chapter 7 Flashcards
(6 cards)
hershey and chase
mid 1900s scientists = unsure if DNA or protein is genetic material of cell
known viruses consist of DNA + protein coat and could transfer genetic material to host
1952 Hershey and chase
conducted experimentsto prove dna was genetic material
hershey and chase experiment
virus (T2 bacteriophage) grown in 1 or 2 isotopic mediums to radioactively label a viral component
Viruses grown in radioactive sulfur (35S) had radiolabelled proteins (sulfur is present in proteins but not DNA)
Viruses grown in radioactive phosphorus (32P) had radiolabeled DNA (phosphorus is present in DNA but not proteins)
viruses then allowed to infect e. coli and then virus and bacteria were. separated by centrifugation
larger bacteria formed solid pellet while smaller viruses remained in supernatant
bacterial pellet found to be radioactive when infected by 32P-viruses (DNA) but not 35S- viruses because DNA WAS TRANSFERRED TO BACTERIA
Rosalind Franklin and Maurice Wilkins investigation of DNA structure by X ray diffraction
Dna purified and fibres were stretched in thin glass tube (to make most strands parallel)
Dna targeted by X ray beam which was diffracted when it contacted an atom
scattering of X ray was recorded on film used to elucidate details fo molecular structure
from scattering pattern produced by Dna molecule certain conclusions can be made abt structure
composition: dna = double stranded molecule
orientation: nitrogenous bases =closely packed together on inside and phosphates from outer backbone
shape: dna molecule twists at regular intervals to form helix (two strands=double helix)
franklins diffraction data was shared by wilkins with james watson and francis crick who
used franklins info to create molecular model of basic structure of dna
