life 14 - BIO 315H Chapter 14 Life Chapter 14 Eukaryotic...

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BIO 315H Chapter 14 Life Chapter 14: Eukaryotic Genome and its expression II. Characteristics of Eukaryotic genes Eukaryotes differ from prokaryotes in the fact that: they have noncoding internal sequences and form gene families (groups of structurally and functionally related cousins within the genome) A. Protein coding genes contain noncoding sequences Eukaryotic RNP does not recognize promoter by itself, like a prokaryote enzyme, but requires help. It has a terminator, signaling the end of transcription -a terminator sequence is after the stop codon and signals the end of transcription by RNA polymerase. -A stop codon is within the coding region and, when transcribed into mRNA, signals the end of translation at the ribosome -nucleic acid hybridization is used to locate introns in eukaryotic genes, done by: 1. Target DNA is denatured to break the H bonds between base pairs and separate the two strands 2. A single-stranded nucleic acid from another source (called a probe) is incubated with the denatured DNA. If the probe has a base sequence complementary to the target DNA, a probe–target double helix forms by hydrogen bonding between the bases. Because the two strands are from different sources, the resulting double-stranded molecule is called a hybrid. black: mRNA blue: pre-mRNA B. Gene families are important in evolution and cel specialization About half of eukaryote protein coding genes exist in only one copy in haploid genome (2 copies in somatic cells) -gene family: closely related genes, a result of mutations. As long as 1 member has original DNA sequence, others can be mutated. The extra genes are important for experiments in evolution and if a mutated gene is useful, it may be selected for in succeeding generations. -differential gene expression: since all cells have genes, a cell S transcription and translation makes them different. It is significant because it also can produce certain proteins at certain points that are crucial in one’s life -pseudo genes: nonfunctional genes resulted from mutations that cause a loss of function. It lacks a promoter, so cannot be transcribed, or lack recognition sites to remove introns. Some pseudogenes are functional so they don’t go away as well. III. How eukaryotic gene transcripts processed? Transcript’s both ends of pre-mRNA modified and introns removed before leaving nucleus A. Primary transcript of a protein coding gene is modified at both ends -A G cap is added to the 5′ end of the pre-mRNA as it is transcribed. The G cap is a chemically modified molecule of guanosine triphosphate (GTP). It apparently facilitates the binding of mRNA to the ribosome for translation and protects the mRNA from being digested by ribonucleases that break down RNAs. -A poly A tail is added to the 3′ end of pre-mRNA at the end of transcription. Near the 3′ end of pre-
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This note was uploaded on 10/30/2008 for the course BIO 315H taught by Professor Payne during the Spring '08 term at University of Texas.

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life 14 - BIO 315H Chapter 14 Life Chapter 14 Eukaryotic...

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