Lecture 16: DNA Replication

Question 1

How does prokaryotic replication occur?

Answer 1

• DNA is “unzipped” from both directions
• From 5 prime to 3 prime direction
• 2 parent template strands created

Question 2

What is RNA polymerase (primase)(prune)?

Answer 2

• An enzyme that makes small RNA primers (starting point for DNA polymerisation)

Question 3

What is helicase? (Honeydew Melon)

Answer 3

• Recognises AT rich origin of replication
• Separates two DNA strands from each other
• Strand replication occurs in 5’ - 3’ direction easily, remember anti parallel, make little strands

Question 4

Replication is semidiscontinuous. What are the two strands called?

Answer 4

• Leading + Lagging Strand

Question 5

What is topoisomerase? (Tomato)

Answer 5

• Releases tension (cut DNA)

Question 6

What do single stranded binding proteins do?

Answer 6

• Protect DNA strand regions from being attacked and destroyed
• Prevent two single strand molecules from snapping back together

Question 7

What is DNA polymerase III? (Potato)

Answer 7

• They will use 3’ hydroxyl group (from RNA) to add nucleotides to the template (leading strand)

Question 8

How does the synthesis of the lagging strand occur?

Answer 8

• Short little fragments made in 5’ –> 3’ direction
• Primase (RNA template), DNA Polymerase adds nucleotides
• Bits are not linked together until DNA pol I appears

Question 9

What does DNA Polymerase I do?

Answer 9

• Has the ability to recognise DNA + RNA hybrids and takeaway RNA
• Will use hydroxyl group and start extending to fill in gap

Question 10

What is the function of Ligase? (Lettuce)

Answer 10

• Creates phosphodiester bond between Phosphate + Hydroxyl bits
• New DNA strand is now completely synthesised

Question 11

What can an exonuclease do?

Answer 11

• Chop away from 5’ to 3’ or 3’ to 5’ (at the ends)

Question 12

What can an endonuclease do?

Answer 12

• Chop away the middle bit of a strand

Question 13

What happens when an incorrect base is inserted during replication?

Answer 13

• DNA Pol III has proofreading mechanism of original strand
• Synthesises a new base
• Exonuclease

Question 14

What happens when an incorrect base is inserted after replication?

Answer 14

• Goes into the middle, removes incorrect and a few other bases on either side
• DNA Pol Synthesises new bases

Question 15

What happens if you don’t correct DNA?

Answer 15

• If not corrected, DNA error becomes permanent (mutation)

Question 16

What are the components of PCR***?

Answer 16

• DNA template
• Primers
• Heat stable DNA polymerase
• dNTPs (deoxynucleotide triphosphates = free nucleotides)
• Buffer
• Ions (cofactors) (Mg2+)

Question 17

How does PCR work?

Answer 17

• Denaturation
• Amnealing
• Extension