DNA: Information Molecule

Transcription

1 DNA: Information Molecule How did scientists use evidence to discover that the DNA molecule contains information for an organism s characteristics (traits)?

2 Objectives Explain with evidence that DNA is the information carrying molecule of organisms Griffith and Avery T2 virus Describe one way DNA can be transferred laterally between organisms. Bacterial transformation Viral transduction

3 Can molecules act as information to determine an organism s traits? Can molecules from one strain of bacteria cause a different strain of bacteria to have similar traits?

4 Words to know Benign not harmful pronounce buh-nine Root word: good (Think bien ) A benign tumor is not dangerous. Virulent harmful (active) bacteria Pronounce veer-you-lent Root word: virus

5 Figure 11.1a There are two strains of Streptococcus pneumoniae. ROUGH COLONY (R) SMOOTH COLONY (S) R strain is benign (Lacking a protective capsule, it is recognized and destroyed by host s immune system) S strain is virulent (Protective capsule prevents detection by host s immune system)

6 Narrated animation of experiment Griffith s experiments

7 Figure 11.1b Explain each treatment: What is purpose for each control? What data shows the heat-killed S strain did not cause death of the mouse in treatment #4? What data shows S strain molecules cannot kill the mouse alone; the streptococcus must be alive? What data shows that the R strain alone will not kill the mouse? What data shows that the S strain IS virulent?

8 Mechanism Bacteria can take in pieces of DNA from their environment. This process is called transformation because in Griffith s experiment the R strain was transformed into an S strain by taking in DNA from the dead molecules.

9 Griffith s Conclusion The R strain was able to take in molecules from the dead S strain. These molecules somehow gave the R strain characteristics of the dead S strain. Ability to make protective coating So, we know that there is a molecule that transfers information BUT we still haven t proved what those molecules are!

10 Which molecules could be responsible for the information in cells? Type of molecule Made of Example Lipids (fats) Proteins DNA RNA

11 Experiment to determine which molecule in cells acts as information for traits 1. Take material from dead virulent (S-strain) Streptococcus. Remove lipid & carbohydrate. 2. Separate remaining molecules into three test tubes. 3. Treat each with a different enzyme to destroy one type of molecule. A. One test tube has DNA and RNA, but NO PROTEIN B. One test tube has DNA and protein, but NO RNA C. One test tube has RNA and protein, but NO DNA

12 Figure 11.2 DETERMINING THAT DNA IS THE HEREDITARY MATERIAL Heat-killed S cells Lipids Carbohydrates 1. Remove the lipids and carbohydrates from a solution of heat-killed S cells. Proteins, RNA, and DNA remain. Add proteinases Sample should Contain NO PROTEIN Add ribonuclease Sample should Contain NO RNA Add deoxyribonuclease Sample should Contain NO DNA 2. Subject the solution to treatments of enzymes to destroy either the proteins, RNA, or DNA. 3. Add a small portion of each sample to a culture containing R cells. Observe whether transformation has occurred by testing for the presence virulent S cells.

13 PREDICTIONS Hypotheses DNA is the information molecule no protein in sample Will the sample make R cells become S? no RNA in sample Will the sample make R cells become S? no DNA in sample Will the sample make R cells become S? RNA is the information molecule Will the sample make R cells become S? Will the sample make R cells become S? Will the sample make R cells become S? Protein is the information molecule Will the sample make R cells become S? Will the sample make R cells become S? Will the sample make R cells become S?

14 Figure 11.2 DETERMINING THAT DNA IS THE HEREDITARY MATERIAL Heat-killed S cells Lipids Carbohydrates 1. Remove the lipids and carbohydrates from a solution of heat-killed S cells. Proteins, RNA, and DNA remain. Add proteinases Sample should contain NO PROTEIN Add ribonuclease Sample should contain NO RNA Add deoxyribonuclease Sample should contain NO DNA 2. Subject the solution to treatments of enzymes to destroy either the proteins, RNA, or DNA. Add R cells S cells appear Transformation occurs Add R cells S cells appear Add R cells No transformation occurs No S cells appear 3. Add a small portion of each sample to a culture containing R cells. Observe whether transformation has occurred by testing for the presence virulent S cells.

15 RESULT no protein in sample S Cells become R cells no RNA in sample S Cells become R cells no DNA in sample S Cells DO NOT become R cells

16 Conclusion: Transformation cannot occur unless DNA is present. Therefore DNA is likely the hereditary material.

17 Is the hereditary information composed of DNA or Protein? T2 Virus Bacterial Cell

18 Figure 11.3 DNA or protein? DNA or protein? 1. Viruses are made of DNA and proteins. To reproduce, the virus injects it s hereditary information into the host cell. 2. Is the protein or the DNA injected? 3. Do proteins or DNA carry the hereditary information for the viruses to replicate?

19 Narrated animation of experiment Bacteriophage experiments

20 PREDICTIONS based on the two different hypotheses Hypotheses DNA is injected by the virus as the information molecule PROTEIN is injected by the virus as the information molecule Viruses with radioactive proteins infect bacteria Where will radioactivity be found? [inside] or [outside] the cells Where will radioactivity be found? [inside] or [outside] the cells Viruses with radioactive DNA infect bacteria Where will radioactivity be found? [inside] or [outside] the cells Where will radioactivity be found? [inside] or [outside] the cells

21 RESULTS Viruses with radioactive proteins infect bacteria Radioactivity is found only OUTSIDE the bacteria Viruses with radioactive DNA infect bacteria Radioactivity is found only INSIDE the bacteria

22 Results: Because the reproduced cells showed radioactivity on the inside when the DNA was injected, but not the protein, we can conclude that DNA is the molecule that acts as information for traits.

23 Figure 11.3 Virus protein coat Host cell membrane Virus DNA 1. Start of infection. Virus DNA enters host cells. Protein coat does not. 2. Virus DNA directs the production of new virus particles. 3. End of infection. New generation of virus particles burst from host cell.

24 What we learned DNA is the molecule that carries information Information in DNA determines which proteins can be made by an organism DNA can be passed between organisms in nature by viruses Bacteria can take in pieces of DNA from their environment. This process is called transformation.

25 How we use this understanding We can manipulate DNA in the laboratory and add it to organisms. Because DNA carries information for an organism s characteristics, we can give new characteristics to organisms In our lab we will change the characteristics of an organism through bacterial transformation We will study the ethics and implications of this technology- genetically modified organisms (GMO s) and GM foods.