Pheoba_8

__** 10 Most Challening Words. **__
 * Lesson # 8: **
 * 1. Nitrogenous **
 * 2. Pyrimidines **
 * 3. Replicating **
 * 4. Mutational **
 * 5. Photomicrographs **
 * 6. Helically **
 * 7. Sugar-phosphate **
 * 8. Deciphering **
 * 9. Cytosine **
 * 10. Thymine **

‍‍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. -DNA must carry information cells from parent to child and contain info.- 2. Clarify why Watson and Crick gathered data about DNA. -They wanted to creat a model. 3. Compare and contrast purines and pyrimidines. -Purines are info, while pyrimidines carry the info.-