6.3 DNA Replication Flashcards
Replication complex (replisome)
- a set of specialized proteins that assist the DNA polymerases
Helicase
the enzyme responsible for unwinding the DNA, generating two single-stranded template strands ahead of the polymerase
DNA topoisomerases
- introduce negative supercoils.
They do so by working ahead of helicase, nicking one or both strands, allowing relaxation of the torsional pressure, and then resealing the cut strands - alleviate this torsional stress and reduce the risk of strand breakage
Semiconservative
- one parental strand is retained in each of the two resulting identical double stranded DNA molecules
How does DNA polyermase read the template strand?
- read the template strand in a 3′ to 5′ direction while synthesizing the complementary strand in the 5′ to 3′ direction.
Which processes occur 5’ to 3’?
- DNA synthesis
- DNA repair
- RNA transcription
- RNA translation (reading of codons)
Leading strand
- stand copied in continuous fashion
Lagging Strand
- strand that is copied in a direction opposite the
direction of the replication fork.
Primase
- synthesizes a short primer (roughly 10 nucleotides) in the 5′ to 3′ direction to start replication on each strand
- These short RNA sequences are constantly being added to the lagging strand because each Okazaki fragment
must start with a new primer
DNA polymerase III
-Synthesizes daughter strands for prokaryotes
DNA polymerases α, δ, and ε
-Synthesizes daughter strands for eukaryotes
- incoming nucleotides are 5′ deoxyribonucleotide
triphosphates: dATP, dCTP, dGTP, and dTTP
DNA polymerase I
- prokaryotes
- removes RNA
- adds DNA nucleotides where the RNA primer had been.
RNase H
- eukaryotes
-removes RNA - adds DNA nucleotides where the RNA primer had been.
DNA polymerase δ (Delta)
- fills in the gaps left behind when RNA primers are removed
DNA polymerase γ (Gamma)
replicates mitochondrial DNA
What do DNA polymerases β (Beta) and ε (epsilon) do?
- important to the process of DNA repair
What do DNA polymerases δ (Delta) and ε (Epsilon) do when together?
- assisted by the PCNA protein, which assembles into a trimer to form the sliding clamp. The clamp helps to strengthen the interaction between these DNA polymerases and the template strand
Limits of DNA polymerase?
- does an excellent job of synthesizing DNA, it unfortunately cannot complete synthesis of the 5′ end of the strand
- Thus, each time DNA synthesis is carried out, the chromosome becomes a little
shorter.
