AP Biology Notes - Ch. 16 & 20

AP Biology Notes - Ch. 16 & 20 - TEXTBOOK...

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TEXTBOOK ASSIGNMENT Chapter 16 1. In 1902, Sutton and Boveri studied eukaryote chromosomes and noted that they behaved in a manner similar to the way Mendel described the segregation of alleles. Their work lead to the chromosome theory which states that chromosomes are the unities of heredity. Chemical analysis determined that chromosomes were composed of 50% proteins (histones) and 50% DNA. Explain how the Hershey and Chase experiment contributed to the determination of what was the heredity material in chromosomes. Avery and his colleagues Maclyn McCarty and Colin MacLeod announced that the transforming agent was DNA. Their discovery was greeted with interest but considerable skepticism, in part because of the lingering belief that proteins were better candidates for the genetic material. Moreover, many biologists were not convinced that the genes of bacteria would be similar in composition and function to those of more complex organisms. But the major reason for the continued doubt was that so little was known about DNA. Once T. H. Morgan’s group showed that genes are located on chromosomes, the two chemical components of chromosomes, which were DNA and protein became the candidates for the genetic material. Until the 1940s, the case for proteins seemed stronger, especially since biochemists had identified them as a class of macromolecules with great heterogeneity and specificity of function, essential requirements for the hereditary material. A key factor in determining the identity of the genetic material was the choice of appropriate experimental organisms. The role of DNA in heredity was first worked out by studying bacteria and the viruses that infect them, which are far simpler than pea plants, fruit flies, or humans. Griffith had two strains of the bacterium, a pathogenic (disease–causing) one and a nonpathogenic, harmless, strain. When he killed the pathogenic bacteria with heat and then mixed the cell remains with living bacteria of the nonpathogenic strain, some of the living cells became pathogenic. This new trait of pathogenicity was inherited by descendants of the new bacteria. Clearly, some chemical component of the dead pathogenic cells caused this heritable change, although the identity of the substance was not known. Griffith called the phenomenon transformation- change in genotype and phenotype due to the assimilation of external DNA by a cell. 2. Produce a chart which describes the structure of each type of nucleotide Nitrogenous base An organic compound that owes its property as a base to the lone pair of electrons of a nitrogen atom. Notable nitrogenous bases include pyrimidine and purine bases, the nucleobases (building blocks of DNA and RNA): adenine, guanine, thymine, cytosine, and uracil.
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