BIOLOGY 111 1st Edition Lecture 22 Outline of Last Lecture I RNA Processing II Intron Splicing III Translation IV Elongation V Termination VI Mutations Outline of Current Lecture I Gene regulation II Operons III Negative and Positive Control IV Chromatin level regulation V Protein Stability Current Lecture Gene Regulation Cellular activity is regulated at multiple levels o Early regulation saves energy BUT it takes more time o Late regulation is much quicker BUT it does not save as much energy Regulation can occur by either enzyme activity or by enzyme production o Enzymatic activity involves the inhibition of the first enzymes in the pathway also known as feedback inhibition and this is a very rapid process o Enzymatic production represses the expression of the genes encoding by all of the enzymes in the pathway and is a longer term response Operons are a unit of genetic function found in bacteria and phages consisting of a promoter an operator and a coordinately regulated cluster of genes whose products function in a common pathway o Operator in bacterial and phage DNA a sequence of nucleotides near the start of an operon to which an active repressor can attach The binding of the repressor prevents RNA polymerase from attaching to the promoter and transcribing the genes of the operon o Promoter a specific nucleotide sequence in the DNA of a gene that binds RNA polymerase positioning it to start transcribing RNA at the appropriate place o Regulatory genes a gene that codes for a protein i e a repressor that controls the transcription of another gene or group of genes o Trp operon An anabolic and repressible operon trp synthesis with negative control These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute When tryptophan is present the repressor is active and the operon is turned of When tryptophan is absent the repressor is inactive and the operon is on Since the operon is usually always on the repressor is always inactive o Lac operon A catabolic lactose metabolism breakdown inducible operon under negative control and sometimes positive control Under negative control If lactose is absent the repressor is active and the operon is of If lactose is present the repressor is inactive an the operon is on Since the operon is usually of the repressor is always active Under positive control CAP ensures that glucose is used before alternative carbon sources and it controls the rate of transcription CAP is a regulatory gene that is in the inactive form It will wait until it is activated by cAMP before it will bind with the promoter It makes transcription much faster It acts as an activator with positive control When CAP is inactive it does not bind to the promotor When CAP is active it will bind to the promoter When lactose is present and glucose is scarce meaning that cyclic AMP levels are high abundant lac mRNA is synthesized Lac operon is fully induced only when lactose is presence and in the absence of glucose When lactose is absent and glucose is present making cAMP levels are down very little lac mRNA is synthesized Negative vs Positive control o Negative regulation the genes in the operon are expressed unless they are switched of by a repressor protein The operon will be turned on constitutively genes will be expressed when the repressor in inactivated Examples are Trp operon and Lac operon o Positive control the genes are expressed only when an active regulator protein is present The operon will be turned of when the positive regulatory protein is absent or inactive Examples when cAMP and its binding protein CAP in lac operon Regulation at the chromatin level o When modifications of histone tails open up the chromatin structure it is made more accessible to transcription factors and RNA polymerase o Major modification is acetylation of lysine which neutralizes the positive charge on this amino acid which promotes transcription by opening up and exposing the DNA o Histone methylation is the adding of histones to the amino end which reduces transcription by condensing chromatin o Phosphorylation is the adding of a phosphate group promotes transcription by loosening up the chromatin o DNA methylation is methyl groups added to cytosine bases reduces transcription o Chromatin modifications do not alter DNA sequences but may be inherited by future generations by epigenetic inheritance Control elements are segments of non coding DNA and that regulate transcription by binding certain proteins o Control elements interacting with specific transcription factors afect rate of gene expression o Activators are proteins that bind to an enhancer and stimulates transcription of a gene o Bound activators cause mediator proteins to interact with proteins at the promoter Protein stability is one of the last steps where gene expression can be regulated o Many proteins are targeted for destruction in proteasomes by receiving a ubiquitin tag o When making RNA CAP and Poly A tails are important to protect from degradation o An error to either of these would alter them enough to prevent binding to the ribosomes