DNA helicase unwinds DNA into ssDNA for what processes?
DNA helicase's process and translocate branched structures
Name (a) branched DNA structure(s)
RNA helicases cannot destabilize RNA secondary structures
RNA helicases help in which of the following processes
A- Promote ribosome assembly
B- RNA translocation
D- RNA editing and transport
A, C & D
B, C & E
All of them
Some helicases can work on both RNA & DNA
Which of the following unwind RNA-DNA hybrids
RNA helicase, then DNA helicase
DNA helicase, then RNA helicase
RNA/DNA helicases perform which of the following functions?
Regulation of DNA replication initiation
All helicases use energy from NTP hydrolysis to translocate along polynucleotides
Helicases are dependent on Fe2+
Helicases can take which of the following forms (commonly)
Helicases can have an oligomeric structure
Helicases can be
Bidirectional or unidirectional
What is the difference between translocases and helicases?
Translocases -transcribe and separate DNA strands
Helicases- transcribed DNA strands only
Helicases-transcribe and separate DNA strands
Translocases- transcribed DNA strands only
Give an example of a DNA/RNA unwinding helicase/translocase
Type 1 restriction enzymes
Ruv B/Reg G
Name a helicase/translocase that effects protein motion on DNA
Type 1 Restriction Enzyme
Ruv B/ Reg G
Name a necleoprotein complex remodelling helicase
Type 1 Restriction Enzymes
Name a DNA/RNA remodelling helicase
Helicases are divided into seven superfamilies based on primary structure, and then 3 structural classes
The two structural classes are monomers and dimers
All helicases contain a Rec B fold
EVERY helicase molecule contains which of the following?
An ATP binding site
An NTP binding site
A separate polynucleotide binding site
A GTP binding site
A linked polynucleotide binding site
The _TP binding site and the nucleotide binding site on a helicase are allosterically linked
Type A helicases (like PCRA) travel in which direction?
3' > 5'
5' > 3'
Rec D is a Type 2 helicase- in which direction does it travel?
3' . 5'
Rec BCD is a bipolar helicase
In a bacterial Holliday Junction with a stalled replication fork, what is required to allow replication to continue?
If Holliday Junctions cannot be repaired, they lead to a cruciform structure
What is the slowest rate of movement of a helicase?
Rate of helicase movement is dramatically dependent on protein partners
The fastest known helicase moves around 4000 bp/sec
Define Helicase Processivity
How fast it moves along the DNA/RNA
How far it can move before it falls off
How far it moves per substrate hydrolysis
Helicases can move around 10-30,000 base pairs before falling off depending on the helicase (and it's protein partners)
Step size is a theoretical limit due to the entropy of NTP hydrolysis
Step size is the theoretical avg no of bp unwound per NTP hydrolysis cycle
The limit on step size = Energy required to melt the bp x step size
What is the experimental limit of step size?
0.7- 7 bp
What is this image showing?
The 'Inchworm' helicase movement model
The 'active rolling model'
Which of the following is believed to be the unwinding mechanism used by helicases?
Passive- DNA is frayed by heat and the translocation occurs in the presence of ATP
Active- ATP activates molecules that bind to and actively distort DNA before ATP dependent translocation can occur
PCRA is made of how many domains?
4 - 1A/B & 2A/B
2 - 1A & 2A
6 1A/B, 2A/B & 3A/B
PCRA activity is dependent on its protein partners
PCRA is an ATPase with...
A 3' > 5' polarity
A 5' > 3' polarity
A low rate of 30 bp/sec
A high rate of 300 bp/sec
A low processivity of 10 bp/sec
A high processivity of 100 bp/sec
A step size of 16 bp/ATP
A step size of 6 bp/ATP
The conserved Helicase motifs of PCRA are in the accessory domains
Aromatic stacking occurs between the inserted aa and bp
Which of the following will bind to the DNA
The complex of PCRA-DNA remains the same during ATP binding and ATP hydrolysis
Duplex distortion in the PCRA substrate complex suggests a Passive unwinding system
Partner proteins are required by PCRA for which processes?
Hexameric helicases can be part of the replisome
Hexameric helicases have a toroidal strcture to confer high processivity
ATP binds where on hexameric helicases?
To the pockets present in each monomer
To the pocket made by the interaction of all 6 monomers
ssDNA is bound in the central channel to a 'spiral staircase' of bining loops
ATP binding pocket changes _ around the ring
Sequentially- one at a time
At the same time
Sequentially- two at a time
ATP binding correlates with loop hight in the central channel