Transcription, lac operon, arginine Flashcards
Describe - Transcription initiation
RNA polymerase binds to promoter region upstream of the gene
guided with sigma factor
Describe - Transcription Elongation
RNA polymerase adds nucleotides complementary to the DNA template strand in the 5’ → 3’
(Uracil (U) is placed complementary to adenine (A)
Describe - Transcription Termination
RNA polymerase recognizes a “STOP” sign in the DNA and releases the transcript (100-1,200 bases long)
Translation list 5 stages
- initiation
- elongation
- termination
- protein folding
- processing
Transcription produces mRNA complementary to the
DNA gene
During translation, tRNAs use their anticodon to interpret the ___ ____ and bring in the specific _____ ____
mRNA codons; amino acids
What are two types of operon?
Inducible
Repressible
Inducible
operon is turned ON by substrate: catabolic operons - enzymes needed to metabolize a nutrient are produced when needed
Repressible
genes in a series are turned OFF by the product synthesized; anabolic operon –enzymes used to synthesize an amino acid stop being produced when they are not needed
Many strains of Staphylococcus are now resistant to
pencillin
One bacterial protein that confers penicillin resistance is called
beta-lactamase
Beta-lactamase function
is an enzyme that cuts up and deactivates penicillin
Gene for beta-lactamase only expressed in the presence of
penicillin
When the bacteria is not exposed to penicillin, that gene is turned off and what happens?
and no beta-lactamase is made
Understanding how beta-lactamase gene is turned on/off, can help us to design a drug to disable that gene’s expression (turn off the gene) can lead to what
making penicillin-resistant strains of Staph again vulnerable to penicillin.
What 3 segments of lactose operon is made of?
regulator
control locus
structural locus
Operon
set of genes under the control of a single promoter
Regulator codes for
gene that codes for repressor
Control locus composed of
promoter and operator
Structural locus made of 3 genes each coding for an enzyme needed to
catabolize lactose
the enzymes needed to catabolize lactose
B - galactosidase
permease
beta-galactosidase transacetylase
B - galactosidase function
hydrolyzes lactose
Permease
brings lactose across cell membrane
Beta-galactosidase transacetylase
uncertain function
When would you need beta-galactosidase?
- when lactose is in the environment
- so it would be useful for lac operon - to give bacteria the ability to control transcription of translation of permease and galactosidase
when is the lac operon is OFF? (think about glucose)
normal -> glucose presenst
glucose is the primary precursor of
lactose
when is lac operon ON? Think about glucose
no glucose
Describes what opens when lac operon off?
NO LACTOSE
In the absence of lactose, a repressor protein (the product of a regulatory gene located elsewhere) attaches to the operator of the operon. This effectively blocks transcription of structural genes downstream (to its right). Suppression of transcription (and translation) prevents the unnecessary synthesis of enzymes for processing lactose.
Is arginine operon inducible or repressible?
repressible
is lac operon inducible or pressible?
inducible
is the arginine operon normally on or off?
ON
Normally on and will be turned off when the product of the pathway is no longer required.
is the lac operon on normally on or off?
off
Describe when operon is on for arginine?
A repressible operon remains on when its nutrient products (here, arginine) are in great demand by the cell. The repressor has the wrong shape to bind to the DNA operator without a corepressor, so that RNA polymerase is free to actively transcribe the genes and translation actively proceeds.
Describe when excess arginine is present
arginine is a ________
When excess arginine is present, it binds to the repressor and changes it. Then the repressor binds to the operator and blocks arginine synthesis. Arginine is the corepressor
describe operon off for arginine
- Operon Off: Arginine building up
The operon is repressed when (1) arginine builds up and, serving as a corepressor, activates the repressor. (2) The activated repressor complex affixes to the operator and blocks the RNA polymerase and further transcription of genes for arginine synthesis.