Intro to Motors and Helicases

Question 1

What is processivity?

Answer 1

The average distance travelled before a motor falls off the track

Question 2

What unit is used to measure processivity?

Answer 2

Distance/binding event

Question 3

What is units is step size measured in?

Answer 3

Distance per ATP hydrolysis

Question 4

What is motor-coupling efficiency?

Answer 4

How many ATPs are used to make a successful step

Question 5

What units are used for motor-coupling efficicency?

Answer 5

ATPs per step

Question 6

What is polarity in relation to Motors?

Answer 6

The tracks are asymmetrical and have a positive and negatie end

Question 7

What is the general structure for a P-loop?

Answer 7

Central beta sheet surrounded by alpha-helices

Question 8

What is the function of the P-loop?

Answer 8

It cradles the triphosphate tail of ATP

Question 9

What metal ion is required in motor proteins and helicases?

Answer 9

Mg2+

Question 10

What are the 3 motifs found in helicases?

Answer 10

• P-loop
• Walker A
• Walker B

Question 11

Why is Mg2+ needed as a cofactor in helicases?

Answer 11

Co-ordinates the beta and gamma phophates of ATP which is important for hydrolysis

Question 12

Why is the walker B motif important?

Answer 12

• It co-ordinates Mg2+
• Often contains a catalytic residue that acts as a base to activate a water molecule to cause ATP hydrolysis

Question 13

What is a helicase?

Answer 13

An enzyme which couples ATP hydrolysis to the unwinding of DNA (separation of duplex DNA into single strands)

Question 14

What is the typical processivity of helicases?

Answer 14

50,000 bp

Question 15

How many ATP are required for 1 step of helicases?

Answer 15

1 ATP

Question 16

What is the step size of helicases?

Answer 16

1 base pair

Question 17

What is the polarity of helicases?

Answer 17

Either 3’ to 5’ or 5’ to 3’

Question 18

What do helicases require to get going on the DNA?

Answer 18

• Overhangs
• Loading factors

Question 19

What is a classical helicase?

Answer 19

A protein which produces ssDNA in biochemical assays

Question 20

Which 3 motifs do all helicases contain?

Answer 20

• Walker A
• Walker B
• Arginine finger

Question 21

What processes are helicases involved in?

Answer 21

• DNA replication
• DNA repair and recombination
• Transcription regulation
• Import/export of DNA/RNA

Question 22

What do translocases do?

Answer 22

Many translocases contain helicase motifs but do not possess classical strand separation

Question 23

How can helicases manipulate DNA besides just unwinding?

Answer 23

• Remodel DNA by remodelling holiday junctions
• Act as a mechanism of moving another enzyme along DNA
• Displace or move other proteins along/off DNA

Question 24

What are ‘non-classical’ helicases?

Answer 24

Proteins which are found to have shared helicase sequence motifs and which move along DNA but which do not necessarily unwind it