1869 – Friedrich MiescherStudied the nuclei of white

blood cells Isolated the material using

HCl(aq) and digestive proteins

Named the substance nuclein

Found the material was rich in nitrogen and phosphorus

1919 – Pheobus LeveneDiscovered that DNA

was made up of chains of nucleotides

ACID

DEOXYRIBOSE

NITROGENRICH

1920 – DNA vs Protein

thought that 4 nucleotides were connected in the same repeated pattern

protein have 20 amino acids which could be combined in many combinations

RNA DNA

sugar

location

bases

RNA DNA

sugar ribose deoxyribose (one less oxygen)

location

bases

RNA DNA

sugar ribose deoxyribose (one less oxygen)

location mainly outside nucleus mainly inside nucleus

bases

RNA DNA

sugar ribose deoxyribose (one less oxygen)

location mainly outside nucleus mainly inside nucleus

bases AGCU AGCT

Nucleotide Pattern

1928 – Frederick Griffithstudied two strains of

pneumococcus bacteria

rough strain = nonvirulentinjection into mouse did not

result in death

smooth strain = virulentinjection caused mouse to

die

Griffith’s Experiment

Griffith’s Conclusionssome “factor” from the dead, virulent smooth strain

“transformed” the living, non-virulent rough strain

non-virulent rough strain picked up DNA to become virulent

1930 – Joachim Hammerling

nucleus at bottom of stalk

Acetabularia – type of alga

Hammerling’s Experiment

Hereditary information is stored in the nucleus.

no regrowth

1940s – Joshua Lederbergdemonstrated

bacterial conjugationbacteria can exchange

DNA

bacteria have no nucleus or chromosomes

1940s – Edwin Chargafffor all organisms

A = T and G = C

Chargaff’s Rule

organisms with more Gs and Cs tend to be more complex

1952 – Hershey & Chaseconducted

experiments to definitively show that DNA is the hereditary material

bacteriophage used to infect bacteriabacterial virus

CH2CH

OH

O

CHO

CH2

CH2 NH3+ C-O CH2

O

CH2SSCH2

CH

CH3

CH3

H3C

H3C

Hydrophobic interactions and van der Waalsinteractions Polypeptid

ebackbone

Hyrdogenbond

Ionic bond

CH2

Disulfide bridge

X-ray Crystallographyphysics approach to examining biological molecules

Rosalind Franklin’s X-raysThe photo indicated:1. Backbone of alternating phosphate and sugars

2. Backbone is a helical structure

3. Double helix structure (molecule is a uniform helix)

4. Nitrogenous bases are in the middle of the molecule

5. Bases are at right angles to the backbone

Base Pairing

1953 – James Watson & Francis Crickinspired by alpha-helix model of proteins

determined how A + T and G + C bonded together

width of purine + pyrimidine bonds fit perfectly between the sugar-phosphate backbone (DNA width = 2 nm)

the double helix model offered an easy method for replication

DNA Backbonealternating sugar-

phosphate backbonesugar and phosphate

backbone attached by a phosphodiester bond

DNA is said to be read from 5’ to 3’

opposing backbones are antiparallel

5’

3’

1’

2’

4’

1’

2’

4’

Complementary Base PairingChargaff’s Rule

adenine : thymine (1:1)guanine : cytosine (1:1)

the diameter of a base pair is 2 nm

3 H-bonds between G&C2 H-bonds between A&T

Overall DNA Structureright handed helix

0.34 nm between adjacent base pairs

one turn of the helix is 10 base pairs (3.4 nm)

0.34 nm

3.4 nm

HomeworkAnswer questions pg. 209 #1-4Read section 4.2Answer questions pg. 216 #1-9