DNA evidence Flashcards
How can cells show that they are undergoing active protein synthesis?
Many ribosomes typically bind to the same strand of mRNA to form larger complexes, called polyribosomes. They are intensely basophilic due to the large number of phosphate groups on the RNA molecules, thus stain bright blue with hematoxylin and basic dyes.
How was the phosphodiester bond between nucleotides proven?
Agents- alkali and enzymes- added that are known to be specific to phosphodiester bonds. Run through electrophoresis, different nucleotides will separate.
Watson and Crick’s experiment
Used X-ray diffraction analysis of crystallised DNA to determine the double helix structure
How was Semi Conservative replication discovered?
Meselson Stahl
- two batches of bacteria grown in nitrogen medium
- one in N-15 heavy and one in N-14 light
- placed in the centrifuge
- DNA had separated to different positions depending on weight
- Heavy bacterial DNA lower down
- bacteria mixed and allowed to divide
- resulted in a middle layer of cells
How were lagging strands proven?
DNA allowed to replicate without DNA ligase, when heated and then placed in western blot, different masses were shown with then one very large one representing the leading DNA strand
Another experiment proving the existence of lagging strands
Sakabe and Okazaki pulse labelled newly replicated areas of chromosomes, denatured and then extracted the DNA, large number of radioactive short units suggested that the process is discontinuous
How are the different RNA Polymerases identified?
Add amanitin, a toxin produced by amanita phalloides.
RNA polymerase I is insensitive to the toxin
RNA polymerase II is completely inhibited
RNA polymerase III is only affected at high concentrations of the toxin
