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BSC 219 (22)
mortimer (22)
Lecture 11

BSC 219 Lecture 11: Genetics Lec 11
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Department
Biological Sciences
Course Code
BSC 219
Professor
mortimer

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They knew that A series of experiments were performed to understand how DNA was used to make a protein DNA is in the nucleus Ribosomes are in the cytoplasm RNA is made in the nucleus RNA moves to the cytoplasm Frederick Griffith performed an amazing experiment in 1927 Using mice and two different strains of the bacteria Streptococcus pneumoniae FREDERICK GRIFFITH EXPERIMENT Injected mice with Streptococcus pneumoniae strain IIIS (smooth strain) Mice died The IIIS (smooth) strain is virulent FREDERICK GRIFFITH EXPERIMENT Injected mice with Streptococcus pneumoniae strain IIR (rough strain) Mice lived The IIR (rough) strain is avirulent FREDERICK GRIFFITH EXPERIMENT Injected mice with "heat-killed" S. pneumoniae strain IIIS Mice lived Virulence factor was destroyed by the heat FREDERICK GRIFFITH EXPERIMENT Injected mice with "heat-killed" S. pneumoniae strain IIIS and live IIR Mice died A mixture of live IIIS and IIR colonies recovered from dead mice Virulence factor wasn’t really destroyed but needed live bacteria FREDERICK GRIFFITH EXPERIMENT Something from the heat-killed IIIS bacteria transformed avirulent IIR bacteria into virulent IIIS bacteria à the "transforming principle” BACTERIOPHAGE Life cycle starts when bacteriophage adsorbs onto the bacterial cell host HERSHEY CHASE EXPERIMENT The substance entering cell must include the viral genetic material Does protein, DNA, or both enter the cell? Infection results in production of virus inside host cell HERSHEY CHASE EXPERIMENT Two radioactive isotopes: 32P and 35S Designed experiments to determine identity of material that entered the bacterial cell Bacteriophage T2 Escherichia coli (E. coli) 32P - is incorporated into DNA, not protein 35S - is incorporated into protein, not DNA HERSHEY CHASE EXPERIMENT If there is radioactive protein inside the bacteria, then the bacteriophage is injecting in protein into the bacteria Does the DNA or the protein go inside the bacteria? If there is radioactive DNA inside the bacteria, then the bacteriophage is injecting in DNA into the bacteria HERSHEY CHASE EXPERIMENT HERSHEY CHASE EXPERIMENT Infected bacteria produced new phage that were NOT radioactive 35S-labeled phage results Infected bacteria were NOT radioactive Phage ghosts (empty protein shell) WERE radioactive HERSHEY CHASE EXPERIMENT Infected bacteria produced new phage that were radioactive 32P-labeled phage results Infected bacteria WERE radioactive Phage ghosts (empty protein shell) were NOT radioactive VOLKIN EXPERIMENT VOLKIN EXPERIMENT In 1958, Elliot Volkin and colleagues tested if bacteriophage infection causes the production of new RNA Moved healthy E. coli to medium with 32P which will get incorporated into new RNA being made VOLKIN EXPERIMENT They isololated the newly transcribed RNA (which is radioactive) and tested if it came from the bacteria or the bacteriophage p32 + p32 new RNA Bacterial or viral? VOLKIN EXPERIMENT p32 new RNA The RNA came from the bacteriophage, and not the E. coli This means that the new RNA produced in the infected bacterial cell was transcribed from the bacteriophage DNA VOLKIN EXPERIMENT The timing: phage DNA enters cell then phage RNA is produced then phage proteins are made Phage RNA production began after infection and before production of phage protein This suggests that RNA is an intermediate between DNA and protein BRENNER, JACOB, AND MESELSON Late 1950s; Brenner, Jacob, and Meselson perform
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