Morgan_8

__** 1.nitrogenous **__ __** 2.purines **__ __** 3.pyrimidness **__ __** 4.repicating **__ __** 5.mutational **__ __** 6.deciphering **__ __** 7.crystalline **__ __** 8.helically **__ __** 9.helix **__ __** 10.cytosine **__ Passage: The Structure of DNA Many scientists were interested in deciphering /the structure of __**DNA**__, among them were __**Francis Crick, James Watson, Rosalind Franklin, and Maurice Wilkens.**__ **__Watson and Crick__** /gathered all available data in an attempt to develop a model /of DNA structure. __**Franklin**__ took X-ray diffraction photomicrographs of crystalline /**__DNA__** extract, the key to the puzzle. /The data known at the time was that **__DNA__** /was a long molecule, and proteins were helically coiled./ __**DNA**__ is a double helix/, with bases to the center (like rungs on a ladder)/ and sugar-phosphate units along the sides of the helix /(like the sides of a twisted ladder). __**The strands**__ are complementary /(deduced by Watson and Crick from Chargaff's data, A pairs with T and C pairs /with G, the pairs held together by hydrogen bonds). /**__Purines__** are Adenine (A) and Guanine (G). Pyrimidines are Cytosine (C) and Thymine (T). /**__The bases__** are complementary/, with A on one side of the molecule you only get/ T on __**the other side**__, similarly with G and C. If we know the base sequence of one strand we know its complement.
 * Erwin Chargaff** analyzed the nitrogenous bases /in many different forms of life, /concluding that the amount of purines/ does not always equal the amount of pyrimidines/ (as proposed by Levene). __**DNA**__ must carry information from parent cell/ to daughter cell. __**It**__ must contain information for replicating itself**./** **__It__** must be chemically stable, relatively unchanging/. However, __**it**__ must be capable of mutational change./ Without **__mutations__**, there would be no process of __**evolution**__.

__**Questions:**__ 1. Recall what DNA must carry, contain, and be. carry info to mommy and daddy cells,it must contain info to make more or itself,must be chemically stable.

2. Clarify why Watson and Crick gathered data about DNA. the to guys got info to make a model of DNA.

3. Compare and contrast purines and pyrimidines purines are adenine and pyrimidines are cytosine.