1

Notch is a receptor protein displayed on the surface of certain cells in developing fruit fly embryos. Notch's ligand is a membrane-bound protein called Delta that is displayed on the surface of adjacent cells. When Notch is activated by its ligand

the intracellular tail of the Notch protein becomes separated from the rest of the protein. This allows the intracellular tail to move to the cell's nucleus and alter the expression of specific genes. Which of the following statements best explains Delta's role in regulating cell communication through the Notch signaling pathway?

Vertebrate immune responses involve communication over short and long distances. Which of the following statements best helps explain how cell surface proteins

such as MHC proteins and T cell receptors

In flowering plants

plasmodesmata are narrow channels through cell walls that connect the cytoplasm's of adjacent cells. An explanation of how plant cells communicate across cell walls will most likely refer to the diffusion through plasmodesmata of which of the following?

A group of researchers cultured yeast cells in a nutrient-rich environment and a nutrient-poor environment and observed the duration of the stages of their cell cycles. The results of their study are summarized in Table 1. Table 1. Duration (in minutes) of yeast cell cycle phases in a nutrient-rich environment and a nutrient-poor environment Cell Cycle Stages Nutrient-rich environment Nutrient-poor environment Sand G2 23 33 Mitosis 48 61 G1 20 57 Cytokinesis 5 10 The cell cycle of yeast cells grown in the nutrient-poor environment is approximately what percent of the cell cycle of yeast cells grown in the nutrient-rich environment?

168

Researchers studying cell cycle regulation in budding yeast have observed that a mutation in the CDC15 gene causes cell cycle arrest in telophase when the yeast cells are incubated at an elevated temperature. Which of the following statements best predicts the effect of the cell cycle arrest on proliferating yeast cells?

The yeast cells will replicate their chromosomes but will fail to complete cytokinesis.

The coagulation cascade controls blood clot formation in response to blood vessel injury. Thrombin is an enzyme that plays a key role in regulating the coagulation cascade. A simplified model of thrombin's role in regulating the coagulation cascade is represented in Figure 1. Argatroban is a competitive inhibitor of thrombin. Which of the following effects on the coagulation cascade is most likely to result from inhibiting thrombin activity with argatroban?

The rate of fibrin formation will decrease.

A student claims that the Y chromosome contains the sex-determining region gene

known as the SRY gene

In a certain signal transduction pathway

the binding of an extracellular molecule to a cell-surface protein results in a rapid increase in the concentration of cyclic AMPinside the cell. The cyclic AMPbinds to and activates cytosolic enzymes that then activate other enzymes in the cell. Which of the following statements best describes the role of cyclic AMPin the signal transduction pathway?

Cancer cells behave differently than normal body cells. For example

they ignore signals that tell them to stop dividing. Which of the following conditions will most likely cause a normal body cell to become a cancer cell?

Figure 1 shows a model of a signal transduction cascade

initiated by the binding of a ligand to the transmembrane receptor protein A A DNAmutation changes the shape of the extracellular domain of transmembrane receptor protein Aproduced by the cell. Which of the following predictions is the most likely consequence of the mutation?

Glycogen synthetase kinase 3 beta is a protein kinase that has been implicated in many types of cancer. Depending on the cell type

the gene for glycogen synthetase kinase 3 beta (GSK3β)can act either as an oncogene or as a tumor suppressor. Which of the following best predicts how GSK3βmutations can lead to the development of cancer?

Glucocorticoids are steroid hormones that control cellular responses through several different signaling pathways. One of the signaling pathways involves the glucocorticoid receptor

an intracellular protein that is activated by binding to a glucocorticoid molecule. A simplified model of the glucocorticoid receptor signaling pathway is represented in Figure 1. Which of the following statements best predicts the effect of a mutation that results in a loss of the glucocorticoid receptor's ligand binding function?

Ethylene causes fruits to ripen. In a signaling pathway

receptors activate transcription factors

Figure 1 is a proposed model of the feedback system controlling erythrocyte (red blood cell) production. Air is less dense at very high elevations

so less oxygen is available than in the denser air at sea level. Based on the model in Figure 1

The epinephrine signaling pathway plays a role in regulating glucose homeostasis in muscle cells. The signaling pathway is activated by the binding of epinephrine to the beta-2 adrenergic receptor. A simplified model of the epinephrine signaling pathway is represented in Figure 1. Cyclic AMP phosphodiesterase is an enzyme that catalyzes the conversion of cyclic AMP to a different molecule. Which of the following best predicts the effect of inhibiting cyclic AMP phosphodiesterase in a muscle cell stimulated by epinephrine?

Phosphorylase kinase will remain active because protein kinase A will no longer be deactivated.

The epinephrine signaling pathway plays a role in regulating glucose homeostasis in muscle cells. The signaling pathway is activated by the binding of epinephrine to the beta-2 adrenergic receptor. A simplified model of the epinephrine signaling pathway is represented in Figure 1. A researcher claims that the epinephrine signaling pathway controls a catabolic process in muscle cells. Which of the following statements best helps justify the researcher's claim?

Glycogen phosphorylase catalyzes the conversion of glycogen to glucose-1-phosphate.

Which of the following outcomes will most likely result from the irreversible binding of GDP to the G protein?

The intracellular concentration of glycogen will increase.

The epinephrine signaling pathway plays a role in regulating glucose homeostasis in muscle cells. The signaling pathway is activated by the binding of epinephrine to the beta-2 adrenergic receptor. A simplified model of the epinephrine signaling pathway is represented in Figure 1. Which of the following statements best describes the role of adenylyl cyclase in the epinephrine signaling pathway?

It accelerates the production of a second messenger.

The epinephrine signaling pathway plays a role in regulating glucose homeostasis in muscle cells. The signaling pathway is activated by the binding of epinephrine to the beta-2 adrenergic receptor. A simplified model of the epinephrine signaling pathway is represented in Figure 1.

In involves enzymes activating other enzymes

Figure 1 shows the number of chromosomes observed in an actively dividing human cell at each stage of cell division. Which of the following presents a correct interpretation of the changes in chromosome number depicted in Figure 1 ?

Chromosomes enter metaphase containing two chromatids attached by a centromere. During anaphase

What is the expected percent change in the DNA content of a typical eukaryotic cell as it progresses through the cell cycle from the start of the G1phase to the end of the G2phase?

+100%

Researchers performed an experiment to determine the effect of certain genetic mutations on mitosis in tropical fruit fly embryos. They determined the percentage of cells in each of four phases of mitosis as shown in Figure 1. Which of the following patterns is shown by the data?

In mutant 3 cells

The relative amount of DNA in a cell at various stages of the cell cycle is shown in Figure 1 . Which of the following best describes how the amount of DNA in the cell changes during M phase?

The amount of DNADNA is halved as the cell divides into two daughter cells.

The compound eyes of arthropods contain photoreceptor cells surrounded by other cells such as cone cells and pigment cells. Scientists studied how interactions between neighboring cells in the developing eyes of larval fruit flies affect the differentiation of R7 precursor cells that normally become the photoreceptors of adult wild-type flies. One of their experiments is illustrated in Figure 1. R7 and R8 cells are both present in a cluster of cells in the developing eye. R8 cells have cell-surface proteins called Boss. R7 precursor cells have cell-surface receptor tyrosine kinases ( RTKs ) called Sev and contain the G protein Ras that is involved in intracellular signaling. RTKs are proteins with an extracellular portion that binds to a ligand and an intracellular portion that transfers phosphate groups from ATP to other proteins. Scientists examined the fate of R7 precursor cells in fly larvae with wild-type (norma

The response indicates that the Sev RTK on the R7 precursor binds with Boss on the R8 cell.

The compound eyes of arthropods contain photoreceptor cells surrounded by other cells such as cone cells and pigment cells. Scientists studied how interactions between neighboring cells in the developing eyes of larval fruit flies affect the differentiation of R7 precursor cells that normally become the photoreceptors of adult wild-type flies. One of their experiments is illustrated in Figure 1. R7 and R8 cells are both present in a cluster of cells in the developing eye. R8 cells have cell-surface proteins called Boss. R7 precursor cells have cell-surface receptor tyrosine kinases ( RTKs ) called Sev and contain the G protein Ras that is involved in intracellular signaling. RTKs are proteins with an extracellular portion that binds to a ligand and an intracellular portion that transfers phosphate groups from ATP to other proteins. Scientists examined the fate of R7 precursor cells in fly larvae with wild-type (norma

The response indicates that the Ras protein cannot bind to the mutated intracellular portion of Sev and become phosphorylated

R7 and R8 cells are both present in a cluster of cells in the developing eye. R8 cells have cell-surface proteins called Boss. R7 precursor cells have cell-surface receptor tyrosine kinases ( RTKs ) called Sev and contain the G protein Ras that is involved in intracellular signaling. RTKs are proteins with an extracellular portion that binds to a ligand and an intracellular portion that transfers phosphate groups from ATP to other proteins. Scientists examined the fate of R7 precursor cells in fly larvae with wild-type (normal) forms of the Boss

Sev

R7 and R8 cells are both present in a cluster of cells in the developing eye. R8 cells have cell-surface proteins called Boss. R7 precursor cells have cell-surface receptor tyrosine kinases ( RTKs ) called Sev and contain the G protein Ras that is involved in intracellular signaling. RTKs are proteins with an extracellular portion that binds to a ligand and an intracellular portion that transfers phosphate groups from ATP to other proteins. Scientists examined the fate of R7 precursor cells in fly larvae with wild-type (normal) forms of the Boss

Sev

Students in a class are studying patterns of inheritance using genes involved in determining the body color and wing shape of Drosophila flies. Each of the genes has only two alleles

one of which is completely dominant to the other. Each student in the class performed a parental cross between a fly that is true-breeding for ebony body and vestigial wings and a fly that is true-breeding for gray body and long wings. Each student then crossed several pairs of the F1flies and determined the phenotypes of 500 of the resulting F2flies with respect to body color and wing shape. The students in the class averaged their data for the frequencies of the four possible phenotypes (Table 1). The students performed a second cross. The parental cross was between flies that are true-breeding for gray bodies and long wings and flies that are true-breeding for ebony bodies and curly wings. They crossed pairs of F1flies and determined

Students in a class are studying patterns of inheritance using genes involved in determining the body color and wing shape of Drosophila flies. Each of the genes has only two alleles

one of which is completely dominant to the other. Each student in the class performed a parental cross between a fly that is true-breeding for ebony body and vestigial wings and a fly that is true-breeding for gray body and long wings. Each student then crossed several pairs of the F1flies and determined the phenotypes of 500 of the resulting F2flies with respect to body color and wing shape. The students in the class averaged their data for the frequencies of the four possible phenotypes (Table 1). The students performed a second cross. The parental cross was between flies that are true-breeding for gray bodies and long wings and flies that are true-breeding for ebony bodies and curly wings. They crossed pairs of F1flies and determined

Students in a class are studying patterns of inheritance using genes involved in determining the body color and wing shape of Drosophila flies. Each of the genes has only two alleles

one of which is completely dominant to the other. Each student in the class performed a parental cross between a fly that is true-breeding for ebony body and vestigial wings and a fly that is true-breeding for gray body and long wings. Each student then crossed several pairs of the F1flies and determined the phenotypes of 500 of the resulting F2flies with respect to body color and wing shape. The students in the class averaged their data for the frequencies of the four possible phenotypes (Table 1). The students performed a second cross. The parental cross was between flies that are true-breeding for gray bodies and long wings and flies that are true-breeding for ebony bodies and curly wings. They crossed pairs of F1flies and determined

Students in a class are studying patterns of inheritance using genes involved in determining the body color and wing shape of Drosophila flies. Each of the genes has only two alleles

one of which is completely dominant to the other. Each student in the class performed a parental cross between a fly that is true-breeding for ebony body and vestigial wings and a fly that is true-breeding for gray body and long wings. Each student then crossed several pairs of the F1flies and determined the phenotypes of 500 of the resulting F2flies with respect to body color and wing shape. The students in the class averaged their data for the frequencies of the four possible phenotypes (Table 1). The students performed a second cross. The parental cross was between flies that are true-breeding for gray bodies and long wings and flies that are true-breeding for ebony bodies and curly wings. They crossed pairs of F1flies and determined

At the start of mitosis

sister chromatids are held together by a complex of proteins. Separase is an enzyme that cleaves the complex

At the start of mitosis

sister chromatids are held together by a complex of proteins. Separase is an enzyme that cleaves the complex

At the start of mitosis

sister chromatids are held together by a complex of proteins. Separase is an enzyme that cleaves the complex

At the start of mitosis

sister chromatids are held together by a complex of proteins. Separase is an enzyme that cleaves the complex