Ch 7 Notes Part I - Chapter7 Lecturenotes...

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Chapter 7   Lecture notes Hereditary material Biologists hypothesized that hereditary material should have the following three properties: 1.  Have information content. 2.  Allow relatively faithful replication to provide for the kind of stability necessary. 3.  Allow for rare changes in the information content that are capable of permanence.   The development of the hypothesis that DNA is the genetic material. By the 1930’s  biologists began to speculate as to what sort of molecules could have these  properties. Protein and not DNA was thought to be the genetic material just prior to the DNA hypothesis for  two reasons. 1.  Biologists believed that the genetic material would have to be complex  to carry all the  information to code for all the various life forms.  Biologists knew that protein was more complex than DNA because they were aware that protein  is composed of 20 different monomers (amino acids) and that DNA was composed of only 4 monomers (The A, T, C, and G nucleotides). 2.  Biologists also reasoned that the genetic material would need to be present in all parts of the  cell (ubiquitous) in order to control all the activities of the cell. Biologists knew that protein was found in all portions of the cell and that the DNA was found  primarily in the nucleus. Until the mid-1940’s there appeared to be no method to directly approach the question of the  gene’s chemical structure. Therefore, biologists began to approach the nature of the gene by attempting to determine how  genes function within cells. The first clues as to how genes function came from studies of humans. Early in the twentieth century  Archibald E. Garrod , an English physician, (p 187) hypothesized 
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that several human diseases show metabolic defects in the metabolism. -The function of the gene is to control metabolism. -Some humans diseases have a genetic cause. He coined the idea that these defects were “inborn errors in metabolism.” Garrod’s observations focused attention on metabolic control as a primary way in which genes  function. In the  early 1940’s , research on the mold  Neurospora , spearheaded by  George Beadle  and  Edward Tatum , was generating observations congruent with Garrod’s hypothesis that genes  work by controlling the synthesis of specific enzymes. -They mutated Neurospora and observed that mutations affected metabolism. Various growth mutants of  Neurospora   obtained from a screen seeking abnormal morphology.
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