Brian_8

most challeging words 1 nitrogenous 2 pyrimidines 3 mutations 4 deciphering 5 photomicrographs 6 crystalline 7 hydrogen 8 Cytosine 9 Thymine 10 helix 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 __mutation__s, there would be /no process of evolution. Many __scientist__s 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. A bunch of DNA carries information through out the cells. 2. Clarify why Watson and Crick gathered data about DNA. Well they just wanted to look smart and get some money. 3. Compare and contrast purines and pyrimidines They are diffrent because they are spelled diffrently