Molecular Biology Molecular Biology of the Geneof the Gene

DNADNA

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

Hershey and Chase Hershey and Chase ExperimentExperiment

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.

Griffith’s ExperimentsGriffith’s Experiments

Figure 9.1

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

Rope Ladder ModelRope Ladder Model

Sugar and Phosphate Backbone

Nitrogenous Base Pairs

Rope Ladder ModelRope Ladder Model

Complementary Base Complementary Base PairsPairs

A-TA-TG-CG-C

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

Structure of DNAStructure of DNA

DNA ReplicationDNA Replication DNA vs. RNADNA vs. RNA

Chromosomes and Chromosomes and MitosisMitosis

Chromosomes Are Made Chromosomes Are Made of DNAof DNA

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

G C

TA

A T

G

G

C

C

T

T

AA C

CG

G

G

G

C

CG

G

G

C

C

CT

T

T

TT

C

A A

A

AA

GTG

CA

TT

T

T

AA

AA

An enzyme “unzips” DNAAn enzyme “unzips” DNA

Replication Bubble

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

Structure of DNAStructure of DNA DNA ReplicationDNA Replication

DNA vs. RNADNA vs. RNA

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