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Transcription is tightly regulated in all cells. In prokaryotes, only 3% or so of the genes are undergoing transcription at any given time. The metabolic conditions and the growth status of the cell dictate which gene products are needed at any moment. Similarly, differentiated eukaryotic cells express only a small percentage of their genes in fulfilling their biological functions, not the full genetic potential encoded in their chromosomes. | Chapter 31 Transcription and Regulation of Gene Expression to accompany Biochemistry, 2/e by Reginald Garrett and Charles Grisham All rights reserved. Requests for permission to make copies of any part of the work should be mailed to: Permissions Department, Harcourt Brace & Company, 6277 Sea Harbor Drive, Orlando, Florida 32887-6777 Outline 31.1 Transcription in Prokaryotes 31.2 Transcription in Eukaryotes 31.3 Regulation of Transcription in Prokaryotes 31.4 Transcription Regulation in Eukaryotes 31.5 Structural Motifs in DNA-Binding Proteins 31.6 Post-Transcriptional Processing of mRNA The Postulate of Jacob and Monod Before it had been characterized in a molecular sense, messenger RNA was postulated to exist by F. Jacob and J. Monod. Their four properties: base composition that reflects DNA heterogeneous with respect to mass able to associate with ribosomes high rate of turnover Other Forms of RNA rRNA and tRNA only appreciated later All three forms participate in protein synthesis All made by DNA-dependent RNA polymerases This process is called transcription Not all genes encode proteins! Some encode rRNAs or tRNAs Transcription is tightly regulated. Only 0.01% of genes in a typical eukaryotic cell are undergoing transcription at any given moment How many proteins is that??? Transcription in Prokaryotes Only a single RNA polymerase In E.coli, RNA polymerase is 465 kD complex, with 2 , 1 , 1 ', 1 ' binds DNA binds NTPs and interacts with recognizes promoter sequences on DNA subunits appear to be essential for assembly and for activation of enzyme by regulatory proteins Stages of Transcription See Figure 31.2 binding of RNA polymerase holoenzyme at promoter sites initiation of polymerization chain elongation chain termination Binding of polymerase to Template DNA Polymerase binds nonspecifically to DNA with low affinity and migrates, looking for promoter Sigma subunit recognizes promoter sequence RNA polymerase holoenzyme and promoter form "closed . | Chapter 31 Transcription and Regulation of Gene Expression to accompany Biochemistry, 2/e by Reginald Garrett and Charles Grisham All rights reserved. Requests for permission to make copies of any part of the work should be mailed to: Permissions Department, Harcourt Brace & Company, 6277 Sea Harbor Drive, Orlando, Florida 32887-6777 Outline 31.1 Transcription in Prokaryotes 31.2 Transcription in Eukaryotes 31.3 Regulation of Transcription in Prokaryotes 31.4 Transcription Regulation in Eukaryotes 31.5 Structural Motifs in DNA-Binding Proteins 31.6 Post-Transcriptional Processing of mRNA The Postulate of Jacob and Monod Before it had been characterized in a molecular sense, messenger RNA was postulated to exist by F. Jacob and J. Monod. Their four properties: base composition that reflects DNA heterogeneous with respect to mass able to associate with ribosomes high rate of turnover Other Forms of RNA rRNA and tRNA only appreciated later All three forms participate in protein synthesis
