Homeostasis Flashcards
What is the characteristic feature of negative control of gene expression?
Involves a repressor protein
How does negative control differ between catabolic operons and biosynthetic operons?
In catabolic operons, the repressor cannot bind to DNA when it is bound to an inducer
In biosynthetic operons, the repressor can only bind to DNA when it is bound to a co-repressor
What is the characteristic feature of positive control of gene expression?
Involves an activator protein
How does positive control differ between catabolic operons and biosynthetic operons?
In catabolic operons, the activator can only bind to DNA when it is bound to an inducer
In biosynthetic operons, the activator cannot bind to DNA when it is bound to an inhibitor
What is a regulon?
A set of operons in different parts of the genome which are controlled by the same mechanism (ie same regulatory protein)
How is it possible for a regulatory protein to control several genes or operons belonging to the same regulon?
The same DNA sequence, which is recognised by the regulatory protein, occurs several times in the genome
How can transcriptional regulatory proteins be activated or inactivated?
Allosteric interaction (eg with an inducer, example lac repressor) Covalent modification (eg by phosphorylation, example two component system)
What is an example of a negatively controlled catabolic operon?
lac operon, in E. coli. lacI codes for repressor
What is an example of a positively controlled catabolic operon?
mal operon, in E. coli. malT codes for activator
What is unusual about the ara operon?
AraC acts as both a repressor and activator of gene expression
What is an example of a negatively controlled biosynthetic operon?
trp operon. trpR codes for repressor
What is the difference between catabolic and biosynthetic operons?
In catabolic operons, operons are inducible
In biosynthetic operons, operons are repressible
How is it possible for the same protein to act as both a transcriptional repressor and activator?
Depends on the position of DNA binding site
Upstream of the RNA polymerase binding site generally results in activation of gene expression, downstream of RNA polymerase binding site will result in repression
What is homeostasis?
The maintenance of the internal environment despite fluctuations of external environment
What do both pH and osmotic homeostasis have in common?
They both involve the translocation of molecules across the cell membrane, K+ ions play a role in both
