DNA Scientists Use Chapter 12, section 1 and the Internet for further information

Johann Miescher, Late 1800’s  Discovered nucleic acids (the 4th biological molecule, proteins, lipids, carbs and nucleic acids) using white blood cells from bandages.  Why did he used white blood cells? Because Red blood cells do not have a nuclei  He treated the WBC with an enzyme to kill the proteins and therefore found nucleic acids.

Walter Sutton, 1902  Discovered the chromosome theory of heredity  Studied numerous organisms to find chromosome but ultimately had the most success with Grasshopper sperm cells.  He expanded on Mendel’s work and found that there are chromosomes that carry heredity information are found in a pair and 1 set is given to offspring from each parent

Thomas Hunt Morgan, 1910  Studies genetics using fruit flies  Established the theory of Chromosome patterns and gene linkage meaning that on a single strand of DNA some genes are so close on the strand that they are linked and therefore passed on to future generations together. For example if a fruit fly has red eyes it is likely to have long wings because those genes are closely located on the DNA however if it has white eyes then it is likely to have short wings.

Frederick Griffith, 1928  Studied how people become ill using mice and pneumonia bacteria  Discovered the theory of transformation  Used a deadly (virulent) strand of bacteria and a non-deadly (non-virulent) strand of bacteria.  Found that if the virulent strand and the non-virulent strand were put together then the non-virulent strand became deadly therefore “something” was transferring from the virulent strand to the non-virulent strand. (See your textbook section 12-1 for a diagram and further details)

Oswald Avery, 1944  Continued Griffiths work on the theory of transformation  Found the transferring agent was DNA  Used enzymes to destroy the proteins and was left with the nucleic acid and therefore identified the transferring agent that Griffith discovered was DNA

Hershey and Chase, 1952  Expanded on previous DNA research to further support the theory of DNA  Used radioactive Sulfur and Phosphorous on bacteriophages (viruses that infect bacteria)  DNA of the virus contains phosphorous and is injected into the bacteria while the protein coat of the virus contains Sulfur and is NOT injected into the bacteria.  Used radioactive phosphorous and sulfur to trace the movement of DNA from the virus to the bacteria and found that only the radioactive phosphorous was found in the bacteria NOT radioactive sulfur therefore proving the presence of DNA.  See section 12-1 in your text book for diagram and further explanation

Chargoff, 1949  Found that the percentage of nitrogenous bases was equal among Adenine – Thymine and Cytosine – Guanine.  % A = T % C = G

Wilkins and Franklin (female), 1952  Discovered the structure of DNA using X-ray diffraction (crystallography)  See the picture in your textbook chapter 12, section 1

Watson & Crick, 1953  Discovered the double helix structure of DNA using Wilkins and Franklins work and Chargoff’s rule of A=T and C=G.  Found that Adenine and Guanine are purines with a double ring nitrogenous base  Found that Cytosine and Thymine are pyrimidines with a singe ring nitrogenous base  Awarded the Nobel Prize for their discovery of the structure of DNA along with Wilkins

Beadle & Tatum, 1930’s  Discovered the 1 gene – 1 enzyme theory.  Found that genes regulate chemical activity in bread mold cells  Radiated the bread mold and mutated the DNA which then affected the enzyme activity and chemical reactions of the bread mold cells.

SCIENTIST QUESTIONS

1. What did Miescher use to conduct his DNA research?

2. What biological molecule did he "kill" in order to determine that genetic

information was made up of nucleic acids?

3. Sutton researched grasshopper sperm to state the ______

theory of ______.

4. Which scientist researched fruit flies to determine that there are sex-linked

chromosomes?

5. What bacterium was used by Griffith in his experiments?

6. Briefly explain how Griffith's used two strains of the bacterium in his experiment.

7. What process did he discover?

8. Which scientists discovered that DNA was the transforming "agent" researched

by Griffith?

9. What two radioactive elements did Hershey and Chase inject into

bacteriophages?

10. What did Hershey and Chase discover at the end of their experiment?

11. What is Chargoff's Rule?

12. What do the letters A, T, C, G represent?

13. What contributions to understanding DNA did Wilkins and Franklin make?

14. What technique did they use?

15. Explain the contribution Watson and Crick made in 1953 to our current

understanding of the structure of DNA.

16. Why are Watson and Crick credited with the Nobel Prize for the structure of DNA

when Franklin was the scientist to gather the initial images of it?

17. What did Beadle and Tatum study in order to understand that genes regulate

chemical reactions?

18. What was Beadle and Tatum's theory?