Unit 2 - Molecular Genetics (1) Flashcards
Griffith
worked with Pneumococcus bacteria which cause pneumonia in mammals
in culture, two different types of colonies can form: smooth, shiny colonies (S-strain), or rough colonies (R-strain)
mice injected with the virulent S-strain died of pneumonia, those injected with the non-virulent R-strain did not
mice injected with heat-killed S-strain were unaffected
mice injected with both the heat killed strain and the live R-strain died
live S-strain bacteria were subsequently isolated from these dead mice
conclusion = genetic information responsible for virulence had been transferred from the dead S-strain bacteria to the live R-strain bacteria in the mice
Oswald Avery
isolated Griffith’s transforming principle
found that its activity was lost in the presence of DNA digesting enzymes but was unaffected by protein digesting enzymes
conclusion = DNA is the hereditary material in bacteria
Hershey and Chase
geneticists were torn between whether the genetic material was made of protein or nucleic acid
Hershey and Chase experimented with a virus made of only a DNA core and protein coat
they reasoned that which material entered the bacterium to causes new viruses to form was the genetic material
a key point to their experimental design is that DNA contains P atoms, but not S atoms, and protein contains S atoms but not P atoms
Hershey and Chase Experiment #1
bacteria were infected with bacteriophages containing DNA radiolabeled with P-32
phage coats were removed from the bacteria by agitation in a blender
the bacterial suspension was centrifuged, leading to pellet of bacteria and a supernatant of viral coats
the supernatant was decanted into another tube
result = bacterial pellet contained the P-32, not the supernatant
conclusion = DNA had entered the cells
Hershey and Chase Experiment #2
experiment 1 was repeated, but this time the viral protein coats were labelled with S35
result = the S35 remained in the supernatant
conclusion = DNA is the genetic material of the bacteriophage
Chargaff
studied the nitrogenous base composition of DNA from a wide variety of organisms
it had previously been believed that adenine, thymine, guanine, and cysteine were found in every nucleotide (tetranucleotide hypothesis)
if this were true, then all DNA would contain 25% of each base
experiment conclusions
base composition varies from species to species
percentages of A and T are equal, as are the percentages of C and G
the tetranucleotide hypothesis is incorrect
Rosalind Franklin
one of the first female researchers in molecular genetics
used X-ray crystallography to produce an X-ray diffraction pattern from a DNA crystal
this X-ray diffraction was apparently borrowed from her desk by her colleague Wilkins and shared with Watson and Crick
she predicted a helical structure of DNA over a year before anyone else, but her work never received widespread recognition
she died of ovarian cancer at 37
Watson and Crick
developed a model which fit previous observations and Franklin’s borrowed X-ray diffraction pattern
DNA is like a twisted ladder with sugar-phosphate sides and hydrogen-bonded nitrogenous bases as rungs
the model allowed for variation of base composition, but %A = %T, and %G = %C
Watson, Crick, and Wilkins received the Nobel Prize
Cohen and Boyer
created the first transgenic organism
Cohen was a plasmid specialist and developed a bacterial plasmid
Boyer studied restriction enzymes and figured out how to insert a frog gene
they transformed E. coli with their recombinant plasmid and developed a bacterial culture that expressed the frog gene and passed it on
Boyer’s company Genentech cloned the human insulin gene into a bacterium, creating the biotech industry
Venter and Collins
Venter’s company Celera and Collin’s National Institute of Health team co-published a first draft of the human genome
Venter destroyed the genome of a host bacterium and replaced it with his own synthetic minimal genome, thus inventing the first artificial bacterial species and creating the field of synthetic biology
