1. The lac regulatory protein is called a repressor.
-because it keeps away RNA polymerase from transcribing the structural genes.
2. When lactose is present, the lac genes are expressed.
-because allolactose binds to the lac repressor protein and keeps it from binding to the operator.
3. The bacterial mRNA synthesized by operon is called polycistronic.
-because it carries information for more than one type of protein.
4. Stem loop structure is called the terminator or attenuator.
-because it causes transcription to terminate.
5. Both repression and induction are examples of negative control.
-because repressor proteins turn off transcription.
6. Activator enhancer complex is unique in eukaryotes.
– because they normally have to be activated to start protein synthesis, which involves the use of transcription factors and RNA polymerase.
7. Two complete female genome cannot produce viable young.
-because of the imprinted genes.
8. Gene regulation may serve as a raw material for evolutionary change.
-because control of timing, location and amount of gene expression may have a profound effect on the function of the genes in the organisms.
9.When estrogen is injected into chickens, only oviduct synthesises mRNA.
-because only oviduct has hormone receptor for estrogen and all other tissues lack the hormone receptors.
10. the trp operon is quite different from the lac operon.
-because the tryptophan acts directly in repression and not as in inducer.
11. About more than 95% of the RNA synthesis by RNA polymerase never reaches the cytoplasm.
-mainly because of removal of introns which accounts for 80% of the total bases.
12. Usually the promoter of pseudogene is inactive.
-due to lack of selective pressure to maintain a functional gene product.
13. Whenever the intracellular cAMP level is low, the lac operon is not functional even in the presence of glucose.
-because CAP protein is unable to bind to the promoter region due to low level of intracellular cAMP.
14. Gene expression occurs by DNA rearrangements.
-because such arrangements:
a) occur mostly at very low rates.
b) allow a cell to express only one of a set of genes at a time.
c) are uninducted and are sometimes reversible.
15. Regulation of gene is essential.
-because the living organisms need a variety of proteins for their cellular activities. All proteins are not needed at a time. There are specific proteins which are needed at specific stage of life cycle. So, there must be a controlling mechanisms for the expression of a particular set of genes at a particular stage and for this reason regulation of gene expression is essential.