Cell Signaling and Beyond

Which of the following properties is associated with a cyclin-dependent kinase (Cdk)? - A Cdk is an enzyme that attaches phosphate groups to other proteins. - The number of Cdk molecules increases during the S and G2 phases and decreases during M. - A Cdk is inactive, or "turned off," in the presence of a cyclin. - A Cdk is an enzyme that catalyzes the attachment of kinetochores to microtubules.

A Cdk is an enzyme that attaches phosphate groups to other proteins.

Which of the following statements best describes a key aspect of a G protein signaling pathway? - A G protein-coupled receptor is active when bound to GTP. - A G protein bound is active when bound to GTP. - A G protein is activated by hydrolysis of bound GTP. - A G protein bound is active when bound to GDP.

A G protein bound is active when bound to GTP.

Which of the following statements best describes a reason that C. elegans is an excellent model organism for investigating apoptosis? - Cells in C. elegans do not naturally undergo apoptosis, but can be induced to do so in the laboratory. - C. elegans undergoes a fixed and easy-to-visualize number of apoptotic events during its normal development. - C. elegans has large cells wherein apoptosis is easily observed without the aid of a microscope. - Death in C. elegans through a well-defined sequence of apoptotic events.

C. elegans undergoes a fixed and easy-to-visualize number of apoptotic events during its normal development.

Which of the following molecules is maintained at a relatively constant level throughout the cell cycle but requires a cyclin to become catalytically active? - PDGF - cyclin - MPF - Cdk

Cdk

Cells from advanced malignant tumors often have very abnormal chromosomes and an abnormal number of chromosomes. Which of the following best explains the association between malignant tumors and chromosomal abnormalities? - Cell cycle checkpoints are not in place to stop cells with chromosome abnormalities. - Transformation introduces new chromosomes into cells. - Cancer cells are no longer density-dependent. - Cancer cells are no longer anchorage-dependent.

Cell cycle checkpoints are not in place to stop cells with chromosome abnormalities.

At puberty, an adolescent female body changes in both structure and function of several organ systems, primarily under the influence of changing concentrations of estrogen and other steroid hormones. How can one hormone, such as estrogen, mediate so many different effects? - Each cell responds in the same way when steroids bind to the cell surface. - Estrogen is produced in very large concentrations by nearly every tissue of the body. - Estrogen binds to specific receptors inside many kinds of cells, each with different responses. - Estrogen is kept away from the surface of any cells, not able to bind it at the surface.

Estrogen binds to specific receptors inside many kinds of cells, each with different responses.

Which of the following statements best describes the relationship between an enzyme and its function? - adenylyl cyclase: conversion of cAMP to AMP - GTPase: hydrolysis of GTP - kinase: addition of a tyrosine - phosphodiesterase: removal of phosphate groups

GTPase: hydrolysis of GTP

Amount of DNA per nucleus over the cell division cycle. At which point in the accompanying figure does MPF reach its highest activity during the cell division cycle? - I - II - III - IV

III

Which of the following statements would best explain the inability of an animal cell to reduce the Ca2+ concentration in its cytosol? - Excessive amounts of calcium are transported from the cytosol into the endoplasmic reticulum. - Insufficient amounts of ATP are present in the cytosol. - Insufficient numbers of protein kinases are present in the cell. - The calcium-gated ion channels in the cell membrane are inactive.

Insufficient amounts of ATP are present in the cytosol.

Which of the following statements best describes the mechanism by which testosterone functions inside a cell? - It coordinates a phosphorylation cascade that reduces spermatogenesis. - It acts as a signal receptor that activates tyrosine kinases. - It acts as a steroid signal receptor that activates ion channel proteins in the plasma membrane. - It binds with a receptor protein that enters the nucleus and activates expression of specific genes.

It binds with a receptor protein that enters the nucleus and activates expression of specific genes.

Which of the following describes the normal function of the p53 gene product? - It causes cells to reduce expression of genes involved in DNA repair. - It allows cells to pass on mutations due to DNA damage. - It inhibits the cell cycle. - It slows down the rate of DNA replication by interfering with the binding of DNA polymerase.

It inhibits the cell cycle.

How does the toxin of Vibrio cholerae cause profuse diarrhea? - It modifies adenylyl cyclase and triggers excess formation of cAMP. - It signals IP3 to act as a second messenger for the release of calcium. - It modifies a ligand-gated ion channel. - It modifies a G protein involved in regulating salt and water secretion.

It modifies a G protein involved in regulating salt and water secretion.

Which of the following characteristics would be most important for a chemotherapeutic drug designed to treat cancer cells? - It specifically inhibits cells entering G0. - It specifically inhibits the cell division cycle in rapidly dividing cells. - It is safe enough to prevent all apoptosis. - It does not interfere with metabolically active cells.

It specifically inhibits the cell division cycle in rapidly dividing cells.

If an animal cell suddenly loses the ability to produce GTP, what will most likely happen to its signaling system? - It will use ATP instead of GTP to activate G proteins on the cytoplasmic side of the plasma membrane. - It will not be able to activate receptor tyrosine kinases. - It will not be able to activate G proteins on the cytoplasmic side of the plasma membrane. - It will be able to carry out reception and transduction but would not be able to respond to a signal.

It will not be able to activate G proteins on the cytoplasmic side of the plasma membrane.

Progression beyond the G2 checkpoint into mitosis is triggered by which of the following molecules? - PDGF - MPF - Cdk - cyclin

MPF

Which of the following statements best explains why testosterone, a lipid-soluble signaling molecule that crosses the membranes of all cells, affects only target cells? - Only target cells retain the appropriate genes regulated by testosterone. - Only target cells possess the cytosolic enzymes that transduce the signal from testosterone to adenylyl cyclase. - Testosterone initiates a phosphorylation cascade only in target cells. - Only target cells contain the intracellular receptors for testosterone.

Only target cells contain the intracellular receptors for testosterone.

In which of the following ways do plant hormones differ from hormones in animals? - Plant hormones may travel through the air as a gas. - Plant hormones typically travel from the hormone producing cell to an adjacent responding cell through gap junctions. - Plant hormones function as only paracrine signals. - Plant hormones may be transported from the hormone producing cell to the responding cell through a vascular system.

Plant hormones may travel through the air as a gas.

Which of the following statements best describes an aspect of signal transduction? - In response to some G protein-mediated signals, a special type of lipid molecule associated with the plasma membrane is cleaved to form IP3 and calcium. - Protein kinase A activation is one possible result of signal molecules binding to G protein-coupled receptors. - In most cases, signal molecules interact with the cell at the plasma membrane, enter the cell, and eventually enter the nucleus. - When signal molecules first bind to receptor tyrosine kinases, the receptors phosphorylate a number of nearby molecules.

Protein kinase A activation is one possible result of signal molecules binding to G protein-coupled receptors.

Which of the following statements best describes the events of apoptosis? - The cell's DNA and organelles become fragmented, the cell shrinks and forms blebs, and the cells's parts are packaged in vesicles that are digested by specialized cells. - The cell's DNA and organelles become fragmented, the cell dies, and it is phagocytized. - The cell dies, it is lysed, its organelles are phagocytized, and its contents are recycled. - The cell's nucleus and organelles are lysed, and then the cell enlarges and bursts.

The cell's DNA and organelles become fragmented, the cell shrinks and forms blebs, and the cells's parts are packaged in vesicles that are digested by specialized cells.

Which of the following statements best describes cells in culture that do not exhibit either density-dependent inhibition or anchorage dependence? - The cells have nonfunctional MPF. - The cells are unable to form spindle microtubules. - The cells follow an altered series of cell cycle phases. - The cells show characteristics of tumors.

The cells show characteristics of tumors.

Which of the following statements best describes what would happen if MPF (maturation-promoting factor) is introduced into immature frog oocytes that are arrested in G2? - The cells would remain arrested in G2. - The cells would begin DNA synthesis. - The cells would enter mitosis. - The cells would enter G0.

The cells would enter mitosis.

Which of the following statements describes a likely effect of a drug that inhibits testosterone binding to its receptor in human cells? - The activity of G proteins would decrease. - The expression of certain genes would increase or decrease. - The cytosolic calcium concentration would increase. - The cytosolic levels of cAMP would decrease.

The expression of certain genes would increase or decrease.

What does it mean to say that a signal is transduced? - The signal enters the cell directly and binds to a receptor inside. - The signal is amplified, such that even one signal molecule evokes a large response. - The physical form of the signal changes as it passes from the cell membrane to the ultimate intracellular target. - The signal triggers a sequence of phosphorylation events inside the cell.

The physical form of the signal changes as it passes from the cell membrane to the ultimate intracellular target.

Which of the following conditions is required for a target organ to respond to a particular hormone? - The target organ must have receptors that recognize and bind the hormone molecule. - The target organ must be the same as the organ that produced the hormone. - The target organ must have the opposite mating type of the organ that produced the hormone. - Cells in the target organ must modify their plasma membranes to allow the hormone to enter the cytoplasm.

The target organ must have receptors that recognize and bind the hormone molecule.

Which of the following characterizes BRCA1 and BRCA2 as tumor-suppressor genes? - The mutant forms of either one of these prevent breast cancer. - The normal genes code for estrogen receptors. - Their normal products participate in repair of DNA damage. - They block penetration of breast cells by chemical carcinogens.

Their normal products participate in repair of DNA damage.

Exposure of zebrafish nuclei to cytosol isolated from eggs at metaphase of mitosis resulted in phosphorylation of NEP55 and L68 proteins by cyclin-dependent kinase 2. NEP55 is a protein of the inner nuclear membrane, and L68 is a protein of the nuclear lamina. What is the mostly likely role of phosphorylation of these proteins in the process of mitosis? - They are involved in migration of centrosomes to opposite sides of the nucleus. - They are involved in chromosome condensation. - They enable the attachment of spindle microtubules to kinetochores. - They are involved in the disassembly of the nuclear envelope.

They are involved in the disassembly of the nuclear envelope.

Which of the following statements correctly describes a characteristic of tumor-suppressor genes? - They encode proteins that help prevent uncontrolled cell growth. - They are frequently overexpressed in cancerous cells. - They often encode proteins that stimulate the cell cycle. - They are cancer-causing genes introduced into cells by viruses.

They encode proteins that help prevent uncontrolled cell growth.

Which of the following statements best explains how neurons and some other specialized cells divide infrequently? - They no longer produce MPF. - They can no longer degrade cyclins. - They no longer have active nuclei. - They have entered into G0.

They have entered into G0.

Which of the following describes the role typical proto-oncogenes have when they are expressed in cells that are not cancerous? - They enhance signaling from growth factor receptors. - They stimulate normal cell growth and division. - They inhibit differentiation. - They suppress tumor growth.

They stimulate normal cell growth and division.

A loss of function of Apaf1, the human homologue of ced-4 in nematodes, is most likely to result in which of the following? - excess activation of the human analog of the ced-3 protease - a form of cancer in which normal apoptosis fails - extensive tissue damage due to excess apoptosis - activation of a developmental pathway found in the nematode but not in humans

a form of cancer in which normal apoptosis fails

Which of the following types of mutations would convert a proto-oncogene into an oncogene? - a deletion of most of the proto-oncogene coding sequence - a mutation that blocks transcription of the proto-oncogene - a mutation that greatly reduces the stability of a proto-oncogene mRNA - a mutation that greatly increases the amount of the proto-oncogene protein

a mutation that greatly increases the amount of the proto-oncogene protein

Which of the following responses is stimulated by cell signaling the formation of biofilms? - formation of mating complexes - inhibition of quorum sensing - secretion of substances that inhibit growth of foreign bacteria - aggregation of bacteria

aggregation of bacteria

Many G protein-coupled receptors contain seven transmembrane α-helical domains. If the amino terminus of such a protein is located on the extracellular side of the membrane, where would you expect to find the carboxyl terminus of the protein? - at the cytosolic surface of the plasma membrane - embedded in the phospholipid bilayer of the membrane - at the exterior surface of the plasma membrane - covalently bound to the amino end of the protein

at the cytosolic surface of the plasma membrane

Many G protein-coupled receptors contain seven transmembrane α-helical domains. If the amino terminus of such a protein is located on the extracellular side of the membrane, where would a coupled G protein most likely interact with this receptor? - along the exterior margin - at the loop between helix 5 and helix 6 - at the amino end - at the carboxyl end

at the loop between helix 5 and helix 6

Caffeine is an inhibitor of phosphodiesterase. Therefore, the cells of a person who has recently consumed coffee would have increased levels of which of the following molecules? - phosphorylated proteins - adenylyl cyclase - cAMP - activated G proteins

cAMP

A genetic test to detect predisposition to cancer would likely examine the APC gene for involvement in which type(s) of cancer? - lung only - colorectal only - lung and breast - lung and prostate

colorectal only

A signal is transmitted via phosphorylation of a series of proteins is generally associated with which of the following events? - binding of a hormone to an intracellular receptor - production of ATP in the process of signal transduction - conformational changes to each protein in the series - activation of a ligand-gated ion channel

conformational changes to each protein in the series

Which of the following pairs of molecules make up an active MPF? - a growth factor and mitotic factor - cyclin and tubulin - cyclin and a cyclin-dependent kinase - ATP synthetase and a protease

cyclin and a cyclin-dependent kinase

Forms of the Ras protein found in tumors usually cause which of the following events to occur? - excessive cell division - decreased cell-to-cell adhesion - cell division to cease - DNA replication to stop

excessive cell division

Which of the following statements best describes scaffolding proteins? - proteins that enter the nucleus of a cell to regulate transcription - relay proteins that orient receptors and their ligands in appropriate directions to facilitate complex formation - microtubule arrays that allow lipid-soluble hormones to get from the cell membrane to the nuclear pores - large molecules to which several relay proteins attach to facilitate cascade effects

large molecules to which several relay proteins attach to facilitate cascade effects

The dots in the space between the two structures in the accompanying figure represent which of the following components of a cell signaling pathway? - neurotransmitters - receptor molecules - second messengers - hormones

neurotransmitters

A type of localized signaling in which a cell secretes a signal molecule that affects neighboring cells is best described as which of the following? - paracrine signaling - hormonal signaling - autocrine signaling - cell-cell contact-dependent signaling

paracrine signaling

Which of the following enzymes essentially reverses the reaction catalyzed by adenylyl cyclase? - protein phosphatase - phosphorylase - phosphodiesterase - protein kinase

phosphodiesterase

Binding of a growth factor to its receptor is most likely to immediately activate which of the following molecules? - phosphorylase - cAMP - adenylyl cyclase - protein kinase

protein kinase

Activation of which of the following molecules generally requires protein phosphorylation? - G protein-coupled receptors - receptor tyrosine kinases - steroid hormone receptors - ligand-gated ion channels

receptor tyrosine kinases

Which of the following signal transduction proteins typically functions by forming dimers after binding to a signal molecule? - ligand-gated ion channels - receptor tyrosine kinases - steroid receptors - G protein-coupled receptors

receptor tyrosine kinases

When a neuron responds to a particular neurotransmitter by opening gated ion channels, the neurotransmitter is serving as which part of the signal pathway? - relay molecule - response molecule - transducer - signal molecule

signal molecule

Which of the following statements best describes why phosphorylation cascades are useful in cellular signal transduction? - they always lead to the same cellular response - they are species specific - they amplify the original signal many times - they counter the harmful effects of phosphatases

they amplify the original signal many times