Transcript PP4 (Ch.12-25)DNA

Chapter 12 DNA & RNA
DNA’s Structure
Purines: A & G - small name big molecule
Pyrimadines: T & C - big name small molecule
Monomer = building block
One Nucleotide is a monomer = nucleic acid + deoxyribose + phosphate
(Nitrogenous Base)
DNA’s Structure
3’ has OH - hydroxide
5’ has Phosphate Molecule
•Directional Structure
•Anti-parallel to each other
•Always builds 5’ to 3’
•DNA Polymerase can only
add to the 3’ end
If DNA were synthesized in the 3' to 5'
direction, the energy for the process
would come from the 5' end of the
growing strand rather than from free
nucleotides. If the 5' nucleotide needed
to be removed this triphosphate end
would be lost, losing the energy source
required to add a new nucleotide to the
end.
DNA’s
Structure
nm = 1 Billionth
of a meter
DNA Replication
Semiconservative
Chromosome Structure
Key Terms:
Histone = the protein
Nucleosome = A cluster of histones
Chromatin = DNA + Protein in an
uncoiled form
Chromosome = condensed chromatin
Chromatid = each side of a chromosome
Centromere = point of attachment of
sister chromatids
Evidence for DNA as Genetic
Material
• Griffith - 1928
– transformation
• Avery, MacLeod, and McCarty - 1944
– Proves DNA is the transforming agent
using enzymes
• Hershey & Chase -1952
– Reproves Avery’s evidence using
bacteriophage
Time Line
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1866 Mendel publishes paper
1900 Mendel’s paper rediscovered
1902 chromosome theory of inheritance
1905 the term “genetics” coined
1950 base pairing discovered
1953 Watson & Crick deduce the
structure of DNA
Griffith’s Transformation
Experiments
• Diplococcus pneumoniae
– two strains: IIR & IIIS
– two differences in genotype
• R = rough, avirulent; S = smooth, virulent
Griffith’s Transformation Experiments
Live IIR
Live IIIS
Heat-killed IIIS
Heat-killed IIIS +
live IIR
Live IIR
Heat-killed
IIIS
Live IIR
Heat-killed
IIIS
Explanations?
• IIR cells mutated to S?
• Serotype was changing
• IIR were changing into IIIS
• 2 mutations?
• Only happened when IIR and dead IIIS
mixed
• Non-living component of IIIS cells
changing genetics of IIR cells
Avery, MacLeod and McCarty
heat-killed IIIS + IIR
removed polysaccharide coat
heat-killed IIIS + IIR
removed protein
Avery, MacLeod and McCarty
heat-killed IIIS + IIR
removed RNA
heat-killed IIIS + IIR
removed DNA
Avery, MacLeod and McCarty
• DNA is the transforming principle
• DNA could change IIR bacteria into IIIS
– Now know bacteria may pick up pieces of
exogenous DNA and incorporate them into
their own chromosomes = transformation
Hershey and Chase
• Studied bacteriophage
– virus which attacks E. coli
• Ran two side-by-side studies
– labeled DNA of phage w/ 32P in one study
– labeled protein of phage w/ 35S in second
• In which study does radioactivity end up
in E. coli?
32P
labeled DNA
35S
labeled protein
Hershey and Chase
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Mix phage and bacteria
Allow infection
Shear off what’s on outside - blender
Centrifuge
Look for radioactivity in pellet (bacteria)
infection
blender
centrifuge
Supernatant w/ protein coats
E. coli w/ hot DNA
infection
centrifuge
blender
Supernatant w/ hot protein
coats
E. coli w/ DNA
Summary Hershey & Chase
Chargaff’s Rules 1947
Provided base pairing and hydrogen bonding
Rosalind Franklin 1920-1958 (1951)
Rosalind Franklin
X-Ray Diffraction
Provided idea of double helix
Nobel Prize (1962)
Made Model 1953
Frederick Wilkins
James Watson
Francis Crick