Genetics Chapter 14: Gene Regulation in Bacteria

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stem loop that acts as a terminator

3-4 stem loop

regions of the lac operon

CAP site, promoter (lacP), operator site (lacO), three structural genes (lacZ,lacY, and lacA), and a terminator

Three operator sites for lac operon

O1: located slightly downstream from the promoter O2: located farther downstream in the lacZ coding sequence O3: located slightly upstream from the promoter When O2 and O3 are missing, repression is greatly reduced. When O1 is missing, repression is nearly abolished. the lac repressor can bind to O1 and O2, or O3 and O1, but not O2 and O3. The DNA forms a loop

CAP site

a DNA sequence recognized by an activator protein called the catabolite activator protein (CAP)

operon

a group of two or more genes under transcriptional control of a single promoter

attenuation

a mechanism of genetic regulation, seen in trp operon, in which a short RNA is made but its synthesis is terminated before RNA polymerase can transcribe the rest of the operon.

lactose permease

a membrane protein required for the active transport of lactose into the cytoplasm of the bacterium

lac repressor

a protein that is important for the regulation of the lac operon. functions as a homotetramer, a protein composed of 4 identical subunits.

activator

a regulatory protein that increases the rate of transcription

attenuator sequence

a segment of DNA that is important in facilitating attenuation. encodes the leader peptide (14 amino acids), stops transcription soon after it has begun

operator site

a sequence of bases that provides a binding site for a repressor protein

corepressor

a small molecule that binds to a repressor protein, thereby causing the protein to bind to DNA

effector molecule

a small molecule that does not bind directly to the DNA; it exerts it's effects by binding to an activator or a repressor. This causes a conformational change in the regulatory protein and affects whether or not it can bind to the DNA

repressor

a type of regulatory protein that binds to the DNA and inhibits transcription

antisense RNA

an RNA strand that is complimentary to a strand of mRNA

inducer

an effector molecule that causes transcription to increase. may accomplish this in two ways: bind to a repressor protein and prevent it from binding to DNA, or bind to and activator protein and cause it to bind to the DNA.

B-galactose

an enzyme that cleaves lactose into glucose and galactose. as a side reaction, B-galactose also converts lactose into allolactose, a structurally similar molecule that works as an effector molecule to regulate the lac operon

galactoside transacetylase

an enzyme that covalently modifies lactose and lactose analogs.

inhibitor

binds to an activator protein and prevents it from binding to DNA

posttranslational covalent modification

covalent attachment of a molecule to a protein after it has been synthesized via ribosomes

polycistronic RNA

encoded by an operon; an RNA that contains a sequence for two or more genes

lacZ

encodes B-galactose

lacA

encodes galactoside transacetylase

lacY

encodes lactose permease

lacI gene

encodes the lac repressor

trpR gene

encodes the trp repressor protein.

allosteric enzyme

enzyme that contains two binding sites: catalytic site and regulatory site

antitermination

function of certain proteins such as N protein in bacteria that prevents transcriptional termination

repressible genes

genes that are regulated by corepressors and inhibitors which reduce the rate of transcription

cyclic AMP (cAMP)

in bacteria, a small effector molecule that binds to CAP (catabolite activator protein), in eukaryotes cAMP functions as a second messenger in a variety of intracellular signaling pathways

effects of glucose and/or lactose on lac operon

in the presence of just lactose: cAMP levels are high, and transcription is high in the absence of glucose and lactose: cAMP is high, transcription is low in the presence of both: cAMP is low, transcription is low in the presence of only glucose: cAMP low, transcription low

riboswitch

mechanism for regulating transcription, translation, RNA stability and splicing in which RNA molecule can switch between two secondary conformations based on whether or not a small molecule such as TPP binds to RNA

trpL gene

mediates attenuation

three common processes regulated at the genetic level

metabolism, response to environmental stress, cell division

catabolite regulation

phenomenon in which a catabolite (glucose) represses expression of certain gene (lac operon)

translational repressors

protein that binds to mRNA and inhibits its ability to be translated

translational regulatory protein

recognizes sequences within the mRNA, such as transcription factors recognize DNA sequences

promoter

signals the beginning of transcription of an operon

terminator

signals then end of transcription on an operon

allosteric site

site on a protein where a small effector molecule binds to regulate the function of the protein

allosteric regulation

the action of a small effector molecule such as allolactose binding to an enzyme's allosteric site

feedback inhibition

the final product of a metabolic pathway inhibits an enzyme that acts earlier in the pathway

posttranslational regulation

the functional control of proteins that are already present in the cell rather than regulation of transcription or translation

enzyme adaptation

the observation that a particular enzyme appears within a living cell only after the cell has been exposed to the substrate of that enzyme

gene regulation

the phenomenon in which the level of gene expression can vary under different conditions

negative control

transcriptional regulation by a repressor protein.

positive control

transcriptional regulation by an activator protein

constitutive genes

unregulated genes. Frequently, these genes encode proteins that are continuously needed for the survival of bacterium.

trp repressor protein

when trp levels are very low, the repressor can not bind, allowing transcription. When trp is present, it acts as a corepressor and causes the trp repressor to bind.


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