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Name the two types of metabolic control
- Cells can adjust the activity of enzymes already present. The activity of the first enzyme in the tryptophan, which the bacterium needs to survive, the cell responds by activating a metabolic pathway that makes tryptophan from another compound. 2. Cells can adjust the production level of certain enzymes, meaning they can regulate the expression of the genes encoding the enzymes. TERM 2
What does a single promoter serve?
DEFINITION 2 Serves all five genes, which together constitute a transcription unit TERM 3
What is the key advantage of grouping genes
into one transcription unit?
DEFINITION 3 A single on/ off switch can control the whole cluster of functionally related genes, these genes are under coordinate control. TERM 4
What is the on/ off switch for a segment of
DNA called?
DEFINITION 4 The promoter TERM 5
What constitutes an operon?
DEFINITION 5 The operator, the promoter, and the genes they control- the entire stretch of DNA required for enzyme production for the tryptophan pathway.
What does the repressor
do?
Binds to the operator and blocks attachment of RNA polymerase to the promoter, preventing the transcription of the genes. TERM 7
What is a regulatory
gene?
DEFINITION 7 A gene expressed at the beginning of the DNA chain, which is located some distance from the operon and controls and has its own promoter TERM 8
Why is the trp operon not switched off
permanently
DEFINITION 8
- The binding of repressors to operators is reversible. An operator vacillates between two states: one without the repressor bound and one without the repressor bound. The relative duration of each state depends of the number of active repressor molecules around. 2. The trp repressor, like most regulatory proteins is an allosteric protein, with two alternative shapes, active and inactive. Only if tryptophan binds to the trp active repressor at allosteric site does the repressor protein change to the active form that can attach to the operator, turning the operon off TERM 9
What is a corepressor?
DEFINITION 9 A small molecule that cooperates with a repressor protein to switch an operon off. TERM 10
What is meant by a repressible operon?
DEFINITION 10 Transcription is ussually on but can be inhibited (repressed) when a specific small molecule (in this case tryptophan binds allosterically to a regulatory protein.
Why does the regulation of the trp and lac
operons involve the negative control of
genes?
because the operons are switched off by the active form of the repressor protein. TERM 17
When is gene regulation said to be positive?
DEFINITION 17 Only when a regulatory protein interacts directly with the genome to switch transcription on. TERM 18
What happens when both glucose and lactose
are both present in E. Coli?
DEFINITION 18 E. coli preferentially uses glucose TERM 19
How does E.coli cell sense the glucose
concentration and relay this information to
the genome?
DEFINITION 19 Cyclic AMP (cAMP) which accumulates when glucose is scarce. TERM 20
What is the regulatory protein in E. Coli?
DEFINITION 20 CAP
What is an activator?
A protein that binds to DNA and stimulates the transcription of a gene.
