Test#3 Notes Questions Flashcards
What do structural genes do?
encode proteins
What do regulatory genes do?
encode proteins that interact with other sequences and affect the transcription and translation of these sequences
What are regulatory elements?
DNA sequences that are not transcribed but play a role in regulating other nucleotide sequences
What is the role of gene regulation in bacteria?
maintains internal flexibility, turning genes on and off in response to environmental changes
What does gene regulation do in multicellular eukaryotic organisms?
brings about cell differentiation
What is constitutive expression?
continuously expressed under normal conditions (some transcription is always happening)
What is positive control?
stimulate gene expression
What is negative control?
inhibits gene expression
What does the structure of an operon consist of?
promotor + additional sequences that control transcription (operator) + structural genes
What is a regulator gene?
DNA sequence- encoding products that affect the operon function but are not part of the operon (Lac I)
What is an operon?
a single transcriptional unit that includes a series of structural genes, promoter, and operator
What are the three genes on the lac operon?
Lac z, lac y, lac a
What protein does lac z encode?
b-galactosidase
What protein does lac y encode?
permease
What protein does lac a encode?
acetylase
What stopes the lac operon from being transcribed?
the repressor protein being to the operator sequence which makes it so that RNA polymerase cannot bind to the promotor
What encodes for the repressor protein?
the regulatory gene lac I
How is the lac operon turned on when lactose is present?
Allolactose binds to the repressor making it inactive because repressor cannot bind to operator
What is a negative repressible operon?
The control at the operator site is negative. But such transcription is usually on and need to be turned off. so the transcription is repressible.
What is the regulatory protein called in positive transcriptional control?
activator
Negative =
repressor
positive =
activator
inducible =
transcription off
repressible =
transcription on
What type of operon is the lac operon?
negative inducible
What is the inducer for the lac operon?
allolactose
What is the lac repressor encoding gene?
lac I
What is the lac operon promotor?
lac P
What is the lac operon, operon operator?
lac O
What is an allosteric binder?
It binds somewhere else other than the active site
What does permease do?
makes membrane permeable for lactose
What does b-galac do?
breaks it down to either glucose or allolactose
Example of an inducer?
allolactose (allows transcription to occur)
What happens in the presence of allolactose?
the lac repressor cannot bind to the operator
What is a partial diploid?
full bacterial chromosome + an extra piece of DNA on F plasmid
Structural gene mutations
affect the structure of the enzymes but not the regulations of their synthesis
(-) =
loss of function
(+)=
normal
What do structural gene mutations do?
affect the structure of the enzymes but not the regulation of their synthesis
Effect of regulator-gene mutations?
lacl- leads to constitutive transcription of three structural genes
What is catabolite repression?
using glucose when available and repressing the metabolite of other sugars (positive control mechanism)
Function of cAMP?
the concentration of cAMP is inversely proportional to the level of available glucose
Function of CAP?
The catabolite activator protein (CAP) binds to the promotor of the lac operon and stimulates transcription.
Effects of I- mutation?
- total loss of function
- recessive mutation
- still have good copy from other gene, still works/ looks normal
What are the results and conclusion of the mutant operator (O^c)
- one lac operon non repressible; mutation is constitutive dominant
- change of sequence of operon
- transcription is never repressed so it is always on
What are the results and conclusion of the mutant repressor gene (I^s)
- allolactose can’t bind, no transcription/ uninducible
- cis + trans dominant
I d- mutation?
- repressor can’t bind DNA
- always transcription
- dominant negative
What type is the tryp operon?
negative repressible
- on when tryp is low
- off when tryp is high
What regulates/ changes Eukaryotic chromatin structure?
- Histone modification
- DNA methylation
- Chromatin remodeling
Effects of histone modification?
- addition of acetyl groups to histone proteins, acetylation of histones loosens DNA and increases transcription
What are the condition for the lac operon to be off?
high glucose, low lactose, low cAMP low LAP
What are the condition for the lac operon to be on?
high lactose, low glucose, high cAMP, high CAP
