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This Concept Map, created with IHMC CmapTools, has information related to: Answers_enzyme_regulation, The trp operon. Tryptophan functions as a corepressor. attenuation: high tryptophan levels When excess tryptophan is available, there is a rapid translation of the early trp leader mRNA enabling domain 2 to pair with domain 1 and form a pause loop. The ribosome pauses at a stop codon causing domain 3 to pair with domain 4 and form a terminator loop. Transcription of the remainder of the trp operon is terminated., The trp operon. Tryptophan functions as a corepressor. attenuation: low tryptophan levels When tryptophan is limited, there is a slow translation of the early trp leader mRNA which enables domain 2 to pair with domain 3 and form an antiterminator loop. Transcription of the remainder of the trp operon continues and the enzymes required for tryptophan synthesis are made., Some repressors are synthesized in a form that readily binds to the operator and blocks transcription. However, the binding of a molecule called an inducer alters the shape of the regulatory protein in a way that now blocks its binding to the operator and thus permits transcription. example The lac operon. Lactose functions as an inducer., competitive inhibition mechanism The inhibitor is the end product of an enzymatic reaction. That end product is also capable of reacting with the enzyme's active site and prevents the enzyme from binding its normal substrate. As a result, the end product is no longer synthesized., The binding of the regulatory protein to the operator prevents RNA polymerase from passing the operator and transcribing the coding sequence for the enzymes. types of repressors Some repressors are synthesized in a form that cannot by itself bind to the operator. The binding of a molecule called a corepressor, however, alters the shape of the regulatory protein to a form that can bind to the operator and block transcription., Activators are regulatory proteins that promote transcription of mRNA. mechanism Activators control genes that have a promotor to which RNA polymerase cannot bind. The activator is an allosteric protein synthesized in a form that cannot normally bind to the activator-binding site. Binding of an inducer to the activator now enables it to bind to the activator-binding site., The lac operon. Lactose functions as an inducer. lactose is present When lactose, the inducer, is present, it binds to the allosteric repressor protein and causes it to change shape in such a way that it is no longer able to bind to the operator. Now RNA polymerase can transcribe the three genes required for the degradation of lactose and the bacterium is able to synthesize the enzymes needed for its utilization., Involves the induction, repression, or enhancement of enzyme synthesis by regulatory proteins that can bind to DNA and either block or enhance the function of RNA polymerase, the enzyme required for transcription. translational control of enzyme synthesis The bacteria produce small RNA that is complementary to the mRNA coding for the enzyme., Involves the induction, repression, or enhancement of enzyme synthesis by regulatory proteins that can bind to DNA and either block or enhance the function of RNA polymerase, the enzyme required for transcription. operon A set of genes transcribed as a polycistronic message that is collectively controlled by a regulatory protein., ENZYME REGULATION general mechanisms Controlling the Enzyme's Activity (Feedback Inhibition)., non-competitive inhibition mechanism The inhibitor is the end product of a metabolic pathway that is able to bind to a second site (the allosteric site) on the enzyme. Binding of the inhibitor to the allosteric site alters the shape of the enzyme's active site thus preventing binding of the first substrate in the metabolic pathway. In this way, the pathway is turned off., Involves the induction, repression, or enhancement of enzyme synthesis by regulatory proteins that can bind to DNA and either block or enhance the function of RNA polymerase, the enzyme required for transcription. activation of enzyme synthesis Activators are regulatory proteins that promote transcription of mRNA., Activators control genes that have a promotor to which RNA polymerase cannot bind. The activator is an allosteric protein synthesized in a form that cannot normally bind to the activator-binding site. Binding of an inducer to the activator now enables it to bind to the activator-binding site. inducer is present Binding of a molecule called an inducer to the activator alters the shape of the activator in a way that now allows it to bind to the activator-binding site. The binding of the activator to the activator-binding site, in turn, enables RNA polymerase to bind to the promotor and initiate transcription., Involves the induction, repression, or enhancement of enzyme synthesis by regulatory proteins that can bind to DNA and either block or enhance the function of RNA polymerase, the enzyme required for transcription. repression of enzyme synthesis Repressors are regulatory proteins that block transcription of mRNA., Genetic Control of Enzyme Synthesis description Involves the induction, repression, or enhancement of enzyme synthesis by regulatory proteins that can bind to DNA and either block or enhance the function of RNA polymerase, the enzyme required for transcription., Controlling the Enzyme's Activity (Feedback Inhibition). types non-competitive inhibition, ENZYME REGULATION general mechanisms Genetic Control of Enzyme Synthesis, The trp operon. Tryptophan functions as a corepressor. tryptophan is present Tryptophan, the end product of these enzyme reactions, however, functions as a corepressor. The tryptophan is able to bind to a site on the allosteric repressor protein, changing its shape and enabling it to interact with the operator region. Once the repressor binds to the operator, RNA polymerase is unable to get beyond the promoter and transcribe the genes for tryptophan biosynthesis. Transcription of the enzymes that allows for tryptophan biosynthesis is turned off., The lac operon. Lactose functions as an inducer. lactose is absent In the absence of lactose, the repressor protein binds to the operator and RNA polymerase is unable to get beyond the operator and transcribe the genes for utilization of lactose and the three enzymes for degradation of lactose are not synthesized., Some repressors are synthesized in a form that cannot by itself bind to the operator. The binding of a molecule called a corepressor, however, alters the shape of the regulatory protein to a form that can bind to the operator and block transcription. example The trp operon. Tryptophan functions as a corepressor.
