concept 18.1: bacteria often respond to environmental change by regulating transcription

where are most prokaryotic genes located

in a circular DNA

what are the three ways changes to bacterial DNA can occur

mutations, genetic recombination’s, rearrangement of transposons

mutation in bacterial DNA

creates adaptive changes in proteins

genetic recombination’s in bacterial DNA

transfers DNA from one bacterium to another

what are the three different kinds of genetic recombinations

transformation- bacterial cell takes up DNA from dead cells and combines it with its own DNA

transduction- infecting bacterial virus (phages) introduces DNA from previous hosts

conjugation- transfer of specific plasmids from one bacterium to another

rearrangement of transposons in bacteria DNA

bacterial DNA segments that move within the DNA molecule affects overall gene expression

natural selection favors what in bacteria

they favor bacteria that express only the genes that they need in the cell

how does a cell regulate the production of enzymes

by feedback inhibition or by gene regulation

what happens in feedback inhibition

the end product of a metabolic pathway shuts down further synthesis of that product by inhibiting enzyme production/activity within the products synthesis pathway

what happens during gene regulation

cells adjust the production level of certain enzymes

operon model

the basic mechanism for enzyme regulation of groups of genes

francois jacob and jaques monod

proposed the operon model

describe how feedback inhibition is shown through isoleucine

as more isoleucine is synthesized, the isoleucine increases enough to cause some to bind onto an allosteric site on threonin deaminase to shut down the metabolic pathway. as isoleucine gets used up, the isoleucine drops and there isnt enough isoleucine to bind onto the allosteric site, and the enzyme becomes active again

operon

a cluster of functionally related genes can be coordinately controlled by a single on-off switch

operator

a segment of DNA that acts as the on- off switch

what is included in the operon

the entire stretch of DNA that includes the operator, promoter and the genes that they control

protein repressor

is able to switch off the operon, prevents gene transcription by binding to the operator and this blocking RNA polymerase binding to the promoter

are repressors able to act on any operon

they are specific to each operon

corepressor

a molecule that cooperates with a repressor protein to switch off an operon

example of a corepressor

E. coli can synthesize the amino acid tryptophan (trp) when it has insufficient tryptophan. if there is too much tryptophan, the tryptophan acts are a corepressor

repressive operon

usually "turned on” binding of a repressor to the operator shuts off transcription

is a repressive operon anabolic or catabolic

anabolic and will always be on for something that needs to be made

inducible operon

is usually “turned off”, a molecule called an inducer inactivates the repressor and turns on transcription

is an inducible operon catabolic or anabolic

catabolic, the stimulus will be something that will be needed to break up

the lac repressor

an inducible operon that contains genes that code for enzyme used in the hydrolysis and metabolism of lactose, it is normally off but is activated by the presence of lactose

repressible enzymes

their synthesis is repressed by high levels of the end product