9- Molecular Strucutre of DNA and RNA

9- Molecular Strucutre of DNA and RNA - Chapter 9 Molecular...

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Chapter 9 Molecular Structure of DNA and RNA I. Identification of DNA as the Genetic Material a. Molecular genetics: the study of DNA structure and function at the molecular level, goal to use DNA structure to understand how it functions as the genetic material b. Genetic material must meet this criteria i. Information: that necessary to construct an entire organism, all that determines inherited traits ii. Transmission: in reproduction genetic material must be passed to offspring iii. Replication: must be copied during cell division iv. Variation: that accounts for known phenotypic differences within each species c. August Weismann and Karl Nageli: chemical substance within living cells is responsible for the transmission of traits from parents to offspring i. Developed chromosome theory of inheritance to show chromosomes are carriers of the genetic material d. Experiments with Pneuococcus Suggested that DNA is the Genetic Material i. Frederick Griffith studied bacterium known as pneumococci then and now called Streptococcus pneumoniae 1. certain strains secrete a polysaccharide capsule while other strains do not ii. capsule secreting strains have a smooth colony morphology and non capsule have a rough appearance iii. in smooth strains, their chemical composition can differ 1. type II smooth strain and type III both make a capsule but differ biochemically iv. smooth can be mutated into rough and vice versa v. type III smooth can mutate to become a rough strain, and can mutate back but only to a type III smooth strain vi. 1928: used type IIIS and type IIR to inject into a live mouse 1. type IIIS proliferated and killed the mouse, capsule prevented mouse’s immune system from killing bacterium 2. type IIR did not cause a lethal infection 3. heat killed type IIIS also did not kill the mouse 4. live type IIR mixed with heat killed type IIIS kills the mouse a. extracted tissue of mouse contained living type IIIS (transformation of the type IIR into type IIIS occurred due to something from the dead type IIIS) vii. transformed bacteria acquired the information to make a type III capsule, then it is replicated so it can be transmitted from mother to daughter cells viii. Oswald Avery, Colin MacLeod, and Maclyn McCarty realized that Griffith’s observations could help identify the genetic material, asked What substance is being transferred from the dead type IIIS to the live type IIR 1. used biochemical purification procedures and prepared bacterial extracts from the type IIIS strains from each type of molecule (DNA, RNA, proteins and carbohydrates)
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This note was uploaded on 04/07/2008 for the course BIO 325 taught by Professor Saxena during the Spring '08 term at University of Texas at Austin.

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9- Molecular Strucutre of DNA and RNA - Chapter 9 Molecular...

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