How do we know DNA is the genetic material

NL 8:30-2:30 Weather Plan?Room #8:30 9:45AP BIOLOGY IJolene Jacquet226 Lab Review 1-6 AP BIOLOGY IINancy Bishop 228 DNA & Protein SynthesisAP BIOLOGY IIICindy Brainard / Brian Elliott229 Evolution Major Concepts &Hardy Weinberg (Brainard)How do we know DNA is the genetic materialWhat is the genetic material?Fredrick GriffithHow do certain bacteria cause pneumonia?2 strains (types) of Streptococcus pneumoniaSmooth when grown in petri dish smooth edged colonies and shinyRough when grown in petri dish rough edged colonies and not shinySMOOTH COLONIES ARE PATHOGENIC disease causingROUGH COLONIES ARE USUALLY DESTROYED BY HOST IMMUNE SYSTME

bacteriumsmooth strain capsulerough strain no capsule

??????????Does the capsule cause disease?DEAD S cells were mixed with live R cells.Bacteria isolated from blood of dead mice were S strain and produced more S strain cellsChange was permanent and heritable capsule did not cause disease.

TRANSFORMATIONSomething in dead, disease-causing bacteria turned harmless bacteria into killers!He called this process TRANSFORMATIONSome factor in dead pathogens turned harmless bacteria into pathogens!

What is the transforming factor?C (somatic) carbohydrate, nucleoproteins, free nucleic acids of both the yeast [RNA] and thymus [DNA] types, lipids and other cell constituents. Try to find in that complex mixture the active principle..!! Try to isolate and chemically identify the particular [transforming] substance....!Some job--full of heartaches and heartbreaks. But at last perhaps we have it....Oswald Avery

What is the transforming factor?Oswald Avery and colleaguesMade extract of bacteriaDestroyed proteins, lipids, carbohydrates, and nucleic acids (RNA and DNA) one-by-one with enzymesWhen DNA was destroyed by enzymes the cells did not become pathogenicConclusion??????

Many people remained unconvinced that DNA was the genetic material!Many thought protein must be the genetic material.Protein is more complicated 20 amino acidsDNA is made of only 4 bases adenine, guanine, cytosine and thymineProtein had greater heterogeneity and specificity of functionLittle was know about nucleic acids at the timeEVIDENCE DNA IS GENETIC MATERIALAlfred Hershey and Martha ChaseWorked with a simple system: E. coli bacteria and bacteriophages viruses that infect bacteriaEVIDENCE DNA IS GENETIC MATERIAL

VIRUSES are not cells. Consist of nucleic acid wrapped in a protein coat. Must infect a cell in order to reproduce.bacteriaEVIDENCE DNA IS GENETIC MATERIALHow could they determine whether DNA or protein from phage entered cell?Protein has sulfur, DNA does not grow phages in radioactive sulfur 35SDNA has phosphorus, protein does not grow phages in radioactive phosphorus 32PVirus capsid protein coat labeled with 35SVirus core DNA labeled with 32PInfect the bacteria and see which one enters the cell

EVIDENCE DNA IS GENETIC MATERIALRadioactive DNA entered the cell but radioactive protein stayed outside.Conclusion?

What does DNA look like?

Watson and CrickRosalind Franklin

HOW IS DNA REPLICATED?Meselson and StahlUse radioactive isotopes to track old and new strands of DNAUse centrifugation to separate DNA molecules by mass

and CHASEHOW DO WE KNOW WHICH MODEL IS CORRECT?

First make the original DNA HEAVY

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