-3’ exonuclease activity
1
What are the 3 helicase proteins in prokaryotic DNA?
Dna A, B, and C
Describe DnaA
proteins responsible for initial steps in unwinding the helix
Describe DnaB and DnaC
further opens and destabilizes the helix
What specific type of topoisomerase reduces supercoiling?
DNA gyrase
DNA polymerase III requires a primer with a free _ ________ ______.
3’ hydroxyl group
Describe concurrent sythesis
Both DNA strands are synthesized concurrently by looping the lagging strand to invert the physical but not biological direction of synthesis
How do polymerases proofread DNA? (what do they look for)
They read the amount of methylation on each strand of DNA
Compare eukaryotic and prokaryotic chromosome and DNA structure.
Eukaryotic chromosomes are linear and the DNA is complexed with proteins
___ _ and ___ _ are the major forms of the enzymes included in initiation and elongation.
Pol α (little Alpha); δ (little Delta)
Describe Pol α’s and δ ‘s functions in synthesis.
Pol α synthesizes RNA primers during initiation on the leading and lagging strands. Polymerase switching occurs, and Pol α is replaced by δ for elongation
Describe telomeres’ function.
They form hairpin loops to make chromosomes appear inert
Why are telomeres important?
They prevent recombination
Why is lagging synthesis at the end of the chromosome a problem?
Once RNA primer is removed, there is no free 3’ hydroxyl group from which to elongate
What does telomerase do?
Direct synthesis of the telomere repeat sequence to fill the gap
Describe the structure of telemoerse
A ribonucleotide protein with a RNA that serves as the template for the synthesis of its DNA compliment.
