Enzymes and Proteins required for DNA replication

Question 1

What is helicase?

Answer 1

An ATP dependent enzyme that separates the two parental DNA strands in advance of the replication fork

Question 2

What is the specific gene that encodes for helicase in E.coli required for DNA replication?

Answer 2

dna B (italicized)

Question 3

What are single stranded binding proteins?

Answer 3

A class of proteins that bind to the single stranded regions of DNA and prevent it from reforming a double helix aka double stranded DNA.

Question 4

What gene in Ecoli codes for the single stranded binding proteins?

Answer 4

ssb (italicized)

Question 5

The binding of the single stranded binding proteins is described as what?

Answer 5

cooperative-the binding of one protein facilates the next

Question 6

When one single stranded binding protein molecule binds to the single stranded DNA by how much is the affinity for the next molecule raised?

Answer 6

thousandfold

Question 7

WHy are single stranded binding proteins extremely important in DNA replication?

Answer 7

They trap DNA in its single stranded form and also stimulate DNA replication by specifically stimulating the appropriate homologous DNA polymerases.

Question 8

Are single stranded binding proteins found in eukaryotes?

Answer 8

No

Question 9

What is topoisomerases?

Answer 9

A class of enzymes that introduce single or double stranded breaks into the DNA that allow it to change its shape (topology). For example it relieves the compensating strain on the strands from DNA unwinding by helicase.

Question 10

What is DNA gyrase?

Answer 10

A type of topoisomer enzyme that releases the strain induced by the unwinding of the DNA molecule.

Question 11

Topoisomerase introduces a ________ single or double stranded break in the DNA allowing it to change _________.

Answer 11

Temporary

topology

Question 12

What does topoisomerase recognize as its substrate?

Answer 12

Superhelical or supercoiled form of DNA

Question 13

What are the two types of topoisomers and what are they classified by?

Answer 13

Type 1 and Type 2

And if they operate by introducing single or double stranded breaks

Question 14

What is type 1 topoisomerase?

Answer 14

It makes single stranded breaks

Question 15

What is type 2 topoisomerase?

Answer 15

It makes double stranded breaks

Question 16

What type of topoisomerase if DNA gyrase in E.coli?

Answer 16

Type 2 topoisomerase

Question 17

How many polymerases are found in E coli?

Answer 17

3:

DNA Polymerase I
DNA Polymerase II
DNA Polymerase III

Question 18

What is the function of DNA Polymerase I in E coli?

Answer 18

DNA repair and primer excision

Question 19

WHat is the function of DNA Polymerase III in E coli?

Answer 19

It is the holoenzyme form and is required for DNA replication in Ecoli.

Question 20

What does the term “holoenzyme” mean?

Answer 20

It is a multi-subunit enzyme.

Question 21

What does the term “core” enzyme mean?

Answer 21

It only contains the essential subunits.

Question 22

What are the three subunits that make up the core enzyme of DNA Pol III?

Answer 22

Alpha
Epsilon
Theta

Question 23

What function does the DNA Pol III Alpha subunit have?

Answer 23

DNA Polymerase activity.

Question 24

What function does the DNA Pol III Epsilon subunit have?

Answer 24

3’—>5’ exonuclease proofreading activity

Question 25

What function does the DNA Pol III Theta subunit have?

Answer 25

Unknown but is required for DNA replication.

Question 26

What are the five types of DNA polymerase in Eukaryotes? ANd what are each of their functions?

Answer 26

1. DNA Polymerase Alpha (priming of both strands) 2. DNA Polymerase Delta (elongation of lagging strand) 3. DNA Polymerase Beta (DNA repair) 4. DNA Polymerase Epsilon (repair/elongation of leading strand) 5. DNA Polymerase Gamma (replication of mitochondrial DNA)