Gene Expression and Regulation Reading Quiz (Unit 6 Standard E)

Histone methyltransferases are a class of enzymes that methylate certain amino acid sequences in histone proteins. A research team found that transcription of gene R decreases when histone methyltransferase activity is inhibited.  Which scientific claim is most consistent with these findings?

• DNA methylation inhibits transcription of gene R.

• Histone modifications of genes are usually not reversible.

• Histone methylation condenses the chromatin at gene R so transcription factors cannot bind to DNA.

• Histone methylation opens up chromatin at gene R so transcription factors can bind to DNA more easily.

Figure 1 represents a metabolic process involving the regulation of lactose metabolism by E. coli bacteria. Lactose is utilized for energy by E. coli when glucose is not present. Allolactose is an isomer of lactose that is in the environment of these bacteria when lactose is present. The CAP site prevents the binding of RNA polymerase when glucose is present in the environment. The lacZ, lacY, and lacA genes code for proteins needed for lactose metabolism.  Which is a scientific claim that is consistent with the information provided and Figure 1 ?

• The presence of excess lactose blocks the functioning of RNA polymerase in this operon.

• When bound to the operator, the repressor protein prevents lactose metabolism in E. coli.

• The binding of the repressor protein to the operator enables E. coli to metabolize lactose.

• Allolactose acts as an inducer that binds to the operator, allowing E. coli to metabolize lactose.

Figure 1 illustrates processes related to control of transcription and translation in a cell.  Which of the following scientific claims is most consistent with the information provided in Figure 1 ?

• Gene X codes for a transcription factor required for transcription of gene D.

• A single transcription factor regulates transcription similarly, regardless of the specific gene.

• Transcription of genes A, B, and C is necessary to transcribe gene E.

• Different genes may be regulated by the same transcription factor.

Arsenic is a toxic element found in both aquatic and terrestrial environments. Scientists have found genes that allow bacteria to remove arsenic from their cytoplasm. Arsenic enters cells as arsenate that must be converted to arsenite to leave cells. Figure 1 provides a summary of the arsenic resistance genes found in the operons of three different bacteria. E. coli R773 is found in environments with low arsenic levels. Herminiimonas arsenicoxydans and Ochrobactrum tritici are both found in arsenic‑rich environments.  Researchers claim that bacteria that live in environments heavily contaminated with arsenic are more efficient at processing arsenic into arsenite and removing this toxin from their cells. Justify this claim based on the evidence shown in Figure 1.

• There are multiple operons controlling the production of proteins that process and remove arsenite from cells in both H. arsenicoxydans and O. tritici. In contrast, E. coli has only one operon devoted to arsenic removal.

• Both H. arsenicoxydans and O. tritici contain the arsR gene that codes for a repressor that turns on the operon to eliminate arsenite from the cell.

• Both O. tritici and E. coli contain the arsD gene, which codes for a protein that helps remove arsenite from the cell.

• Both H. arsenicoxydans and O. tritici. have more arsenic resistance genes than has E. coli.

Both liver cells and lens cells have the genes for making the proteins albumin and crystalline. However, only liver cells express the blood protein albumin and only lens cells express crystalline, the main protein in the lens of the eye. Both of these genes have enhancer sequences associated with them.  The claim that gene regulation results in differential gene expression and influences cellular products (albumin or crystalline) is best supported by evidence in which of the following statements?

• Liver cells possess transcriptional activators that are different from those of lens cells.

• Liver cells and lens cells use different RNA polymerase enzymes to transcribe DNA.

• Liver cells and lens cells possess the same transcriptional activators.

• Liver cells and lens cells possess different general transcription factors.

Phytochromes are molecules that change light stimuli into chemical signals, and they are thought to target light-activated genes in plants. A study was conducted to determine how certain cell proteins were made in a plant cell using a phytochrome. Figures 1 and 2 represent findings from the study.  Use the response models shown in Figures 1 and 2 to justify the claim that phytochromes regulate the transcription of genes leading to the production of certain cellular proteins.

• When inactive phytochrome Pr is activated by red light to become phytochrome Pfr, it is transported into the nucleus where it binds to the transcription factor PIF3 at the promoter. This stimulates transcription, ultimately leading to protein production. Far-red light inactivates the phytochrome, which will turn transcription off by not binding to PIF3.

• Far-red light activates phytochrome Pr, causing it to travel to the nucleus where it binds to PIF3 at the promoter. This stimulates transcription, ultimately leading to protein production. Red light inactivates the phytochrome, which will turn transcription off by not binding to PIF3.

• MYB, and not Pfr, is activated by red light, causing it to bind to the promoter and stimulate transcription and translation of cellular proteins.

• PIF3 binds to the promoter only in the presence of red light and Pfr. Any time PIF3 is bound to the promoter,  MYB is transcribed, initiating transcription of various other proteins in the cell.

Which of the following best explains how some cells of an individual produce and secrete a specific enzyme, but other cells of the same individual do not?

• The cells contain different genes and therefore do not make the same proteins.

• The cells have evolved under different selective pressures, resulting in some cells making proteins that others cannot.

• The cells transcribe and translate different combinations of genes, leading to the production of different sets of proteins.

• The cells produce different types of ribosomes that enable the translation of different genes.

 What is the function of the operator portion of the operon?

• Coding for repressor molecules

• Producing mRNA for gene expression

• Binding location for the RNA polymerase

• Binding location for the repressor protein