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DNA The Genetic Material. The genetic material must meet 4 criteria 1. Information: 2. Transmission: 3. Replication: 4. Variation: 9-3 IDENTIFICATION.

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Presentation on theme: "DNA The Genetic Material. The genetic material must meet 4 criteria 1. Information: 2. Transmission: 3. Replication: 4. Variation: 9-3 IDENTIFICATION."— Presentation transcript:

1 DNA The Genetic Material

2 The genetic material must meet 4 criteria 1. Information: 2. Transmission: 3. Replication: 4. Variation: 9-3 IDENTIFICATION OF DNA AS THE GENETIC MATERIAL

3 Two strains of Streptococcus pneumoniae S  Smooth Secrete a polysaccharide capsule Produce smooth colonies on solid media virulent R  Rough Unable to secrete a capsule Produce colonies with a rough appearance avirulent Two coat types II III Four possible phenotypes IIS or IIIS or IIR or IIIR Frederick Griffith’s Transformation Experiments

4 Griffith’s Experiments 9-6 Figure 9.1 Rare mutations convert strains S into R strain & vice versa But mutations do not change coat types II into III or vice versa

5 9-8 Figure 9.2

6 9-9 Something from the dead type IIIS transformed type IIR into type IIIS Called this process transformation The unknown substance was termed the transforming principle Griffith’s Conclusions

7 Griffith’s transforming principle was the genetic material Transformation assay to identify actual biomolecule Major constituents - DNA, RNA, proteins, carbohydrates, & lipids Made cell extracts from type IIIS cells containing each of these macromolecules Avery, MacLeod & McCarty Identify the Genetic Material 9-10

8 9-11 Figure 9.3 Mixed each extract with type IIR cells to test for transformation Only extract containing purified DNA transformed type IIR to type IIIS Verify that DNA, not RNA or protein, is the genetic material Avery’s Experiments

9 1952- Hershey & Chase Confirm DNA is Genetic Material Using Phage T2

10 Figure 9.5 Life cycle of phage T2

11 Phage Attached to E. coli Cell

12 The Hershey and Chase experiment: Used radioisotopes to distinguish DNA from proteins 32 P labels DNA specifically 35 S labels protein specifically Infect non-radioactive E. coli with radioactively- labeled phages Remove phage coats from cells Is 32 P or 35 S inside bacteria? 9-14

13 Hershey & Chase Experiment S

14

15 The Data 9-18

16 9-20 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display In 1956, A. Gierer and G. Schramm isolated RNA from the tobacco mosaic virus (TMV) Purified TMV RNA caused the same lesions as intact TMV viruses Therefore, the viral genome is composed of RNA Since that time, many RNA viruses have been found RNA is Genetic Material in Some Viruses

17 9-21 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display


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