Dylan_8

Most challenging words 1. chargaff 2. analyzed 3. nitrogenous 4.concluding 5. purines 6. pyrimidines 7. parent. 8. replicating 9. mutations 10. deciphering

Passage: The Structure of DNA __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. 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.

__**Questions:**__ 1. Recall what DNA must carry, contain, and be. It carries information from parent to daughter 2. Clarify why Watson and Crick gathered data about DNA. They wanted to develope of a dna molecule 3. Compare and contrast purines and pyrimidines. Pyrimidines are cytosine and cytosine is not.