DNA Replication and Repair Flashcards
Replication of DNA occurs in a ____-_____ manner
semi-conservative
______ replication of DNA is a model where each DNA strand serves as a template for DNA synthesis, but the original DNA remains intact
Conservative
note: if this model was correct, there would be no DNA molecules composed of parental an daughter strands together in one molecule
Each new DNA molecule consists of an old strand (the template) and a new strand in semi-conservative replication. True or false?
true
Bacteria have single chromosomes which are circular and possess a unique replication origin. True or false?
true
Eukaryotic chromosomes have how many separate origins of replication per chromosome?
1000-2000
Bidirectional replication (two replication forks proceeding in opposite directions) does not occur in DNA. True or false?
false; it does
DNA replication proceeds only in the ___ –> ____ direction
5’ –> 3’
DNA replication is initiated from pre-existing ____ (short section of RNA which is complementary to the template strand)
primers
DNA synthesis proceeds from discreet sites meaning it must unravel two parental DNA strands at particular sites and use each single strand as a ___ to direct synthesis of new complementary daughter strands
template
In this strand, replication is continuous
leading strand
in this strand, replication proceeds from multiple primers and results in forming short DNA sequences which are eventually joined; synthesis is discontinuous
lagging strand
____ problems must be overcome in DNA replication. Both prokaryotic and eukaryotic DNAs exist not as linear molecules with free ends but rather as closed-loop molecules. ____ of the DNA molecule during replication creates torsional strain which must be removed for replication to proceed
topological; supercoiling
In regards to prokaryotic DNA replication, DNA polymerases catalyze the following reaction:
(dNMP)n + dNTP —-> (dNMP)n+1 + PPi –> 2 Pi
Only _______ ____ can serve as substrates
deoxyribonucleic triphosphates
All DNA polymerases require both a template and a primer. True or false?
true
During DNA replication in both prokaryotic and eukaryotic cells, both of the strands of the parent DNA molecule serve as _____ and small fragments of RNA serve as ____
template; primer
In regards to prokaryotic replication, RNApolymerase (primase) is necessary for what?
the synthesis o the RNA primers required for DNA replication
In regards to prokaryotic replication, DNA polymerases require a free ___-___ terminal from which to start. The RNA polymerase adds an oligonucleotide from 10-60 bases to serve as a ____.
3’-OH; primer
The short sections of primer RNA plus DNA which form on the lagging strand are called what?
okazaki fragments
During DNA replication, unwinding of DNA must occur as well as strand separation. The enzymes which carry out unwinding are known as _____
helicases
The helices bind to sing-stranded DNA and require ____ which is hydrolyzed in order to drive enzyme function
ATP
Define replisome
total proteins and enzymes required for DNA synthesis at replication fork
During DNA replication, unwinding of DNA creates ___ supercoiling which must be removed by enzymes called ____
positive; topoisomerases
Topoisomerases catalyze interconversion of different topological isomers of DNA. These enzymes relieve ____ ahead of the replication fork
tension
Explain the difference between Type I and Type II topoisomerases
type I: makes a break in one strand of the DNA helix and passes the other strand though the break to relax the supercoil. The break is then sealed. Doesn’t require ATP
type II: also known as DNA gyrase - produces an enzyme-bridged break in both strands of DNA. Another region of duplex DNA is passes through the gap by the enzyme, thus two supercoils are removed in one step. This enzyme requires ATP