Molecular Biology l Introduction –Definitions –History –Central Dogma.
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Transcript of Molecular Biology l Introduction –Definitions –History –Central Dogma.
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Molecular BiologyMolecular Biology
Introduction– Definitions– History– Central Dogma
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Molecular BiologyMolecular Biology
Definitions– Chromosomes– DNA– Gene– Genotype– Phenotype
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Molecular BiologyMolecular Biology
Chromosomes– The structure in cells that carries
hereditary information– Composed of DNA and protein– Prokaryotic - circular– Eukaryotic - linear
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Molecular BiologyMolecular Biology
DNA– Nitrogenous base (4 bases - A,T,G & C– Deoxyribose sugar– Phosphate– Nitrogenous bases are paired
»AT»GC
– Double helix structure
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Molecular BiologyMolecular Biology
Genes– Segments of DNA– Functional or regulatory– Mutability and variation
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Molecular BiologyMolecular Biology
Genotype– The genetic make-up of an organism;
the information that codes for all the characteristics of an organism
Phenotype– The expression or physical
manifestation of a gene; how it appears
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Molecular BiologyMolecular Biology
Molecular biology seeks to understand the molecular or chemical basis of genetics
History of molecular biology is a melding of biochemistry, especially nucleic acid biochemistry and genetics
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Molecular BiologyMolecular Biology
Biochemistry– Meischer– Avery & MacLeod– Hershey & Chase– Watson & Crick
Genetics– Mendel– Sutton– Morgan– Griffith– Delbruck– Beadle & Tatum– Tatum &
Lederberg
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Molecular Biology - Molecular Biology - GeneticsGenetics Mendel (1865)
– Fluid vs. particulate inheritance– Studied pure breeding pea plants– Law of Segregation– Law of Independent Assortment– Rediscovered by de Vries & others
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Molecular BiologyMolecular Biology
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Molecular BiologyMolecular Biology
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Molecular Biology - Molecular Biology - GeneticsGenetics
P p
P PPpurple
Pppurple
p Pppurple
ppwhite
Cross of pure breeding purple flowers with pure breeding white flowers produces all purpleplants with genotype Pp; crossing Pp plantsproduces following distribution:
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Molecular Biology - Molecular Biology - GeneticsGenetics 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
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Molecular Biology - Molecular Biology - GeneticsGenetics
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Molecular Biology - Molecular Biology - GeneticsGenetics 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
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Molecular Biology - Molecular Biology - GeneticsGenetics 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
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Molecular Biology - Molecular Biology - GeneticsGenetics
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Molecular Biology - Molecular Biology - GeneticsGenetics 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
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Molecular Biology - Molecular Biology - GeneticsGenetics Beadle & Tatum
– developed Neurospora as an experimental organism
– established one gene one enzyme hypothesis
– generation time is even shorter with Neurospora
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Molecular Biology - Molecular Biology - GeneticsGenetics
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Molecular Biology - Molecular Biology - GeneticsGenetics
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Molecular Biology - Molecular Biology - GeneticsGenetics Tatum & Lederburg
– discovered conjugation in bacteria
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Molecular Biology - Molecular Biology - BiochemistryBiochemistry 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
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Molecular Biology - Molecular Biology - BiochemistryBiochemistry 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
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Molecular BiologyMolecular Biology
Substance Enzyme Transform
Capsule Carbohydrase Yes
Protein Protease Yes
RNA RNAse Yes
DNA DNAse No
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Molecular Biology - Molecular Biology - BiochemistryBiochemistry Hershey & Chase (1952)
– used newly developed radioisotopes» 35S for protein» 32P for nucleic acid
– labeled bacteriophage (a virus of bacteria)
– found 32P went into cells but 35S did not implying that nucleic acid transfer information to cell for new bacteriophages
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Molecular Biology - Molecular Biology - BiochemistryBiochemistry 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
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Molecular BiologyMolecular Biology
Central Dogma– DNA Structure– Genetic Code– Replication– Transcription– Translation
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Molecular BiologyMolecular Biology
DNA Structure– Sugars– Bases– Phosphates– Double Helix– Anti-parallel
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Molecular BiologyMolecular Biology
Genetic Code– 4 bases / 20 amino acids– codons– punctuation
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Molecular BiologyMolecular Biology
UniversalGeneticCode
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Molecular BiologyMolecular Biology Central Dogma states a hypothesis
regarding information flow in cell Replication - the copying of DNA or
information for next generation Transcription - the copying of
information for use by the cell Translation - the conversion of
information into useful products -enzymes
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Molecular BiologyMolecular Biology
DNA mRNA Protein
Replication
Transcription Translation
DNAPolymerase
RNAPolymerase
mRNAtRNA
Ribosomes
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Molecular BiologyMolecular Biology
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
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Molecular BiologyMolecular Biology
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Molecular BiologyMolecular BiologyThe Meselson Stahl Experiment
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Molecular BiologyMolecular Biology
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Molecular BiologyMolecular Biology
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Molecular BiologyMolecular BiologyContinuous/Discontinuous DNA Synthesis
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Molecular BiologyMolecular Biology
Transcription– RNA polymerase – promoters– produces messenger RNA (mRNA)– requires NO primer
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Molecular BiologyMolecular Biology
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Molecular BiologyMolecular Biology Differences between prokaryotic and
eukaryotic mRNA Prokaryotic
– often polygenic– turns over quickly– translated almost immediately
Eukaryotic post transcription modification– Heterogenous introns & exons - excision of
introns– mRNA stability – days to weeks – Addition of 5’ cap and 3’ polyadenylation
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Molecular BiologyMolecular Biology
Translation– tRNA– amino acid synthase– ribosomes– initiation– termination
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Molecular BiologyMolecular Biology
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Molecular BiologyMolecular Biology
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’