Download Bacterial Classification

Molecular Biology

Introduction
– Definitions
– History
– Central Dogma
Molecular Biology

Definitions
–
–
–
–
–
Chromosomes
DNA
Gene
Genotype
Phenotype
Molecular Biology

Chromosomes
– The structure in cells that carries hereditary
information
– Composed of DNA and protein
– Prokaryotic - circular
– Eukaryotic - linear
Molecular Biology

DNA
–
–
–
–
Nitrogenous base (4 bases - A,T,G & C
Deoxyribose sugar
Phosphate
Nitrogenous bases are paired
» AT
» GC
– Double helix structure
Molecular Biology

Genes
– Segments of DNA
– Functional or regulatory
– Mutability and variation
Molecular 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
Molecular 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

Molecular Biology

Biochemistry
–
–
–
–
Meischer
Avery & MacLeod
Hershey & Chase
Watson & Crick

Genetics
–
–
–
–
–
–
–
Mendel
Sutton
Morgan
Griffith
Delbruck
Beadle & Tatum
Tatum & Lederberg
Molecular Biology - Genetics

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
Molecular Biology - Genetics
Cross of pure breeding purple flowers with
pure breeding white flowers produces all purple
plants with genotype Pp; crossing Pp plants
produces following distribution:
P
p
P
PP
purple
Pp
purple
p
Pp
purple
pp
white
Molecular Biology - Genetics

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
Molecular Biology - Genetics

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

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
Molecular Biology - Genetics

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

Beadle & Tatum
– developed Neurospora as an experimental
organism
– established one gene one enzyme
hypothesis
– generation time is even shorter with
Neurospora
Molecular Biology - Genetics
Molecular Biology - Genetics
Molecular Biology - Genetics

Tatum & Lederburg
– discovered conjugation in bacteria
Molecular Biology - Biochemistry

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

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
Substance Enzyme
Transform
Capsule
Carbohydrase Yes
Protein
Protease
Yes
RNA
RNAse
Yes
DNA
DNAse
No
Molecular Biology - Biochemistry

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 - Biochemistry

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

Central Dogma
–
–
–
–
–
DNA Structure
Genetic Code
Replication
Transcription
Translation
Molecular Biology

DNA Structure
–
–
–
–
–
Sugars
Bases
Phosphates
Double Helix
Anti-parallel
Molecular Biology

Genetic Code
– 4 bases / 20 amino acids
– codons
– punctuation
Molecular Biology
Universal
Genetic
Code
Molecular 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

Molecular Biology
Replication
Transcription
DNA
DNA
Polymerase
Translation
mRNA
RNA
Polymerase
mRNA
tRNA
Ribosomes
Protein
Molecular 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
Molecular Biology
Molecular Biology
The Meselson Stahl Experiment
Molecular Biology
Molecular Biology
Molecular Biology
Continuous/Discontinuous DNA Synthesis
Molecular Biology

Transcription
–
–
–
–
RNA polymerase
promoters
produces messenger RNA (mRNA)
requires NO primer
Molecular Biology
Molecular 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
Molecular Biology

Translation
–
–
–
–
–
tRNA
amino acid synthase
ribosomes
initiation
termination
Molecular Biology
Molecular 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’