24 - DNA Replication

Question 1

Which eukaryotic enzyme has the ability to synthesize DNA using RNA as template?

Answer 1

Telomerase

Question 2

What does DNA polymerase need to make it active?

Answer 2

Mg

Question 3

What is a characterization of the 5 prime end?

Answer 3

Presence of a phosphate group

Question 4

What is the difference between nucleoside and nucleotide?

Answer 4

Nucleosides do not have the phosphate group. Nucleotides might have 1,2,3 phosphate groups

Question 5

What do kinases do?

Answer 5

add phosphates

Question 6

What happens when AZT gets incorporated into the viral DNA and how does it get incorporated?

Answer 6

When added to the viral DNA, DNA synthesis is stopped because it can not form phosphodyester bond (no 3’ OH). It gets incorporated by kinase adding three phosphates.

Question 7

How and what happens when the wrong base is added?

Answer 7

It happens by a tautomeric shift (bipolar base) and it is fixed by 3’-5’ proofreading exonuclease.

Question 8

What shape are bacterial genomes in and how many origins of replication are there?

Answer 8

Circle and only one origin

Question 9

What replication is seen in bacteriophage and plasmids?

Answer 9

Rolling circle model.

Question 10

Which strand goes toward and away from the replication fork?

Answer 10

The leading strand (continuous) goes toward the replication fork and the lagging strand (not continuous) goes away

Question 11

How to prevent re annealing and hairpinning in a single strand of DNA?

Answer 11

SSB - single strand binding proteins

Question 12

What synthesizes the Okazaki fragment and the leading strand?

Answer 12

DNA Polymerase III

Question 13

What replaces the RNA primer with DNA?

Answer 13

DNA Polymerase I

Question 14

How are the Okazaki Fragments joined?

Answer 14

DNA Ligase but must use ATP

Question 15

How does DNA polymerase III stay on the singe stranded DNA?

Answer 15

It uses clamp proteins

Question 16

What stops positive super coiling in prokaryotes?

Answer 16

While replication is happening, positive supercoiling is also happening and Gyrase (topoisomerse) can fix that. Positive super coiling is not wanted because it makes the DNA to condensed and hare to unwind but Negative super coiling is favorable.

Question 17

What does Ciprofloxacin do to prokaryotes?

Answer 17

Inhibits gyrase which increase the amount of positive super coiling which will kill the cell.

Question 18

Differences between Pro and Eukaryotes with regards to:

• Origin of Replication
• Polymerases
• Ends?
• RNA Primer removal?

Answer 18

• Pro has 1 origin of replication and Euk has multiple
• Pro has DNA polymerase 1 (which removes RNA primer and replaces with DNA) and DNA polymerase III (synthesizes the Leading and Lagging strand, main replication enzyme) Euk’s have polymerase alpha (synthesize RNA primer) and polymerase delta (synthesize DNA from leading and lagging strand)(3’ - 5’ exonuclease proofreading activity)
• Pro’s are circles and Euk’s have ends so they need Telomerase
• Pro RNA polymerase is used, Euk uses RNAaseH and FEN1

Question 19

Eukaryotic DNA polymerases?

Answer 19

Polymerase alpha - Synthesize RNA primer on leading and lagging
Polymerase delta - Synthesize DNA on leading and lagging strand, 3’-5’ exonuclease proofreading activity
Polymerase beta - DNA repair, mitochondria DNA replication
Polymerase Gama - DNA repair, mitochondria DNA replication

Question 20

What does Camptothecin do?

Answer 20

It’s an anti cancer drug that Inhibits Topoisomerase I which results in apoptosis.
- Topoisomerase I prevents positive supercoiling by cutting one strand which relaxes it and then re-connects the strand

Question 21

What does Etoposide do?

Answer 21

It’s an anti cancer drug that Inhibits Topoisomerase II which results in apoptosis of the cancer cells.
- Topoisomerase II prevents positive supercoiling by cutting both strands and then re-connecting.