Chapter 18

Why is the lac operon said to be an inducible operon? When allolactose is present, it induces the inactivation of the lac repressor. When activated, the lac operon induces repression of gene expression. When allolactose is present, it induces repression of gene expression. When activated, the lac operon induces the production of lactose-digesting enzymes. When allolactose is present, it induces the activation of the lac repressor.

Which of the following is a protein produced by a regulatory gene? promoter corepressor repressor inducer operon

Transcription of the structural genes in an inducible operon starts when the pathway's product is present. occurs continuously in the cell. starts when the pathway's substrate is present. stops when the pathway's product is present. does not result in the production of enzymes.

Suppose an experimenter becomes proficient with a technique that allows her to move DNA sequences within a prokaryotic genome. If she moves the operator to the far end of the operon, past the transacetylase (lacA) gene, which of the following would likely occur when the cell is exposed to lactose? The structural genes will be transcribed continuously. The repressor protein will no longer be produced. The operon will never be transcribed. The repressor will no longer bind to the operator. The inducer will no longer bind to the repressor.

DNA methylation is a mechanism used by eukaryotes to do what? terminate transcription cause apoptosis inactivate genes increase the rate of transcription facilitate the binding of DNA to intermediate filaments

If you were to observe the activity of methylated DNA, you would expect it to have turned off or slowed down the process of transcription. be unwinding in preparation for protein synthesis. be replicating nearly continuously. be very actively transcribed and translated. induce protein synthesis by not allowing repressors to bind to it.

A geneticist introduces a transgene into yeast cells and isolates five independent cell lines in which the transgene has integrated into the yeast genome. In four of the lines, the transgene is expressed strongly, but in the fifth there is no expression at all. Of the lines that express the transgene, one is transcribed but not translated. Which of the following is a likely explanation? no AUG in any frame no promoter missing transcription factor no compatible ribosome high histone acetylation

A researcher found a method she could use to manipulate and quantify phosphorylation and methylation in embryonic cells in culture. One of her colleagues suggested she try increased methylation of C nucleotides in a mammalian system. Which of the following results would she most likely see? decreased chromatin condensation decreased binding of transcription factors inactivation of the selected genes increased chromatin condensation activation of histone tails for enzymatic function

The phenomenon in which RNA molecules in a cell are destroyed if they have a sequence complementary to an introduced double-stranded RNA is called RNA obstruction. RNA disposal. RNA targeting. RNA blocking. RNA interference.

Since Watson and Crick described DNA in 1953, which of the following might best explain why the function of small RNAs is still being explained? Ethical considerations prevented scientists from exploring this material until recently. The functions of small RNAs could not be approached until the entire human genome was sequenced. Changes in technology as well as our ability to determine how much of the DNA is expressed have now made this possible. As RNAs have evolved since that time, they have taken on new functions. Watson and Crick described DNA but did not predict any function for RNA.

Which of these is true of the cytoplasm of an unfertilized egg? It does not contain substances that are important in directing development. These substances are produced by the DNA of the fertilized zygote. It does not contain substances that are important in directing development. These substances are supplied by the sperm. It is an unevenly distributed mixture of mRNA, proteins, organelles, and other substances. It is a homogeneous mixture of mRNA, proteins, organelles, and other substances. It does not contain substances that are important in directing development. Development is directed solely by the surrounding cells.

How do cells become differentiated? Paternal effect genes begin the process of differentiation by providing positional information. Some cells contain maternal chromosomes and some contain paternal chromosomes. The DNA in each cell changes so that the appropriate proteins are produced. They differentiate through the process of mitosis. Different genes are expressed so that different proteins are produced.

A gene on human chromosome 15 is expressed throughout the body. However, in the brain, only the maternal copy of the gene is expressed, whereas the paternal copy of the gene is silent and not transcribed. What accounts for this pattern of expression this gene displays in the brain? The copies of this gene in brain cells are coordinately controlled with the copies of the gene in body cells. In the brain, the maternal copy of the gene is methylated whereas the paternal copy is un-methylated. Through genomic imprinting, methylation regulates expression of the paternal copy of the gene in the brain.

Which statement(s) about repressible operons is/are correct? Select all that apply. In a repressible operon, the repressor is synthesized in an active form. A repressible operon is on unless a corepressor is present. Repressible enzymes generally function in anabolic pathways.

Which statement(s) about inducible operons is/are correct? Select all that apply. Inducible enzymes generally function in synthetic pathways that produce end products from raw materials. In an inducible operon, the repressor is synthesized in an active form. In an inducible operon, an inducer inactivates the repressor.

In positive control of several sugar-metabolism-related operons, the catabolite activator protein (CAP) binds to DNA to stimulate transcription. What causes an increase in CAP? increase in glucose and increase in cAMP decrease in glucose and decrease in repressor decrease in glucose and increase in cAMP increase in glucose and decrease in cAMP decrease in glucose and increase in repressor

Transcription factors in eukaryotes usually have DNA binding domains as well as other domains that are also specific for binding. In general, which of the following would you expect many of them to be able to bind? tRNA other transcription factors repressors ATP protein-based hormones

Embryonic lethal mutations result in phenotypes that are never born/hatched. homeotic phenotype changes. death during pupation. failure to express maternal effect genes. phenotypes that prevent fertilization.

Which noncoding RNAs are correctly matched with their function? Piwi-associated RNAs (piRNAs) reestablish appropriate methylation patterns in the genome during gamete formation. MicroRNAs (miRNAs) bind to complementary sequences in mRNA and block its translation. Small interfering RNAs (siRNAs) bind to complementary sequences in mRNA and block its translation.

How are genes coordinately controlled in eukaryotic cells? Select all that apply. Coordinately controlled genes in eukaryotic cells are activated by the same chemical signals. Coordinately controlled genes in eukaryotic cells share a set of control elements. Coordinately controlled genes in eukaryotic cells are located together on the same chromosome.