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68 Cards in this Set
- Front
- Back
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What is Constitutive Transcription?
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Transcription that occurs continuously with no regulatory control that occurs in genes
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What is Regulated Transcription?
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Condition in which gene expression is controlled at the transcriptional level in response to changing environmental conditions.
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What does the first level of regulation of transcription in bacterial genes regulate?
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It regulates the initiation of transcription: determines whether a gene or group of genes gets transcribed at all
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What does the second level of regulation of transcription in bacterial genes regulate?
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It regulates the amount of transcription: either the duration or the amount of mRNA produced in the gene
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Negative control of transcription involve the binding of what to a regulatory DNA sequence?
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Binding of a Repressor Protein
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What is Negative Control?
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In transcription, negative control is when genes are prevented from transcribing.
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What is Positive Control?
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In transcription, positive control is when genes are initiated to be transcribed.
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Positive control of transcription involves the binding of WHAT to regulatory DNA to initiate gene transcription?
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Activator protein
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What are repressor proteins?
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Broad category of regulatory proteins that exert negative control on (aka: prevent) transcription
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What do repressor protein binding block?
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Blocks transcription initiation by occupying space on regulatory DNA where RNA polymerase would normally bind.
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What is the Allosteric Domain?
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Domain of protein that allows the protein to change shape when it binds to a specific molecule
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What is DNA-Binding Domain?
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Domain of protein that is responsible for locating and binding operator DNA sequences or other target regulatory sequences.
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What is Allostery?
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Property of some enzymes that change conformation at the active site as a result of binding a substance at a different site.
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Certain repressor proteins undergo inactivation of their DNA-Binding Domain because of changes brought about by what?
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An INDUCER compound
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If an inducer is bound to a repressor protein, does transcription occur?
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Yes!
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Some repressor proteins require the binding of what at the allosteric site to activate the DNA-Binding site?
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a COREPRESSOR
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With a corepressor absent, can the repressor bind? Does transcription occur?
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If corepressor is absent, the repressor protein can't bind and transcription occurs!
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Activator proteins bind to regulatory DNA sequences called what?
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Activator Binding Sites
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Some activator proteins need what in order for transcription to occur?
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Need an allosteric effector compound that activates DNA-Binding Domain
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Some activator proteins can be inactivated by the binding of what to the functional DNA-Binding Domain?
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Inhibitor compounds!
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What kind of gene has a product that interacts with other nucleotide sequences affecting their transcription?
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Regulatory Genes
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A typical operon contains several regions. Which region is where a regulator protein binds?
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Operator region
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A BLANK operon is normally turned on, and is turned off by BLANK.
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repressible operon; repressor
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What kind of operon is normally turned on?
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A repressible operon
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What is Catabolite Repression?
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System of gene control which preferentially uses glucose in cellular respiration
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What are Operons?
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Clusters of genes undergoing coordinated transcriptional regulation by a shared regulatory region
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TRUE OR FALSE: Genes that are part of a given operon almost always participate in the same metabolic or biosynthesis pathway.
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TRUE!
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What is the Lactose Operon of E. Coli?
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Operon responsible for the production of 3 polypeptides that permit E. Coli to utilize the sugar lactose as a carbon source for growth
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The genetic switch to lactose utilization in bacteria requires what two things?
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1. depletion of glucose
2. lactose be present in the cell |
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Is the lac operon an inducible or repressible operon?
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Inducible operon!
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What is an Inducible Operon?
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Operons that are normally off and turned on when inducing compound becomes available.
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How do lac+ strains able to grow on medium containing lactose but lacking glucose?
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They produce a gated channel allowing lactose to enter and by producing Beta-galactosidase that breaks the beta-galactoside to release glucose and galactose.
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Glucose produced by lactose breakdown can immediately enter what process?
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Glycolysis
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What is Lactose?
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Disaccharide consisting of glucose and galactose joined by a covelent beta-galactoside linkage.
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Besides glucose and galactose, the breakdown of lactose produces what?
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A small amount of Allolactose, a modified form of lactose
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What role does Allolactose play?
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It helps in regulating the transcription of the lac operon genes by acting as an inducer compound
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What are the 3 main genes that are part of the Lac Operon?
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1. LacZ
2. LacY 3. LacA |
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What is the 4th gene related to the Lac Operon that produces the lac repressor protein?
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LacI
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What does LacZ code for?
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Codes for Beta-galactosidase
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What does LacY code for?
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Codes for lactose permease
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What does LacA code for?
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Codes for transacetylase
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LacZ, LacY, and LacA are transcribed as what kind of mRNA?
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Polycistronic mRNA!
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What is polycistronic mRNA?
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mRNA that is the transcript of all genes in the operon
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What is the function of lactose permease?
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Functions at the cell membrane to facilitate the entry of lactose into the cell
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What is the function of Transacetylase?
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Its not essential for lactose utilization but in bacteria it protects against damaging by-products of lactose metabolism.
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What is LacP?
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It is the lac operon promoter.
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What is LacO?
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It is the lac operator
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In the absence of production of beta-galactosidase, there is no allolactose in the cell. Constitutively produced lac repressor protein binds to what? What does this cause?
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Binds to LacO where the lac repressor blocks RNA polymerase from binding to LacP and prevents transcription.
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By binding to the allosteric domain of the repressor complex, allolactose forms what?
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The inducer-repressor complex!
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What is the function of the inducer-repressor complex?
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It induces an allosteric change that alters the conformation of the DNA-binding domain of the repressor protein to form that does NOT bind the operator (thus it stays open).
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Where is the CAP-Binding site located?
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-60 of LacP
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What is the CAP-cAMP complex?
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Small complex composed of CAP and cAMP that when bound to its binding site increases the ability of RNA polymerase to transcribe lac operon genes.
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In the absence of glucose, does the production of cAMP increase or decrease?
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INCREASES!
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What is cAMP?
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cyclic adenosine monophosphate
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What is CAP?
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Catabolite activator protein
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What are the two types of control of the lac operon?
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Negative and Positive
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What is the Positive Control of the Lac Operon?
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CAP-cAMP binds to the promoter region and increases RNA polymerase binding by 1000 times.
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How is cAMP synthesized?
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From ATP by adenylate cyclase
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When glucose is available, are concentrations of cAMP high or low? Why?
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Concentrations are low because glycolysis needs the ATP that would go to form cAMP.
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The effect of glucose in blocking lac operon gene transcription due to its presence is called what?
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Catabolite Repression
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What is attenuation?
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Second regulatory capability of some repressible operons that allows for fine-tuning transcription to match the momentary requirements of the cell
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The leader region of tryptophan is called what? What does it contain?
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TrpL contains the attenuator region
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In order, what are the 5 structural genes transcribed in the tryptophan operon?
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1. TrpE
2. TrpD 3. TrpC 4. TrpB 5. TrpA |
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The Tryptophan Operon is responsible for the protein synthesis of what?
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Tryptophan!
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In the absence of tryptophan, can the repressor bind to the operator? What will happen to transcription?
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The repressor CANNOT bind to the operator and thus transcription proceeds
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In the presence of tryptophan, can the repressor-tryptophan complex bind to the operator? What happens to transcription?
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The complex CAN bind to the operator and transcription is blocked
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In the presence of lesser amounts of tryptophan, does attenuation increase or decrease the number of full length transcripts? What happens?
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Attenuation DECREASES the number of full length transcripts and produces instead short transcripts which do not include any of the structural genes
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What is the key signal of attenuation?
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The concentration of Trp-tRNA in the cell
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