DNA replication

Question 1

What type of replication does DNA undergo?

Answer 1

Semi Conservative

Question 2

What is required to form a new DNA strand?

Answer 2

Template strand, free DNA nucleotides (dNTPs), enzymes

Question 3

What is the pre-replication complex?

Answer 3

Protein complex that forms at the origin of replication

Question 4

What is required to initiate replication?

Answer 4

Formation of the pre-RC

Question 5

What enzymes promote DNA opening ?

Answer 5

DNA helicase

Question 6

How does DNA helicase promote DNA opening?

Answer 6

Cleaving the inter-base hydrogen bonds using ATP hydrolysis energy.

Question 7

What enzyme synthesises short RNA primers?

Answer 7

Primase

Question 8

What do the RNA primers do?

Answer 8

Primers anneal to the strand of DNA to initiate replication and the action of DNA polymerase.

Question 9

Which strand are RNA primers added to?

Answer 9

RNA primer added to both the leading and lagging strands.

Question 10

Why is a primer used?

Answer 10

Provides a 3-OH’ (prime) terminus to initiate replication

Question 11

How many primers are needed in the leading strand vs lagging strand?

Answer 11

1 in leading (at the start)

Several in lagging for each okazaki fragment

Question 12

What about DNA means there is a lagging and a leading strand?

Answer 12

Anti-parallel

Question 13

DNA polymerase can only add new dNTPs to the … end

Answer 13

3’

Question 14

DNA polymerase can only add new dNTPs to the 3’ end in a ….. direction

Answer 14

5’ to 3’

Question 15

Where does the DNA polymerase move in the leading strand?

Answer 15

5’ to 3’ (following new strand)

Question 16

How does DNA polymerase move along the strand?

Answer 16

Sliding clamp - PCNA

Question 17

What direction does the template strand lie in leading strand?

Answer 17

3’-5’

Question 18

What direction does the template strand lie in lagging strand?

Answer 18

5’-3’

Question 19

Why cant DNA polymerase not add dNTPs on lagging strand in 3’-5’ direction?

Answer 19

DNA polymerase can only add to 3’ end

Question 20

What direction does the new strand lie in leading strand?

Answer 20

5’-3’

Question 21

What direction does the new strand lie in lagging strand?

Answer 21

3’-5’

Question 22

How can both strands be replicated in the same direction?

Answer 22

Okazaki fragments

Lagging strand replicated in ‘backstitch’ method

Question 23

Describe how the lagging strand is replicated

Answer 23

Primase inserts a primer onto the DNA in the direction the DNA needs to grow

Polymerase associates with the primer and will move 5’ to 3’ away from the primer in the opposite direction as the leading strand.

Then another primer is placed further back until the full strand is replicated in Okazaki fragments.

Question 24

What is the function of PCNA?

Answer 24

Clamp that tethers polymerase to the DNA and displaces the primase enzyme.

Question 25

What proteins loads clamp onto the DNA?

Answer 25

Protein RFC

Question 26

What does protein RFC require to attach PCNA to DNA?

Answer 26

ATP

Question 27

What unwinds the DNA further along to prevent coil strain and risk of breaking?

Answer 27

Topoisomerase

Question 28

What is the role of topoisomerase?

Answer 28

Topoisomerases unwind the DNA at fork to prevent tortional strain and risk of breaking.

Question 29

What removes and degrades the RNA primer flaps in the lagging strands?

Answer 29

FEN1

Question 30

What pushes the RNA primers out the way?

Answer 30

DNA polymerase

Question 31

What does FEN1 do?

Answer 31

Removes the RNA primer flap after it is pushed aside by DNA polymerase. It also degrades it.

Question 32

What joins together Okazaki fragments?

Answer 32

DNA ligase

Question 33

What do telomeres consist of?

Answer 33

Long tandem repeats, constitutive chromatin

Question 34

What do telomeres do?

Answer 34

Specific structures at the end of chromosomes that prevent chromosome shortening during cell division

Question 35

Why do telomeres shorten with each division?

Answer 35

There is no template for primase on the telomere so RNA primer can not form for the last Okazaki fragment. So with each round there is shortening and senescence.

Question 36

How is telomere shortening prevented?

Answer 36

Telomerase enzyme Has an RNA component and is a reverse transcriptase so uses RNA template to make complimentary DNA.

Question 37

What is a proof-reading polymerase?

Answer 37

Polymerases with 3' to 5' exonuclease activity can correct mistakes.

Question 38

What can 3'-5' exonuclease polymerases do?

Answer 38

Remove the wrong nucleotide when a mistake is made in replication