DNA replication

Question 1

Central Dogma of Molecular Biology

Answer 1

“Genetic information carried by DNA is transmitted between generations of ells through DNA replication. Within a cell, the genetic information of genes is used to make proteins through transcription

Question 2

Charge of DNA

Answer 2

DNA is negatively charged since it has a negative phosphate group

Question 3

Purines

Answer 3

Adenine and Guanine

Question 4

Pyrimidines

Answer 4

Thymine/Uracil and Cytosine

Question 5

DNA base pairing

Answer 5

Adenine with Thymine/Uracil (2 H-bonds)
Guanine with Cytosine (3 H-bonds)

Question 6

Structure of DNA

Answer 6

1. Double-stranded
2. Double-helical structure held together by h-bonds between complementary bases
3. Purine-Pyrimidine pair ensures DNA helix has a constant 2nm width
4. Each turn is 3.4nm, 10 base pairs
5. 2 strands are anti-parallel

Question 7

Semi-conservative replication

Answer 7

1. DNA unwinds into 2 strands
2. Each strand is a template for the synthesis of a new daughter strand
3. Hence each new DNA molecule contains one parent and one daughter strand

Question 8

Conservative replication

Answer 8

1. DNA unwinds into 2 strands
2. 2 daughter strands synthesized
3. 2 daughter strands form daughter DNA molecule
4. 2 parental strands form back original parental DNA molecules

Question 9

Dispersive replication

Answer 9

1. DNA unwinds into 2 strands
2. Both strands break up into small segments that act as templates
3. Each daughter strands contains a mix of old and new fragments

Question 10

Process of DNA replication

Answer 10

1. Begins at orgin of replication
2. Helicase unwinds DNA by breaking h-bonds
3. SSB proteins bind to DNA strands to stabilised them and keep them separated
4. Replication bubble forms with replication forks on both ends
5. Primase catalyses synthesis of an RNA primer complementary to DNA bases at origin
6. DNA polymerase III added on free DNA nucleotides to free 3’ OH end of RNA primer
7. DNA polymerases III catalyses formation of phosphodiesterase bonds between adjacent DNA molecules
8. After adding a nucleotide, DNA polymerase II will proofread it and correct any mistake
9. In the lagging strand, DNA polymerase III constantly detaches and reattaches
10. RNA primers at Okazaki fragments and leading strand are replaced by corresponding DNA nucleotides by DNA polymerase I

Question 11

Okazaki fragements

Answer 11

• DNA is anti-parallel
• DNA polymerase can only bind to free 3’ OH ends of RNA primer
• On the lagging strand, the 3’ end is not immediately available, as helicase must first unwind the double-stranded DNA to expose the template.
• Hence RNA primers constantly have to constantly detach and reattach