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Lecture 23

BIO 1801 Lecture 23: Lecture 23 Bio 1801

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Appalachian State University
BIO 1801
Ray S.Williams

Clicker Question: Which is true of the lagging stand in DNA? discontinuous, 5’ to 3’ Clicker Question: Which is true of an Okazaki fragment? found on the lagging strand, goes from 5’ to 3’ Clicker question: Telomerase function is related to cancer in what way? Its activity level allows cells to live longer • Beadle and Tatum conclude that single gene controls synthesis of a single enzyme ◦ one gene - one enzyme (polypeptide hypothesis) ▪ all genes do not make enzymes ◦ DNA is responsible for making proteins • Central Dogma of Gene Expression ◦ transcription ▪ produces an RNA copy or transcript of a gene ◦ translation ▪ process of synthesizing specific polypeptide on a ribosome • Bacteria ◦ transcription and translation in cytoplasm • other organisms ◦ transcription occurs in the nucleus, translation occurs in the cytoplasm • DNA determines the sequence of proteins • There are 20 possible amino acids • Transcription analogy ◦ cookbook = genome ◦ take out one of those recipe from the cook book = message Process of Transcription ◦ promoter regulatory sequence transcribed region terminator • Stretch of DNA with amino acids, this is called the transcribed region • promoter says where to start transcribing • terminator says where to start • regulatory sequence, controls the process / how fast it goes ◦ promoter regulatory sequence transcribed region terminator • Step I: The piece of DNA is transcribed on to mRNA - messenger RNA 3 step process of transcription ◦ RNA- polymerase, enzyme that puts the sequence together in the mRNA • Initiation ◦ protein called sigma factor attaches to the RNA polymerase, which initiates attachment to the promoter • Enlongation ◦ RNA polymerase rides along DNA as it unwinds while it is copying • Termination ◦ says stop transcribing • note that there are no T’s in mRNA • always goes from 5’ to 3’ Transcription factors: other molecules that have to attach to portions of the DNA to control the process • Direction of transcription and DNA used varies among genes • In all cases, synthesis of RNA transcription is 5’ to 3’ and DNA template strand reads 3’ to 5’ • Orientation of the DNA determines which strand is copied
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