Chapter 12 Study Guide

Chapter 12 Study Guide - Study Guide 12 UNIT III...

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Study Guide 12 UNIT III: - Meiosis (and Genetic Variation) - Mendel & the Gene (linkage and crossing over) - How Do Genes Work ( DNA = genes; the genetic code) - DNA Synthesis ... (Replication) - Transcription and Translation - Control of Gene Expression in Bacteria - Control of Gene Expression in Eukaryotes A. Different RNAs 1. Cells make three major kinds of RNA : mRNA, rRNA and tRNA. All three participate in decoding the information in genes into polypeptides. mRNA : codes for polypeptides; tRNA : actually decodes mRNA: its folded “clover-leaf “structure contains an anticodon complementary to a codon, and is bound to a corresponding amino acid (Fig. 16.14). rRNA : part of ribosome structure ; there are 3 (prokaryotes) or 4 (eukaryotes) different rRNAs associated with large and small ribosome subunits , e.g., the bacterial ribosome: B. Prokaryotic Transcription 32088. All RNA is synthesized from information (genes) in DNA by the process called transcription (see illustration at right and Fig. 16.1 ), in which an enzyme called RNA Polymerase recognizes and binds to a sequence of bases on DNA called the promoter . This allows the enzyme to begin transcription of the DNA into a molecule of RNA at the correct starting place (the initiation site ). Only one of the two strands of DNA is transcribed into an RNA molecule . The strand of DNA in a gene for a protein that is transcribed into an mRNA is called the coding strand . RNA transcripts are synthesized from their 5’ end to their 3' end. The basic process is illustrated here.
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32089. Prokaryotic and eukaryotic genes differ in their structure and organization in several key ways, summarized here: Genes for more than one protein may be transcribed as a single unit in bacteria ( Fig. 17.5 ), with translation of the different proteins from the same RNA molecule occurring at the same time: Of course, not all prokaryotic genes are organized in multiple gene operons, but those that are usually code for proteins of related function, allowing them to be controlled at the same time (see Chapter 17 & Study Guide 13). The synthesis of any polymer, RNA includes, can be seen as occurring in 3 steps, initiation, elongation and termination. In bacterial transcription initiation , a protein called sigma factor unites with RNA polymerase so that this dimmer protein recognizes a DNA sequence at the start of a gene, called the promoter ( Fig. 16.3 ). The sigma factor dissociates from the RNA polymerase after transcription has begun. Elongation is the successive addition of new nucleotides to a growing RNA molecule. Termination , or the end of transcription is signaled by the formation of a hairpin loop near the 3’ end of the nascent transcript ( Fig. 16.4 ). The hairpin loop (with or without the help of a termination factor protein) weakens the interaction between RNA polymerase and the template, so that transcription ends. C. Eukaryotic Transcription and Processing
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This note was uploaded on 11/22/2009 for the course BIO SCI 150 taught by Professor Geraldbergstrom during the Spring '08 term at Wisconsin Milwaukee.

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Chapter 12 Study Guide - Study Guide 12 UNIT III...

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