Chapter 18.1-18.2 Flashcards
Intinsic terminators
cause RNA pol to terminate transciption on its own
extrinsic terminators
requires additional proteins - Rho proteins
Prokaryotes mRNAs
have multiple ribosome binding sites (RBSs) and can thus direct the synthesis of several diffrent polypeptides
Regulation of gene expression can occur at multiple stages:
-Transcription
*mRNA half life
*Translation initiation
*Protein stability or activity
Positive regulation = enhancement of RNA polymerase activity
catabolic functions are induced by
the presence of substrate
Anabolic functions are often repressed by
he presence of an end
product
Lactose to isomerized to
Allolactose (inducer of the genes for lactose utization)
inducible regulation
gene control where transcription occurs only in the presence of an inducer.
repressible regulation
gene control where transcription occurs only in the absence of a repressor.
operon
a unit of DNA composed of two or more genes transcribed as a polycistronic mRNA under the control of a single promoter and operator.
lac operon
a single DNA unit in E. coli, composed of the lacZ, lacY, and lacA genes together with the promoter (P) and operator site (o), that enables the simultaneous regulation of the three structural genes in response to environmental changes.
allosteric proteins
proteins that undergo reversible changes in conformation when bound to another molecule (an effector).
Promotor of lac operon acts in
cis, affecting the expression of only downstream strucural lac genes on the same molecule
repressor of lac operon acts in
trans that binds to operator
lac operon translation
B-gal, permease, transacetylase
Lac repressor protein (LacI)
allosteric
IPTG
non-metabolizable analog of lactose and an inducer of lac operon
lacZ
encodes B-galactosidase
lacY
encodes Lac permease
inability to break down lactose resulted from mutations in two genes
lacZ and lacY
lacA
encodes a transacetylase enzyme that adds a acetyl (CH3CO) group to lactose and other sugars (not used for breakdown)
lacI
loss of function mutation located near but not within the lac operon
lacI produce
constitutive mutants or repressor
constitutive mutants
strains in which certain gene products are made all the time, irrespective of environmental conditions.
constitutive mutants can synthesize
B-gal and Lac permease even in the absense of lactose
repressor
a type of transcription factor that can bind to specific cis-acting elements and thereby diminish or prevent transcription. Repressors bind operators in prokaryotes and enhancers (or CpG islands) in eukaryotes.
Mutant operator Oc
Nucleotide sequence is change
Repressor cannot recognize and bind to operator. lac enzymes are synthesized constitutively
lacIS mutant
results in no expression of the Lac operon, even
in the presence of Lactose
PaJaMo experiment
Transfer of the F’ (episome) during conjugation can
generate a “merodiploid” (partially diploid)
LacI+ protein acts
in trans and is dominant to lacI-
As a general principle of gene regulation through operons, regulatory genes encode
trans-acting proteins that interact with cis-acting DNA elements
LacI binds to the
lac operator DNA
DNaseI foot printing assay
To find the binding site for the
repressor
catabolite repression
the repression of transcription in sugar-metabolizing operons like the lac operon when glucose or another preferred catabolite is present.
cAMP regulatory protein (CRP)
can bind to the lac promoter region to allow max transciption only in the absense of glucose, when cAMP levels are high
