lecture 1 : nucleic acids and chromosomes

Question 1

what is a nucleotide?

Answer 1

a nucleotide is a sugar + base + phosphate

Question 2

what is a nucleoside?

Answer 2

a nucleoside is a sugar + base

Question 3

what is the difference between deoxyribose and ribose?

Answer 3

ribose contains oxygen deoxyribose does not contain oxygen

Question 4

where is 1 carbon attached?

Answer 4

attached to the carbon with the base

Question 5

where is the 5’ carbon attached ?

Answer 5

to the phosphate

Question 6

what are purines?

Answer 6

adenosine and guanine

Question 7

what are pyrimidines?

Answer 7

cytosine and thymine and uracil

Question 8

* show a diagram of purines

Answer 8

insert pic

Question 9

* show a diagram of pyrimidines

Answer 9

insert pic

Question 10

*what is the overall structure of DNA ? insert pic of DNA

Answer 10

• phosphate of one nucleotide and 3’hydroxyl group of adjacent nucleotide are linked via phosphodiester link - the phosphate is liked to the 5’OH of an adjacent sugar - the chain has 2 ends 3’ and 5’ - the first nucleotide has a free 5’ phosphate and the last nucleotide has a free 3’ hydroxyl group - therefore it is conventionally written as 5’ to 3’ - the chains are antiparallel - there is a minor and major groove

Question 11

how many hydrogen bonds between A- T? (skinny)

Answer 11

2 hydrogen bonds

Question 12

how many hydrogen bonds between C- G? (fat)

Answer 12

3 hydrogen bonds

Question 13

how to melt or denature DNA?

Answer 13

heat or use low salt

Question 14

how to re anneal or hybridise DNA

Answer 14

cool conditions and high salt

Question 15

what is a karyotype? why are karyotypes important?

Answer 15

• the organised profile of someones chromosomes - consisting of 22 autosomal chromosomes and one pair of sex chromosomes - can be an important diagnostic tool

Question 16

what is chromatin?

Answer 16

this is when the DNA is packaged tightly forming a complex with the histone proteins

Question 17

* what is the level of packing of a nucleosome?

Answer 17

• the lowest level of packaging - consists of DNA wrapped around histones - linker DNA present between the DNA - 200bp of DNA per nucleosome insert pic

Question 18

what level of packaging is 30nm fibre?

Answer 18

• this is when the nucleosomes are further packed to generate a more compact structure - 40 fold condensing of DNA

Question 19

what is the structure of the nucleosome?

Answer 19

• histones are positively charged so they interact with the negative sugar phosphate backbone - there are 8 histones around which the DNA is wrapped - histone 1 is between the nucleosomes - nucleosome causes the 7 fold condensing of DNA

Question 20

what is a further level of organisation after the 30nm fibre

Answer 20

chromatin is folded into loops and then fits into being part of the chromosome

Question 21

what are the overall levels of organisation of the DNA ?

Answer 21

short strand of DNA *

string of chromatin *

30nm chromatin fibre - nucleosomes

chromatin fibre folded into loops

chromosome