Structure of DNA and Chromosomes

Question 1

Sia and Dawson’s Demonstration of Transformation

Answer 1

2 strains of pneumonia

IIR- rough colonies, non virulent

IIS- smooth colonies, virulent

IIS killed by boiling it in liquid culture

Mixed 2 strains, non virulent strain removed, found that live virulent cells remained (non virulent cells transformed into virulent cells)

Question 2

Avery, MacLeod, and McCarthy’s Transforming Principle

Answer 2

DNA from heat killed virulent strain purified

Mixed live non virulent cells with DNA from virulent cells, resulted in virulent cells

Added protease to DNA purification to destroy proteins (to see if proteins were transforming principle), still got live virulent strains

Added RNase, RNA not transforming factor

Added DNase, did not get transformation (no live virulent cells)…. therefore DNA is transforming principle

Question 3

RNA Is Also Genetic Material

Answer 3

Tobacco Mosaic Virus (TMV) has RNA protein, but no DNA

Different strains have different coat proteins that are specified by RNA

RNA from protein A and protein coat from protein B combined

If genetic info was in RNA, virus would only be type A, if genetic info was in protein, then virus would only be type B

Virus injected into tobacco host, offspring had RNA and protein coat from protein A

Question 4

Purines

Answer 4

A, G

larger, 2 ring molecules

Question 5

Pyrimidines

Answer 5

C, U, T

small, 1 ring molecules

Question 6

Connecting Nucleotides

Answer 6

Nucleotides joined by phosphodiester bonds

Linke C-3 of one sugar with C-5 of another

one full turn is 10 bp (3.4 nm)

Question 7

H Bonding between nucleotides

Answer 7

2 H bonds between A-T

3 H bonds between C-G

Question 8

Supercoiling DNA

Answer 8

Nick one strand of DNA, proteins twist DNA, nick then sealed by ligase

End up with scrunched up ball of DNA

Question 9

Chromosome Structure in Prokaryotes

Answer 9

Circular- 350 micrometer
Folded into 40-50 loops on a protein scaffold (30 micrometer)
Supercoiled along loops (2 micrometer)

Question 10

Eukaryotic Chromosome

Answer 10

One large linear molecule of DNA
Contains:
5 types of histones (high positive charged polypeptides)
Non histone proteins

Question 11

Chromosome Structure in Eukaryotes: Nucleosomes

Answer 11

146 nucleotide pairs of 2nm DNA wrapped as 1 3/4 turn around octamer of histones to form nucleosomes
Nucleosomes connected by linker DNA, varying from 8 to 114 nucleotide pairs

Reduces to 11 nm

Question 12

Nucleosome Core

Answer 12

Contains 2 each of 4 kinds of histones

Question 13

Complete Nucleosome

Answer 13

Histone H1 binds to nucleosome (nucleosome core + DNA)

Question 14

Chromosome Structure in Eukaryotes: Solenoid

Answer 14

Strand of nucleosomes condense into a 30 nm finer

Question 15

Chromosome Structure in Eukaryotes: Metaphase Chromosomes

Answer 15

30 nm fiber wrapped around a scaffold to form metaphase chromosome