Lecture 26 Flashcards
Prokaryotes 2
Where is the operator located compared to the promoter
it is downstream to the promoter
why are operons useful/economical?
it puts all the enzymes and proteins involved in the same process under her control of a single promoter
polycistronic mRNA
multiple genes on a single mRNA stand, but they are translated independently
housekeeping genes
genes that are constantly expressed throughout the lifetime of the organism. eg ones in metabolic process
What does expressing the gene mean?
for the gene to show a phenotype. (DNA-mRNA-protien). Some do not to the protein stage.
Activators
they are proteins that increase the expression level of genes by binding to DNA, increasing activity of the RNA polymerase
Repressors
they are proteins that reduce the expression levels of genes by binding to DNA, decreasing the activity of the RNA polymerase
Effectors
they bind to an activator or repressor to alter the affinity the activator or repressor has for the gene. It can induce or repress gene expression
positive regulation
when an activator binds to DNA enhancing the activity of the RNA polymerase
negative regulation
when a repressor bind to DNA blocking the activity of the RNA polymerase
what is an Inducer
When an effector decreases the affinity of a repressor to DNA so gene expression occurs (negative regulation)
When an effector decreases the affinity of an activator a DNA…
it stops gene expression
What is a co-repressor?
When an effector increases the affinity of a repressor to DNA helping it stop gene expression (negative regulation)
When an effector increases the affinity of an activator to DNA…
it helps transcription occur. It cannot activate gene expression without the effector.
What genes encode repressors?
regulator genes
What is the lac operon?
it is 3 genes that make the enzymes to catalyze lactose into glucose and galactose when glucose is not present.
What is lacZ?
structural gene that encodes B-galactosidease
What is lacY?
structural gene that encodes galactoside permease and its used for transporting lactose across the bacterial membrane
What is lacA?
structural gene that encodes thiogalactoside transacetylase to export unwanted toxins that come into the cell from the permease activity
what is the lacI?
its a regulatory gene adjacent to the lac operon that makes the lac repressor protein LacI (lac inhibitor). it binds to the lac operator when lactose is absent
Negative regulation of the lac operon
When lactose is present, the B-gal turns it into glucose and galactose. It also changes some of it into its isomer allolactose which then acts like an inducer on the lac repressor. That inhibits the lac repressor from blocking the expression of the lac operon and gene expression occurs.
how does the repressor bind to the operon
it binds at 35 base pairs in a near perfect symmetry called the helix turn helix motif. It binds as dimers
Positive regulation of the lac operon
an effector called cAMP binds to the activator protein CRP (cAMP receptor protein) to increase affinity for the lac promoter. it increases expression because it distorts the DNA enough for RNA pol to bind more effectively
where does cAMP come from?
it is produce by adenylate cyclase
