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 –transformation Avery, MacLeod, and McCarty –Proves DNA is the transforming agent using enzymes Hershey & Chase –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/ 32 P in one study –labeled protein of phage w/ 35 S in second In which study does radioactivity end up in E. coli?

32 P labeled DNA 35 S 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 protein coats

Summary Hershey & Chase

Chargaff’s Rules 1947 Provided base pairing and hydrogen bonding

Rosalind Franklin (1951)

Rosalind Franklin X-Ray Diffraction Provided idea of double helix

Nobel Prize (1962) Frederick Wilkins James Watson Francis Crick Made Model 1953