NL 8:30-2:30 Weather Plan? Room #8:30 – 9:45 AP BIOLOGY I Jolene Jacquet 226 Lab Review 1-6 AP BIOLOGY II Nancy Bishop 228 DNA & Protein Synthesis AP BIOLOGY III Cindy Brainard / Brian Elliott 229 Evolution Major Concepts &Hardy Weinberg (Brainard)

How do we know DNA is the genetic material

What is the genetic material? Fredrick Griffith How do certain bacteria cause pneumonia? 2 strains (types) of Streptococcus pneumonia –Smooth – when grown in petri dish smooth edged colonies and shiny –Rough – when grown in petri dish rough edged colonies and not shiny SMOOTH COLONIES ARE PATHOGENIC – disease causing ROUGH COLONIES ARE USUALLY DESTROYED BY HOST IMMUNE SYSTME

bacterium smooth strain – capsule rough strain – no capsule

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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 cells Change was permanent and heritable – capsule did not cause disease.

TRANSFORMATION Something in dead, disease-causing bacteria turned harmless bacteria into killers! He called this process TRANSFORMATION Some 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 colleagues Made extract of bacteria Destroyed proteins, lipids, carbohydrates, and nucleic acids (RNA and DNA) one-by- one with enzymes When DNA was destroyed by enzymes the cells did not become pathogenic Conclusion??????

Many people remained unconvinced that DNA was the genetic material! Many thought protein must be the genetic material. Protein is more complicated – 20 amino acids DNA is made of only 4 bases – adenine, guanine, cytosine and thymine Protein had “greater heterogeneity and specificity of function” Little was know about nucleic acids at the time

EVIDENCE DNA IS GENETIC MATERIAL Alfred Hershey and Martha Chase Worked with a simple system: E. coli bacteria and bacteriophages – viruses that infect bacteria

EVIDENCE 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. bacteria

EVIDENCE DNA IS GENETIC MATERIAL How could they determine whether DNA or protein from phage entered cell? Protein has sulfur, DNA does not – grow phages in radioactive sulfur 35 S DNA has phosphorus, protein does not – grow phages in radioactive phosphorus 32 P Virus capsid – protein coat labeled with 35 S Virus core – DNA labeled with 32 P Infect the bacteria and see which one enters the cell

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

What does DNA look like? Watson and Crick Rosalind Franklin

HOW IS DNA REPLICATED? Meselson and Stahl Use radioactive isotopes to track old and new strands of DNA Use centrifugation to separate DNA molecules by mass and … CHASE

HOW DO WE KNOW WHICH MODEL IS CORRECT?

First make the original DNA “HEAVY”

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