Lecture 1-2

Question 1

How did Avery’s work prove that DNA was the genetic material?

Answer 1

Used heat killed IIS and tested for transforming ability by mixing with IIR cells, treated each colony with proteases, RNase, DNase to see their effect on transforming ability, one treated with DNase had an effect on transforming activity

Question 2

How did hersey and chase show that DNA is the genetic material from phage T2?

Answer 2

grew ecoli where only source was 32 phorphorus which would produce phage particles which all radioactivity will be in DNA, and grew another colony where only source of sulfur was 35S which would radioactively label the protein

allowed to infect cell, what was injected into the infected cell would be what contained the genetic material

blended and centrifuged, the radioactivity in the cells was 35P so the phage protein was not transferred to cell but DNA

Question 3

What are the structural difference of purines and pyrimidines?

Answer 3

purines, A and G have two rings

pyrimidines, C and T have single rings

Question 4

describe the polarity of N bases, and the numbering of carbons

Answer 4

5’ to 3’ polarity meaning 5 at top and 3 at bottom, carbons are numbered clockwise

Question 5

describe the bonds present, and the hydrophilic and hydrophobic interactions of DNA

Answer 5

glycosidic bonds between the sugar and base, phosphodiester between the sugar and the phosphate
hydrogen bonds between the bases

sugar phosphate back bone is hydrophilic and interactions with aqueous solution
the bases are hydrophobic and interact with each other
this makes the molecule stable

Question 6

What is supercoiling?

Answer 6

supercoling is done by cutting, rotation and rejoining all carried out by topoisomerases, will collapse into coils

Question 7

Describe how prokaryotic chromosomes are packed

Describe how eukarotic chromosomes are packed,

Answer 7

prokaryotic chromosome are circular and are folded into loops (held together by RNA) each loop is super coiled

eukaryotic chromosomes are linear,

1. negatively supercoiled 2nm
2. wrapped around nucelosome 11 nm
3. 30 nm chromatin fibre in zig zag model, 30 nm
4. Organization around protien scaffold

Question 8

What is the structure of a nuecleosome?

Answer 8

core: 146 bp, 2 moleclues of each histone H2a H2b H3 and H4 to form an octamer
complete: 166 bp addition of H1 to stabilize

Question 9

Describe the metaphase chromosome

Answer 9

in metaphase non histone chromosomal proteins for a scaffold that is involved in condensing the 30 nm chromatin fiber into a tightly packed metaphase chromosome

Question 10

What are histones?

Answer 10

Organizational proteins that ou DNais coiled around, they contain an abundance of Arg and Lys residues (+ve) that makes in interact easily with the DNA