by123 chapter 17 - CHAPTER 17: FROM GENE TO PROTEIN •...

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Unformatted text preview: CHAPTER 17: FROM GENE TO PROTEIN • Proteins are the link between genotype and phenotype • Transcription- the synthesis of RNA under the direction of DNA (DNA to RNA, takes place in the nucleus) • mRNA- RNA that carries a genetic message from the DNA to the protein-synthesizing machinery of the cell • Translation- the synthesis of a polypeptide, which occurs under the direction of mRNA (RNA to protein, takes place on ribosomes) • Central dogma- DNA RNA protein • In prokaryotes, which lack a nucleus, mRNA is produced by transcription is immediately translated without additional processing • In a eukaryotic cell, the nucleus provides a separate compartment for transcription. The original RNA transcript, called pre- mRNA, is processed in various ways before leaving the nucleus as mRNA. • Primary transcript- initial RNA transcript from any gene, including those coding for RNA that is not translated into protein • Triplet code- the genetic instructions for a polypeptide chain are written in the DNA as a series of three-nucleotide words • During transcription, the gene determines the sequence of bases along the length of an mRNA molecule o For each gene, only one of the two DNA strands is transcribed. This strand is called the template strand. o mRNA is read from 5’ to 3’ o RNA molecule is synthesized in an anti-parallel direction to the template strand of the DNA • The genetic code is used for most organisms- bacteria can be programmed by the insertion of human genes to synthesize certain human proteins for medical use, such as insulin • TRANSCRIPTION o RNA polymerase pries the two strands of DNA apart and joins the RNA nucleotides as they base-pair along the DNA template in the 5’ to 3’ direction o RNA polymerases do not need a primer o Promoter- The DNA sequence where RNA polymerase attaches and initiates transcription o Terminator- the DNA sequence that signals the end of transcription in bacteria o Transcription unit- the stretch of DNA that is transcribed into an RNA molecule o Initiation- after an RNA polymerase binds to the promoter, the DNA strands unwind, and the polymerase initiates RNA synthesis at the start point on the template strand A eukaryotic promoter includes a TATA box, a nucleotide sequence including TATA, about 25 nucleotides upstream from the transcriptional start point Several transcription factors, one recognizing the TATA box, must bind to the DNA before RNA polymerase II can do so...
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This note was uploaded on 08/07/2009 for the course BY 123 taught by Professor Cusic during the Spring '07 term at University of Alabama at Birmingham.

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by123 chapter 17 - CHAPTER 17: FROM GENE TO PROTEIN •...

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