Jared_8

"Most Challenging Words" 1.nitrogenous 2.purines 3.pyrimidines 4.deciphering 5.diffraction 6.crystalline 7.helically 8.helix 9.phosphate 10.molecule

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.
 * 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.
 * 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/.

__**Questions:**__ 1. Recall what DNA must carry, contain, and be. //**It must carry information from mother to daughter.**// 2. Clarify why Watson and Crick gathered data about DNA. //**They gathered all the information they could to develop a model for DNA structure.**// 3. Compare and contrast purines and pyrimidines. //**Th****e bases are complementary, with A on one side of the molecule you only get T on the other side, similarly with G and C.**//