Unit 6.6 Quiz

Gibberellic acid stimulates the cells of germinating grass seeds to produce mRNA molecules that code for hydrolytic enzymes. In this case the role of gibberellic acid can best be described as that of a. a regulator of gene activity b. a stimulator of hydrolase secretion c. a stimulator of DNA replication d. an allosteric activator of hydrolase e. an activator of translation

a. a regulator of gene activity

The p53 protein regulates a cellular response to DNA damage. Based on the diagram above, which of the following best describes the role of p53 in the response to DNA damage? a. Phosphorylated p53 binds to DNA and repairs the damage. b. Phosphorylated p53 stimulates transcription of p21, and the resulting p21 protein suppresses cell division until the DNA damage is repaired. c. Phosphorylated p53 binds cyclin−Cdk complexes, and the resulting protein complex repairs the DNA damage. d. Phosphorylated p53 activates p21 proteins, and the p21 proteins in turn repair the DNA damage.

b. Phosphorylated p53 stimulates transcription of p21, and the resulting p21 protein suppresses cell division until the DNA damage is repaired.

Dystrophin is a protein that is expressed in certain muscle cells. In combination with other cellular proteins, dystrophin strengthens protein fibers in muscle cells to allow muscles to contract without injury. Nucleotide deletions in the gene that encodes dystrophin are associated with the genetic disorder Duchenne Muscular Dystrophy (DMD). a. Each cell has different genes as a result of changes that occur during development and cell specialization. b. The presence of different transcription factors in different cell types results in differential gene expression. c. A cell can only translate mRNA transcripts that have gene-specific sequences that are recognized by the ribosomes. d. The promoter region of the gene is necessary for expression to occur, and this region is only present in certain cell types.

b. The presence of different transcription factors in different cell types results in differential gene expression.

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

In prokaryotes, the genes of the trp operon encode enzymes used in the synthesis of tryptophan. The genes of the trp operon are actively expressed (Figure 1A) unless abundant tryptophan is present in the environment. The repressor protein is encoded by the trpR gene which is not a part of the trp operon. a. Transcription from the operon occurred only in the presence of abundant tryptophan. b. The strain of E. coli required more tryptophan for its metabolic processes than does a strain of E. coli with typical tryptophan regulatory controls. c. Enzymes required for the synthesis of tryptophan were continuously produced whether tryptophan was absent or present in large quantities. d. The cells died when they were grown in nutrient medium that lacked tryptophan.

c. Enzymes required for the synthesis of tryptophan were continuously produced whether tryptophan was absent or present in large quantities.

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.

POU4f3 genes have been associated with a form of hereditary hearing loss in humans. Researchers studying the genes have proposed that POU4f3 encodes a transcription factor that influences the regulation of MYo6. Which of the following questions will best help guide the researchers toward a direct test of their proposal? Responses a. Have mutations in other genes also been associated with hearing loss? b. In what types of cells are the mutant forms of the POU4f3 gene expressed? c. Are mutations in the MYo6 and POU4f3 genes also found in mice? d. Do mutations in the POU4f3 gene affect MYo6 mRNA levels in cells?

d. Do mutations in the POU4f3 gene affect MYo6 mRNA levels in cells?

The functions of the loci of the lac operon shown in the diagram are described in the table below. The diagram above represents a segment of the E. coli chromosome that contains the lacI gene and part of the lac operon, a coordinately regulated set of genes that are required for the metabolism of lactose. The presence of lactose, which causes the repressor to be released from the operator, results in increased transcription of the lac operon. a. Expression of the lacI gene requires lactose. b. RNA polymerase is rapidly degraded by the product of the lacP locus. c. The repressor binds to DNA only when the cellular concentration of glucose is low. d. The lacZ gene is highly expressed only when lactose is available.

d. The lacZ gene is highly expressed only when lactose is available.