End-of-topic test: Regulation of Gene Expression

A soil bacterium carries a gene for an enzyme that breaks down nylon. A biologist grows the bacterium in a broth with no nylon and tests one cell for three things: the gene, the gene's mRNA, and the enzyme.

Which set of results shows that the cell carries the gene and the gene is silent?

Four plants of one species carry the same version of a gene for an enzyme that builds the waxy layer on a leaf. The table gives, for each plant, the mRNA of that gene in its leaf cells and the thickness of the leaf wax.

Which of the following best explains the relationship between the gene and the wax?

A biologist grows a fungus's cells in a broth with iron scarce and in the same broth with iron plentiful. The table gives the mRNA of three of the fungus's genes in each broth.

Which of the genes are constitutively expressed?

In a yeast cell, a regulatory protein binds a 16-base stretch of DNA beside a gene. A biologist measures the gene's mRNA in cells that have the original stretch and in cells whose stretch is changed at four of its sixteen bases, each with and without the regulatory protein. The table gives the results.

Which of the following explains the pattern in the table?

A bacterium has three genes for taking up and breaking down trehalose, a sugar. They sit side by side on the chromosome. A biologist measures the mRNA of each gene in the normal strain, without and with trehalose, and in a changed strain, in which a change removed the DNA just before the first gene. The table gives the results.

Which of the following conclusions do the results best support?

In the drawing, the small circle is a small molecule bound to the repressor. A full rectangle is the repressor in the shape that fits the operator. A block with its lower corners cut away is the repressor in its changed shape. An oval above the promoter is RNA polymerase off the DNA. A bacterium's operon holds three cellobiose-breaking genes. The drawing shows it just after cellobiose has entered the cell.

Which of the following happens next?

In the drawing, the small circle is a small molecule bound to the repressor. A full rectangle is the repressor in the shape that fits the operator. A block with its lower corners cut away is the repressor in its changed shape. An oval above the promoter is RNA polymerase off the DNA. A bacterium's operon holds four genes for building the amino acid serine. The drawing shows the operon at one moment.

Which of the following describes the cell at this moment?

A bacterium can build the amino acid proline. A biologist measures the mRNA of four of the bacterium's operons in a broth with no proline added and in the same broth with proline added. The table gives the results.

Which operon is a repressible system with proline as its corepressor?

Suppose a change in an E. coli cell's DNA removes the stretch of DNA that the lac operon's activator binds, and changes nothing else. The cell grows in a broth of lactose alone, beside a normal cell in the same broth.

How much of the lactose enzymes does the changed cell make, compared with the normal cell?

In the drawings, beads set apart with the DNA open between them are a loosely wound gene. Beads packed along a wave are a tightly wound gene. Two cells of one goat each carry a copy of the same gene; the two copies match base for base. The drawing shows how each copy is wound on its histones: copy Q in the first cell and copy U in the second.

Which of the following could make copy Q wind the way copy U does?

Cells of a green alga grow in a dish. A signal molecule added to the dish makes the cells add methyl groups to one gene's promoter. A biologist treats four dishes of the cells as the table describes; the drug used in the last dish blocks the enzymes that remove methyl groups from DNA. The table gives the methyl groups on the promoter and the gene's mRNA in each dish.

Which of the following explains the difference between the third and fourth dishes?

A biologist measures the mRNA of three genes in two kinds of cell from one person: the cells of a sweat gland and the sound-sensing cells of the inner ear. Both kinds of cell carry all three genes. The table gives the results.

Which of the following best explains why the sweat-gland cells transcribe gene Q often and the inner-ear cells transcribe it rarely?

Suppose a change in an E. coli cell's DNA means the cell makes no lac repressor at all. The changed cell grows in a broth of glucose only. A normal E. coli cell grows in a broth of lactose only.

How much of the lactose enzymes does the changed cell make?

Copper ions enter a fungus's cell. Within an hour, six of the cell's genes switch on together. The six genes sit on four different chromosomes. Copper switches on one transcription factor in the cell.

Which of the following does each of the six genes have beside its promoter?

A bacterium grows at 37 °C. A technician moves it into a broth at 12 °C. The table gives the mRNA and the protein of two of the bacterium's genes at 37 °C and after 30 minutes at 12 °C.

Which claim do the data support about gene Q?

Cells from a sea sponge grow in a dish and transcribe a gene steadily. A technician adds a drug that blocks the enzymes that add acetyl groups to histones. After two days, the gene's histones carry half as many acetyl groups as before.

What happens to the gene's transcription over the two days?

In a kale plant's leaf cells, a signal from a neighboring cell switches on a kinase. The kinase adds a phosphate group to a transcription factor, and the factor then binds the DNA beside gene Q. Suppose a change in the factor's gene gives a factor with no site for the kinase to add a phosphate group to.

What happens to gene Q in a leaf cell with the changed factor after the signal arrives?

Cells taken from a toad embryo grow in a dish. At 0 minutes a signal reaches them. Gene Q codes for a transcription factor. A cell that lacks gene Q never transcribes gene U after the signal. The table gives the mRNA of the two genes at four times after the signal.

Which of the following best explains why gene U's mRNA rises only after 15 minutes?