1323441843_CHAPTER_17_SPR

1323441843_CHAPTER_17_SPR - EVOLUTION/LECTURE1...

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EVOLUTION/LECTURE1 file:///E|/CH17-PRECAMBRIAN-SPRING-2008/CHAPTER%2017_SPR_2008.HTML[12/8/2011 2:57:27 PM] Evolution ( PCB 4674 ). Chapter 17. The origins of life and Precambrian evolution Main topics of lecture: I: The RNA world: 1.- Defining life 2.- Ribozymes as evidence for the origin of life 3.- The case for RNA as an early life form 4.- Self-replication II: How do we get to RNA?: 5.- The problem of moving from an abiotic to a biotic environment 6.- Where did the stuff of life come from? 7.- The Oparin-Haldane model 8.- From simple inorganic to the building blocks of life 9.- Early evidence of life III: When life went cellular: 10.- Early evidence of cells 11.- The phylogeny of all living things 12.- The origin of organelles I: The RNA world: 1.- Defining life 1.1.- All living organisms possess both a genotype and a phenotype. In fact, when we consider what life really is, and how living systems can be distinguished from non- living ones, the ability to store and transmit information (a genotype) and the ability to express that information (a phenotype) are perhaps the most important criteria that set life apart from nonlife. 1.2.- Unfortunately, there is no neat list of characters that define life. Most biologists would include traits like growth and reproduction on such a list, but they cannot agree on what else should be used to exclude such life-like systems as a growing salt crystal or a computer virus.
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EVOLUTION/LECTURE1 file:///E|/CH17-PRECAMBRIAN-SPRING-2008/CHAPTER%2017_SPR_2008.HTML[12/8/2011 2:57:27 PM] 1.3.- However, many now agree that the ability to evolve is a crucial component of any definition of life. Evolution - or change over time - requires both the ability to record and make alterations in heritable information, and some way of distinguishing valuable changes from detrimental ones. The former is carried out by the genotype , while the later is carried our by a phenotype . 2.- Ribozymes as evidence for RNA as an early life form 2.1.- In the early 1980s, two teams of scientists independently discovered small enzymes that could break and reform the chemical bonds that hold strings of nucleic acids intact. These enzymes are able to catalyze the breakage of a phosphodiester bond of other nucleotide molecules (most of the times mRNA). These enzymes are extremely important in the reactions of intron splicing, and splicing of precursors of tRNAs. 2.2.- However these enzymes were made not of protein , but of nucleic acid - specifically RNA. Until 1982, all known enzymes were proteins. RNA was often considered to be DNA's poor cousin, relegated to the task of shuttling biological information from DNA, where the information is stored, to proteins, which carry out all the work of the cell. 2.3.- The finding of RNA enzymes, or ribozymes has changed how biologists view the operations of the cell. Perhaps more importantly, the existence of ribozymes has forever changed how biologists view the origin of the first cells - how they believe life originated and evolved on the early Earth.
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