Ch11_Lecture - 11 DNA and Its Role in Heredity 11 DNA and...

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11 DNA and Its Role in Heredity
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11 DNA and Its Role in Heredity 11.1 What Is the Evidence that the Gene Is DNA? 11.2 What Is the Structure of DNA? 11.3 How Is DNA Replicated? 11.4 How Are Errors in DNA Repaired? 11.5 What Are Some Applications of Our Knowledge of DNA Structure and Replication?
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11.1 What Is the Evidence that the Gene Is DNA? By the 1920s, it was known that chromosomes consisted of DNA and proteins. A new dye stained DNA and provided circumstantial evidence that DNA was the genetic material: It was in the right place It varied among species It was present in the right amount
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11.1 What Is the Evidence that the Gene Is DNA? Frederick Griffith, working with two strains of Streptococcus pneumoniae determined that a “ transforming principle ” from dead cells of one strain produced a heritable change in the other strain.
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Figure 11.1 Genetic Transformation of Nonvirulent Pneumococci
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11.1 What Is the Evidence that the Gene Is DNA? Identifying the transforming principle, Oswald Avery: Treated samples to destroy different molecules; if DNA was destroyed, the transforming principle was lost.
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11.1 What Is the Evidence that the Gene Is DNA? Hershey-Chase experiment: Determined whether DNA or protein is the genetic material using bacteriophage T2 virus. Bacteriophage proteins were labeled with 35 S; the DNA was labeled with 32 P.
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Figure 11.3 Bacteriophage T2: Reproduction Cycle
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Figure 11.4 The Hershey–Chase Experiment (Part 1)
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Figure 11.4 The Hershey–Chase Experiment (Part 2)
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11.2 What Is the Structure of DNA? The structure of DNA was determined using many lines of evidence. One crucial piece came from X-ray crystallography . A purified substance can be made to form crystals; position of atoms is inferred by the pattern of diffraction of X-rays passed through it.
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Figure 11.6 X-Ray Crystallography Helped Reveal the Structure of DNA
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11.2 What Is the Structure of DNA? Chemical composition also provided clues: DNA is a polymer of nucleotides: deoxyribose, a phosphate group, and a nitrogen-containing base. The bases: Purines: adenine (A), guanine (G) Pyrimidines: cytosine (C), thymine (T)
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Figure 3.23 Nucleotides Have Three Components repeat fig 3.23 here
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11.2 What Is the Structure of DNA? 1950: Erwin Chargaff found in the DNA from many different species: amount of A = amount of T amount of C = amount of G Or, the abundance of purines = the abundance of pyrimidines— Chargaff’s rule .
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Figure 11.7 Chargaff’s Rule
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11.2 What Is the Structure of DNA? Model building started by Linus Pauling —building 3-D models of possible molecular structures. Francis Crick and James Watson used model building and combined all the knowledge of DNA to determine its structure.
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Figure 11.8 DNA Is a Double Helix (A)
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11.2 What Is the Structure of DNA?
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