4-4-2 Search for the Physical carrier of inheritance Flashcards
Golden Age of Genetics (when)
The period from the early 1900s to World War II
Golden Age of Genetics (significance)
During this time, a great many genetic discoveries were made.
link established between genetics and evolution.
Consideration of both Mendel’s work and that of cell biologists led to the chromosomal theory of inheritance.
Golden age of genetics (remaining question)
whether DNA or protein was the hereditary material
Friedrich Miescher (date 1769, 1869, or 1969)
In 1869, the Swiss biochemist Friedrich Miescher
Friedrich Miescher (accomplishments)
isolated DNA from fish sperm and the pus of open wounds.
Robert Feulgen (1814, 1914, 1964, or 2014)
In 1914,
the German chemist Robert Feulgen (accomplishments)
discovered that when a modified dye was applied to the cell, it stained only DNA. DNA was then found in the nuclei of all eukaryotic cells.
Russian-born biochemist P.A. Levene (accomplishments)
he determined which chemicals make up the DNA molecule.
He found that it contained four nitrogen-containing bases, deoxyribose sugar, and a phosphate group.
He concluded that the basic unit (the nucleotide) was one of these four nitrogenous bases attached to the sugar molecule. The phosphate group also attached to the sugar.
Levene found that the four types of nucleotides corresponded to the four different bases: cytosine (C), guanine (G), adenine (A), or thymine (T).
Russian-born biochemist P.A. Levene (years 1920s, 1940s, or 1960’s)
1920s
British physician Frederick Griffith (dates 1920s, 1940s, or 1960’s)
1920s (following the 1919 flu epidemic)
British physician Frederick Griffin (accomplishments)
Discovered that the genetic material of a dead virulent strain of bacteria could be transferred to a non-virulent strain to make it virulent.
British physician Frederick Griffin (remaining question after Griffin’s work)
What was the genetic material that had been transferred to the non-virulent strain of bacteria?
what are the bases that make up DNA, and the categories of bases? Which bases go in which categories? Which are double ring? single ring?
purines (double ring) Adenine, Guanine. Pyrimidines (single ring): thymine, cytosine
Oswald Avery, Colin MacLeod, and Maclyn McCarty (years 1920s, 1940s, or 1980s)
During the 1940s,
Oswald Avery, Colin MacLeod, and Maclyn McCarty (accomplishment)
demonstrated that the genetic “transforming factor” that made non-virulent bacteria virulent was DNA.
Oswald Avery, Colin MacLeod, and Maclyn McCarty (experiment)
Repeated Griffith’s work, but added certain enzymes that inactivate either DNA or protein. When the enzyme that inactivates protein was added, the transformation from R to S bacteria still occurred. However, when the enzyme that cuts up (digests) DNA was added, no transformation occurred. Avery’s team concluded that the hereditary material must be more like DNA than protein.
British physician Frederick Griffin (experiment)
studied the difference between a strain of the pneumonia-causing bacteria (Streptococcus pneumoniae) and a strain of bacteria that did not cause pneumonia. He identified that cells of the pneumonia-causing strain (the S strain) were surrounded by a structure known as a capsule. The nonpathogenic strain (the R strain) did not have a capsule and did not cause pneumonia. In 1928, Griffith injected the different strains of bacteria into mice. As expected, the S strain killed the mice and the R strain did not. He also noted that if heat was used to kill the S strain that was injected into a mouse, it did not cause pneumonia. The surprise came when Griffith injected a mixture of heat-killed S and live R into the mice. Remember, neither the heat-killed S nor the R alone could cause pneumonia. However, when combined the mice developed pneumonia and died! Somehow, live R bacteria had been changed into live S bacteria. Griffith concluded that this transformation occurred when material of some kind had been transferred from the dead S bacteria into the live R bacteria. He determined that this “transforming factor” was genetic because it was passed down to later generations of bacteria.
American scientists, Alfred D. Hershey (1908-1997) and Martha Chase (1927-2003),
carried out a set of experiments in 1952 to determine conclusively whether protein or DNA was the hereditary material. The scientists worked on viruses called bacteriophages that attack bacteria. Bacteriophages consist of protein coats covering DNA.
American scientists, Alfred D. Hershey and Martha Chase, (year of their discovery 1922, 1952, or 1982)
1952
American scientists, Alfred D. Hershey and Martha Chase (experiment)
Bacteriophages infect a cell by injecting material into the bacteria that causes the host cell to make new bacteriophages instead of new bacteria.
Hershey and Chase labeled the DNA and protein of bacteriophages with radioisotopes to determine which chemical (DNA or protein) was getting into the bacteria. Because DNA contains phosphorous (P) but no sulfur (S), they tagged the DNA with the radioactive isotope phosphorous-32. Protein lacks phosphorous but does have sulfur, so it was tagged with the radioactive isotope sulfur-35. Hershey and Chase discovered the radioactive sulfur of the protein remained outside the bacterial cell while the radioactive phosphorous of the DNA was found inside the cell. Furthermore, the radioactive DNA was passed down to later generations of the bacteriophages. This indicated that DNA and not protein was the physical carrier of heredity.
American scientists, Alfred D. Hershey and Martha Chase (significance)
confirmed that DNA and not protein was the physical carrier of heredity.
