🌺microbiology 130🌺chapter 8C ..Lac Operon...🌺️Exam 3

1.Explain what happens lactose is present, and glucose is scarce. 2.Will cAMP level be high or low?

🌺1.If glucose is scarce, the high level of cAMP activates CAP, and the lac Operon produces large amounts of mRNA for lactose digestion 🌺2.cAMP level is high. :)

1.Explain what happens lactose is present, and glucose is present. 2.Will cAMP level be high or low?

🌺1.when glucose is present cAMP is scarce, and CAP is unable to stimulate transcription 🌺2. cAMP level is low :(

️define cyclic AMP (cAMP)

🌺A molecule derived from ATP, in which the phosphate group has a cycle structure; acts as a cellular messenger. 🌺serves as a cellular alarm signal. 🌺is an inducer of the lac Operon. It binds to an activator called CAP that helps to turn on Lac Operon.

Bacteria use most of their energy to _______ substances needed for growth.

🌺Bacteria use most of their energy to synthesize substances needed for growth.

If lactose is not present are the operons on or off? Explain

🌺OFF! Because when lactose isn't present the repressor protein is bound to the operator. RNA polymerase is not bound. Transcription is off.

Regulation of lactose Operon also depends on the level of _____in the medium.

🌺Regulation of lactose Operon also depends on the level of glucose in the medium.

Repressor proteins are inactive unless ______ tryptophan is ________. If repressor proteins are active where is their binding site?

🌺Repressor proteins are inactive unless excess tryptophan is available. thus preventing the excess production of tryptophan. 🌺once activated by tryptophan the repressor proteins can bind to the operon.thus the genes for tryptophan can not be transcribed in mRNA.

The lac Operon is an _____ ______.

🌺The lac Operon is an inducible Operon. 🌺inducible Operons are not transcribed unless they are activated by an inducer.

Explain what happens when repressor is active, and Operon off in an inducible Operon.

🌺The repressor protein binds with the operator, preventing transcription from the Operon.

Explain what happens when repressor is inactive, and Operon on in an inducible Operon.

🌺When the inducer allolactose binds to the repressor protein, the inactive repressor can no longer block transcription. The structural genes are transcribed, ultimately resulting in the production of the enzyme needed for lactose catabolism.

️Define corepressor

🌺a molecule that binds to a repressor proline, enabling the repressor to bind to an operator.

What does the I gene do?

🌺a regulatory gene called the I gene encodes a repressor proteins that switches inducible and repressive operons on or off.

what does the operator do?

🌺acts like a traffic light that acts as a go or stop signal for transcription of the structural gene. 🌺binding site for the repressor protein.

What will bacteria preferably use? (Glucose or lactose) Explain.

🌺bacterial cells will preferentially utilize glucose as an energy source, even if lactose is present. Glucose represses the lac Operon. 🌺when glucose is used up and lactose is present, the lac Operon will be induced and lactose will be utilized as an energy source.

What happens to cAMP when glucose is no longer available? What does CAP do? What does transcription of the lac Operon need (lactose or glucose)?

🌺cAMP accumulates in the cell. It then binds to the allosteric site of catabolic activator protein (CAP). 🌺CAP then binds to the lac promoter, which initiates transcription by making it easier for RNA polymerase to bind to the promoter. 🌺Thus transcription of the lac Operon requires both the presence of lactose and the absence of glucose. 🌺Operon is ON

️define CAP and what does it do?

🌺catabolic activator protein (CAP) 🌺binds to the binds to the lac promoter, which initiates transcription by making it easier for RNA polymerase to bind to the promoter.

What are structural genes?

🌺genes which determine the structure of proteins.

What happens in repressive operons?

🌺in repressive operons, the structure genes are transcribed until they are turned off, or repressed (always transcribed! UNLESS THEY ARE TURNED OFF)

What is catabolic repression?

🌺inhibition of the metabolism of alternative carbon sugars by glucose. (Is also called glucose affect)

Define mutation

🌺is a permanent change in a DNA nucleotide sequence. (Base sequence)

What is a lac Operon

🌺is the combination of the three lac structural genes and the adjoined control region which is called the lac Operon.

What is constitutive gene mean? Give an example of one.

🌺many genes, meaning 60-80% are constitutive 🌺when a gene is constitutive it means that their products are constantly produced at a fix rate. (ALWAYS ACTIVE) 🌺usually these genes which are turned on all the time code for enzymes that the cell needs in fairly large amounts for its major life process 🌺an example is the enzyme of glycolysis.

define operons

🌺multiple genes that are a part of a single gene expression unit. Which includes a promoter, and an operator.

What big role does a constitutive gene play?

🌺play indispensable roles in the central metabolic pathways.

️define activators

🌺regulatory proteins that facilitate transcription 🌺genes controlled by an activator have an ineffective promoter preceded by an activator-binding site. 🌺is called positive control 🌺binding of the activator to the DNA enhances the ability of RNA polymerase to imitate transcription at that promoter.

️define repressors.

🌺repression is mediated by regulatory proteins called repressors, which block the ability of RNA polymerase to initiate transcription from the repressed gene. 🌺bind to sequence of DNA called an operator 🌺specific molecules can bind to the repressor and altar the ability of the repressor to bind DNA

What is repression?

🌺repressor protein is produced that binds to the operator and prevents gene transcription. 🌺gene expression is inhibited and enzyme production is decreased 🌺gene repressed due to an overabundance of an end product.

what is the structure of an operon.

🌺the Operon consists of the promoter and operator sites and structural genes that code for the protein.

What is induction?

🌺the process of turning on transcription of a gene or genes. 🌺lactose binds to the repressor and prevents it from binding to the operator. Genes are transcribed.

Explain what happens when repressor is inactive, and Operon is on in a repressible Operon.

🌺the repressor is inactive, and transcription and translation proceed, leading to the synthesis of tryptophan.

What happens to the repressor when tryptophan is present?

🌺tryptophan acts as a corepressor and binds to the repressor proteins. This binding allows the repressor to bind to the operator of the Operon. Stopping tryptophan synthesis.

What happen to cAMP when Glucose is available? What does CAP do?

🌺when glucose is available, the level of cAMP in the cell is low. 🌺and consequently CAP is not bound. 🌺Operon is OFF

What happens when lactose is not present?

🌺when lactose is not available, the repressor proteins are active and are bound to the operator. The structural genes of the lac operon are not transcribed. this control, prevents the cell from producing the proteins for lactose catabolism when lactose is not available. 🌺RNA polymerase is not bound and transcription is OFF.

What happens when lactose is not present, and what happen when lactose is present?

🌺when lactose is not present the repressor binds to the operator site, thus preventing transcription. (they are on) 🌺When lactose is present the repressor binds to a metabolite of lactose instead of the operator, and lactose-digesting enzymes are transcribed. Also the Operon is induced, or stimulated to produce the proteins of lactose catabolism.

What happens when lactose is present?

🌺when lactose is present in the cell, some lactose molecules are converted to allolactose. Allolactose binds to and inactivates the repressor proteins, preventing them from binding to the operator. The structural genes are transcribed resulting in the production of the enzymes needed to catabolize lactose. (since Allolactose induces, or stimulates transcription of the lac operon, its called an inducer. notice that inducer acts by turning OFF the repressor, not by actively stimulating the genes to be transcribed. 🌺Allows RNA polymerase to bind to the promoter. Transcription is ON 🌺THIS ONLY HAPPEN IF GLUCOSE IS NOOTTT PRESENT.

Explain what happens when repressor is active, and Operon off in a repressible Operon.

🌺when the corepressor tryptophan. Binds to the repressor protein, the active repressor binds with the operator, preventing transcription from the Operon.

What is an inducer?

🌺️an inducer is a substance that acts to induce transcription of a gene. 🌺acts by turning off the repressor, not by actively stimulating the gene to be transcribed.

What are repressive enzymes?

🌺enzymes are routinely produced. 🌺expression can be turned off as long as necessary 🌺️example:when the enzymes produce is present in a sufficient quantity (Tryptophan Operon)

What are inducible enzymes?

🌺enzymes that are not routinely produced (genes not usually transcribed) 🌺mechanisms can turn on expression for as long as needed. 🌺️example: Beta-Galacotosidase is produced when lactose is present.