2 I. Gene Regulation in Eukaryotes Transcriptional Controls1. Gene amplification2. Chemical ModificationPost-transcriptional ControlsTranslational Controls
3 A. Transcriptional Control 1. Gene Amplification: A gene sequence can be repeated many times on a DNA sequence…resulting in multiple mRNA transcripts, therefore more gene expression.
4 Different gene regions of a DNA molecule TRANSCRIPTIONDifferent gene regions of a DNA moleculemRNArRNAtRNATranscript processingproteinsmature mRNAsubunits for ribosomesmature tRNAconvergence of RNAsTRANSLATIONPools of amino acids, tRNAs, and ribosomal subunits in the cytoplasmsynthesis of polypeptide chain on the platform of an intact ribosomeFINAL PROTEINFig. 15.5, p. 245for use in cell or for export
5 A. Transcriptional Control 2. Chemical Modification: A DNA segment may be wrapped tightly with histones, preventing gene expression.In mammalian females, theextra “X” is tightly bound,resulting in the presenceof a Barr Body in thenucleus.
7 B. Post TranscriptionSplicesomes: Enzymes that rearrange segements of introns, creating new combinations of proteins.
8 C. Translational Controls mRNA transcript will be digested when it reaches the cytoplasm (a good thing, or once a gene were turned on it would be forever expressed). A transcript has a cap added to the 5’ end and a poly-A tail added to the 3’ end. If these tails/caps are long, it will take the enzymes in the cytoplasm a greater amount of time to digest the coding region of the transcript.
9 unit of transcription in a DNA strand exonintronexonintronexon3’5’transcription into pre-mRNApoly-Atailcap5’3’(snipped out)(snipped out)5’3’mature mRNA transcriptFig. 14.9, p. 229
10 II. Gene Regulation in Prokaryotes Prokaryotes have only one DNA molecule (circular and not protected by nuclear envelope) and this DNA molecule is not bound up with histones. Thus, gene regulation in prokaryotes is unique. One of the best known pathways of gene recognition is the lac Operon, a regulatory pathway by which bacteria are able to produce the enzyme to digest lactose only when necessary (when lactose is present in the environment).
11 A. Operon and DNAOperon is a regulatory system that controls DNA transcription in prokaryotes.Operon contains a promoter (the specific nucleotide sequence that tells a cell to begin or start transcription), an operator (a segment of DNA that can be used to turn gene expression on or off) and more than one gene.
12 B. Actors in Lac OperonRegulatory or Repressor Protein – Binds with operator (segment of DNA) to prevent a gene from being transcribed.Substrate/Inducer – Interacts with protein to prevent it from adhering to DNA.Operator – Section of DNAPromoter – Section of DNA.Operon – The entire system.
13 (codes for trans-acetylase) regulator genegene 1(codes forb-galactosidase)gene 2(codes for premease)gene 3(codes for trans-acetylase)transcription,translationpromoter (binding site for RNA polymerase)operator (binding site for repressor)repressor proteinlactose operonFig. 15.4a, p. 243
14 translation into three polypeptide chains for three different enzymes RNA polymerasemRNA transcripttranslation into three polypeptide chains for three different enzymeslactoseb-galactosidasepermeasetrans-acetylaseFig. 15.4b, p. 243
15 Without Lactose:Describe the chain of events that occurs in a bacterial colony when no lactose is present.
16 With Lactose:Describe the chain of events that occur when lactose is present in a bacterial culture:
17 Positive Control: Glucose Digestion Bacterial cells digest glucose before lactose.If glucose is present, cAMP is converted to ATP.cAMP, when present, bonds to promoter region and helps RNA polymerase begin transcription of lactose digestion genes.