LEC02A.PPT [Compatibility Mode]

LEC02A.PPT [Compatibility Mode] - Last time Griffith...

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Last time: ! Griffith experiment and Avery et. al. experiments, ! Transforming agent is DNA ! Not accepted universally ! Did open scientific thought to the possibility that DNA may be the chemical associated with “genes” ! Stimulated experiments in other systems to confirm or refute this finding ! Hershey Chase Experiment Hershey-Chase Experiment ! Radioisotopes ! bacteriophage ! DNA Structure ! Hybridization
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Elements are defined by the number of protons they possess Electrons = protons in non-ionized forms Radioisotopes #Neutrons can vary leading to different isotopes Additional radioisotopes used in Molecular Biology: P 15 32 - important for labeling nucleic acids and phosphorylated proteins mass # atomic # S 16 35 - important for labeling proteins
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Radioactive decay ! Various particles are emitted ( ! i l eg. !" particles, # - rays , etc ) ! Several detection methods are available ! geiger counters (emissions in air) ! scintillation counters (radioactive emissions are converted to light) ! autoradiography (X-ray film) autoradiogram Most biological radioisotopes are beta-emitters ! Equivalent to an electron ! Vary in energy ! 3 H- low energy ! 32 P-high energy ! Half-life (t 1/2 )- time at which 1/2 of substance has decayed ! 3 H-12.3 years ! 32 P-14.3 days
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Viruses that infect bacteria are called bacteriophages ! Viruses are parasites! ! Depend on host cell for energy, enzymes, etc. ! Step 1: enter cell ! Step 2: reproduce inside of cell ! Step 3: release progeny from cell
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Hershey-Chase, 1952 L b l b t i h T2 ith t ! Label bacteriophage T2 with two different radioisotopes ! 32 P - label DNA !
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