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27 Cards in this Set

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how does individual bacteria respond to environmental change?
By regulating their gene expression.

**They respond to environmental fluntuations by metabolic control
metabolic control occurs on two levels what are they?
1. cells can adjust the activity of enzymes already present. A fast response, which relies on the sensitivity of many enzymes to chemical cues that incr or decr thier catalytic activity

2. Cell can adjust the amt of substance being made of certain enzymes. That is they can regulate the expression of the genes encodig the enzymes.
The control of enzymes production occurs at the level of ______.
trancription
The basic machanism for this control of gene expression in bacteria is descride as _____
operon model
what is the advantage of grouping genes of related funtions into one trancription unit?
is that a single on-off "switch" can control the whole cluster of functionally related genes
the switch is a segment of DNA called an _____
operator
**position w/in the promoter or b/w the promoter and the enzyme encoding the genes.
what does the operator control?
it controls the acess of RNA polymerase to the genes

**all togehter, the operator, the promoter, and the genes-- they control the entire stretch of DNA required for enzyme reduction
[if the operator is the switch for controlling transcription how does this switch work?]
by it self, the (___) operon is turned on, that is RNA polymerase can bind to the promoter and transcribe the genes of the operon. The operon can be switched off by a protein (___) repressor. The repressor binds to the operator and blocks attachment of RNA polymerase to the promoter (preventing transcription of genes)
A repressor is a product of _____
regulatory gene, which is located some distance away from the operon it controls and has its own promoter
The operon is said to be a ____
repressible operon b/c transcription is usally on but can be inhibited (repressed)
inducible operon is
usually off but can be stimulated (induced) when a molecule interacts w/ a regulatory protein
what is an example of inducible operon
lac operon
lactose metabolism begins w/ hydrolysis of the disaccharide into its component _____
monosaccharides, glucose and galactose, a reaction catalyzed by the enzyme Beta galactosidase
Beta galactosidase is part of the ____
lac operon
E coli uses three enzmyes to take up and metabolize lactose. the genes for these three enzymes are clustered in the lac operon. these three genes are
lacZ--- codes for B-galactosidase, which hydroyzes lactose to glucose and galactose.

lacY-- codes for a permease, the membrane protein that transports lactose into the cell

lacA-- codes for an enzyme caled transacetylase, whose function in lactose metabolism is still unclear
The gene, LacI, located outside the operon, codes for an ______ protein that can switch off the lac operon by binding to the operator
allosteric repressor


**the lac repressor (protein) is active all by itself, binding to the operator and switching the lac operon off.
what inactivates the repressors?
a specific small molecule called an inducer (allolactose)
In the absence of lactose the lac repressor is in [active/inactive configuration]
active configuration
if lactose is added to the cell's surrounding, allolactose binds to the _____ and alters its conformation
lac repressorin
in gene regulation the enzymes of the lactose pathway are referred to as ____
inducible enzymes--- functions in catabolic pathway conserving energy
regulation of lac operons involves the negative control of genes, because the operons are
swtiched off by active form of the repressor protein
gene regulation is said to be positive only when a regulatory proteins
interacts directly with the genome to switch transcription on
[positve gene regulation]
[How does the E.coli sense the glucose concentration and how is this information relayed to the genome?] what is the mechanism for this
the mechanism depends on the interaction of an allosteric regulatory protein with a small organic molecule cyclic AMP (which accumulates when glucose is scarce)
the regulatory protein called _____, is an activator of transcription.
catabolite activator protein (CAP)
when cAMP binds to CAP, the regulatory protein (CAP) assumes its active shape and can bind to a specific site at the upstream end of the lac promoter ---- what does this do to the promoter?
it stimulates gene expression
if the amto of glucose in the cell increases, the cAMP conctrations rise/fall
falls
trascription of the lac operon proceeds at only a ____
low level