DNA replication Flashcards
(26 cards)
replication fork
“growing fork” - site of active DNA synthesis (helix unwound creates a fork)
leading strand
continuous synthesis in direction of replication fork opening (5’–> 3’)
lagging strand
discontinuous synthesis in direction opposite of replicaiton fork, Okazaki fragments
semi-conservative DNA replication
each new double strand of DNA has a parent and a daughter strand (one old and one new)
origin of replication
starting site for replication on the chormosome, replication occurs bidirectionally
DNA Ligase
- joins fragments together in lagging strand (any gap between a 5’ end and a 3’ end) 2. can only join DNA to DNA, not RNA to DNA or RNA to RNA
reverse transcriptase
enzyme that creates DNA from an RNA template, requires template, primer, and nucleosides, no exonuclease activity makes it error prone (Telomerase and retroviruses)
okazaki fragments
series of discontinuous framents synthesized from multiple primers on laggin strand (still primase and DNA Polymemrase at work - 5’ –> 3’)
3 Steps for DNA replication initiation
- single-stranded DNA 2. RNA primer (DNA polymerases cannot start synthesis w/o a template) 3. deoxynucleotides
Differences of Mitochondrial DNA Replication (3)
- circular DNA (no telomeres) 2. replication form is unidirectional (no okazaki fragments) 3. not cell cycle regulated (can have lots of different genomes and multiple mitochondria)
Differences of Eukaryotic DNA replication (5)
- many origins of replication 2. Replication is regulated by the cell cycle 3. Mitochondrial DNA replication 4. Telomeres bc chromosomes are linear 5. Chromatin/organization is different
What are the Watson-Crick nucloetide base pairings?
A–T, C—G
What is the structure or DNA
antiparallel double stranded helix
What is the most prevelant non-covalent bond in DNA secondary structure?
Hydrogen bonding between base pairs (A-T has 2, C-G has 3)
What is the direction of DNA synthesis?
5’–>3’ for the new strand
Which end are bases added to in a growing polynucleotide chain?
3’
4 Steps of initiation of DNA replication in Prokaryotes
- DNAA binds origin or replication and uses ATP to part the strands 2. 2 Helicases (DNAB) bind each single strand and continue to unwind using ATP 3. single stranded binding proteins (ssb) stabilize single strands 4. Primase (RNA polymerase) synthesizes primer for DNA polymerase
Is DNA Polymerase processive?
Yes. It is able to stay attached and carry out multiple rounds of nucleotide addition and not fall off thanks to Beta clamp subunit (on lagging strand, clamp goes on and off to move DNA Pol up)
Explain the DNA Polymerase “dimer.”
DNA Polymerase on the lagging strand is linked to the DNA Pol on the leading strand by a protein , this helps for coordinated synthesid of both strands
DNA Polymerase 3
fastest rate (30,000 nucleotides/min), polymerizes 5’->3’, exonuclease 3’->5’
DNA Polymerase 1
slower rate (600 nu/min), polymerizes 5’->3’, exonuclease 5’->3’ and 3’->5’ (removes RNA primers on lagging strand and replaces it with DNA)
Topoisomerase
enzyme to untagle DNA, nicks one strand and passes the other through it and reseals it
Error rate of DNA polymerases
1 in 100,000 bases
How can DNA polymerase correct errors?
DNA polymerase has 2 active sites (synthesis and exonuclease), it can exonuclease back a few bases and resynthesize that area
