Foothill High School Science Department DNA & RNA DNA.

Foothill High School Science DepartmentFoothill High School Science Department

DNA & RNADNA & RNA

DNADNA


Griffith & TransformationGriffith & Transformation

• 1928• Studying Natural Bacterial

Pneumonia caused by:– Streptococcus pneumoniae• Smooth (pathogenic)• Rough (non-pathogenic)

S. pneumonia in sputumNotice capsule

Gram Positive Diplococci


Streptococcus pneumoniaStreptococcus pneumonia

OptochinDisc

Type 3VERY Mucoid


Griffith’s ExperimentsGriffith’s Experiments

• Injected Mice–Smooth – Mice Died–Rough – Mice Didn’t Get Sick

–Heat Killed Smooth Heat Killed Smooth – Mice Didn’t Get Sick• Illness Not Caused By Poison


TransformationTransformation

Mixed Heat Killed Smooth With Mixed Heat Killed Smooth With Rough Live Bacteria.Rough Live Bacteria.

–Mice DiedMice Died

–Autopsy Revealed Lungs Full Of Smooth Strain of Bacteria

HOW?? Rough Bacteria Don’t Kill!HOW?? Rough Bacteria Don’t Kill!


Griffiths TransformationGriffiths Transformation


TransformationTransformation

• Heat Killed Smooth Bacteria– Still Contained The Information On How To

Become Smooth–And Could Transmit That Info–And Transform Rough Bacteria To The

Smooth (Pathogenic) Form


Avery & DNAAvery & DNA

• 1944• Repeated Griffith’s Work• Then Did Experiments to

Find Out What Was Transforming the Bacteria

• By Treating The Extract From Heat Killed Smooth Bacteria To Destroy Specific Types Of Compounds



Treated Extract To DestroyProteinsProteins

LipidsLipidsCarbohydratesCarbohydrates

RNARNATransformation Still OccurredTransformation Still Occurred



Then They Treated The Extract & Then They Treated The Extract & Destroyed The DNADestroyed The DNA

Transformation DidTransformation Did NOTNOT Occur Occur

DNA Was The Transforming FactorDNA Was The Transforming Factor



Key ConceptAvery and other scientists discovered Avery and other scientists discovered

that DNA stores and transmits the that DNA stores and transmits the genetic information from one genetic information from one generation of an organism to the next generation of an organism to the next generationgeneration..


The Structure of DNAThe Structure of DNA

Chargaffs RulesChargaffs Rules–Discovered That Certain Nucleotides

Were Always Present In The Same Percentages:– AdenineAdenine & ThymineThymine–GuanineGuanine & CytosineCytosine–% In Each Species Different–Nobody Knew Why


Hershey-Chase ExperimentHershey-Chase Experiment

• 19521952• Studied Virus Particles, Studied Virus Particles,

Especially Especially BacteriophagesBacteriophages

Martha Chase & Alfred Hershey


Hershey-Chase ExperimentHershey-Chase Experiment

• Bacteriophages– Composed of DNA or RNA– and a Protein Coat

– Figured Whichever Part Entered The Bacteria – Carried The Genes

• Used Radioactive Markers


Radioactive MarkersRadioactive Markers

• Grew Viruses In Cultures ContainingGrew Viruses In Cultures Containing– Radioactive Phosphorus ( Radioactive Phosphorus ( 3232P )P )

andand

– Radioactive Sulfur ( Radioactive Sulfur ( 3535S )S )

Proteins Contain Proteins Contain NoNo Phosphorous PhosphorousDNA Contains DNA Contains NoNo Sulfur Sulfur


Radioactive MarkersRadioactive Markers

Therefore:Therefore:IfIf The Interior Of The Bacteria Contained The Interior Of The Bacteria Contained::

( ( 3232P ) Then DNA Contained GenesP ) Then DNA Contained Genes( ( 3535S ) Then Protein Contained GenesS ) Then Protein Contained Genes

Nearly All The Bacteria ContainedNearly All The Bacteria Contained( ( 3232PP ) )

Therefore Therefore DNA Contained GenesDNA Contained Genes


Hershey-ChaseHershey-Chase

Bacteriophage(virus that infects bacteria)

Outer, Protein CoatContains Sulfur – No Phosphorus

E. coli bacteria(infected by Bacteriophage)

Bacteriophage DNA injected into the E. coli

Bacteriophage DNA contains Phosphorous but NO Sulfur


Hershey-ChaseHershey-Chase


Hershey - ChaseHershey - Chase

Key Concept:Hershey and Chase concluded that

the genetic material of the bacteriophage was:

DNA, not Protein.DNA, not Protein.



• X-Ray Diffraction– Early 1950’s–Rosalind Franklin–Doesn’t Show Structure

But Provides Clues• DNA Twisted In Coils• Two Strands• Nitrogenous Base In

Center


Photo 51Photo 51


• Watson & CrickWatson & Crick– Building 3Building 3

Dimensional ModelsDimensional Models– 1953 Saw Franklins1953 Saw Franklins

X-ray WorkX-ray Work– Immediately Recognized Immediately Recognized

What The Structure Had What The Structure Had To Be:To Be:

A Double Helix

The Double HelixThe Double Helix



• Scientists still didn’t know:Scientists still didn’t know:–How information was carried between How information was carried between

generationsgenerations–How genes were structuredHow genes were structured–How genes were copiedHow genes were copied


The Structure of DNAThe Structure of DNA• DNA is a long Molecule of DNA is a long Molecule of

repeating nucleotidesrepeating nucleotides• Each nucleotide has 3 Each nucleotide has 3

parts:parts:– 5 Carbon Sugar 5 Carbon Sugar

(Deoxyribose)(Deoxyribose)– 1 Phosphate Group1 Phosphate Group– 1 Nitrogenous Base1 Nitrogenous Base



• There are 4 Nitrogenous Bases 4 Nitrogenous Bases in DNA• The 4 Bases are two types:– PurinesPurines which are Double Ring Molecules

• Adenine• Guanine

– PyrimidinesPyrimidines which are Single Ring Molecules

• Cytosine• Thymine


Purines PyrimidinesPurines Pyrimidines


Watson & CrickWatson & Crick

Key ConceptKey Concept::Watson & Crick’s Model of DNA Watson & Crick’s Model of DNA

was a Double Helix, was a Double Helix,

in which Two (2) Strands were in which Two (2) Strands were wound around each other.wound around each other.



Nitrogenous BasesNitrogenous BasesForms Rungs of DNA LadderForms Rungs of DNA Ladder

Phosphate/DeoxyribosePhosphate/DeoxyriboseForm Sides of the DNA Form Sides of the DNA

LadderLadder


Watson & CrickWatson & Crick

• Discovered The Double Helix• Held Together By Hydrogen Bonds

Between The Nitrogenous Bases• Base Pairing

A:TA:T and G:CG:CExplained Chargaff’s Rule


Double HelixDouble Helix

Foothill High School Science Department DNA & RNA DNA.

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