End-of-topic test: Gene Expression and Cell Specialization

In a eukaryotic cell of a mackerel, a change in RNA polymerase gives it a binding site that fits none of the transcription factors bound to a promoter. The factors still bind every promoter as before.

Which of the following describes transcription of the cell’s protein-coding genes after the change?

In cells from a lamprey, a team joins an enhancer and a promoter to a reporter gene in four constructs, with and without one nuclear protein. The table gives the reporter mRNA in each case.

Which of the following conclusions do the results best support?

A biologist notes three regulatory sequences on the gene map of a eukaryotic gene. The first lies 850 bp before the transcription start site. The second lies inside the gene’s third intron. The third lies 1,500 bp beyond the gene’s last exon.

Which of the three sequences lie downstream of the transcription start site?

In the drawings, an open box is a piece of DNA joined in, and the filled box is the reporter gene. The arrow inside the stretch’s box shows which way round the stretch was joined. A team tests a stretch of DNA from near a squid’s ink-pigment gene. The table gives the glow of three constructs, in units.

In which kind of cell does the stretch raise transcription?

In the drawings, an open box is a piece of DNA joined in, and the filled box is the reporter gene. The arrow inside the stretch’s box shows which way round the stretch was joined. A team tests a stretch of DNA from near a squid’s ink-pigment gene; the table gives three constructs and their glow. The fourth construct joins the same stretch after the reporter gene’s end, the original way round, with the promoter, in ink-gland cells.

Which glow should the team predict for the fourth construct?

In a walrus’s cell, a repressor is bound to a short stretch of DNA 9,000 bp upstream of a gene’s transcription start site, and the gene is silent. The drawing shows the DNA around the gene before the drug. A technician adds a drug that blocks the enzymes that take acetyl groups off histones.

An hour after the technician adds the drug, which of the following describes the gene and the repressor?

In a scallop’s cell, a repressor keeps one gene silent by winding its DNA tight. The gene’s promoter has also been deleted from the cell’s DNA. Now imagine the repressor’s gene is deleted.

What happens to transcription of the silent gene?

Four biologists each delete the gene for one regulatory protein in one cell and measure the mRNA of a gene that protein had been bound beside. The table gives the mRNA before and after the deletion, in each cell.

In which cell was the deleted protein a repressor of the gene?

In a herring’s cell, one regulatory protein is bound to a short stretch of DNA beside a gene. A biologist adds a chemical that binds the protein. The protein’s shape changes, so its binding site fits the stretch no more, and the protein leaves the DNA. Within an hour, the gene is transcribed three times as often as before.

Which kind of protein was the bound protein, for that gene?

A hagfish’s slime-gland cells are packed with the slime protein, which thickens the water around the fish when a predator bites. Its heart cells hold none of the protein. Sequencing shows the slime-protein gene in the DNA of both kinds of cell, base for base the same. In the drawing, a light strand hanging from a gene is that gene’s mRNA.

Which of the following explains why only the slime-gland cells hold the slime protein?

Suppose a chard plant is moved from shade into strong sunlight. Over several days its leaves redden: the leaf cells build far more of an enzyme that makes a red, sun-shielding pigment. The leaf cells’ DNA is unchanged.

Which of the following describes what the strong sunlight changed in the leaf cells?

A buckwheat plant transcribes one of its own genes into a short RNA that pairs with the mRNA of a gene for a protein of the plant’s stem fibers. A second buckwheat plant lacks the short RNA’s gene, so it has no short RNA. The table gives the fiber-protein mRNA and the fiber protein in the stems of both plants.

Which of the following does the short RNA do in the normal plant?

A biologist supplies a short RNA to cells from a lungfish. The short RNA pairs with the mRNA of one gene. The table gives, for untreated cells and the treated cells, transcription of the gene, the gene’s mRNA and its protein.

At which step does the short RNA act on the gene’s expression?

Cells taken from a jellyfish flash blue light when they are shaken. A biologist gives half the cells an siRNA against one gene, whose job is unknown. The table gives, for control cells and siRNA cells, transcription of the gene, its mRNA, its protein and what the cells do.

Which of the following does the result show about the gene?

A pheasant’s feather cells transcribe one gene often; its beak cells transcribe the same gene rarely. Both kinds of cell carry the gene, its promoter and its enhancer, base for base the same, and both transcribe most of their other genes.

Which of the following explains the difference?

A biologist finds, in a cell of a razor clam, a short RNA paired with the mRNA of one gene. The cell holds far less of that gene’s protein than its neighbors do.

Which finding would show that the short RNA is a microRNA, one the cell made itself?