Lecture 9 Flashcards
In bacteria (but not eukaryotes) clusters of genes called ___ produce___ mRNA
Operons, polycistronic
Such groups of genes dedicated to the same biochemical pathway are called
Operons
is one mRNA for multiple genes/proteins
Polycistronic mRNA
In an operon, the start codon of each gene is preceded by a
Shine-Delgarno Sequence
Does eukaryotes contain Shine-Delgarno Sequence
No, except in mitochondria and chloroplasts
Breakdown of a substance, inducible
Catabolism
In E. coli and other bacteria, the Lac Operon encodes three enzymes that ___ lactose
catabolize
When lactose is NOT available to be metabolized, the lac operon is…
Shut down by lac repressor binding to lac operator and blocking transcriptional activation
When lac repressor binds operator, what happens to transcription of operon
No transcription
When exposed to lactose, a small portion is converted to __ that binds to the lac repressor,___ it.
allolactose, inactivating
What happens to transcription if glucose is present (basal transcription)
Low level
when glucose is also present in addition to the lactose, E. coli uses ___ first. The lac operon is transcribed ____because the CAP protein needed for high transcription is ___
glucose, only slightly, inactive
When CAP binds, what happens to transcription rate
It’s low
The absence of glucose causes _____ to accumulate.
cyclic AMP (cAMP)
When cAMP binds CAP and CAP binds CAP site, what happens to transcription?
Promotes transcription of lac operon
Biosynthesis of a substance , repressible
Anabolism
Ex ample of repressor + co-repressor:
Trp operon
When the amino acid tryptophan level is _____, the operon is transcribed in order to synthesize tryptophan
low
The trpR is expressed when?
All the time
When trp levels are low, what happens to transcription ?
Transcription of entire trp operon occurs
___tryptophan levels cause the Trp operon to be repressed
High
In bacteria, genetic regulation is predominantly at the level of…
Transcription
In Bacteria, regulation of gene expression can, alternatively, be…
Translational, posttranslational
A protein can also bind outside the start
codon and act as a…
Translational repressor
Translational repressor prevents ribosome from binding…
S-G sequence
What RNA inhibits translation? What gene is used?
Antisense, micF gene
binds the ompF RNA to prevent translation and reduce pores
MicF
A common mechanism to regulate the activity of allosteric enzymes is
feedback inhibition
Another way to control protein function is by the covalent modification of their structure.
Some modifications are ___
irreversible
Proteolytic processing is what kind of modification
Irreversible
Covalent modifications are what kind of modifications
Irreversible
Methylation is what kind of modification
Reversible
Acetylation is what kind of modification
Reversible
Phosphorylation is what kind of modification
Reversible
proteins that influence the
ability of RNA polymerase to transcribe a given gene
Transcription factors
Required for the binding of the RNA pol to the core promoter and
its progression to the elongation stage
General transcription factors
What is necessary for basal transcription?
General transcription factors
They influence the ability of RNA pol to begin transcription of a particular gene
Regulatory transcription factors
Transcription factor proteins contain regions, called ___, that have specific functions
Domains
a domain or portion of a domain that has a very similar structure in many different proteins
Motif
What motifs bind DNA
Helix-turn-helix motif & helix-loop-helix motif
Composed of one a-helix and two b-sheets held together by a zinc (Zn++) metal ion
Zinc Finger Motif
Two a-helices intertwined
due to leucine motifs, results in dimerization
Leucine zipper motif
Tr anscriptional activators bind ___ to up-regulate transcription
enhancers
The transcriptional activator up-regulates transcription by recruiting ___ and/or activating its function
TFIID
Tr anscriptional repressors bind ___ to down-regulate transcription
Silencers
The transcriptional repressor inhibits the binding of __ or inhibits its function.
TFIID
Most enhancers and silencers are located within a few hundred nucleotides….
Upstream of the promoter
links/bridges enhancers and silencers to core promotor
Mediator
An effector molecule that activates an activating transcription factor is called an
Inducer molecule
Inducer ____ repressor when bound
Inactivates
