2 - DNA and chromosome replication

Question 1

How is the DNA double helix opened

Answer 1

H bonds cleaved by helicase. Requires ATP

Question 2

How does replication start

Answer 2

Replication forks. Y shaped DNA structures

Question 3

Direction of replication

Answer 3

5’ –> 3’ direction

Question 4

Leading strand

Answer 4

5’–>3’ direction, made continously

Question 5

Leading strand

Answer 5

5’–>3’ direction, made continuously

Question 6

Lagging strand

Answer 6

3’ –> 5’ direction, made discontinuously (Okazaki fragments) in opposite direction to replication fork unzipping

Question 7

DNA pol epsilon

Answer 7

Leading strand (adds nts 5’ –> 3’)

Question 8

DNA pol delta

Answer 8

Lagging strand (adds nts 5’ –>3’)

Question 9

DNA pol proofreading

Answer 9

3’–>5’ exonuclease activity allows DNA pol to ‘chew back’ to remove the error (only gamma, delta and epsilon

Question 10

How is DNA pol held onto DNA

Answer 10

Sliding clamp and clamp loader

Question 11

Clamp loader

Answer 11

Replication factor C, acts like screw nut (threads matching grooves of DNA)

Question 12

Sliding clamp

Answer 12

Proliferating cell nuclear antigen. Locks DNA pol to DNA

Question 13

DNA Ligase

Answer 13

Seals DNA strands by forming phosphodiester bonds between adjacent fragments

Question 14

Origin recognition complex

Answer 14

Multi protein complex that binds origin and separates DNA strands. Recruits replication proteins

Question 15

Proteins involved in initiation

Answer 15

• Origin recognition complex
• Cell divison cycle 6 (S phase)
• Minochromosome maintenance (helicase)
• CDC-dependent transcript 1

Question 16

Chromosome end replication problem

Answer 16

At end of newly synthesised lagging strand, no template for RNA primer to base pair with. chromosomes get shorter evert replication round

Question 17

Solution to chromosome end replication problem

Answer 17

Telomerase Reverse Transcriptase enzyme (TERT) completes the chromosome end and maintains chromosome length

Question 18

T loop

Answer 18

The ssDNA at end of 3’ DNA forms T loop which interacts with a complex of proteins to protect chromosome ends.

Question 19

Which histone subunits aren’t removed during replication

Answer 19

H3 and H4. Allow nucleosomes to be rebuilt