Chapter 10.1-10.3: Identifying the Substance of Genes

“Success seems to be largely a matter of hanging on after the others have let go.” William Feather  Ch. 10.1 – 10.3 Identifying the Substance of Genes The Structure of DNA Learning Objectives Today you will learn to: – Describe the key events leading to th...

“Success seems to be largely a matter of hanging on after the others have let go.” William Feather  Ch. 10.1 – 10.3 Identifying the Substance of Genes The Structure of DNA Learning Objectives Today you will learn to: – Describe the key events leading to the development of the structural model of DNA. – Describe the basic structure of DNA and its function in inheritance.  Unit Organizer DNA is about The Code of Life the Historical its Experiments to discover it Structure Shape Components  Think about it… What organelle is known as the “control center” of the cell? – Nucleus What structures are found in the nucleus? – Chromosomes (which are made up of DNA and proteins) What is located in chromosomes that carries the genetic code? – DNA How do genes in the DNA control cell activity? – By producing proteins that regulate cellular functions or become part of the cell structure. Scientists call this the: DNA Core of RNA o l e c u l a r M Bio l o g y ! Protein How do we know that all of our genetic information comes from DNA?  Griffith’s Experiment with Pneumonia and the accidental discovery of Transformation Frederick Griffiths was a bacteriologist studying pneumonia He discovered two types of bacteria: – Smooth colonies – Rough colonies  Griffith’s Experiment with Pneumonia and the accidental discovery of Transformation CONCLUSION: The smooth colonies must carry the disease!  Griffith’s Experiment with Pneumonia and the accidental discovery of Transformation When heat was applied to the deadly smooth type… And injected into a mouse… The mouse lived!  Griffith’s Experiment with Pneumonia and the accidental discovery of Transformation Griffith injected the heat- killed type and the non- deadly rough type of bacteria. The bacteria “transformed” itself from the heated non- deadly type to the deadly type. Griffith’s Experiment did not prove that DNA was responsible for transformation How would you design an experiment to prove that DNA was responsible for transformation?  Avery, McCarty, and MacLeod Repeated Griffith’s Experiment Oswald Avery Maclyn McCarty Colin MacLeod  Avery, McCarty, and MacLeod Added the non-deadly Rough Type of Bacteria to the Heat-Killed Smooth Type To the Heat-Killed Smooth Type, added enzymes that destroyed… Carbohydrates Lipid Protein RNA DNA  S-Type S-Type S-Type S-Type S-Type Carbohydrates Lipids Proteins RNA DNA Destroyed Destroye Destroye Destroye Destroye d d d d Conclusion: DNA was the transforming factor that carried the genetic code!  The Hershey-Chase Experiment Protein coat Alfred Hershey & Martha Chase worked with a bacteriophage: A virus that invades DNA bacteria. It consists of a DNA core and Protein coats of bacteriophages labeled with Sulfur-35 Phage 1. Hershey and Chase Bacterium mixed the radioactively- labeled viruses with the bacteria Phage The viruses infect Bacterium the bacterial cells. DNA of bacteriophages labeled with Phosphorus-32 Protein coats of bacteriophages labeled with Sulfur-35 2. Separated the viruses from the bacteria by agitating the virus- bacteria mixture in a blender DNA of bacteriophages labeled with Phosphorus- 32 Protein coats of bacteriophages labeled with Sulfur-35 3. Centrifuged the mixture so that the bacteria would form a pellet at the bottom of the test tube 4. Measured the radioactivity in the pellet and in the liquid DNA of bacteriophages labeled with Phosphorus- 32 The Hershey-Chase results reinforced the Avery, McCarty, and MacLeod conclusion: DNA carries the genetic code! However, there were still important details to uncover…  How did DNA: 1. Store information? 2. Duplicate itself easily? These questions would be answered by discovering DNA’s structure The Race to Discover DNA’s Structure The Components and Structures of DNA 4 kinds of nitrogenous bases: – Purines- 2 rings Adenine Guanine – Pyrimidines- 1 ring Cytosine Thymine  The Race to Discover DNA’s Structure 1950 Chargaff’s Rule: DNA is made up of equal amounts of Adenine and Thymine, and equal amounts of Guanine and Cytosine Erwin Chargaff  The Race to Discover DNA’s Structure From this analysis Chargaff concluded the bases must pair like so… Erwin Chargaff  The Race to Discover DNA’s Structure Why do you think Purine + Purine = Too wide the bases match up this way? Pyrimidine + Pyrimidine = Too Narrow Erwin Chargaff Purine + Pyrimidine = Perfect Fit from X-ray  The Race to Discover DNA’s Structure X-Ray diffraction image of Maurice DNA taken by Franklin in Rosalind Wilkins 1951 Franklin  The Race to Discover DNA’s Structure 1953 Compiled data from previous scientists to build the first double-helical James Watson model of DNA Francis Crick Figure 10.3b  The DNA Model Watson, Franklin and Crick’s collaborative efforts contributed to the development of the DNA model. DNA Stands for Deoxyribonucleic Acid The Race to Discover DNA’s Structure was Over DNA has 3 parts: – Deoxyribose – a 5 carbon sugar – Phosphate group Held to the sugar group by a covalent bond Together they make up the sugar phosphate backbone – Nitrogenous bases stick out from these. The Race to Discover DNA’s Structure was Over DNA has 3 parts: – Deoxyribose – a 5 carbon sugar – Phosphate group Held to the sugar group by a covalent bond Together deoxyribose and the phosphate group make up the sugar phosphate backbone – Nitrogenous bases stick out from these. Figure 10.2a-0 A T C G T A Sugar-phosphate backbone C G A T Phosphate G C group G A A Nitrogenous Nitrogenous base Covalent base A T (can be A, G, C, or T) G C bond Sugar T A joining C C T A nucleotides C G T A DNA Thymine A DNA T nucleotide T (T) Phosphate double helix group G G Sugar (deoxyribose) DNA nucleotide G G Two representations of a DNA polynucleotide  The Nitrogen Bases 4 Nitrogen bases: – Adenine – Thymine – Guanine – Cytosine These follow the rules of base- pairing: Adenine bonds with Thymine Guanine bonds with Cytosine  The Nitrogen Bases 4 Nitrogen bases: – Adenine – Thymine – Guanine – Cytosine These follow the rules of base- pairing: Adenine bonds with Thymine Guanine bonds with Cytosine  The Nitrogen Bases 4 Nitrogen bases: – Adenine – Thymine – Guanine – Cytosine These follow the rules of base- pairing: Adenine bonds with Thymine Guanine bonds with Cytosine DNA is the shape of a double-helix  The Nitrogen Bases 4 Nitrogen bases: – Adenine – Thymine – Guanine – Cytosine These follow the rules of base- pairing: Adenine bonds with Thymine Guanine bonds with Cytosine DNA is the shape of a double-helix Animation: DNA Double Helix  Section Review 1. Describe the key events leading to the development of the structural model of DNA. Which scientist x-rayed the structure of DNA Which scientist proposed the double helix model of DNA? 2. Describe the basic structure of DNA. Components and shape Animation: DNA and RNA Structure