Biology 9.1 Identifying Genetic Material

1. Biology 9.1 Identifying Genetic Material Genetic Material: Viral Genes and DNA

2. Transformation • Mendel’s experiments answered many questions about why you resemble your parents. • You resemble your parents because you have copies of chromosomes from each. Chromosomes are each made up of many genes. • The question that remained was what were these genes made up of?

3. Griffith’s Experiments • In 1928, an experiment completely unrelated to the study of genetics led to an astounding discovery about DNA. • Frederick Griffith, a bacteriologist, was trying to prepare a vaccine against pneumonia.

4. Griffith’s Experiments • A vaccine is a substance that is prepared from a killed or weakened disease-causing agent, including certain bacteria.

5. Griffith’s Experiments • The vaccine is introduced into the body to protect the body against future infections by the disease causing agent.

6. Griffith’s Experiments • Griffith worked with two types of strains of S. pneumonia. The first strain was enclosed in a capsule of polysaccharides. The capsule protects the bacterium from the body’s defense systems. • This helps make the microorganism virulentor able to cause disease.

7. Griffith’s Experiments • The second strain of the bacterium lacks the capsule and does notcause the disease. • Those bacterium grown in the capsule developed smooth edges. Those in the second strain grown freely developed rough-edge colonies.

8. Griffith’s Experiments • Griffith knew that mice infected with the virulent material grew sick and died, while mice infected with the non-lethal material were unharmed. • To determine if the capsule on the lethal bacteria were causing the mice to die, Griffith injected the mice with dead S bacteria. • The mice remained healthy and did not die.

9. Griffith’s Experiments • Griffith than prepared a vaccine of weakened S bacteria by raising the temperature to a point where the bacteria were “heat-killed”, meaning that they could no longer reproduce. • When Griffith injected mice with the heat-killed S bacteria, the mice lived.

10. Griffith’s Experiments S • He than mixed the harmless live R bacteria with the harmless heat-killed bacteria. • Mice injected with these previously harmless materials died. • When Griffith examined the blood of the dead mice, he discovered that the live R bacteria had acquired capsules. R heat killed S R + Heatkilled S

11. Griffith’s Experiments • Somehow the harmless R bacteria had changed and become virulent S bacteria. • Griffith had discovered what is now called transformation. • Transformationis a change in a genotype caused when cells take up foreign genetic material.

12. Avery’s Experiments • Avery’s Experiments: • The search for the substance responsible for transformation continued until 1944. • Than, a series of experiments showed that the activity of the material responsible for transformation is not affected by protein-destroying enzymes.

13. Avery’s Experiments • Avery’s Experiments: • The activity is stopped instead by a DNA-destroying enzyme. • Oswald Avery and his fellow scientists at Rockefeller Institute in New York City demonstrated that DNA is the material responsible for transformation.

14. Avery’s Experiments • Although Avery’s experiments proved that the genetic material is composed of DNA, many scientists remained skeptical. • In 1952, Alfred Hershey and Martha Chase performed an experiment that settled the controversy.

15. Avery’s Experiments • It was known at the time that viruses, which are much simpler than cells, are composed of DNA or RNA surrounded by a protective protein. • Abacteriophage (also known as a phage)is a virus that infects bacteria.

16. Avery’s Experiments • It was also known that when these phages infect bacterial cells, the phages are able to produce more viruses, which are released when the bacteria cells rupture. • Hershey and Chase concluded that the DNA of viruses is injected into bacterial cells, while most of the viral proteins remain outside. • This meant that theDNA, rather than the proteins, is the heredity material, at least in viruses.

17. Avery’s Experiments • These important experiments have shown that DNAis the molecule that stores genetic information in living cells.

18. Computer Lab: • Today’s assignment, after completing your worksheet 9.1, is to use the internet to research and answer the following with a short written report. Answer all of the following in your report. DO NOT COPY, CUT,OR PASTE • Who was Frederick Griffith and what did his experiments with viruses discover? • Who was Oswald Avery and what did his experiments with viruses discover? • Who were Alfred Hershey and Martha Chase and what did their experiments discover?