DNA and genomics

Question 1

DNA structure

Answer 1

• double helix structure
• consisting of nucleotides: a phosphate group, deoxyribose sugar, and a nitrogenous base
• forms phosphodiester bonds between consecutive nucleotides
• hydrogen bonds btwn the two antiparallel strands’ nitrogenous bases

Question 2

what is a nucleoside

Answer 2

nucleotide without the phosphate group

Question 3

difference btwn DNA and RNA

Answer 3

• de? oxyribose sugar
  -4th nitrogenous base: T or U
• double/single strand polynucleotides
  RNA can still fold back on itself–> DS
• length

Question 4

enzymes involved in DNA replication

Answer 4

• helicase
• primase
• DNA polymerase
• DNA ligase

Question 5

DNA replication mechanism (incompleted)

Answer 5

• double helix DNA unzips at origin of replication to form a replication fork (helicase)
• (primase) forms the primers
• DNA strand used as template for elongation- form phosphodiester bonds
  i)

Question 6

2 functions of DNA polymerase in DNA replication

Answer 6

1. DNA polymerase catalyses the formation of phosphodiester bond linking DNA nucleotides
2. RNA primers removed and replaced by DNA by another DNA polymerase

Question 7

what are okazaki fragments

Question 8

Advantage of DNA molecules having two strands each

Answer 8

• many hydrogen bonds between base pairs can allow DNA molecules to become more stable in structure
• One DNA strand can act as a template for DNA repair of the other strand

Question 9

3 possible hypothesis to explain DNA replication

Answer 9

• dispersive
• conservative
• semi-conservative

Question 10

How was the semi-conservative hypothesis proved? Explain the steps.

Answer 10

Use of 2 different isotopes of nitrogen
1. Stock of E.coli grown for many gens in medium containing only N^15 so it incorporate into the nitrogenous bases of all bacterial DNA, forming denser DNA than normal DNA

2. Transferred into medium containing only N^14
3. Transferred E.coli divide once and we’re then collected, aka first gen cells and subsequently
4. Extract DNA from these cells and centrifuged at very high speeds for several days in a solution of CsCl

Density gradient of CsCl will be est. as there is increasing concentration of CsCl towards the bottom of the tubes due to sedimentation under centrifugal force

DNA will settle as its respective density with N^15-labelled DNA being denser than N^14-labelled DNA

5. UV absorption photographs reveal dark bands where DNA is present