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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 229 Evolution Major Concepts &Hardy Weinberg (Brainard) AP BIOLOGY III Cindy Brainard / Brian Elliott 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 ?????????? 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-byone 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 bacteria VIRUSES are not cells. Consist of nucleic acid wrapped in a protein coat. Must infect a cell in order to reproduce. 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 35S • DNA has phosphorus, protein does not – grow phages in radioactive phosphorus 32P • Virus capsid – protein coat labeled with 35S • Virus core – DNA labeled with 32P • 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” http://www.sumanasinc.com/webcontent/anima tions/content/meselson.html