ap bio quiz 6.5-6.6 gene expression

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 CAPCAP site prevents the binding of RNARNA 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 ? A The presence of excess lactose blocks the functioning of RNARNA polymerase in this operon. B When bound to the operator, the repressor protein prevents lactose metabolism in E. coli. C The binding of the repressor protein to the operator enables E. coli to metabolize lactose. D Allolactose acts as an inducer that binds to the operator, allowing E. coli to metabolize lactose.

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

The lac operon in E. coli consists of genes that code for enzymes necessary for the breakdown of lactose. When lactose is absent, the operon is inactive because a repressor protein binds to a specific site in the lac operon. When lactose is present, lactose molecules bind to the repressor protein, causing the repressor protein to dissociate from the binding site. In the absence of glucose (a preferred energy source for bacteria), the protein CAP binds to a regulatory site near the lac promoter to activate transcription of the lac operon. The following symbols represent the macromolecules involved in regulation of the lac operon. In the diagrams below, the horizontal line represents the lac operon and the bent arrow represents the transcription start site of the lac operon. Which of the following diagrams best represents the scenario in which lactose is available to the cell and glucose is absent?

C

Lactase is the enzyme needed to digest lactose, the sugar found in milk. Most mammals produce lactase when they are young but stop once nursing ends. In humans however, many people continue to produce lactase into adulthood and are referred to as lactase-persistent. Which of the following mutations is most likely to cause lactase persistence in humans? A A nucleotide substitution in the coding region of the lactase gene that interferes with the interaction between lactase and lactose B A mutation that turns off the expression of transcription factors that activate the expression of lactase C A mutation that increases the binding of transcription factors to the promoter of the lactase gene D The insertion of a single nucleotide into the lactase gene that results in the formation of a stop codon

C A mutation that increases the binding of transcription factors to the promoter of the lactase gene

Protein XX activates gene expression only in cells exposed to a specific signaling molecule. In a study, researchers determined the intracellular location of Protein XX in cultured cells both before and after exposing the cells to the signaling molecule. The results of the study are shown in the diagram. Based on the results, which of the following best describes what Protein XX is? A Protein XX is an RNARNA splicing enzyme. B Protein XX is a cell membrane receptor protein. C Protein XX is a transcription factor. D Protein XX is a hormone.

C Protein XX is a transcription factor.

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? A The cells contain different genes and therefore do not make the same proteins. B The cells have evolved under different selective pressures, resulting in some cells making proteins that others cannot. C The cells transcribe and translate different combinations of genes, leading to the production of different sets of proteins. D The cells produce different types of ribosomes that enable the translation of different genes.

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

Which of the following scientific claims is most consistent with the information provided in Figure 1 ? A Gene X� codes for a transcription factor required for transcription of gene D�. B A single transcription factor regulates transcription similarly, regardless of the specific gene. C Transcription of genes A�, B�, and C� is necessary to transcribe gene E�. D Different genes may be regulated by the same transcription factor.

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

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? A DNADNA methylation inhibits transcription of gene R�. B Histone modifications of genes are usually not reversible. C Histone methylation condenses the chromatin at gene R� so transcription factors cannot bind to DNADNA. D Histone methylation opens up chromatin at gene R� so transcription factors can bind to DNADNA more easily.

D Histone methylation opens up chromatin at gene R� so transcription factors can bind to DNADNA more easily.

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? A Liver cells possess transcriptional activators that are different from those of lens cells. B Liver cells and lens cells use different RNARNA polymerase enzymes to transcribe DNADNA. C Liver cells and lens cells possess the same transcriptional activators. D Liver cells and lens cells possess different general transcription factors.

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

Which of the following best explains how the prokaryotic expression of a metabolic protein can be regulated when the protein is already present at a high concentration? A Repressor proteins can be activated and bind to regulatory sequences to block transcription. B Transcription factors can bind to regulatory sequences to increase RNARNA polymerase binding. C Regulatory proteins can be inactivated to increase gene expression. D Histone modification can prevent transcription of the gene.

A Repressor proteins can be activated and bind to regulatory sequences to block transcription.

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. A 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. B 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. C Both O. tritici and E. coli contain the arsD���� gene, which codes for a protein that helps remove arsenite from the cell. D Both H. arsenicoxydans and O. tritici. have more arsenic resistance genes than has E. coli.

A 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.

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. 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. A When inactive phytochrome PrPr is activated by red light to become phytochrome PfrPfr, it is transported into the nucleus where it binds to the transcription factor PIF3PIF3 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 PIF3PIF3. B Far-red light activates phytochrome PrPr, causing it to travel to the nucleus where it binds to PIF3PIF3 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 PIF3PIF3. C MYBMYB, and not PfrPfr, is activated by red light, causing it to bind to the promoter and stimulate transcription and translation of cellular proteins. D PIF3PIF3 binds to the promoter only in the presence of red light and PfrPfr. Any time PIF3PIF3 is bound to the promoter, MYBMYB is transcribed, initiating transcription of various other proteins in the cell.

A When inactive phytochrome PrPr is activated by red light to become phytochrome PfrPfr, it is transported into the nucleus where it binds to the transcription factor PIF3PIF3 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 PIF3PIF3.