molecular biology of the gene dna. identification of genetic material identification of genetic...
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Identification of Genetic Identification of Genetic MaterialMaterial
Structure of DNAStructure of DNA DNA ReplicationDNA Replication
Genetic Material –DNA or Genetic Material –DNA or Protein?Protein?
Bacteriophage Bacteriophage ReplicationReplication
Martha Chase and Alfred Hershey (1952)
Roles of the Genetic Roles of the Genetic MaterialMaterial
““A genetic material must carry out two A genetic material must carry out two jobs: duplicate itself and control the jobs: duplicate itself and control the development of the rest of the cell in a development of the rest of the cell in a specific way.”specific way.”
-Francis Crick-Francis Crick
Bacterial Bacterial TransformationTransformation
Frederick Griffith, 1928Frederick Griffith, 1928 Diplococcus pneumoniaeDiplococcus pneumoniae infects mice infects mice Mice develop pneumonia and dieMice develop pneumonia and die
Two types of bacteria:Two types of bacteria: R bacteria rough coat R bacteria rough coat no pneumonia no pneumonia S bacteria smooth coat S bacteria smooth coat pneumonia pneumonia Coat type is associated with virulence.Coat type is associated with virulence.
The “Transforming The “Transforming Principle”Principle”
Avery, MacLeod, and McCarty, 1944
• Treated lysed S bacteria with protease and DNase• DNase prevented transformation• Therefore DNA is the transforming principle
Figure 9.2
Monomers and PolymersMonomers and Polymers
Polymers are made up of monomersPolymers are made up of monomers Mono = oneMono = one
Poly = manyPoly = many
For example: For example: Proteins are made up of amino acidsProteins are made up of amino acids
PolynucleotidesPolynucleotides Polynucleotides are made up of Polynucleotides are made up of
nucleotidesnucleotidesSugar-phosphate backbone
Phosphate group
Nitrogenous baseSugar
DNA nucleotide
DNA polynucleotide
DNA nucleotide
Sugar(deoxyribose)
Thymine (T)
Nitrogenous base(A, G, C, or T)
Phosphategroup
A
C
T
G
T T
G
T
C
A
Basic Structure of a Basic Structure of a NucleotideNucleotide
Phosphate Group Nitrogenous
Base
Sugar
Nitrogenous Bases Nitrogenous Bases (DNA)(DNA)
Thymine (T) Cytosine (C) Adenine (A) Guanine (G)
PyrimidinesOne Ring
PurinesTwo Rings
And the Nobel Prize Goes And the Nobel Prize Goes To…To…
Physiology or Medicine 1962Physiology or Medicine 1962"for their discoveries concerning "for their discoveries concerning the molecular structure of nucleic the molecular structure of nucleic acids and its significance for acids and its significance for information transfer in living information transfer in living material" material"
Rosalind Franklin (1920-1958) Watson and Crick with their model of DNA
DNA: The Double HelixDNA: The Double Helix
Hydrogen bond
Basepair
Ribbon model Partial chemical structure Computer model
G C
T A
A T
TA
C
C
G
G
GC
T
T
T
T
A
A
A
A
G C
A T
A
C
T
G
CG
AT
Orientation of DNA Orientation of DNA The 5’ phosphate of one nucleotide is attached to the 3’ hydroxyl group of the previous nucleotide
The directionality of a DNA strand is due to the orientation of the phosphate-sugar backbone
Figure 9.11
DNA ReplicationDNA Replication
DNA Replication is SemiconservativeDNA Replication is Semiconservative
Parentalmoleculeof DNA
Both parentalstrands serveas templates
Two identicaldaughter molecules
of DNA
T
Nucleotides
C G
A
G C
A
A
T
T
A
AA
A
C C
C
T
T
G
G
A
C
A
A A
A
A
A
C C
C
CG
T
G
T
T
T
T
G
T
T
T
G
G
Each new double Each new double helix contains one helix contains one parental strand parental strand and one daughter and one daughter strandstrand
Origin of replication
Bubble
Parental strand
Daughter strand
Two daughter DNA molecules
Replication Replication BubblesBubbles
3 end 5 end
5 end 3 end
P
4A
T
C
G
HO
OH
P
13
2
5P
P
P
P
C
G
P
P
A
T
P
43 1
2
5DNA is DNA is synthesized synthesized from 5from 5’’ to 3 to 3’’
One Little One Little Problem…Problem…
DNA polymerasemolecule
Parental DNA
3
5
3
5
5
3
LEADING STRANDDaughter strand synthesizedcontinuously
LAGGING STRANDDaughter strand synthesized In pieces
DNA Polymerase Can Only DNA Polymerase Can Only Move 5Move 5’’ to 3 to 3’’
DNA polymerase adds nucleotides to the 3DNA polymerase adds nucleotides to the 3 ’’ end end““ase” = enzymease” = enzyme
DNA LigaseDNA Ligase
35
DNA ligase
35
LEADING STRAND
LAGGING STRAND
DNA ligase “glues” the fragments DNA ligase “glues” the fragments togethertogether
Nitrogenous Bases (DNA Nitrogenous Bases (DNA and RNA)and RNA)
Thymine (T) Cytosine (C) Adenine (A) Guanine (G)
H
Uracil (U)
PyrimidinesOne Ring
PurinesTwo Rings
DNA vs. RNADNA vs. RNADeoxyribonucleic Acid Ribonucleic Acid
H OH
Phosphate Group
Ribose
Phosphate Group
Deoxyribose
Nitrogenous Bases
T C A GNitrogenous Bases
U C A G
Nitrogenous Base
Nitrogenous Base
CH3H
Thymine
Uracil