BGM1002/L17 Transcription Regulation Flashcards
How do cells react to changes in their environment? (2)
Changing sets of genes expressed
Changing the level at which they are expressed
What is the key step for regulation of transcription?
Initiation
Name the 2 strategies for regulation of transcription initiation.
Repression
Activation
Describe how a repressor stops transcription initiation. (2)
Strong promoter sequence
Repressor binds to DNA and ‘turns it off’
Describe how an activator allows transcription initiation. (2)
Weak promoter sequence
Activator binds to RNA polymerase and aids binding to promoter sequence
What enzyme does lacZ encode?
Beta-galactosidase
What enzyme does lacY encode?
Permease
What enzyme does lacA encode?
Acetylase
Define ‘polycistronic’.
A gene that encodes more than one protein
When does high transcription of lac structural genes (lacZYA) occur?
Lactose present & glucose absent
Define ‘operon’.
A cluster of genes under the control of a single promoter
What is a constitutive promoter?
A promoter whose expression is not regulated and gives a set level of transcription
How many amino acids is the lac repressor?
360
Where does the lac repressor bind?
To the lac operator
Describe the lac operator.
35 base pair palindrome
What is the association constant of the lac operator?
2x10^13 M^-1
What is the association constant of DNA?
2x10^6 M^-1
Why is the lac repressor a tetramer?
It forms a DNA loop by binding to the primary operator and one of two secondary operators
What is the inducer called for the lac operon?
Allolactose
What can act as an inducer for the lac operon?
Other beta-galactosidases
What occurs when allolactase binds to the lac repressor? (2)
DNA binding subunits separate by 3.6A
Affinity for operator reduced by factor of 1000
What do glucose levels affect in cells? (2)
Inhibits adenylate cyclase
Prevents cAMP accumulation
What is CAP/CRP?
Catabolite Activator Protein
cAMP receptor protein
When does the CAP protein bind to the CAP binding site? (2)
When glucose levels are low
When cAMP levels are high
Where is the CAP binding site located?
Just upstream of the -35 region
How can high levels of recombinant proteins be expressed? (3)
Place gene of interest under control of lac repressor which inhibits expression
Grow cells
Induce expression by addition of IPTG which mimics allolactose
