Chaper 12: DNA
12-1 1 DNA: Identifying the Substance of Genes Vocabulary: Transformation Bacteriophage Nucleotide Base pairing Double helix Key Concepts: What did scientists discover about the relationship between genes and DNA? What is the overall structure of the DNA molecule?
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?
Animal Husbandry Goat herders 5000 years ago knew Offspring tend to look like their parents. What is this process or molecule that makes this happen????
DNA s Experiment History Fredrich Miescher (1869) Studied pus cells he collected from bandages in hospitals White blood cells are huge. Used an enzyme to digest away the proteins in nucleus A strange phosphorous molecule remained Molecule of heredity?
Fredrick Griffith (1928) 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.
Fredrick Griffith (1928) He injected mice with the one strain of bacteria and they died. When he did the same with another strain of bacteria they didn t die. He could use heat to kill the deadly bacteria so it wouldn t kill mice. Injected mice with a mixture of harmless bacteria and the heat killed bacteria
Genetic Info. Transferred
The mice died!! Something had passed from the heat killed deadly bacteria to the living harmless bacteria. He called this process TRANSFORMATION.
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 (1952) 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?
Hershey & Chase Wanted to REALLY make sure it was DNA Viruses are made of only protein and DNA Proteins have sulfur but no phosphorous. DNA has phosphorous but no sulfur Bacteriophage
Grew viruses in the presence of radioactive markers 32P P 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 DNA
What DNA does Deoxyribonucleic Acid = DNA 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 A = T (A pairs with T) C 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
Adenine and guanine are purines Thymine and cytosine are pyrimidines