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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, carbohydrates and nucleic acids) using white blood cells from bandages. Why did he use white blood cells? Because Red blood cells do not have a nuclei He treated the white blood cells with an enzyme to kill the proteins and therefore found nucleic acids. Walter Sutton, 1902 Proposed the Chromosome Theory of Inheritance Studied numerous organisms to find chromosomes but ultimately had the most success with grasshopper sperm cells. He expanded on Mendel’s work and found that chromosomes are what carry genetic information; they are found in a pair in body cells and one set is given to offspring from each parent through gametes (sperm/egg). Thomas Hunt Morgan, 1910 Studied 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 passed on to future generations together, thus we say they are “linked genes”. 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 heat-killed 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 & Chase, 1952 Expanded on previous DNA research to further support the hypothesis that DNA was the genetic material. Used radioactive Sulfur and Phosphorous on bacteriophages (viruses that infect bacteria) DNA of the virus contained phosphorous and was injected into the bacteria while the protein coat of the virus contained sulfur and was NOT injected into the bacteria. Used radioactive phosphorous and sulfur to trace the movement of DNA and protein from the virus to the bacteria and found that only the radioactive phosphorous was found in the bacteria NOT radioactive sulfur, therefore proving that DNA was the genetic material passed into the bacteria. See section 12-1 in your text book for diagram and further explanation Chargaff, 1949 Found that the percentage of nitrogenous bases was equal among Adenine – Thymine and Cytosine – Guanine. %A=T %C=G Wilkins & Franklin, 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 picture and Chargaff’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 One Gene – One 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.