Lecture 2 DNA replication Flashcards
What is a false statement regarding DNA replication?
The only 3 enzymes required for DNA replication are DNA polymerase, helicase, and ligase
DNA synthesis proceeds:
bidirectionally from the replication origin
DNA replication begins
replication origions
An enzyme that breaks, DNA dispels the tension, and reseals the strand ahead of a DNA replication growing fork is called a(n)
topoisomerase
The Meseleson- Stahl experiment showed that:
DNA replication is semiconservative
What is the function of the sliding loader?
opens the clamp and loads the clamp onto the ssDNA
The sliding clamp:
is part of the replisome
DNA synthesis:
utilizes energy obtained through hydrolysis of pyrophosphate
Okazaki fragments are small fragments of DNA that eventually are ligated to form which of the following strands of DNA?
Lagging
What are initiator proteins responsible for?
recruiting the helicase and stabilize the ssDNA
The replication machinery:
moves along the DNA copying both strands
How is torsional stress from supercoiling in replicating DNA revealed ahead of the replication fork?
Topoisomerase generates nicks in the DNA strand
Which enzymes mediates the processing of Okazaki fragments?
ligase
DNA ligase
catalyzed the formation of a phosphodiester bond
Initiator Proteins - Prokaryotes
DnaA
Initiator Proteins- Eukaryotes
ORC
Helicase Prokaryotes
DnaB loaded onto ssDNA (5’-3’)
Helicase eukaryotes
MCM complex loaded on dsDNA(3’-5’)
Prokaryotes SSB (single stranded binding protein) - RPA Eukaryotes replication factor A
stabilizes and protects ssDNA, prevents helix reassociation and interacts with other proteins
Topoisomerases Gyrase in prokaryotes and Topo I,II in eukaryotes
acts on dsDNA ahead of helicase, transiently creates nicks in DNA to relive torsional stress
Ligase
seals nicks in Okazaki fragments (lagging strand)
Primate (RNA polymerase)
primate in prokaryotes and alpha primate complex in eukaryotes it adds ~10bp RNA primer in 5’-3’ for DNA polymerase to bind to, part of primisome complex
What is the sliding clamp?
stable ring, highly conserved, binds and keeps polymerase tethered to DNA remains until replication ends
What is clamp loaders?
5 subunit structure, opens clamp and loads onto DNA, ATP hydrolysis binds clamp on DNA and releases loader removes clamp when replication finished
What is holoenzyme?
3x core enzyme, 3x clamp, 1x loader
