Week 5- DNA Replication Flashcards
What direction do DNA polymerases synthesize DNA?
5’ to 3’
DNA polymerases can only add nucleotides to the free 3’ end of a growing strand.
What are the two types of activity that DNA polymerase possesses?
3’ to 5’ exonuclease activity
This activity allows for proofreading during DNA replication.
What is the size of DNA molecules typically measured in?
Base pairs (bp)
1 bp corresponds to approximately 0.34 nm of length along the strand.
What is the range of DNA sizes mentioned?
5 kb to over 250,000 kb
kb = kilo base pairs, Mb = mega base pairs, Gb = giga base pairs.
What temperature can E. coli undertake DNA replication down to?
70°C
Some extremophiles, like P. halocryophilus, can replicate DNA at -150°C.
Who won the Nobel Prize in 1959 for the discovery of the mechanisms of DNA synthesis?
Arthur Kornberg
He shared the prize with Ochoa.
What is the primary role of DNA polymerase I?
DNA repair
It is involved in removing RNA primers during DNA replication.
Which DNA polymerase is the major replicative enzyme in E. coli?
DNA polymerase III
Temperature-sensitive mutants of Pol III cannot replicate DNA at restrictive temperatures.
What are the nucleotides used in DNA synthesis called?
Nucleoside triphosphates (dNTPs)
Examples include dATP, dTTP, dGTP, and dCTP.
What is the rate of elongation for DNA replication in bacteria?
500 nucleotides per second
In human cells, the rate is approximately 50 nucleotides per second.
What initiates the synthesis of RNA primers during DNA replication?
RNA primase
DNA polymerase III cannot initiate synthesis de novo.
What are Okazaki fragments?
Short segments synthesized on the lagging strand
They are later joined together by DNA ligase.
How many origins of replication do prokaryotes have?
One origin of replication
This leads to a single replication bubble.
What is the typical replication time for prokaryotes?
<1 hour
Eukaryotes, with multiple chromosomes, take approximately 2-3 hours.
What is the role of helicase in DNA replication?
Unwinds the double helix
ATP is required for this process.
What is the purpose of single-strand binding proteins during DNA replication?
Prevent the re-annealing of unwound DNA strands
They stabilize the unwound template strands.