A: A repressible operon is usually on but can be inhibited when a specific small molecule binds allosterically to a regulatory protein. In contrast, an inducible operon is usually off but can be stimulated when a specific small molecule interacts with a regulatory protein.
Q: What are the three interrelated processes of transformation?
A: Cell division, cell differentiation, and morphogenesis.
Q: What is a maternal effect gene?
A: A gene that when mutant in the mother results in a mutant phenotype in the offspring, regardless of the offspring's own genotype.
1. Bacteria often respond to environmental change by regulating transcription.
2. Eukaryotic gene expression can be regulated at any stage.
3. Noncoding RNAs play multiple roles in controlling gene expression.
4. A program of differential gene expression leads to the different cell types in a multicellular organism.
5. Cancer results from genetic changes that affect cell cycle control.
Figure 18.3
(b) Tryptophan present, repressor active, operon off. As trytophan accumulates, it inhibits its own production by activating the repressor protein, which blinds to the operator, blocking transcription.
Accumulation of trytophan, the end product of the pathway, represses transcription of the trp operon, thus blocking synthesis of all the enzymes in hte pathway.
The controls that act on gene expression are much more complex in eukaryotes than in prokaryotes. In bacteria, genes are clustered into operons: gene clusters that encode the proteins necessary to perform coordinated function.
During normal growth on a glucose-based medium, the lac repressor is bound to the operator region of the lac operon, preventing transcription. However, in the presence of an inducer of the lac operon, the repressor protein binds the inducer and is rendered incapable of interacting with the operator region of the operon.
The trp operon encodes the genes for the synthesis of tryptophan. Since the activity of the trp repressor is enhanced in the presence of tryptophan, the rate of expression of the trp operon is graded in response to the level of tryptophan in the cell.
No comments:
Post a Comment