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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.