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Chapter 12 DNA & RNA
DNA’s StructurePurines: A & G - small name big molecule Pyrimadines: T & C - big name small molecule
Monomer = building blockOne Nucleotide is a monomer = nucleic acid + deoxyribose + phosphate
(Nitrogenous Base)
DNA’s Structure
3’ has OH - hydroxide5’ 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 Structurenm = 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
• 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
Heat-killed IIIS
Live IIR
Heat-killed IIIS
Live IIR
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
removed protein
heat-killed IIIS + IIR
Avery, MacLeod and McCarty
heat-killed IIIS + IIR
removed RNA
removed DNA
heat-killed IIIS + IIR
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
• Mix phage and bacteria
• Allow infection
• Shear off what’s on outside - blender
• Centrifuge
• Look for radioactivity in pellet (bacteria)
infection blender
centrifuge
E. coli w/ hot DNA
Supernatant w/ protein coats
infection blender
centrifuge
E. coli w/ DNA
Supernatant w/ hot proteincoats
Summary Hershey & Chase
Chargaff’s Rules 1947
Provided base pairing and hydrogen bonding
Rosalind Franklin 1920-1958 (1951)
Rosalind FranklinX-Ray Diffraction
Provided idea of double helix
Nobel Prize (1962)
Frederick Wilkins James Watson Francis Crick
Made Model 1953