Nucleic Acids 8 Flashcards
(11 cards)
What are “housekeeping genes “ ?
They encode products that are needed constantly so they are expressed at all time and in all tissues
What does the Lac Operon consist of ?
- Lac Z Gene- encodes B-galactosidase
- Lac Y Gene- encodes galactosidase permease (has the ability to move a compound from the extracellular to intracellular side of a cell
- Lac A Gene- encodes galactosidase transacetylase
What does the presence of the CAP complex do ?
Stimulates transcription of Lac Z, Y and A
What is an operon ?
A cluster of several genes transcribed into a single mRNA
Describe what happens when lactose is absent ?
The lac repressor protein binds to the operator.
This means that RNA polymerase cannot bind to the promotor, so transcription does not occur.
What happens when lactose is present ?
Some of lactose is converted into an isomer called allolactose.
Allolactose binds to the lac repressor protein, inducing a conformational change so that lac repressor cannot bind to the operator.
This means that RNA polymerase binds to the operator, and transcribes Lac Z, Y and A.
How to determine a weak promotor ?
The more a promotor on an actual gene differs from the consensus sequence, the weaker the promotor
What happens when lactose and glucose are both present ?
cAMP conc is low since glucose conc is high
RNA polymerase can transcribe the genes but levels of transcription are low because the promotor is weak
This effect is called catabolite repression.
What does the removal of catabolite repression require ?
- The catabolite activator protein (CAP)
- Cyclic AMP
What happens when glucose concentration is low ?
cAMP binds to CAP, forming a complex which binds to the CAP site and stimulates binding of RNA polymerase, increasing transcription of Lac Z, Y and A genes
Describe the control of gene expression in eukaryotes
They have promotors that consist of core promoter and several proximal promotor elements (PPEs).
They are also influenced by enhancers
They have transcription factors
