Wade_8

1.Nitrogeneous 2.pyrimidines 3.deciphering 4.photomicrographs 5.helically 6.cytosine 7.thymine 8.purines 9.adenine 10.helix __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.
 * Most Challenging Words**
 * The Structure of DNA**
 * __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.//DNA transfers information from parent cell through daughter cell.DNA has information of replicating itself.DNA has a chemically stable, realtively unchanging.//

2. Clarify why Watson and Crick gathered data about DNA. //Watson & Crick got information for to build a dna model.//

3. Compare and contrast purines and pyrimidines. //pyrimidines are cytosine & Purines are Adenine.//