Chapter 7 Exam 3 Flashcards
(31 cards)
What is semiconservative replication?
Each daughter DNA molecule contains one parental strand and one newly synthesized strand.
What is the replication fork and how many are there?
The replication fork is the Y-shaped region where DNA is split into two strands for copying.
There are two forks per origin of replication, and they move in opposite directions (bidirectional replication).
In what direction is DNA synthesized?
DNA is always synthesized in the 5’ to 3’ direction.
What is the difference between the lagging strand and the leading strand?
Leading strand is synthesized continuously toward the replication fork.
Lagging strand is synthesized discontinuously in Okazaki fragments away from the fork because DNA polymerase can only synthesize 5’ to 3’.
What are the three parts of DNA replication?
Initiation: Begins at oriC; DnaA binds, melts DNA, helicase and primase are loaded.
Elongation: DNA polymerase III synthesizes DNA; leading and lagging strands formed.
Termination: Occurs at ter sites; Tus protein halts replication.
What is oriC?
Origin of replication on the chromosome.
What are ter sequences?
Termination sequences.
What does DnaA do?
Binds oriC to initiate replication.
What is the role of DnaB (Helicase)?
Unwinds DNA at the fork.
What does DnaC (Helicase loader) do?
Loads DnaB (helicase) onto DNA which unwinds the fork.
What is the function of DnaG (DNA primase)?
Synthesizes RNA primers.
What is the role of DNA polymerase III?
Main enzyme for elongation.
What does DNA polymerase I do?
Replaces RNA primers with DNA.
What is SeqA’s function?
Inhibits DnaA binding; regulates initiation.
What do single-stranded binding proteins (SSBs) do?
Stabilize unwound DNA.
What is the purpose of the sliding clamp?
Holds polymerase onto DNA.
What are Okazaki fragments?
Short DNA pieces on lagging strand.
What is the role of DNA ligase?
Joins Okazaki fragments.
What does RNaseH do?
Removes RNA primers.
What is the role of methylation in DNA replication?
Methylation marks DNA as ‘ready’ for replication.
SeqA binds hemimethylated DNA to delay re-initiation. High DnaA levels promote initiation at oriC.
What does DnaA bind to and what happens after it binds?
DnaA binds to 9-mer repeats at oriC → DNA melts at AT-rich 13-mer repeats → recruits helicase and primase.
What is deoxyadenosine methylase (Dam)?
An enzyme that methylates adenines in GATC sequences, important for timing replication.
How many DNA polymerases does E. coli have?
E. coli has 5 DNA polymerases. Only Pol III (main synthesis) and Pol I (primer removal) are involved in replication.
All DNA polymerases require an RNA primer with a free 3’-OH.
What is the replisome?
A large complex of proteins (Pol III, helicase, primase, etc.) that coordinates DNA synthesis at the replication fork.
