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Test 4 - BSC 2010 Exam 4 Notes Fall 2010 Chapter 16 The...

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BSC 2010 Exam 4 Notes Fall 2010 Chapter 16: The Molecular Basis of Inheritance Need to know: Scientists’ Biographies, their experiments in detail, DNA replication - What was known in 1950 : They knew that hereditary material was located on the chromosomes. Chromosomes are composed of 2 things: protein and DNA. Most people thought proteins contained genetic material because they were more diverse than DNA (since DNA only has 4 nucleotides, ATGC) - Alfred Hershey & Martha Chase (1952) o Discovered that DNA, not protein, is the genetic material of life o Studied the virus bacteriophage T2 Infects E.coli Instead of E.coli making more E.coli, T2 reprograms it to produce T2 phages o Why did they study a virus ? Virus only has 2 things: DNA surrounded by protein coat o Their Question: Which viral component was responsible for reprogramming the host bacterial cell? The protein or the DNA? They answered the question by devising an experiment that showed that only 1 component actually enters E.coli during infection. o Their Experiment: [See Fig 16.4] STEP 1: In separate dishes, label viral protein with radioactive sulfur and viral DNA with radioactive phosphorous *Know that protein was tagged with radioactive sulfur *Know that DNA was tagged with radioactive phosphorous STEP 2a: Allow protein labeled phages to infect E.coli STEP 2b: Allow DNA labeled phages to infect E.coli STEP 3: Blend the cultures, this shakes the loose phage components outside the bacterial cells (DNA inside cell) STEP 4: Spun it really hard in a centrifuge, heavier bacterial cells collected in a pellet at the bottom of the centrifuge tube RESULTS: Radioactive phosphorous ended up in the DNA labeled pellet, meaning DNA reprogrammed the host cell to produce more viruses. o Conclusion: Only DNA actually enters the cell, while proteins remain outside the cell o Nobel Prize: 1969 - Circumstantial evidence to support this theory for eukaryotes: o Cell doubles its DNA prior to mitosis o During mitosis, doubled DNA is equally divided into daughter cells o Diploid cells have 2x DNA - Erwin Chargaff (Biochemist) o Compared number and ratio of nitrogenous bases in many eukaryotes (how many A/T/G/C?
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