12- Gene Transcription and RNA Modification

12 Gene - Chapter 12 Gene Transcription and RNA Modification I Overview of Transcription a Gene Expression Requires Base Sequences That Perform

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Chapter 12: Gene Transcription and RNA Modification I. Overview of Transcription a. Gene Expression Requires Base Sequences That Perform Different Functional Roles i. A gene is a transcriptional unit; it can be transcribed into RNA ii. Promoter: sequences provides a site to begin transcription iii. Terminator: specifies the end of transcription iv. Promoter and terminator cause RNA synthesis to occur within a defined location v. For structural genes that encode proteins, the nontemplate DNA strand is the coding strand or the sense strand vi. Regulatory sequences: those involved in regulation of gene expression, act as bindin sites for genetic regulatory proteins vii. Ribosomal-binding site: in bacteria, short sequences provides a location for the ribosomes to recognize and begin translation 1. ribosome recognizes it because it has a complementary sequences to it viii. to synthesize a polypeptide, sequence of nucleotides within the mRNA is read as groups of three nucleotides, codons 1. first codon near the ribosomal binding site is the start codon, stop codon ends translation b. The three stages of transcription are initiation, elongation, and Termination i. Initiation: recognition step 1. sequence of bases within the promoter region is recognized by proteins called transcription factors, the transcription factors bind here 2. closed promoter complex: initial binding of transcription factors and RNA polymerase to the promoter when DNA is still in a double helix ii. Elongation: synthesis of the RNA transcript 1. open promoter complex, open complex: separated DNA strands allowing one of the two to be used as a template for synthesis of a complementary strand of RNA, creates a small bubblelike structure iii. termination 1. RNA polymerase and the newly made RNA transcript dissociate from DNA at the termination sequence c. RNA Transcripts have different functions i. Structural gene transcribes into mRNA (messenger RNA), 90% of genes ii. mRNA: functions to specify the amino acid sequence of a polypeptide, uses its codon sequence in translation to make a polypeptide iii. nonstructural genes: encode for different RNAs 1. RNA transcript can become part of a complex that contains both protein subunits and one or more RNA molecules a. Ex. Protein- RNA complexes include: ribosomes, signal recognition particles, spliceosomes, certain enzymes like RNaseP II. Transcription in Bacteria a. A Promoter is a short sequence of DNA that is necessary to initiate transcription i. Much of the promoter region is located just upstream from the site where transcription of a gene actually begins, the bases in a promoter are numbered in relation to the transcriptional start site 1. first base used as a template for RNA transcription is denoted +1, the bases preceding are in a negative direction, no base is numbered 0 2. several dozen nucleotides in length ii. sequence elements 1. short, critical for promoter recognition, necessary to create a functional promoter, occur at certain
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This note was uploaded on 04/07/2008 for the course BIO 325 taught by Professor Saxena during the Spring '08 term at University of Texas at Austin.

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12 Gene - Chapter 12 Gene Transcription and RNA Modification I Overview of Transcription a Gene Expression Requires Base Sequences That Perform

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