DNA Replication Flashcards
Explain why DNA replication is semiconservative
when the double helix unwinds it exposes bases on each strand, each of these strands can act as a template for synthesis of new strands, the new strands form by insertion of complementary base pairing, single double helix becomes two identical daughter double helixes
what 3 phases does DNA replication happen in?
Initiation, elongation, and termination
Describe initiation
Initiator Protein binds to Ori. Single stranded binding proteins open up the double helix to prepare it for complementary base pairing, helicase unwinds the helix, primase adds (synthesizes) RNA primer. Two replication forks are formed
What proteins open up the double helix and prepare it for complementary base pairing in initiation?
single stranded binding proteins
where does initiation occur?
At the origins (ORI) of replication. In plasmids this is just one location, in chromosomes it’s many locations
Why do we need RNA primer?
So that DNA polymerase can add nucleotide sequences on
Primers are _____ and ______ to each template strand
complementary and antiparallel
What is the purpose of initiation?
preparation of double helix for complementary base pairing
What are the 4 main steps in elongation?
- DNA polymerase III catalyzes phosphodiester bond formation between adjacent nucleotides, this is called polymerization
- DNA polymerase I replaces RNA primer with DNA sequence
- DNA ligase covalently joins successive Okazaki fragments together (that have nicks in the backbone)
- DNA topoisomerase may need to reduce supercoiling by cutting DNA phosphate backbone to let unwind ahead of replication fork
What is the phosphodiester bond?
The link in DNA between a 5’ and 3’
Catalyze
to cause an action or process to begin
Synthesize
to form _____ by combining parts or elements
DNA polymerase
Catalyzes new phosphodiester bonds
what do I mean when I say ‘catalyzes new phosphodiester bonds’?
Nucleotides are matched based on base pairing then attached to form new DNA strand
what are DNA polymerase reactants?
high-energy dNTPs (nucleotide triphosphates)
what is elongation doing in one sentence?
Makes sure the correct nucleotide sequence is copied from template strand to newly synthesized strand of DNA
DNA synthesis new strand goes from?
5’ to 3’
The template and newly synthesized strands are…
antiparallel
why is it important to use nucleotide triphosphates instead of nucleotide monophosphates when catalyzing new phosphodiester bonds?
because these high energy dNTP provide the energy for the formation for the phosphodiester bonds. Monophosphates don’t have enough energy
What does DNA topoisomerase do?
Relaxes supercoils by cutting the sugar phosphate backbone bonds strands of DNA. Once it does this it can rotate the cut site and rejoin ends, the unwound broken strands are then sealed by ligase
What is termination?
A releasing of the DNA and the component enzymes. No proteins involved
How many replication forks depart from an origin of replication?
Two
The step in DNA replication in which the replication proteins open up the double helix and prepare for complementary base pairing is called
initiation
a group of enzymes that seals nicks in the phosphodiester backbone and is very important in the lagging strand replication
ligases
the group of enzymes able to relax supercoils in DNA is called
topoisomerases
