Molecular Biology l Introduction –Definitions –History –Central Dogma

Molecular BiologyMolecular Biology

Introduction– Definitions– History– Central Dogma


Definitions– Chromosomes– DNA– Gene– Genotype– Phenotype


Chromosomes– The structure in cells that carries

hereditary information– Composed of DNA and protein– Prokaryotic - circular– Eukaryotic - linear


DNA– Nitrogenous base (4 bases - A,T,G & C– Deoxyribose sugar– Phosphate– Nitrogenous bases are paired

»AT»GC

– Double helix structure


Genes– Segments of DNA– Functional or regulatory– Mutability and variation


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


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


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



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 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 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 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


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


Central Dogma– DNA Structure– Genetic Code– Replication– Transcription– Translation


DNA Structure– Sugars– Bases– Phosphates– Double Helix– Anti-parallel


Genetic Code– 4 bases / 20 amino acids– codons– punctuation


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


DNA mRNA Protein

Replication

Transcription Translation

DNAPolymerase

RNAPolymerase

mRNAtRNA

Ribosomes


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 BiologyMolecular BiologyThe Meselson Stahl Experiment



Molecular BiologyMolecular BiologyContinuous/Discontinuous DNA Synthesis


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


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


Translation– tRNA– amino acid synthase– ribosomes– initiation– termination



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’

Documents

Molecular Biology l Introduction –Definitions –History –Central Dogma