Genetics Final

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gal operon

Back 1

involved in utilization of the sugar galactose, a classic example of negative regulation
has two promoters, two operators, two repressors

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Galk Gene

Back 2

a kinase that phosphorylates galactose to make galactose-1-phosphate

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galT gene product

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transferase that transfers the galactose-1-phosphate to UDPglucose, displacing the glucose to make UDP galactose (released glucose can then be used as carbon source of energy)

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GalE gene product

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an epimerase that conversts UDPgalactose to UDPglucose to continue the cycle

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galU gene product

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synthesizes UDPglucose (located in a different region of the chromosome)

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GalR

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one of the gal operon repressors, encoded by the galR gene. Discovered first because mutations in galR cause consitiutive expression of the gal operon. Binds the inducer glactose, is responsible for most of the repression of the gal operon in the absence of galactose.

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GalS

Back 7

repressor of the gal operon, encoded by galS, binds to the inducer galactose, plays only a minor role in regulating the gal operon but solely controls the genes of the galactose in the cell.

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Oe and Oi

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the operators for the gal operon. One is upstream (Oi) and the other is internal to the galE gene (Oe), cooperate to block transcription

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PG1 and PG2

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two promoters of the gal operon
enzymes are needed even when a better carbon source is available, since they are involved in making polysaccharides as well as in utilizing galactose.

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catabolite repression & the PG's

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only one of the two gal operon promoters is repressed. The other promoter is active even in the presence of glucose and continues making the Gal enzymes.

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enzymes encoded by these operons synthesize compound needed by the cell, such as nucleotides amino acids and vitamins
ex: trp Operon

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biosynthetic operon

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a biosynthetic operon that is negatively regulated by a repressor, has genes transcribed from a single promoter

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tryptophan (trp) operon

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protein whose gene is unlinked to the rest of the trp operon. regulates the aroH operon as well, and autoregulates

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TrpR repressor protein

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binding of this alters the HTH conformation, allowing repressor to bind to the operators.

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tryptophan corepressor

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two states that the AraC protein can exist in. In the absence o the inducer L-arabinose the AraC protein is in the first state and inactie. Upon binding to araI the protein conformation changes to the other state

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the P1 and P2 state

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in this state the AraC protein preferentially binds to the operator araO2

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the P1 state

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the first example of positive regulation in bacteria discovered. Is responsible for the utilization of the five-carbon sugar L-arabinose

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the L-ara operon, or the ara operon

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in the presence of L-arabinose the AraC protein changes to...

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the P2 form and binds to araI1 and araI2.

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positively regulated operon for the utilization of the sugar maltose in E. coli

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Maltose Operons: four clusters at 36, 75, 80, and 91

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two genes at the 75 min operon whose products are involved in converting maltose and other polymers into glucose and glucose-1-phosphate

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malQ and malP

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malT

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regulatory gene located on the 75 min cluster of the Maltose operon

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malS

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gene at 80 min of the E. coli genetic map that encodes an enzyme that breaks down polymers of maltose

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Function of the 91 and 36 min clusters of the E. coli genetic map

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91: two operons whose gene products can transport maltose into the cell
36: encodes enzymes that degrade polymers of maltose.

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alterior function of the products of the maltose operons

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to enable the cell to transport and degrade polymers of maltose called maltodextrins

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maltodextrins

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products of the breakdown of starch molecules.

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malP-malQ enzymes

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can break the maltodextrins down into maltose and then into glucose-1-phosphate, which can enter other pathways

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genes that transport the maltodextrin through the inner membrane

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MalF, MalG, and MalK

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maltotriose

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inducer of the mal operons, is composed of three molecules of glucose held together by the maltose linkage

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Activation of the genes of the mal regulon by MalT involves...

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the DNA wrapping around many copies of the protein, thereby changing the DNA conformation.

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Maltose polymers

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natural components of the cell and play many roles including protecting the cell against high osmolarity

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attenuation of transcription

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the attenuation mechanism works by terminating transcription before the RNA polymerase reaches the first structural gene of the operon.
ex: trp and his operons

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Require that the cell sense changes in the external environment and change the expression of its genes or the activity of its proteins accordingly

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regulation mechanisms

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examples of regulation mechanisms

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motility in response to chemical attractants and induction of pathogenesis operons upon entry into a suitable host.

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regulation mechanisms: two-component

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Two proteins, one of which is a sensor histidine kinase and a second which is a response regulator

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sensor histidinekinase

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part of 2 component, protein which phosphorylates itself in response to a particular environmental stimulus. the phosphorylation occurs on a histidine that is conserved among the various histidine kinases.