Post on 22-Dec-2015
Molecular BiologyMolecular Biology
Introduction– Definitions– History– Central Dogma
Molecular BiologyMolecular Biology
Definitions– Chromosomes– DNA– Gene– Genotype– Phenotype
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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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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Genes– Segments of DNA– Functional or regulatory– Mutability and variation
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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 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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Biochemistry– Meischer– Avery & MacLeod– Hershey & Chase– Watson & Crick
Genetics– Mendel– Sutton– Morgan– Griffith– Delbruck– Beadle & Tatum– Tatum &
Lederberg
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 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:
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
Molecular Biology - Molecular Biology - GeneticsGenetics
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
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
Molecular Biology - Molecular Biology - GeneticsGenetics
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
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
Molecular Biology - Molecular Biology - GeneticsGenetics
Molecular Biology - Molecular Biology - GeneticsGenetics
Molecular Biology - Molecular Biology - GeneticsGenetics Tatum & Lederburg
– discovered conjugation in bacteria
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
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
Molecular BiologyMolecular Biology
Substance Enzyme Transform
Capsule Carbohydrase Yes
Protein Protease Yes
RNA RNAse Yes
DNA DNAse No
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
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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Central Dogma– DNA Structure– Genetic Code– Replication– Transcription– Translation
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DNA Structure– Sugars– Bases– Phosphates– Double Helix– Anti-parallel
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Genetic Code– 4 bases / 20 amino acids– codons– punctuation
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UniversalGeneticCode
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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DNA mRNA Protein
Replication
Transcription Translation
DNAPolymerase
RNAPolymerase
mRNAtRNA
Ribosomes
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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 BiologyThe Meselson Stahl Experiment
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Molecular BiologyMolecular BiologyContinuous/Discontinuous DNA Synthesis
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Transcription– RNA polymerase – promoters– produces messenger RNA (mRNA)– requires NO primer
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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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Translation– tRNA– amino acid synthase– ribosomes– initiation– termination
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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’