Chapter 5 Book Notes

Double helix dna bases hold key to hereditary a t c g

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Double helix DNA bases hold key to hereditary (A-T, C-G) DNA replication Conclusion: DNA is complex and probably was not the original hereditary molecule for life on Earth. DNA may have evolved from RNA. How is heredity encoded in DNA? Gene: instructions representing any individual function such as the instructions for building a single protein Noncoding DNA Genome: complete sequence of DNA bases in an organism, encompassing all of the organism’s genes as well as its noncoding DNA Genetic code: set of rules for reading DNA; read in triplets It is believed that early life forms used only a two-base language, which later evolved into the current three-base language of the genetic code Genetic code is same in almost all organisms on Earth RNA has a different backbone and uses U instead of T Conclusion: Suggest common origin . . . RNA carries out instructions encoded in DNA. How does life evolve? Mutation: any chance in the base sequence of an organism’s DNA If cell survives, mutation will be copied every time its DNA is replicated Conclusion: It seems a near certainty that any form of life anywhere else will have some molecule that plays the same functional role that DNA plays on Earth. What kinds of conditions can life survive? Volcanic vents – black smokers Archaea thrive in extremely hot water around black smokers and other vents Thermophiles – lovers of heat Hyperthermophiles – highest temperatures Extremophiles – lovers of the extreme; live without oxygen Psychrophiles – lovers of the cold Endoliths can live several km below surface of Earth in water that fills pores within rock Endospores – special “resting” cells produced by some bacteria Conclusion: Possibility that live could survive journeys aboard meteorites that are blasted off one planet and land on another. Are extremophiles really extreme? Extreme life appears to be much more the norm than is life that lives in an environment suitable to humans Conclusion: Any world containing an environment in which some type of extremophile might survive becomes a good candidate for the search for life. Is evolution a fact or a theory?
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Darwin’s theory captures main features of evolution but is not complete
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Double helix DNA bases hold key to hereditary A T C G DNA...

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