DNA replication Flashcards
T/F During DNA synthesis, the template is always read in the 3’ to 5’ direction
True
When using a P32 labeled nucleotide in a DNA synthesis reaction, it is critical to make sure that the label is on the gamma phosphate
False, should be on alpha phosphate
DNA synthesis reaction has a strong negative net free energy and is essentially irreversible because a high energy bond is transferred from the incoming nucleotide to the growing DNA chain
False.
The processivity of a DNA polymerase is the average number of nucleotides added to a DNA chain each time it binds to a primer:template junction
True
When positioned in the active site of DNA polymerase, the template strand is kinked 90 degrees between the last paired base and the first unpaired base.
False
Proof-reading DNA polymerase contains a 3’ to 5’ exonuclease activity
True
No known DNA polymerase can initiate synthesis of a DNA strand de novo (without a primer)
True
DNA primase is actually a specialized RNA polymerase
False
Function of RNase H in DNA replication is to cleave ribonucleotides that have been mistakenly added to the end of an elongating DNA chain by DNA polymerase.
False
DNA helicases involved in replication are ring-shaped enzymes that surround both DNA strands while unwinding them.
False
Sliding clamps are enzymes that encircle newly synthesized DNA duplexes during DNA synthesis and clamp the two DNA strands together so they do not dissociate.
False, they keep the polymerase from dissociating from the template.
Origins of replication are defined DNA sequences in E. Coli but not in any eukaryotes that have been tested thus far.
False
Replication origins usually contain one or more stretches of AT-rich, easily unwound DNA
True
Replication origins serve as binding sites for initiator proteins and the replicative DNA helicases.
False, the initiator proteins recruit the DNA helicases to the origins.
In the 2-D gel technique for mapping replication origins, the presence of a bubble arc on the gel indicates that the restriction fragment being analyzed contains a replication origin
True
In mammals, replication origins can be identified on the basis of binding of the ORC complex
True
At chromosome ends there is a division of labor: telomerase extends the 3’ ends while the regular DNA polymerase extends the 5’ ends.
True
in telomere t-loops, the ss 3’ ends of chromosomes are base-paired with internal telomere repeats
True
In E.coli, the clamp loader must hydrolyze its bound ATP in order to bind and open a sliding clamp.
False
The inherent processivity of most DNA polymerases is less than 100 bases
True
Telomerase exhibits higher activity on long telomeres than on short telomeres.
False, when telomeres are long, there are inhibitory binding proteins that bind and prevent telomeric activity.
The eukaryotic initiator protein is a six subunit protein called ORC
True
In E.Coli, if the helicase becomes separated from the DNA pol III holoenzyme, the activity of the helicase is decreased.
True
If a DNA helicase that binds ssDNA and translocates along the DNA in the 3’ to 5’ direction was mixed with a standard primer-template complex in the presence of ATP, it would dissociate the primer from the template.
False, this is the job of RNase H.
The eukaryotic version of SSB protein is RFC
False, it is RPA. RFC is the eukaryotic sliding clamp loader.
In E.coli, there can be as many as 3 DNA pol III enzymes actively engaged in synthesizing DNA at a single replication fork at the same time.
True
In eukaryotes, the primer is synthesized by :
complex of DNA primase and DNA pol alpha
In E. coli, DNA replication the sliding clamp interacts with :
DNA helicase, and the clamp loader (gamma complex)
What happens to the lagging strand DNA pol III when it encounters 5’ end of previous okazaki fragment?
it stops synthesizing DNA, spontaneously dissociates from the DNA and the sliding clamp, but does not diffuse away from replication fork because it remains attached to the t protein.
What order do the replication proteins bind to newly unwound stretch of template DNA?
SSB, primase, sliding clamp, pol III, pol I
In eukaryotes, the MCM-27 complex is recruited to replication origins when :
CDK activity is low, and cdc6 and cdt1 are present
in yeast, telomerase is activated by ____ proteins bound to ds telomere sequences.
cdc13
DNA synthesis reaction is initiated by nucleophilic attack of ___ on ____
The terminal 3’ O of primer strand, the alpha phosphorous of the incoming nucleotide.
Okazaki fragments are synthesized on the ___ in the ____ direction.
lagging strand, 5’-3’
What happens when the wrong nucleotides is accidentally incorporated into a growing DNA chain by DNA polymerase?
DNA synthesis slows drastically, the last 3-4 nucleotides of the primer strand become single-stranded and the end of the primer strand is relocated into the editing site of the enzyme where the incorrect nucleotide is cleaved off.
If an incoming dCTP underwent tautomeric shift, it would preferentially bp with a ____ in the template strand.
A
What triggers closing of the “fingers” of the DNA polymerase via rotation of the O helix?
successful base pairing of the incoming nucleotide with the template strand.
what are the enzymatic activities of E.coli DNA Pol I?
DNA synthesis, 5’ to 3’ exonuclease, and 3’ to 5’ exonuclease
In prokaryotes, the leading strand is synthesized by DNA pol ____ and the lagging strand is synthesized by DNA pol ____
iii, iii
to activate the eukaryotic replication origin :
phosphorylation of MCM2-7 complex and binding of the GINS and cdc45 proteins to MCM2-7 complex
What complex encircles both DNA strands before origin activation but only one DNA strand after origin activation?
MCM-2-7 complex
