Lecture 17 and 18

Question 1

In which direction are nucleotides added to the growing DNA strand?

Answer 1

5’-3’

Question 2

What enzyme catalyses DNA replication?

Answer 2

DNA polymerase

Question 3

In what direction does DNA replication occur?

Answer 3

It is bi-directional

Question 4

Where does DNA synthesis occur?

Answer 4

Replication origins

Question 5

How does the double helix open up?

Answer 5

With aid of initiator proteins

Question 6

How big are replication origins in bacteria?

Answer 6

Around 100 bp

Question 7

How fast do bacterial replication forks move? How long does this take?

Answer 7

500-100nucleotides/sec

30 minutes

Question 8

How fast is eukaryotic replication fork?

Answer 8

50 to 100 nts/sec

Question 9

What protein helps opens the DNA helix?

Answer 9

DNA helicase

Question 10

What does DNA helicase consist of?

Answer 10

6 identical subunits

Question 11

Why doesn’t the lagging strand fold back on its self?

Answer 11

Single-strand DNA binding proteins (helix destabilizing proteins)

Question 12

What should the fidelity of 5’-3’ polymerisation be? What is it really?

Answer 12

1 error in 10^5 nucleotides

1 error in 10^7 nucleotides

Question 13

What are the two proofreading mechanisms used by DNA polymerase?

Answer 13

Monitoring, exonucleolytic proofreading

Question 14

How does polymerase start replication?

Answer 14

DNA primase doesn’t need base paired end, use ribonucleodie triphosphate to synthesis RNA primers

Question 15

At what intervals are DNA primase (RNA polymerase) made in eukaryotes?

Answer 15

100-200 nucleotides

Question 16

What enzyme joins okazaki fragments?

Answer 16

DNA ligase

Question 17

What enzyme degrades RNA primers?

Answer 17

A nuclease

Question 18

What enzyme replaces the RNA with DNA?

Answer 18

Repair DNA polymerase

Question 19

What holds DNA polymerase in place?

Answer 19

Sliding clamp

Question 20

What is the sliding clamp in eukaryotes?

Answer 20

Proliferating nuclear cell antigen (PCNA)

Question 21

What does the sliding clamp do?

Answer 21

Improve prossesivity of DNA polymerase

Question 22

What binds the sliding clamp?

Answer 22

Clamp loader

Question 23

What enzyme relieves tension and prevents supercoiling?

Answer 23

DNA topoisomerases

Question 24

What topoisomerase I do?

Answer 24

Produces a transient single-strand break

Question 25

What does topoisomerase II do?

Answer 25

Transient double strand break in entangled helices

Question 26

How are the ends of chromosomes replicated?

Answer 26

Telomerase (reverse transcriptase) is a ribonucleo-protein

Question 27

How do cells distinguish between ends of chromosomes and double-strand DNA breaks?

Answer 27

T-loops

Question 28

How many errors are there after mismatch repair?

Answer 28

1 in 10^3

0-3 mutations

Question 29

What 2 proteins are involved in mismatch repair?

Answer 29

MutS and MutL

Question 30

What is depurination

Answer 30

removes a purine base from a nucleotide

Question 31

Deaminanation of adenine makes

Answer 31

Hypoxanthine

Question 32

Deamination of Guanine makes

Answer 32

Xanthine

Question 33

In what 2 ways is DNA damage removed?

Answer 33

Base excision repair

Nucleotide excision repair

Question 34

What enzymes remove the sugar phosphate in base excision repair?

Answer 34

AP endonuclease and phosphodiesterase