Garette_8

the most challangeing words

1.nitrogenous 2.pyrimidines 3.evolution 4.photomicrographs 5.crystalline 6.helically 7.phosphate 8.adenine 9.purines 10.cytosine

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 __mutationa__l 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.__**dna must be carried from both parents.**__3. Compare and contrast purines and pyrimidines.**__they are both extracted from dna.__** 2. Clarify why Watson and Crick gathered data about DNA.**__attempted to develop a model of dna__**