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What we’ve learned so far… •Cells make proteins •Genetic information is passed on through chromosomes •Compacted DNA and proteins= chromosomes •Genetic information is stored in the nucleus •Genetic information is essential so that each cell is identical (mitosis) To truly understand genetics, biologists first had to discover the chemical nature of the gene. –How do genes control what you look like? 12-1 DNA • Vocabulary: • • • • Transformation Bacteriophage Nucleotide Base pairing Key Concepts: •What did scientists discover about the relationship between genes and DNA? •What is the overall structure of the DNA molecule? DNA’s “Experiment” History • Griffith: How do certain types of bacteria cause pneumonia? – The experiment that tested this question led to new knowledge. – Genetic information could be transformed from one bacterium to another. Genetic Info. Transferred Transformation • Heat killed bacteria had passed their disease causing ability to the harmless strain • Griffith called this transformation – One strain of bacteria (harmless) had changed into the other (disease causing) • Some factor was transferred from the heat killed cells to the live cells – This factor might contain a gene with information that could change harmless bacteria into disease causing ones! Avery & DNA • Avery and a group of scientists decided to repeat Griffith’s experiment – determine which molecule in the heat killed bacteria was needed for transformation • Made an extract (juice) from heat killed bacteria and added enzymes that destroy proteins, carbohydrates, & lipids – Transformation still occurred! • Repeated the experiment but added enzymes that destroy DNA – Transformation DID NOT occur!! Avery’s Conclusion • What was the “transforming factor”? • DNA • Conclusion: DNA is the nucleic acid that stores and transmits genetic info from generation to generation Hershey-Chase Experiment • Studied viruses; specifically bacteriophages – Bacterio = bacteria – Phage = eater – Bacteria eater • Viruses—made up of: – DNA + protein coat • Research Question: Which part of the virus enters the infected bacteria cell? • Grew viruses in the presence of radioactive markers 32P and 35S. – Sulfur is found in protein coat – Phosphorus is found in DNA No Sulfur! Phosphorus! Hershey-Chase Conclusion • Genetic information of the bacteriophage that they infected with bacteria was DNA – NOT protein What DNA does… • Carries information from one generation to the next • Put that information to work by determining heritable characteristics • Must be easily copied since almost every new cell gets a copy DNA Structure • Made up of nucleotides (monomer) • Each composed of 3 parts: – Deoxyribose: sugar – Phosphate group – Nitrogenous (nitrogen containing) base • • • • Adenine (A) Thymine (T) Guanine (G) Cytosine (C) DNA Structure= Double Helix • Backbone – Deoxyribose & Phosphate Group of each nucleotide • “Steps of Ladder” – bases • Any base sequence is possible Chargaff’s Rules Percentage of Bases in Four Organisms Source of DNA A T G C Streptococcus 29.8 31.6 20.5 18.0 Yeast 31.3 32.9 18.7 17.1 Herring 27.8 27.5 22.2 22.6 Human 30.9 29.4 19.9 19.8 What does this data suggest to you? Oooooohhhh!! Aaaaaahhhhh!!!! • A = T (A pairs with T) • C = G (C pairs with G) What DNA Looks Like • Rosalind Franklin: used X-Ray diffraction patterns to discover that DNA twisted around each other like a helix • Watson & Crick: while trying to build a 3-D model of DNA, Watson was shown Franklin’s photograph and within weeks, figured out the structure of DNA What’s holding the strands together? • HYDROGEN BONDS!!! • Hydrogen Bonds form between A and T base pairs as well as between C and G base pairs