chapter 14.1-14.2

trp operon

-an example of a repressible system. -in both E coli and Slamonella -consist of 5 structural genes that code for enzymes the cell needs to make amino acid tryptophan -different from the lac operon because the repressor made from the repressor gene, makes it in an inactive form so it cannot bind to the operator region

eukaryotes

-eukaryotic cells have long lifespan. -new enzymes are not necessarily made each time the cells respond to a stimulus instead they are the enzymes and other proteins are converted from an inactive to active state. -Ex: the mRNA of an egg cell becomes activated when the egg is fertilized

three enzymes affected equally

-mutation affects gene regulation -enzymes are not present even when lactose is present/ mutant strain is not constitutive./ mutation is located outside the lac operon/ defective repressor cannot bind to the inducer but can bind to the operator. -enzyme always present, even when lactose is absent/ mutant strain is constitutive / mutation located outside the lac operon or whitin the lac operon/ defective repressor cannot bind to operator or normal repressor cannot bind to defective operator.

one enzyme affected

-mutation is in a structural gene -B galactosidase, lactose permease, galactoside transacetylase are all absent. -conclusion is that there is mutation in the Lac Z,Y, and A genes.

cAMP

CAP is active when ... is bound to its allosteric site.

e.coli

Is a bacteria common in the intestines of humans and other mammals. It functions by regulation many enzymes to use available organic molecules efficiently.

French researchers

Jacob and Jacques Monod are credited with the first demonstration of gene regulation. They performed studies on the genes that code for enzymes that metabolize lactose. -Jacob and Monod isolated genetic mutants to study the lac operon.

transcriptional level control

The primary requirement of bacterial gene regulation is the production of enzymes and other proteins when needed and ... is the most efficient mechanism. -also in eukaryotes but they have other control at other levels of gene expression. gene regulation is complex in eukaryotes.

mutations

a mutant repressor remain bound to the operon keeping it "turned off"

repressible operon

a repressive gene is transcribed unless a specific repressor- corepressor complex is bound to the DNA -This gene regulation system is involved mainly with ANABOLIC pathways such as these in which cells make amino acids, nucleotides, and other essential biological molecules from simpler materials. -these genes are usually "turned ON". -when the supply of the end product becomes low, all enzymes in the pathway are actively made. -when the products rise, enzyme making is repressed. Stop overproducing and wasting energy. -trp operon is an example of this system

post translational controls

act as switches that activate or inactivate one or more existing enzymes, letting the cell respond to changes in the intracellular concentrations. -an example of this control, is feedback inhibition in the metabolic pathway. Where the end product of the metabolic pathway binds to an allosteric site on the first enzyme which temporarily inactivates the enzyme. When the first enzyme does not function all the others will not either. -DIFFERENT from repression caused by tryptophan. (because in top operon: it prevented the formation of NEW enzymes) / in the feedback inhibition it regulates the activity of the EXISTING enzymes in the metabolic pathway.

inducible operon

an inducible gene is not transcribed unless a specific inducer inactivates its repressor. The lac operon is an .... A repressor controls an inducible gene or operon by keeping it "turned OFF" -the inducer is allolactose, which inactivates the repressor, ultimately permitting the gene or operon to be transcribed. -inducible genes or operons code for enzymes that are part of CATABOLIC pathways, they break down molecules to provide energy and components for anabolic reactions. -this process saves energy

IGF2

another example of how gene regulation in multicellular organisms affects expression in different tissues. A genetic mutation in pigs makes them develop more muscle tissue. The mutation is in a gene, designated insulin-like growth factor 2 (IGF2), which codes for a protein produced by both muscle and liver tissues. A base substitution mutation in this gene makes it 3 times more active in pig muscles, resulting in Leaner meat. this is a regulatory mutation located in an intron. and it is not in the protein coding portion of the gene.

constitutive genes are

are transcribed at different rates. the genes that encode for proteins required in large amounts are transcribed more rapidly than genes coding for proteins required in smaller amounts. -the promoter elements of these genes control their transcriptional rate. -"weak"- for those genes like repressors and activator proteins that are ... genes because they are needed in small amounts.

repressor protein

binds tightly to the operator. But when this is bound to the promoter the RNA polymerase cannot transcribe DNA. -This is made by a repressor gene which is located upstream from the promoter site. (the cell constantly makes repressor protein)

corepressor

binds to an allosteric site on the repressor -in the top operon it would be tryptophan. -when tryptophan binds to the repressor then it is in active form and bound to the operator region, RNA polymerase cant transcribe.

CAP

catabolite activator protein the lac operon has an inefficient porter element therefore it has a low affinity for RNA polymerase even when the repressor protein is not there. However a DNA sequence adjacent to the promoter site for another regulatory protein the ... -when activated ... stimulate transcription of the lac operon and several other bacterial operons. -The biding of active ... bends DNAs double helix -A dimer consisting of two identical polypeptide chains each of which has one molecule of cAMP

transcription

control at ... is the most effective in gene expression

operons

functionally related genes are regulated together in gene complexes called... -facilitate the coordinated control of functionally related genes -Jacob and Monod coined the term for this complex consisting of a group of structural genes with related functions plus the closely liked DNA sequences responsible for controlling them.

multicellular organisms

gene regulation in ... is focused on the differential expression of genes in the cells in various tissues. Ex: hemoglobin (transport protein) for red blood cells but in muscle cells it is myoglobin and not hemoglobin.

catabolic hydrolysis

glucose is a product of the ... of lactose it is the most efficient for Ecoli cells to use available supply of glucose first, sparing the cell energy to make additional enzymes.

map positions

in genetic crosses of mutant strains investigators determine the ... or linear order of the genes on the DNA and to infer normal gene functions by studying what happens when they are missing or altered.

Cell metabolic activity

is controlled in two ways. -One is by regulating the activity of certain enzymes (how effectively an enzyme molecule works), and -the other is by regulating the number of enzyme molecules present in each cell. Some enzymes are regulated in both ways.

lactose permease

it transports lactose efficiently across the bacterial plasma membrane without It only small amounts of lactose enter the cell.

lactose present

lactose is converted to allolactose (structural isomer) by B galactosidase, and this binds to the repressor at the allosteric site which changes its shape and it can no longer bind to the operator. Now RNA polymerase can transcribe the structural genes. -lactose "turns on" or induces the transcription of the lac operon -when the repressor has the allolactose bound to it it is inactivated.

galactoside transacetylase

may function in a minor aspect of lactose metabolism although its role is not clear

negative control

negative regulators inhibit transcription. -the lac and top operons are both examples of ... a regulatory mechanism in which the DNA binding regulatory protein is a repressor that turns off the transcription of the gene.

glucose high

postive control of the lac operon lactose high, ..., cAMP low. When glucose levels are ... cAMP is low. CAP is therefore in an inactive state and cannot stimulate transcription (sometimes it does but at a low level or not at all) -RNA polymerase binds poorly

glucose low

postive control of the lac operon when glucose concentrations are ... each CAP polypeptide has a cAMP bound to its allosteric site. The active form of CAP bind to the DNA sequence and transcription can be done. -RNA polymerase binds efficiently

positive control

postive regulators stimulate transcription -is a regulation by activator proteins that bind to DNA and thereby stimulate the transcription of a gene. -lac operon is both a negative regulator (lactose repressor) and a positively acting activator protein. -this requires the cell to recognize the absence of the sugar glucose which is the initial substrate in the glycolysis pathway.

post transcriptional controls

regulatory mechanism after transcription, occur at various levels of gene expression. -include translational controls: regulate the rate at which an mRNA molecule is translated, the faster mRNA in baceria is translated the more proteins it makes. The rate at which they are translated are due to the rate at which ribosomes attach to the mRNA and begin translation

Lactose absent

repressor protein is bound to the operator, blocking the transcription of the structural genes

high levels of tryptophan

since tryptophan is present it binds to an allosteric site on the repressor protein changing its conformation. Now the repressor binds to the operator inhibiting RNA polymerase to transcribe more tryptophan until it is required by the cell. -when the repressor in bound to the operator the switch is now off for the operon because it is blocking transcription

low levels of tryptophan

the repressor protein is inactive and cannot bind to the operator region of the DNA. so the enzymes required to make tryptophan are made. the end result is tryptophan levels increasing.

lac operon

the structural genes of this operon contain lac Z ( B-galactosidase), lac Y (lactose permease), lac A( transacetylase) -

operator

the switch that controls mRNA synthesis is the ... which is a sequence of bases upstream from the first structural gene in the operon.

constitutive genes

these genes are constantly transcribed ex: enzymes that are always needed are those that are involved In glycolysis.

promoter

transcription of the operon beings as RNA polymerase binds to this single ... region upstream from the coding sequences.

B galactosidase

use lactose as an energy source E Coli first has to cleve the sugar into the monosacarhides glucose and galactose using an enzyme called... -Further in the pathway other enzymes convert galactose to glucose and through glycolysis it gets broken even more.