Griffith’s Transformation Experiment
Fredrick Griffith was a medical officer that performed experiments with several different strains of the bacteria Diplococcus pneumoniae. Some he founded to be virulent which could cause pneumonia in certain vertebrates such as mice and humans and others were avirulent strains which did not cause any illness. The difference in virulence is due to the polysaccharide capsule of the bacterium: virulent strains have this capsule and avirulent do not. Virulent strains are not readily engulfed by the phagocytic cells present in the organism’s body as the avirulent strains, thus they are able to multiply and cause pneumonia. The capsule also allows the differentiation of the avirulent and virulent strains as the avirulent strains produce rough colonies (R) and the virulent produce smooth colonies (S). Griffiths used types II and III pneumonia in his experiments. He knew from the work of others that only living virulent cells would produce pneumonia in mice. If heat killed virulent bacterial cells were injected into mice then, no illness would result just like the avirulent cells. Thus Griffith performed an experiment whereby he injected into the mice living IIR (avirulent) cells com
As this interpretative figure indicates, their results show that DNA molecules are not degraded and reformed from free nucleotides between cell divisions, but instead, each original strand remains intact as it builds a complementary strand from the nucleotides available to it. This is called semi-conservative replication because each daughter DNA molecule is one-half "old" and one-half "new". bined heat-killed IIIS (virulent) cells. Since neither killed the mice, Griffith expected the double injection not to kill the mice; however the mice that received the double injections were all dead. When their blood cells were analyzed, a large number of living type IIIS (virulent) bacteria. The control mice living with the avirulent IIR bacteria for this experiment did not develop pneumonia and remained healthy. From this it was concluded that it couldn’t have been the avirulent IIR cells had mutated. Griffith concluded that the heat-killed IIIS bacteria was somehow responsible for the converting the live avirulent IIR cells into the virulent IIIS ones. He called this phenomenon transformation and that the transforming principle might be apart of the polysaccharide capsule or some
Some topics in this essay:
Meselson Stahl,
II III,
Fredrick Griffith,
Erwin Chargaff,
Chargaff's Rule,
Proof DNA,
ammonium ions,
virulent strains,
avirulent strains,
cause pneumonia,
avirulent iir,
residue proportional amount,
avirulent virulent strains,
proportional amount,
avirulent iir cells,
chargaff’s rule,
polysaccharide capsule,
mice living,
avirulent virulent,
ammonium ions 14nh4+,
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Approximate Word count = 799
Approximate Pages = 3 (250 words per page double spaced)
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