Molecular Biology l Introduction –Definitions –History –Central Dogma

Molecular Biology l Definitions –Chromosomes –DNA –Gene –Genotype –Phenotype

Molecular Biology l Chromosomes –The structure in cells that carries hereditary information –Composed of DNA and protein –Prokaryotic - circular –Eukaryotic - linear

Molecular Biology l DNA –Nitrogenous base (4 bases - A,T,G & C –Deoxyribose sugar –Phosphate –Nitrogenous bases are paired »AT »GC –Double helix structure

Molecular Biology l Genes –Segments of DNA –Functional or regulatory –Mutability and variation

Molecular Biology l Genotype –The genetic make-up of an organism; the information that codes for all the characteristics of an organism l Phenotype –The expression or physical manifestation of a gene; how it appears

Molecular Biology l Molecular biology seeks to understand the molecular or chemical basis of genetics l History of molecular biology is a melding of biochemistry, especially nucleic acid biochemistry and genetics

Molecular Biology l Biochemistry –Meischer –Avery & MacLeod –Hershey & Chase –Watson & Crick l Genetics –Mendel –Sutton –Morgan –Griffith –Delbruck –Beadle & Tatum –Tatum & Lederberg

Molecular Biology - Genetics l Mendel (1865) –Fluid vs. particulate inheritance –Studied pure breeding pea plants –Law of Segregation –Law of Independent Assortment –Rediscovered by de Vries & others

Molecular Biology

Molecular Biology - Genetics Pp PPP purple Pp purple pPp purple pp white Cross of pure breeding purple flowers with pure breeding white flowers produces all purple plants with genotype Pp; crossing Pp plants produces following distribution:

Molecular Biology - Genetics l Walter Sutton (1902) –Studied meiosis in grasshoppers (insects have large readily observable chomosomes) –Observed that chromosomes behave in manner similar to segregation of hereditary material –Found that chromosomes occur in morphologically similar pairs –Pairs separate during meiosis

Molecular Biology - Genetics

l Morgan –Developed modern science of genetics –Used fruit flies because they had a shorter generation time than peas –Discovered sex-linkage –Students developed techniques of mapping genes on chromosomes

Molecular Biology - Genetics l Griffith –discovered transformation in 1927 –is a means of genetic transfer in microorganisms –a process by which a nonpathogenic strain is transformed into a pathogenic strain

Molecular Biology - Genetics

l Delbruck –developed quantitative methods for analysis of bacteriophage; viruses of bacteria –organized course to teach biologists methods at Cold Spring Harbor resulting in a large number of biologists trained in molecular techniques

Molecular Biology - Genetics l Beadle & Tatum –developed Neurospora as an experimental organism –established one gene one enzyme hypothesis –generation time is even shorter with Neurospora

Molecular Biology - Genetics

l Tatum & Lederburg –discovered conjugation in bacteria

Molecular Biology - Biochemistry l Meischer (1869) –Austrian doctor –isolated a substance called “nuclein” from the nuclei of cells obtained from the pus of surgical bandages –found to contain nitrogenous chemicals, sugar and phosphate

Molecular Biology - Biochemistry l Avery & MacLeod (1944) –isolated Griffith’s transforming factor to a high degree of purity –characterized transforming factor using highly purified enzymes –found transforming factor to be DNA

Molecular Biology

Molecular Biology - Biochemistry l Hershey & Chase (1952) –used newly developed radioisotopes » 35 S for protein » 32 P for nucleic acid –labeled bacteriophage (a virus of bacteria) –found 32 P went into cells but 35 S did not implying that nucleic acid transfer information to cell for new bacteriophages

Molecular Biology - Biochemistry l Watson & Crick (1953) –used X-ray crystallography to study structure of DNA –by combining chemical data and X-ray data were able to construct a model of DNA –structure inferred function leading to Central Dogma

Molecular Biology l Central Dogma –DNA Structure –Genetic Code –Replication –Transcription –Translation

Molecular Biology l DNA Structure –Sugars –Bases –Phosphates –Double Helix –Anti-parallel

Molecular Biology l Genetic Code –4 bases / 20 amino acids –codons –punctuation

Molecular Biology Universal Genetic Code

Molecular Biology l Central Dogma states a hypothesis regarding information flow in cell l Replication - the copying of DNA or information for next generation l Transcription - the copying of information for use by the cell l Translation - the conversion of information into useful products - enzymes

Molecular Biology DNAmRNA Protein Replication TranscriptionTranslation DNA Polymerase RNA Polymerase mRNA tRNA Ribosomes

Molecular Biology l Replication –replication is semi-conservative –replication occurs at replication fork –replication is discontinuous process –uses DNA polymerase –Uses RNA polymerase –requires a primer with free 3’-hydroxyl

Molecular Biology

The Meselson Stahl Experiment

Molecular Biology

Continuous/Discontinuous DNA Synthesis

Molecular Biology l Transcription –RNA polymerase –promoters –produces messenger RNA (mRNA) –requires NO primer

Molecular Biology

l Differences between prokaryotic and eukaryotic mRNA l Prokaryotic –often polygenic –turns over quickly –translated almost immediately l Eukaryotic post transcription modification –Heterogenous introns & exons - excision of introns –mRNA stability – days to weeks –Addition of 5’ cap and 3’ polyadenylation

Molecular Biology l Translation –tRNA –amino acid synthase –ribosomes –initiation –termination

Molecular Biology

l DNA Sequence Analysis –DNA coding (sense) »5’CCG ATG AAT GTC GAG CTA TCC TAC 3’ –DNA non-coding (nonsense)(template) »3’GGC TAC TTA CAG CTC GAT AGG ATG 5’ –mRNA »5’CCG AUG AAU GUC GAG CUA UCC UAC 3’