Pair Seatwork: The Search for the Genetic Material Computer-Aided Activity – Visit http://www.dnai.org/timeline/ and explore the various important scientists and fill in the blanks with their contributions to the discovery of DNA as the genetic material. You may also copy this file onto an email message and send it to me at email@example.com.
1869 – Friedrich Miescher worked on (1)__________________ he obtained from bandages at the local hospital. Lysis and alkalinization of these cells produced an acidic substance with high phosphorus content from the nuclei of all the cells studied. He called this substance (2)__________________, and thought that its purpose was for (3)_____________
1904 – Thomas Hunt Morgan established the chromosomal theory of inheritance using Drosophila melanogaster or (4)__________________. These organisms were known to be prolific breeders, producing hundreds of offspring and a new generation every two weeks. They also had four pairs of chromosomes: 3 pairs of autosomes and 1 pair of sex chromosomes. After many breeding experiments, he discovered a mutant male which had (5)__________________ instead of the wild-type (or usual) red colored eyes. Upon performing many more experiments, he discovered that this trait is carried in the (6) __________________ – chromosome, leading him to the discovery of sex-linked genes.
1928 – Frederick Griffith studied Streptococcus pneumoniae bacteria that cause pneumonia in mammals. He had two strains the pathogenic (7)__________________ strain which had capsules to protect themselves from the mouse’s immune system and the harmless (8)__________________ strain or mutant bacteria with no capsules. Summarize the experiment below:
|Mice injected with living S cells||(9)
|Mice injected with living R cells||(10)
|Mice injected with heat-killed S cells||(11)
|Mice injected with heat-killed S cells mixed with live R cells||(12)
1944 – Oswald Avery, Maclyn McCarty, and Colin MacLeod set to work discovering the identity of Griffith’s transforming substance. They purified various chemicals from heat-killed S cells, combined these with R cells, and checked for transformation. Summarize the experiment below:
(Lysate from S-cells)
|Sugar coat + Protein + DNA + RNA||(15)|
|Protein + DNA + RNA||(16)|
1949 – Erwin Chargaff already knew that DNA was a polymer of nucleotides consisting of a combination of four nitrogenous bases (A, T, G, C), deoxyribose sugar, and a phosphate group. He analyzed the composition of the bases in the DNA of of various species and compared them with each other. He found that DNA composition varies between species and that (20)_________________________________________________________________________________. These are now known as Chargaff’s rules.
1951 – Rosalind Franklin and Maurice Wilkins worked on (21)____________________________________ that can provide information about the shapes and structures of molecules. When a stream of rays is directed at a crystallized substance, some of them are diffracted or scattered. These can also interfere with each other producing spots of different intensities that can be recorded on film producing a unique signature for that structure. Working on data from a particular DNA fiber, she was able to (22)______________________________________________________________.
1952 – Alfred Hershey and Martha Chase studied viruses that attack bacteria called (23)__________________. The two components that make up these viruses are (24)__________________ and (25)__________________. The question they wanted answered was which of these two biomolecules are responsible for infecting cells and reprogramming them to produce viruses. They distinguished between the two by (26)_________________________________________
__________________________________________________________________________________________________. They then waited long enough for these to be assimilated into the phages’ biomolecules and spun them in Waring blenders and centrifuged them. Summarize the experiment below:
|Tube with 35S label||(27)|
|Tube with 32P label||(28)|
1953 – James Watson and Francis Crick built on the work of previous researchers. For instance, Phoebus Levene found that (30)____________________________________, but Oswald Avery’s findings showed that (31)_________________
____________________________________. Chargaff’s rules for DNA composition can be summarized simply as %A = (32)_____ and %G = (33)_________. Linus Pauling discovered that similar to many proteins, DNA had a (34)___________________ structure.Rosalind Franklin’s X-ray photos further showed the following measurements: (35)______________________. From these, Watson and Crick deduced that the structure of DNA had to be a (36)__________________ helix. When playing around with paper models of the bases, they decided that the only possible pairing combinations would be (37)__________________ and (38)__________________. The two helices run (39)__________________ to each other because of certain bond angles and base pair proximity. The conclusion to their groundbreaking paper stated that (40)______________ ____________________________________. After this, Francis Crick proposed the Central Dogma which states that (41)________________________________________________________________________________.
1957 – Matthew Meselson and Franklin Stahl hypothesized that a new DNA strand is made from copying the old. This type of replication is described as being (42)__________________. They used the organism (43)__________________ and the isotope (44)__________________. This isotope is used by the organisms in creating (45)__________________. They then transferred the organisms to fresh media and used normal nitrogen. They took samples of the organisms every time their populations doubled and compared these samples with organisms grown using normal nitrogen. They isolated DNA and centrifuged it. Summarize the results of the experiment below:
|TREATMENT||CONDITIONS OF GROWTH OF THE BACTERIA||RESULTS UPON CENTRIFUGATION AND INTERPRETATIONS|