Exam 4 Test Bank

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Compared to the normal situation, in which actin monomers carry ATP, what do you predict would happen if actin monomers that bind a nonhydrolyzable form of ATP were incorporated into actin filaments? (a) Actin filaments would grow longer. (b) Actin filaments would grow shorter because depolymerization would be enhanced. (c) Actin filaments would grow shorter because new monomers could not be added to the filaments. (d) No change, as addition of monomers binding nonhydrolyzable ATP would not affect actin filament length.

(a) Actin filaments would grow longer

What is the role of the nuclear localization sequence in a nuclear protein? (a) It is bound by cytoplasmic proteins that direct the nuclear protein to the nuclear pore. (b) It is a hydrophobic sequence that enables the protein to enter the nuclear membranes. (c) It aids in protein unfolding so that the protein can thread through nuclear pores. (d) It prevents the protein from diffusing out of the nucleus through nuclear pores.

(a) It is bound by cytoplasmic proteins that direct the nuclear protein to the nuclear pore

Which of the following statements about kinetochores is true? (a) Kinetochores assemble onto chromosomes during late prophase. (b) Kinetochores contain DNA-binding proteins that recognize sequences at the telomere of the chromosome. (c) Kinetochore proteins bind to the tubulin molecules at the minus end of microtubules. (d) Kinetochores assemble on chromosomes that lack centromeres.

(a) Kinetochores assemble onto chromosomes during late prophase

Which organelle fragments during mitosis? (a) endoplasmic reticulum (b) Golgi apparatus (c) mitochondrion (d) chloroplast

(b) Golgi apparatus

When a signal needs to be sent to most cells throughout a multicellular organism, the signal most suited for this is a _______. (a) neurotransmitter. (b) hormone. (c) dissolved gas. (d) scaffold.

(b) hormone

Progression through the cell cycle requires a cyclin to bind to a Cdk because _________. (a) the cyclins are the molecules with the enzymatic activity in the complex. (b) the binding of a cyclin to Cdk is required for Cdk enzymatic activity. (c) cyclin binding inhibits Cdk activity until the appropriate time in the cell cycle. (d) without cyclin binding, a cell-cycle checkpoint will be activated.

(b) the binding of a cyclin to Cdk is required for Cdk enzymatic activity

Vesicles from the ER enter the Golgi at the ______. (a) medial cisternae. (b) trans Golgi network. (c) cis Golgi network. (d) trans cisternae.

Which of the following statements about apoptosis is true? (a) Cells that constitutively express Bcl2 will be more prone to undergo apoptosis. (b) The prodomain of procaspases contains the catalytic activity necessary for procaspase activation. (c) Bax and Bak promote apoptosis by binding to procaspases in the apoptosome. (d) Apoptosis is promoted by the release of cytochrome c into the cytosol from mitochondria.

(d) Apoptosis is promoted by the release of cytochrome c into the cytosol from mitochondria

Which of the following protein families are not involved in directing transport vesicles to the target membrane? (a) SNAREs (b) Rabs (c) tethering proteins (d) adaptins

(d) adaptins

Name the membrane-enclosed compartments in a eukaryotic cell where each of the functions listed below takes place. A. photosynthesis B. transcription C. oxidative phosphorylation D. modification of secreted proteins E. steroid hormone synthesis F. degradation of worn-out organelles G. new membrane synthesis H. breakdown of lipids and toxic molecules

A photosynthesis = chloroplast B. transcription = nucleus C. oxidative phosphorylation = mitochondrion D. modification of secreted proteins = Golgi apparatus and rough endoplasmic reticulum (ER) E. steroid hormone synthesis = smooth ER F. degradation of worn-out organelles = lysosome G. new membrane synthesis = ER H. breakdown of lipids and toxic molecules = peroxisome

Indicate whether each of the following is true for meiosis, mitosis, both, or neither. A. formation of a bivalent B. genetically identical products C. condensation of chromosomes D. segregation of all paternal chromosomes to one cell E. involvement of DNA replication

A. meiosis, B. mitosis, C. both, D. neither, E. both

Match the target of the G protein with the appropriate signaling outcome. adenylyl cyclase ________ ion channels _________ phospholipase C _________ A. cleavage of inositol phospholipids, B. increase in cAMP levels, C. changes in membrane potential

B, C, A

Irradiated mammalian cells usually stop dividing and arrest at a G1 checkpoint. Place the following events in the order in which they occur. A. production of p21 B. DNA damage C. inhibition of cyclin-Cdk complexes D. accumulation and activation of p53

B, D, A, C

The following proteins are important for cell movement. Match the following proteins with their function. myosin _____ ARP proteins _____ profilin _____ integrins _____ formins _____ A. nucleation of new actin filaments at the side of an existing filament, B. regulation of the availability of actin monomers, C. important for the growth of straight, unbranched actin filaments, D. contracting the rear of the cell, E. involvement in focal contacts

D, A, B, E, C

Match the class of cell-surface receptor with the best description of its function G-protein-coupled receptors ______ ion-channel-coupled receptors ______ enzyme-coupled receptors ______ A. alter the membrane potential directly by changing the permeability of the plasma membrane B. signal by opening and closing in a ligand-independent manner C. must be coupled with intracellular monomeric GTP-binding proteins D. all receptors of this class are polypeptides with seven transmembrane domains E. discovered for their role in responding to growth factors in animal cells

D, A, E

Cells can pause in G1 when DNA is damaged, and can pause in S when there are replication errors. Indicate whether the mechanism below applies to a G1 arrest, an S-phase arrest, both types of arrest, or neither. A. p53 activates the transcription of a Cdk inhibitor. B. Cyclins are phosphorylated and destroyed. C. Cdk is unable to phosphorylate its substrates. D. The Cdc25 phosphatase is inhibited.

G1, neither, both S-phase

Which of the following statements is true? (a) Another name for the fertilized egg cell is the zygote. (b) Diploid organisms reproduce only sexually. (c) All sexually reproducing organisms must have two copies of every chromosome. (d) Gametes have only one chromosome.

(a) Another name for the fertilized egg cell is the zygote

Which of the following statements about vesicle budding from the Golgi is false? (a) Clathrin molecules are important for binding to and selecting cargoes for transport. (b) Adaptins interact with clathrin. (c) Once vesicle budding occurs, clathrin molecules are released from the vesicle. (d) Clathrin molecules act at the cytosolic surface of the Golgi membrane.

(a) Clathrin molecules are important for binding to and selecting cargoes for transport

Which of the following statements about meiosis is true? (a) During meiosis, the paternal chromosomes pair with the maternal chromosomes before lining up at the metaphase plate. (b) Unicellular organisms that have a haploid state undergo meiosis instead of mitosis during cell division. (c) Meiosis produces four genetically identical cells. (d) In general, meiosis is faster than mitosis.

(a) During meiosis, the paternal chromosomes pair with the maternal chromosomes before lining up at the metaphase plate

Which of the following statements is true? (a) Extracellular signal molecules that are hydrophilic must bind to a cellsurface receptor so as to signal a target cell to change its behavior. (b) To function, all extracellular signal molecules must be transported by their receptor across the plasma membrane into the cytosol. (c) A cell-surface receptor capable of binding only one type of signal molecule can mediate only one kind of cell response. (d) Any foreign substance that binds to a receptor for a normal signal molecule will always induce the same response that is produced by that signal molecule on the same cell type.

(a) Extracellular signal molecules that are hydrophilic must bind to a cellsurface receptor so as to signal a target cell to change its behavior

Which of the following statements about membrane-enclosed organelles is true? (a) In a typical cell, the area of the endoplasmic reticulum membrane far exceeds the area of plasma membrane. (b) The nucleus is the only organelle that is surrounded by a double membrane. (c) Other than the nucleus, most organelles are small and thus, in a typical cell, only about 10% of a cell's volume is occupied by membrane enclosed organelles; the other 90% of the cell volume is the cytosol. (d) The nucleus is the only organelle that contains DNA.

(a) In a typical cell, the area of the endoplasmic reticulum membrane far exceeds the area of plasma membrane

Which of the following statements about the function of the centrosome is false? (a) Microtubules emanating from the centrosome have alternating polarity such that some have their plus end attached to the centrosome while others have their minus end attached to the centrosome. (b) Centrosomes contain hundreds of copies of the γ-tubulin ring complex important for microtubule nucleation. (c) Centrosomes typically contain a pair of centrioles, which is made up of a cylindrical array of short microtubules. (d) Centrosomes are the major microtubule-organizing center in animal cells.

(a) Microtubules emanating from the centrosome have alternating polarity such that some have their plus end attached to the centrosome while others have their minus end attached to the centrosome

Which of the following statements about peroxisomes is false? (a) Most peroxisomal proteins are synthesized in the ER. (b) Peroxisomes synthesize phospholipids for the myelin sheath. (c) Peroxisomes produce hydrogen peroxide. (d) Vesicles that bud from the ER can mature into peroxisomes.

(a) Most peroxisomal proteins are synthesized in the ER

Which of the following statements about microtubules is true? (a) Motor proteins move in a directional fashion along microtubules by using the inherent structural polarity of a protofilament. (b) The centromere nucleates the microtubules of the mitotic spindle. (c) Because microtubules are subject to dynamic instability, they are used only for transient structures in a cell. (d) ATP hydrolysis by a tubulin heterodimer is important for controlling the growth of a microtubule.

(a) Motor proteins move in a directional fashion along microtubules by using the inherent structural polarity of a protofilament

Which of the following statements about the cell cycle is false? (a) Once a cell decides to enter the cell cycle, the time from start to finish is the same in all eukaryotic cells. (b) An unfavorable environment can cause cells to arrest in G1. (c) A cell has more DNA during G2 than it did in G1. (d) The cleavage divisions that occur in an early embryo have short G1 and G2 phases.

(a) Once a cell decides to enter the cell cycle, the time from start to finish is the same in all eukaryotic cells

Which of the following statements about phagocytic cells in animals is false? (a) Phagocytic cells are important in the gut to take up large particles of food. (b) Phagocytic cells scavenge dead and damaged cells and cell debris. (c) Phagocytic cells can engulf invading microorganisms and deliver them to their lysosomes for destruction. (d) Phagocytic cells extend pseudopods that surround the material to be ingested.

(a) Phagocytic cells are important in the gut to take up large particles of food

Which of the following statements about molecular switches is false? (a) Phosphatases remove the phosphate from GTP on GTP-binding proteins, turning them off. (b) Protein kinases transfer the terminal phosphate from ATP onto a protein. (c) Serine/threonine kinases are the most common types of protein kinase. (d) A GTP-binding protein exchanges its bound GDP for GTP to become activated.

(a) Phosphatases remove the phosphate from GTP on GTP-binding proteins, turning them off

Which of the following statements about the benefits of sexual reproduction is false? (a) Sexual reproduction permits enhanced survival because the gametes that carry alleles enhancing survival in harsh environments are used preferentially during fertilization. (b) Unicellular organisms that can undergo sexual reproduction have an increased ability to adapt to harsh environments. (c) Sexual reproduction reshuffles genes, which is thought to help species survive in novel or varying environments. (d) Sexual reproduction can speed the elimination of deleterious alleles.

(a) Sexual reproduction permits enhanced survival because the gametes that carry alleles enhancing survival in harsh environments are used preferentially during fertilization

When Ras is activated, cells will divide. A dominant-negative form of Ras clings too tightly to GDP. You introduce a dominant-negative form of Ras into cells that also have a normal version of Ras. Which of the following statements is true? (a) The cells you create will divide less frequently than normal cells in response to the extracellular signals that typically activate Ras. (b) The cells you create will run out of the GTP necessary to activate Ras. (c) The cells you create will divide more frequently compared to normal cells in response to the extracellular signals that typically activate Ras. (d) The normal Ras in the cells you create will not be able to bind GDP because the dominant-negative Ras binds to GDP too tightly.

(a) The cells you create will divide less frequently than normal cells in response to the extracellular signals that typically activate Ras

Which of the following statements about secretion is true? (a) The membrane of a secretory vesicle will fuse with the plasma membrane when it discharges its contents to the cell's exterior. (b) Vesicles for regulated exocytosis will not bud off the trans Golgi network until the appropriate signal has been received by the cell. (c) The signal sequences of proteins destined for constitutive exocytosis ensure their packaging into the correct vesicles. (d) Proteins destined for constitutive exocytosis aggregate as a result of the acidic pH of the trans Golgi network.

(a) The membrane of a secretory vesicle will fuse with the plasma membrane when it discharges its contents to the cell's exterior

Both budding yeast and the bacteria E. coli are unicellular life. Which of the following statements explains why budding yeast can undergo sexual reproduction while E. coli cannot. (a) Unlike E. coli, budding yeast can alternate between a diploid state and a haploid state. (b) Unlike E. coli, budding yeast cannot multiply by undergoing cell division. (c) Unlike E. coli, haploid budding yeast cells can undergo meiosis to produce the gametes necessary for sexual reproduction. (d) E. coli DNA is unable to undergo homologous recombination, making it incapable of producing gametes.

(a) Unlike E. coli, budding yeast can alternate between a diploid state and a haploid state

During fertilization in humans, _________. (a) a wave of Ca2+ ions is released in the fertilized egg's cytoplasm. (b) only one sperm binds to the unfertilized egg. (c) a sperm moves in a random fashion until it encounters an egg. (d) several sperm pronuclei compete in the cytoplasm to fuse with the egg nucleus.

(a) a wave of Ca2+ ions is released in the fertilized egg's cytoplasm

You are interested in cell-size regulation and discover that signaling through a GPCR called ERC1 is important in controlling cell size in embryonic rat cells. The G protein downstream of ERC1 activates adenylyl cyclase, which ultimately leads to the activation of PKA. You discover that cells that lack ERC1 are 15% smaller than normal cells, while cells that express a mutant, constitutively activated version of PKA are 15% larger than normal cells. Given these results, which of the following treatments to embryonic rat cells should lead to smaller cells? (a) addition of a drug that causes cyclic AMP phosphodiesterase to be hyperactive (b) addition of a drug that prevents GTP hydrolysis by Gα (c) addition of a drug that activates adenylyl cyclase (d) addition of a drug that mimics the ligand of ERC1

(a) addition of a drug that causes cyclic AMP phosphodiesterase to be hyperactive

Which of the situations below will enhance microtubule shrinkage? (a) addition of a drug that inhibits GTP exchange on free tubulin dimers (b) addition of a drug that inhibits hydrolysis of the GTP carried by tubulin dimers (c) addition of a drug that increases the affinity of tubulin molecules carrying GDP for other tubulin molecules (d) addition of a drug that blocks the ability of a tubulin dimer to bind to γ- tubulin

(a) addition of a drug that inhibits GTP exchange on free tubulin dimers

Which of the following precede the re-formation of the nuclear envelope during M phase in animal cells? (a) assembly of the contractile ring (b) decondensation of chromosomes (c) reassembly of the nuclear lamina (d) transcription of nuclear genes

(a) assembly of the contractile ring

Programmed cell death occurs ________. (a) by means of an intracellular suicide program. (b) rarely and selectively only during animal development. (c) only in unhealthy or abnormal cells. (d) only during embryonic development.

(a) by means of an intracellular suicide program

The principal microtubule-organizing center in animal cells is the _______. (a) centrosome. (b) centromere. (c) kinetochore. (d) cell cortex.

(a) centrosome

Which of the following mechanisms is not directly involved in inactivating an activated RTK? (a) dephosphorylation by serine/threonine phosphatases (b) dephosphorylation by protein tyrosine phosphatases (c) removal of the RTK from the plasma membrane by endocytosis (d) digestion of the RTK in lysosomes

(a) dephosphorylation by serine/threonine phosphatases

Cells in the G0 state _______. (a) do not divide. (b) cannot re-enter the cell cycle. (c) have entered this arrest state from either G1 or G2. (d) have duplicated their DNA.

(a) do not divide

Mitogens are _____. (a) extracellular signals that stimulate cell division. (b) transcription factors important for cyclin production. (c) kinases that cause cells to grow in size. (d) produced by mitotic cells to keep nearby neighboring cells from dividing.

(a) extracellular signals that stimulate cell division

Which of the following does not occur during M phase in animal cells? (a) growth of the cell (b) condensation of chromosomes (c) breakdown of nuclear envelope (d) attachment of chromosomes to microtubules

(a) growth of the cell

Cytokinesis in animal cells _______. (a) requires ATP. (b) leaves a small circular "scar" of actin filaments on the inner surface of the plasma membrane. (c) is often followed by phosphorylation of integrins in the plasma membrane. (d) is assisted by motor proteins that pull on microtubules attached to the cell cortex.

(a) requires ATP

Which of the following items is not important for flagellar movement? (a) sarcoplasmic reticulum (b) ATP (c) dynein (d) microtubules

(a) sarcoplasmic reticulum

A large protein that passes through the nuclear pore must have an appropriate _______. (a) sorting sequence, which typically contains the positively charged amino acids lysine and arginine. (b) sorting sequence, which typically contains the hydrophobic amino acids leucine and isoleucine. (c) sequence to interact with the nuclear fibrils. (d) Ran-interacting protein domain.

(a) sorting sequence, which typically contains the positively charged amino acids lysine and arginine

All intermediate filaments are of similar diameter because _________. (a) the central rod domains are similar in size and amino acid sequence. (b) the globular domains are similar in size and amino acid sequence. (c) covalent bonds among tetramers allow them to pack together in a similar fashion. (d) there is only a single type of intermediate filament in every organism.

(a) the central rod domains are similar in size and amino acid sequence

Proteins that are fully translated in the cytosol and lack a sorting signal will end up in ____. (a) the cytosol. (b) the mitochondria. (c) the interior of the nucleus. (d) the nuclear membrane.

(a) the cytosol

A friend declares that chromosomes are held at the metaphase plate by microtubules that push on each chromosome from opposite sides. Which of the following observations does not support your belief that the microtubules are pulling on the chromosomes? (a) the jiggling movement of chromosomes at the metaphase plate (b) the way in which chromosomes behave when the attachment between sister chromatids is severed (c) the way in which chromosomes behave when the attachment to one kinetochore is severed (d) the shape of chromosomes as they move toward the spindle poles at anaphase

(a) the jiggling movement of chromosomes at the metaphase plate

A diploid cell containing 32 chromosomes will make a haploid cell containing ___ chromosomes. (a) 8 (b) 16 (c) 30 (d) 64

(b) 16

Which of the following statements is false? (a) Cytochalasins prevent actin polymerization. (b) Actin filaments are usually excluded from the cell cortex. (c) Integrins are transmembrane proteins that can bind to the extracellular matrix. (d) ARPs can promote the formation of branched actin filaments.

(b) Actin filaments are usually excluded from the cell cortex

Which of the following statements about transport into mitochondria and chloroplasts is false? (a) The signal sequence on proteins destined for these organelles is recognized by a receptor protein in the outer membrane of these organelles. (b) After a protein moves through the protein translocator in the outer membrane of these organelles, the protein diffuses in the lumen until it encounters a protein translocator in the inner membrane. (c) Proteins that are transported into these organelles are unfolded as they are being transported. (d) Signal peptidase will remove the signal sequence once the protein has been imported into these organelles.

(b) After a protein moves through the protein translocator in the outer membrane of these organelles, the protein diffuses in the lumen until it encounters a protein translocator in the inner membrane

You create cells with a version of Cdc6 that cannot be phosphorylated and thus cannot be degraded. Which of the following statements describes the likely consequence of this change in Cdc6? (a) Cells will enter S phase prematurely. (b) Cells will be unable to complete DNA synthesis. (c) The origin recognition complex (ORC) will be unable to bind to DNA. (d) Cdc6 will be produced inappropriately during M phase.

(b) Cells will be unable to complete DNA synthesis

You are working in a biotech company that has discovered a small-molecule drug called H5434. H5434 binds to LDL receptors when they are bound to cholesterol. H5434 binding does not alter the conformation of the LDL receptor's intracellular domain. Interestingly, in vitro experiments demonstrate that addition of H5434 increases the affinity of LDL for cholesterol and prevents cholesterol from dissociating from the LDL receptor even in acidic conditions. Which of the following is a reasonable prediction of what may happen when you add H5434 to cells? (a) Cytosolic cholesterol levels will remain unchanged relative to normal cells. (b) Cytosolic cholesterol levels will decrease relative to normal cells. (c) The LDL receptor will remain on the plasma membrane. (d) The uncoating of vesicles will not occur.

(b) Cytosolic cholesterol levels will decrease relative to normal cells

Consider the mechanism by which actin and tubulin polymerize. Which of the items below does not describe something similar about the polymerization mechanisms of actin and microtubules? (a) Although both filaments can grow from both ends, the growth rate is faster at the plus ends. (b) Depolymerization initiates at the plus ends of filaments. (c) Nucleotide hydrolysis promotes depolymerization of filaments. (d) Free subunits (actin and tubulin) carry nucleoside triphosphates.

(b) Depolymerization initiates at the plus ends of filaments

Acetylcholine is a signaling molecule that elicits responses from heart muscle cells, salivary gland cells, and skeletal muscle cells. Which of the following statements is false? (a) Heart muscle cells decrease their rate and force of contraction when they receive acetylcholine, whereas skeletal muscle cells contract. (b) Heart muscle cells, salivary gland cells, and skeletal muscle cells all express an acetylcholine receptor that belongs to the transmitter-gated ion channel family. (c) Active acetylcholine receptors on salivary gland cells and heart muscle cells activate different intracellular signaling pathways. (d) Heart muscle cells, salivary gland cells, and skeletal muscle cells all respond to acetylcholine within minutes of receiving the signal.

(b) Heart muscle cells, salivary gland cells, and skeletal muscle cells all express an acetylcholine receptor that belongs to the transmitter-gated ion channel family

You discover a protein, MtA, and find that it binds to the plus ends of microtubules in cells. The hypothesis that best explains this localization is ________. (a) MtA is involved in stabilizing microtubules. (b) MtA binds to GTP-bound tubulin on microtubules. (c) MtA is important for the interaction of microtubules with the centrosome. (d) MtA will not bind to purified microtubules in a test tube.

(b) MtA binds to GTP-bound tubulin on microtubules

Which of the following statements is false? (a) Asexual reproduction typically gives rise to offspring that are genetically identical. (b) Mutations in somatic cells are passed on to individuals of the next generation. (c) Sexual reproduction allows for a wide variety of gene combinations. (d) Gametes are specialized sex cells.

(b) Mutations in somatic cells are passed on to individuals of the next generation

Which of the following statements about organellar movement in the cell is false? (a) Organelles undergo saltatory movement in the cell. (b) Only the microtubule cytoskeleton is involved in organellar movement. (c) Motor proteins involved in organellar movement use ATP hydrolysis for energy. (d) Organelles are attached to the tail domain of motor proteins.

(b) Only the microtubule cytoskeleton is involved in organellar movement

Which of the following statements is true? (a) MAP kinase is important for phosphorylating MAP kinase kinase. (b) PI 3-kinase phosphorylates a lipid in the plasma membrane. (c) Ras becomes activated when an RTK phosphorylates its bound GDP to create GTP. (d) STAT proteins phosphorylate JAK proteins, which then enter the nucleus and activate gene transcription.

(b) PI 3-kinase phosphorylates a lipid in the plasma membrane

Which of the following statements about the protein quality control system in the ER is false? (a) Chaperone proteins help misfolded proteins fold properly. (b) Proteins that are misfolded are degraded in the ER lumen. (c) Protein complexes are checked for proper assembly before they can exit the ER. (d) A chaperone protein will bind to a misfolded protein to retain it in the ER.

(b) Proteins that are misfolded are degraded in the ER lumen

Which of the following statements about the endoplasmic reticulum (ER) is false? (a) The ER is the major site for new membrane synthesis in the cell. (b) Proteins to be delivered to the ER lumen are synthesized on smooth ER. (c) Steroid hormones are synthesized on the smooth ER. (d) The ER membrane is contiguous with the outer nuclear membrane.

(b) Proteins to be delivered to the ER lumen are synthesized on smooth ER

Which of the following statements about skeletal muscle contraction is false? (a) When a muscle cell receives a signal from the nervous system, voltagegated channels open in the T-tubule membrane. (b) The changes in voltage across the plasma membrane that occur when a muscle cell receives a signal from the nervous system cause an influx of Ca2+ into the sarcoplasmic reticulum, triggering a muscle contraction. (c) A change in the conformation of troponin leads to changes in tropomyosin such that it no longer blocks the binding of myosin heads to the actin filament. (d) During muscle contraction, the Z discs move closer together as the myosin heads walk toward the plus ends of the actin filaments.

(b) The changes in voltage across the plasma membrane that occur when a muscle cell receives a signal from the nervous system cause an influx of Ca2+ into the sarcoplasmic reticulum, triggering a muscle contraction

Which of the following statements is false? (a) DNA synthesis begins at origins of replication. (b) The loading of the origin recognition complexes (ORCs) is triggered by SCdk. (c) The phosphorylation and degradation of Cdc6 help to ensure that DNA is replicated only once in each cell cycle. (d) DNA synthesis can only begin after prereplicative complexes assemble on the ORCs.

(b) The loading of the origin recognition complexes (ORCs) is triggered by SCdk

Which of the following events does not usually occur during interphase? (a) Cells grow in size. (b) The nuclear envelope breaks down. (c) DNA is replicated. (d) The centrosomes are duplicated.

(b) The nuclear envelope breaks down

Which of the following statements is true? (a) Lysosomes are believed to have originated from the engulfment of bacteria specialized for digestion. (b) The nuclear membrane is thought to have arisen from the plasma membrane invaginating around the DNA. (c) Because bacteria do not have mitochondria, they cannot produce ATP in a membrane-dependent fashion. (d) Chloroplasts and mitochondria share their DNA.

(b) The nuclear membrane is thought to have arisen from the plasma membrane invaginating around the DNA

Which of the following statements is true? (a) Because endocrine signals are broadcast throughout the body, all cells will respond to the hormonal signal. (b) The regulation of inflammatory responses at the site of an infection is an example of paracrine signaling. (c) Paracrine signaling involves the secretion of signals into the bloodstream for distribution throughout the organism. (d) The axons of neurons typically signal target cells using membrane-bound signaling molecules that act on receptors in the target cells.

(b) The regulation of inflammatory responses at the site of an infection is an example of paracrine signaling.

The growth factor RGF stimulates proliferation of cultured rat cells. The receptor that binds RGF is a receptor tyrosine kinase called RGFR. Which of the following types of alteration would be most likely to prevent receptor dimerization? (a) a mutation that increases the affinity of RGFR for RGF (b) a mutation that prevents RGFR from binding to RGF (c) changing the tyrosines that are normally phosphorylated on RGFR dimerization to alanines (d) changing the tyrosines that are normally phosphorylated on RGFR dimerization to glutamic acid

(b) a mutation that prevents RGFR from binding to RGF

Male cockroaches with mutations that strongly decrease the function of an RTK called RTKX are oblivious to the charms of their female comrades. This particular RTK binds to a small molecule secreted by sexually mature females. Most males carrying loss-of-function mutations in the gene for Ras protein are also unable to respond to females. You have just read a paper in which the authors describe how they have screened cockroaches that are mutant in RTKX for additional mutations that partly restore the ability of males to respond to females. These mutations decrease the function of a protein that the authors call Z. Which of the following types of protein could Z be? Explain your answer. (a) a protein that activates the Ras protein by causing Ras to exchange GDP for GTP (b) a protein that stimulates hydrolysis of GTP by the Ras protein (c) an adaptor protein that mediates the binding of the RTKX to the Ras protein (d) a transcriptional regulator required for the expression of the Ras gene

(b) a protein that stimulates hydrolysis of GTP by the Ras protein

Molecules to be packaged into vesicles for transport are selected by ________. (a) clathrin. (b) adaptins. (c) dynamin. (d) SNAREs.

(b) adaptins

Which of the following conditions is likely to decrease the likelihood of skeletal muscle contraction? (a) partial depolarization of the T-tubule membrane, such that the resting potential is closer to zero (b) addition of a drug that blocks Ca2+ binding to troponin (c) an increase in the amount of ATP in the cell (d) a mutation in tropomyosin that decreases its affinity for the actin filament

(b) addition of a drug that blocks Ca2+ binding to troponin

The formation of a bivalent during meiosis ensures that _______. (a) one chromatid from the mother and one chromatid from the father will segregate together during meiosis I. (b) all four sister chromatids remain together until the cell is ready to divide. (c) recombination will occur between identical sister chromatids. (d) the sex chromosomes, which are not identical, will line up separately at the metaphase plate during meiosis I.

(b) all four sister chromatids remain together until the cell is ready to divide

Condensins _________. (a) are degraded when cells enter M phase. (b) assemble into complexes on the DNA when phosphorylated by M-Cdk. (c) are involved in holding sister chromatids together. (d) bind to DNA before DNA replication begins.

(b) assemble into complexes on the DNA when phosphorylated by M-Cdk

After the first meiotic cell division ________. (a) two haploid gametes are produced. (b) cells are produced that contain the same number of chromosomes as somatic cells. (c) the number of chromosomes will vary depending on how the paternal and maternal chromosomes align at the metaphase plate. (d) DNA replication occurs.

(b) cells are produced that contain the same number of chromosomes as somatic cells

During recombination _________. (a) sister chromatids undergo crossing-over with each other. (b) chiasmata hold chromosomes together. (c) one crossover event occurs for each pair of human chromosomes. (d) the synaptonemal complex keeps the sister chromatids together until anaphase II.

(b) chiasmata hold chromosomes together

The activation of the serine/threonine protein kinase Akt requires phosphoinositide 3-kinase (PI 3-kinase) to _________. (a) activate the RTK. (b) create phosphorylated lipids that serve as docking sites that localize Akt to the plasma membrane. (c) directly phosphorylate Akt. (d) to create DAG.

(b) create phosphorylated lipids that serve as docking sites that localize Akt to the plasma membrane

A cell with nuclear lamins that cannot be phosphorylated in M phase will be unable to ________. (a) reassemble its nuclear envelope at telophase. (b) disassemble its nuclear lamina at prometaphase. (c) begin to assemble a mitotic spindle. (d) condense its chromosomes at prophase.

(b) disassemble its nuclear lamina at prometaphase

Intermediate filaments help protect animal cells from mechanical stress because ______. (a) filaments directly extend from the interior of the cell to the extracellular space and into the next cell, linking one cell to the next, helping to distribute locally applied forces. (b) filaments in each cell are indirectly connected to the filaments of a neighboring cell through the desmosome, creating a continuous mechanical link between cells. (c) filaments remain independent of other cytoskeletal elements and keep the mechanical stress away from other cellular components. (d) filaments make up the desmosome junctions that connect cells; these junctions are more important than the internal network of filaments for protecting cells against mechanical stress.

(b) filaments in each cell are indirectly connected to the filaments of a neighboring cell through the desmosome, creating a continuous mechanical link between cells

You have isolated a strain of mutant yeast cells that divides normally at 30°C but cannot enter M phase at 37°C. You have isolated its mitotic cyclin and mitotic Cdk and find that both proteins are produced and can form a normal M-Cdk complex at both temperatures. Which of the following temperature-sensitive mutations could not be responsible for the behavior of this strain of yeast? (a) inactivation of a protein kinase that acts on the mitotic Cdk kinase (b) inactivation of an enzyme that ubiquitylates M cyclin (c) inactivation of a phosphatase that acts on the mitotic Cdk kinase (d) a decrease in the levels of a transcriptional regulator required for producing sufficient amounts of M cyclin

(b) inactivation of an enzyme that ubiquitylates M cyclin

In mammals, there are two sex chromosomes, X and Y, which behave like homologous chromosomes during meiosis. Normal males have one X chromosome and one Y chromosome, and normal females have two X chromosomes. Males with an extra Y chromosome (XYY) are found occasionally. Which of the following could give rise to such an XYY male? Explain your answer. (a) nondisjunction in the first meiotic division of spermatogenesis; normal meiosis in the mother (b) nondisjunction in the second meiotic division of spermatogenesis; normal meiosis in the mother (c) nondisjunction in the first meiotic division of oogenesis; normal meiosis in the father (d) nondisjunction in the second meiotic division of oogenesis; normal meiosis in the father

(b) nondisjunction in the second meiotic division of spermatogenesis; normal meiosis in the mother

An individual transport vesicle ________. (a) contains only one type of protein in its lumen. (b) will fuse with only one type of membrane. (c) is endocytic if it is traveling toward the plasma membrane. (d) is enclosed by a membrane with the same lipid and protein composition as the membrane of the donor organelle.

(b) will fuse with only one type of membrane

You examine a worm that has two genders: males that produce sperm and hermaphrodites that produce both sperm and eggs. The diploid adult has four homologous pairs of chromosomes that undergo very little recombination. Given a choice, the hermaphrodites prefer to mate with males, but just to annoy the worm, you pluck a hermaphrodite out of the wild and fertilize its eggs with its own sperm. Assuming that all the resulting offspring are viable, what fraction do you expect to be genetically identical to the parent worm? Assume that each chromosome in the original hermaphrodite is genetically distinct from its homolog. (a) all (b) none (c) 1/16 (d) 1/256

In the absence of recombination, how many genetically different types of gamete can an organism with five homologous chromosome pairs produce? (a) 5 (b) 10 (c) 32 (d) 64

Which of the following statements about the unfolded protein response (UPR) is false? (a) Activation of the UPR results in the production of more ER membrane. (b) Activation of the UPR results in the production of more chaperone proteins. (c) Activation of the UPR occurs when receptors in the cytoplasm sense misfolded proteins. (d) Activation of the UPR results in the cytoplasmic activation of gene regulatory proteins.

You are examining a cell line in which activation of the Rho family member Rac promotes lamellipodia formation. Which of the following statements is most likely to be true? (a) Cells carrying a Rac mutation that makes Rac act as if it is always bound to GTP will polymerize more unbranched actin filaments than normal cells. (b) Cells carrying a Rac mutation that makes Rac unable to exchange GDP for GTP will polymerize more unbranched actin filaments than normal cells. (c) Cells carrying a Rac mutation that makes Rac act as if it is always bound to GTP will polymerize more branched actin filaments than normal cells. (d) Cells carrying a Rac mutation that makes Rac unable to exchange GDP for GTP will polymerize more branched actin filaments than normal cells.

(c) Cells carrying a Rac mutation that makes Rac act as if it is always bound to GTP will polymerize more branched actin filaments than normal cells

Which of the following statements is true? (a) The signal sequences on mitochondrial proteins are usually at the Cterminus. (b) Most mitochondrial proteins are not imported from the cytosol but are synthesized inside the mitochondria. (c) Chaperone proteins in the mitochondria facilitate the movement of proteins across the outer and inner mitochondrial membranes. (d) Mitochondrial proteins cross the membrane in their native, folded state.

(c) Chaperone proteins in the mitochondria facilitate the movement of proteins across the outer and inner mitochondrial membranes

Which of the following statements about the cytoskeleton is false? (a) The cytoskeleton is made up of three types of protein filaments. (b) The cytoskeleton controls the location of organelles in eukaryotic cells. (c) Covalent bonds between protein monomers hold together cytoskeletal filaments. (d) The cytoskeleton of a cell can change in response to the environment.

You engineer yeast cells that express the M cyclin during S phase by replacing the promoter sequence of the M cyclin gene with that of S cyclin. Keeping in mind that yeast cells have one common Cdk that binds to all cyclins, which of the following outcomes is least likely during this experiment? (a) There will be both M cyclin-Cdk and S cyclin-Cdk complexes in the cell during S phase. (b) Some substrates that are normally phosphorylated in M phase will now be phosphorylated in S phase. (c) G1 cyclins will be expressed during S phase. (d) S-Cdk targets will be phosphorylated during S phase.

Which of the following statements about the anaphase-promoting complex (APC) is false? (a) It promotes the degradation of proteins that regulate M phase. (b) It inhibits M-Cdk activity. (c) It is continuously active throughout the cell cycle. (d) M-Cdk stimulates its activity.

How does S-Cdk help guarantee that replication occurs only once during each cell cycle? (a) It blocks the rise of Cdc6 concentrations early in G1. (b) It phosphorylates and inactivates DNA helicase. (c) It phosphorylates the Cdc6 protein, marking it for destruction. (d) It promotes the assembly of a prereplicative complex.

You are studying nuclear lamins in yeast. Using recombinant DNA technology, you alter the coding sequence of a nuclear lamin gene such that the gene now codes for a nuclear lamin protein that can no longer be phosphorylated when the nuclear envelope is broken down during mitosis. What do you predict would happen if the yeast cell only had the altered nuclear lamin gene (and not the unaltered version)? (a) Mitosis should proceed as usual because the dephosphorylation of the lamin is what is important for nuclear lamina assembly during mitosis, so phosphorylation will not be necessary. (b) Disassembly of the nuclear lamins will occur prematurely because the lamins cannot be phosphorylated. (c) Nuclear lamins will no longer disassemble properly during mitosis. (d) Nuclear lamins will be unable to produce dimers, as coiled-coil formation will be disrupted.

Which of the following statements about nuclear transport is true? (a) mRNAs and proteins transit the nucleus through different types of nuclear pores. (b) Nuclear import receptors bind to proteins in the cytosol and bring the proteins to the nuclear pores, where the proteins are released from the receptors into the pores for transit into the nucleus. (c) Nuclear pores have water-filled passages that small, water-soluble molecules can pass through in a nonselective fashion. (d) Nuclear pores are made up of many copies of a single protein.

(c) Nuclear pores have water-filled passages that small, water-soluble molecules can pass through in a nonselective fashion

Your friend works in a biotechnology company and has discovered a drug that blocks the ability of Ran to exchange GDP for GTP. What is the most likely effect of this drug on nuclear transport? (a) Nuclear transport receptors would be unable to bind cargo. (b) Nuclear transport receptors would be unable to enter the nucleus. (c) Nuclear transport receptors would be unable to release their cargo in the nucleus. (d) Nuclear transport receptors would interact irreversibly with the nuclear pore fibrils.

Which of the following statements is true? (a) Proteins destined for the ER are translated by a special pool of ribosomes whose subunits are always associated with the outer ER membrane. (b) Proteins destined for the ER translocate their associated mRNAs into the ER lumen where they are translated. (c) Proteins destined for the ER are translated by cytosolic ribosomes and are targeted to the ER when a signal sequence emerges during translation. (d) Proteins destined for the ER are translated by a pool of cytosolic ribosomes that contain ER-targeting sequences that interact with ER associated protein translocators.

(c) Proteins destined for the ER are translated by cytosolic ribosomes and are targeted to the ER when a signal sequence emerges during translation

The lab you work in has discovered a previously unidentified extracellular signal molecule called QGF, a 75,000-dalton protein. You add purified QGF to different types of cells to determine its effect on these cells. When you add QGF to heart muscle cells, you observe an increase in cell contraction. When you add it to fibroblasts, they undergo cell division. When you add it to nerve cells, they die. When you add it to glial cells, you do not see any effect on cell division or survival. Given these observations, which of the following statements is most likely to be true? (a) Because it acts on so many diverse cell types, QGF probably diffuses across the plasma membrane into the cytoplasm of these cells. (b) Glial cells do not have a receptor for QGF. (c) QGF activates different intracellular signaling pathways in heart muscle cells, fibroblasts, and nerve cells to produce the different responses observed. (d) Heart muscle cells, fibroblasts, and nerve cells must all have the same receptor for QGF.

(c) QGF activates different intracellular signaling pathways in heart muscle cells, fibroblasts, and nerve cells to produce the different responses observed

Which of the following statements about vesicular membrane fusion is false? (a) Membrane fusion does not always immediately follow vesicle docking. (b) The hydrophilic surfaces of membranes have water molecules associated with them that must be displaced before vesicle fusion can occur. (c) The GTP hydrolysis of the Rab proteins provides the energy for membrane fusion. (d) The interactions of the v-SNAREs and the t-SNAREs pull the vesicle membrane and the target organelle membrane together so that their lipids can intermix.

Which of the following descriptions is consistent with the behavior of a cell that lacks a protein required for a checkpoint mechanism that operates in G2? (a) The cell would be unable to enter M phase. (b) The cell would be unable to enter G2. (c) The cell would enter M phase under conditions when normal cells would not. (d) The cell would pass through M phase more slowly than normal cells

The following happens when a G-protein-coupled receptor activates a G protein. (a) The β subunit exchanges its bound GDP for GTP. (b) The GDP bound to the α subunit is phosphorylated to form bound GTP. (c) The α subunit exchanges its bound GDP for GTP. (d) It activates the α subunit and inactivates the βγ complex.

There are organisms that go through meiosis but do not undergo recombination when forming haploid gametes. Which of the following statements correctly describes the gametes produced by such an organism. (Assume that these organisms are diploid, that each of the two homologous chromosomes are genetically distinct as typically found in the wild, and that these organisms have more than one chromosome.) (a) All gametes formed during a single meiosis will be identical. (b) Due to the random assortment of homologs, each of the gametes formed during a single meiosis will be different. (c) This organism could potentially produce 2n genetically distinct gametes, where n is its haploid number of chromosomes. (d) The fusion of any two gametes produced by such an organism that does not undergo recombination during meiosis will create a cell that is genetically identical to that individual.

(c) This organism could potentially produce 2n genetically distinct gametes, where n is its haploid number of chromosomes

Which of the following does not describe a situation of asexual reproduction? (a) A bacterium multiplying by simple cell division. (b) Using a part of a plant to create a new independent plant. (c) Using in vitro fertilization to combine a sperm and an egg to create an embryo. (d) The parthenogenetic development of eggs produced by some species of lizards.

The growth factor Superchick stimulates the proliferation of cultured chicken cells. The receptor that binds Superchick is a receptor tyrosine kinase (RTK), and many chicken tumor cell lines have mutations in the gene that encodes this receptor. Which of the following types of mutation would be expected to promote uncontrolled cell proliferation? (a) a mutation that prevents dimerization of the receptor (b) a mutation that destroys the kinase activity of the receptor (c) a mutation that inactivates the protein tyrosine phosphatase that normally removes the phosphates from tyrosines on the activated receptor (d) a mutation that prevents the binding of the normal extracellular signal to the receptor

(c) a mutation that inactivates the protein tyrosine phosphatase that normally removes the phosphates from tyrosines on the activated receptor

Which of the following would not lead to aneuploidy during meiosis? (a) sister chromatids segregating inappropriately (b) non-sister chromatids segregating inappropriately (c) a reciprocal rearrangement of parts between nonhomologous chromosomes (for example, the left arm of Chromosome 2 exchanging places with the right arm of Chromosome 3) (d) an extra set of chromosomes produced during S phase (for example, if paternal Chromosome 3 were replicated twice)

(c) a reciprocal rearrangement of parts between nonhomologous chromosomes (for example, the left arm of Chromosome 2 exchanging places with the right arm of Chromosome 3)

Most proteins destined to enter the endoplasmic reticulum _________. (a) are transported across the membrane after their synthesis is complete. (b) are synthesized on free ribosomes in the cytosol. (c) begin to cross the membrane while still being synthesized. (d) remain within the endoplasmic reticulum.

Apoptosis differs from necrosis in that necrosis _______. (a) requires the reception of an extracellular signal. (b) causes DNA to fragment. (c) causes cells to swell and burst, whereas apoptotic cells shrink and condense. (d) involves a caspase cascade.

At the end of DNA replication, the sister chromatids are held together by the _______. (a) kinetochores. (b) securins. (c) cohesins. (d) histones.

The local mediator nitric oxide stimulates the intracellular enzyme guanylyl cyclase by ________. (a) activating a G protein. (b) activating a receptor tyrosine kinase. (c) diffusing into cells and stimulating the cyclase directly. (d) activating an intracellular protein kinase.

Your friend has just joined a lab that studies vesicle budding from the Golgi and has been given a cell line that does not form mature vesicles. He wants to start designing some experiments but wasn't listening carefully when he was told about the molecular defect of this cell line. He's too embarrassed to ask and comes to you for help. He does recall that this cell line forms coated pits but vesicle budding and the removal of coat proteins don't happen. Which of the following proteins might be lacking in this cell line? (a) clathrin (b) Rab (c) dynamin (d) adaptin

Signal sequences that direct proteins to the correct compartment are _________. (a) added to proteins through post-translational modification. (b) added to a protein by a protein translocator. (c) encoded in the amino acid sequence and sufficient for targeting a protein to its correct destination. (d) always removed once a protein is at the correct destination.

The concentration of mitotic cyclin (M cyclin) ________. (a) rises markedly during M phase. (b) is activated by phosphorylation. (c) falls toward the end of M phase as a result of ubiquitylation and degradation. (d) is highest in G1 phase.

In which cellular location would you expect to find ribosomes translating mRNAs that encode ribosomal proteins? (a) the nucleus (b) on the rough ER (c) in the cytosol (d) in the lumen of the ER

The Retinoblastoma (Rb) protein blocks cells from entering the cell cycle by ______. (a) phosphorylating Cdk. (b) marking cyclins for destruction by proteolysis. (c) inhibiting cyclin transcription. (d) activating apoptosis.

Foreign substances like nicotine, morphine, and menthol exert their initial effects by _____. (a) killing cells immediately, exerting their physiological effects by causing cell death. (b) diffusing through cell plasma membranes and binding to transcription factors to change gene expression. (c) interacting with cell-surface receptors, causing the receptors to transduce signal inappropriately in the absence of the normal stimulus. (d) removing cell-surface receptors from the plasma membrane.

(c) interacting with cell-surface receptors, causing the receptors to transduce signal inappropriately in the absence of the normal stimulus

A protein kinase can act as an integrating device in signaling if it ______. (a) phosphorylates more than one substrate. (b) catalyzes its own phosphorylation. (c) is activated by two or more proteins in different signaling pathways. (d) initiates a phosphorylation cascade involving two or more protein kinases.

Somatic cells _______. (a) are not necessary for sexual reproduction in all eukaryotic organisms. (b) are used to produce germ-line cells when organisms reach sexual maturity (c) leave no progeny. (d) do not contain sex chromosomes.

Which of the following organelles is not part of the endomembrane system? (a) Golgi apparatus (b) the nucleus (c) mitochondria (d) lysosomes

Which of the following statements is correct? Kinesins and dyneins ________. (a) have tails that bind to the filaments. (b) move along both microtubules and actin filaments. (c) often move in opposite directions to each other. (d) derive their energy from GTP hydrolysis.

Which of the following structures shorten during muscle contraction? (a) myosin filaments (b) flagella (c) sarcomeres (d) actin filaments

The microtubules in a cell form a structural framework that can have all the following functions except which one? (a) holding internal organelles such as the Golgi apparatus in particular positions in the cell (b) creating long, thin cytoplasmic extensions that protrude from one side of the cell (c) strengthening the plasma membrane (d) moving materials from one place to another inside a cell

Which of the following statements about the cytoskeleton is true? (a) All eukaryotic cells have actin, microtubules, and intermediate filaments in their cytoplasm. (b) The cytoskeleton provides a rigid and unchangeable structure important for the shape of the cell. (c) The three cytoskeletal filaments perform distinct tasks in the cell and act completely independently of one another. (d) Actin filaments and microtubules have an inherent polarity, with a plus end that grows more quickly than the minus end.

(d) Actin filaments and microtubules have an inherent polarity, with a plus end that grows more quickly than the minus end

MPF activity was discovered when cytoplasm from a Xenopus M-phase cell was injected into Xenopus oocytes, inducing the oocytes to form a mitotic spindle. In a control experiment, Xenopus interphase cytoplasm was injected into oocytes and shown not to induce the formation of a mitotic spindle. Which of the following statements is not a legitimate conclusion from the control experiment? (a) The piercing of the oocyte membrane by a needle is insufficient to cause mitotic spindle formation. (b) An increased volume of cytoplasm is insufficient to cause mitotic spindle formation. (c) Injection of extra RNA molecules is insufficient to cause mitotic spindle formation. (d) Components of an interphase nucleus are insufficient to cause mitotic spindle formation.

(d) Components of an interphase nucleus are insufficient to cause mitotic spindle formation

Which of the following statements is false? (a) Nucleotides and amino acids can act as extracellular signal molecules. (b) Some signal molecules can bind directly to intracellular proteins that bind DNA and regulate gene transcription. (c) Some signal molecules are transmembrane proteins. (d) Dissolved gases such as nitric oxide (NO) can act as signal molecules, but because they cannot interact with proteins they must act by affecting membrane lipids.

(d) Dissolved gases such as nitric oxide (NO) can act as signal molecules, but because they cannot interact with proteins they must act by affecting membrane lipids

Which of the following statements about disulfide bond formation is false? (a) Disulfide bonds do not form under reducing environments. (b) Disulfide bonding occurs by the oxidation of pairs of cysteine side chains on the protein. (c) Disulfide bonding stabilizes the structure of proteins. (d) Disulfide bonds form spontaneously within the ER because the lumen of the ER is oxidizing.

(d) Disulfide bonds form spontaneously within the ER because the lumen of the ER is oxidizing

Which of the following choices reflects the appropriate order of locations through which a protein destined for the plasma membrane travels? (a) lysosome -> endosome -> plasma membrane (b) ER -> lysosome -> plasma membrane (c) Golgi -> lysosome -> plasma membrane (d) ER -> Golgi -> plasma membrane

(d) ER -> Golgi -> plasma membrane

Which of the statements below about intermediate filaments is false? (a) They can stay intact in cells treated with concentrated salt solutions. (b) They can be found in the cytoplasm and the nucleus. (c) They can be anchored to the plasma membrane at a cell-cell junction. (d) Each filament is about 10 μm in diameter.

(d) Each filament is about 10 μm in diameter

Which of the following statements is true? (a) Anaphase A must be completed before anaphase B can take place. (b) In cells in which anaphase B predominates, the spindle will elongate much less than in cells in which anaphase A dominates. (c) In anaphase A, both kinetochore and interpolar microtubules shorten. (d) In anaphase B, microtubules associated with the cell cortex shorten.

(d) In anaphase B, microtubules associated with the cell cortex shorten

Which of the following statements most correctly describes meiosis? (a) Meiosis involves two rounds of DNA replication followed by a single cell division. (b) Meiosis involves a single round of DNA replication followed by four successive cell divisions. (c) Meiosis involves four rounds of DNA replication followed by two successive cell divisions. (d) Meiosis involves a single round of DNA replication followed by two successive cell divisions.

(d) Meiosis involves a single round of DNA replication followed by two successive cell divisions

Which of the following statements is false? (a) Cytokinesis in plant cells is mediated by the microtubule cytoskeleton. (b) Small membrane vesicles derived from the Golgi apparatus deliver new cell-wall material for the new wall of the dividing cell. (c) The phragmoplast forms from the remains of interpolar microtubules of the mitotic spindle. (d) Motor proteins walking along the cytoskeleton are important for the contractile ring that guides formation of the new cell wall.

(d) Motor proteins walking along the cytoskeleton are important for the contractile ring that guides formation of the new cell wall

Different glycoproteins can have a diverse array of oligosaccharides. Which of the statements below about this diversity is true? (a) Extensive modification of oligosaccharides occurs in the extracellular space. (b) Different oligosaccharides are covalently linked to proteins in the ER and the Golgi. (c) A diversity of oligosaccharyl transferases recognizes specific protein sequences, resulting in the linkage of a variety of oligosaccharides to proteins. (d) Oligosaccharide diversity comes from modifications that occur in the ER and the Golgi of the 14-sugar oligosaccharide added to the protein in the ER.

(d) Oligosaccharide diversity comes from modifications that occur in the ER and the Golgi of the 14-sugar oligosaccharide added to the protein in the ER

You are interested in Fuzzy, a soluble protein that functions within the ER lumen. Given that information, which of the following statements must be true? (a) Fuzzy has a C-terminal signal sequence that binds to SRP. (b) Only one ribosome can be bound to the mRNA encoding Fuzzy during translation. (c) Fuzzy must contain a hydrophobic stop-transfer sequence. (d) Once the signal sequence from Fuzzy has been cleaved, the signal peptide will be ejected into the ER membrane and degraded.

(d) Once the signal sequence from Fuzzy has been cleaved, the signal peptide will be ejected into the ER membrane and degraded

Keratins, neurofilaments, and vimentins are all categories of intermediate filaments. Which of the following properties is not true of these types of intermediate filaments? (a) They strengthen cells against mechanical stress. (b) Dimers associate by noncovalent bonding to form a tetramer. (c) They are found in the cytoplasm. (d) Phosphorylation causes disassembly during every mitotic cycle.

(d) Phosphorylation causes disassembly during every mitotic cycle

Cell movement involves the coordination of many events in the cell. Which of the following phenomena is not required for cell motility? (a) Myosin-mediated contraction at the rear of the moving cell. (b) Integrin association with the extracellular environment. (c) Nucleation of new actin filaments. (d) Release of Ca2+ from the sarcoplasmic reticulum.

(d) Release of Ca2+ from the sarcoplasmic reticulum

Which of the following statements about a protein in the lumen of the ER is false? (a) A protein in the lumen of the ER is synthesized by ribosomes on the ER membrane. (b) Some of the proteins in the lumen of the ER can end up in the extracellular space. (c) Some of the proteins in the lumen of the ER can end up in the lumen of an organelle in the endomembrane system. (d) Some of the proteins in the lumen of the ER can end up in the plasma membrane.

(d) Some of the proteins in the lumen of the ER can end up in the plasma membrane

Which of the following statements is false? (a) Mitotic Cdk must be phosphorylated by an activating kinase (Cak) before it is active. (b) Phosphorylation of mitotic Cdk by the inhibitory kinase (Wee1) makes the Cdk inactive, even if it is phosphorylated by the activating kinase. (c) Active M-Cdk phosphorylates the activating phosphatase (Cdc25) in a positive feedback loop. (d) The activating phosphatase (Cdc25) removes all phosphates from mitotic Cdk so that M-Cdk will be active.

(d) The activating phosphatase (Cdc25) removes all phosphates from mitotic Cdk so that M-Cdk will be active

What would be the most obvious outcome of repeated cell cycles consisting of S phase and M phase only? (a) Cells would not be able to replicate their DNA. (b) The mitotic spindle could not assemble. (c) Cells would get larger and larger. (d) The cells produced would get smaller and smaller.

(d) The cells produced would get smaller and smaller

Which of the following statements is false? (a) The cleavage furrow is a puckering of the plasma membrane caused by the constriction of a ring of filaments attached to the plasma membrane. (b) The cleavage furrow will not begin to form in the absence of a mitotic spindle. (c) The cleavage furrow always forms perpendicular to the interpolar microtubules. (d) The cleavage furrow always forms in the middle of the cell.

(d) The cleavage furrow always forms in the middle of the cell

Which of the following statements about G-protein-coupled receptors (GPCRs) is false? (a) GPCRs are the largest family of cell-surface receptors in humans. (b) GPCRs are used in endocrine, paracrine, and neuronal signaling. (c) GPCRs are found in yeast, mice, and humans. (d) The different classes of GPCR ligands (proteins, amino acid derivatives, or fatty acids) bind to receptors with different numbers of transmembrane domains.

(d) The different classes of GPCR ligands (proteins, amino acid derivatives, or fatty acids) bind to receptors with different numbers of transmembrane domains

Which of the following statements about actin is false? (a) ATP hydrolysis decreases actin filament stability. (b) Actin at the cell cortex helps govern the shape of the plasma membrane. (c) Actin filaments are nucleated at the side of existing actin filaments in lamellipodia. (d) The dynamic instability of actin filaments is important for cell movement.

(d) The dynamic instability of actin filaments is important for cell movement

Which of the following statements is true? (a) The mitotic spindle is largely made of intermediate filaments. (b) The contractile ring is made largely of microtubules and actin filaments. (c) The contractile ring divides the nucleus in two. (d) The mitotic spindle helps segregate the chromosomes to the two daughter cells.

(d) The mitotic spindle helps segregate the chromosomes to the two daughter cells

Which of the following statements regarding dynamic instability is false? (a) Each microtubule filament grows and shrinks independently of its neighbors. (b) The GTP cap helps protect a growing microtubule from depolymerization. (c) GTP hydrolysis by the tubulin dimer promotes microtubule shrinking. (d) The newly freed tubulin dimers from a shrinking microtubule can be immediately captured by growing microtubules and added to their plus end.

(d) The newly freed tubulin dimers from a shrinking microtubule can be immediately captured by growing microtubules and added to their plus end

Imagine meiosis in a diploid organism that only has a single chromosome. Like most diploid organisms, it received one copy of this chromosome from each of its parents and the two homologs are genetically distinct. If only a single homologous recombination event occurs during meiosis, which of the following choices below correctly describes the four gametes formed. (a) None of the gametes will contain chromosomes identical to the chromosomes found in the original diploid cell. (b) All four of the gametes will have chromosomes identical to the chromosomes found in the original diploid cell. (c) Three of the gametes will have chromosomes identical to the chromosomes found in the original diploid cell, while one of the gametes will have chromosomes that are different. (d) Two of the gametes will have chromosomes identical to the chromosomes found in the original diploid cell, while two of the gametes will have chromosomes that are different.

(d) Two of the gametes will have chromosomes identical to the chromosomes found in the original diploid cell, while two of the gametes will have chromosomes that are different

Which of the following is not good direct evidence that the cell-cycle control system is conserved through billions of years of divergent evolution? (a) A yeast cell lacking a Cdk function can use the human Cdk to substitute for its missing Cdk during the cell cycle. (b) The amino acid sequences of cyclins in plants are similar to the amino acid sequences of cyclins in humans. (c) The Cdk proteins in humans share conserved phosphorylation sites with the Cdk proteins in yeast. (d) Yeast cells have only one Cdk, whereas humans have many Cdks.

(d) Yeast cells have only one Cdk, whereas humans have many Cdks

You are interested in understanding the regulation of nuclear lamina assembly. To create an in vitro system for studying this process you start with partly purified nuclear lamina subunits to which you will add back purified cellular components to drive nuclear lamina assembly. Before you start doing experiments, your instructor suggests that you consider what type of conditions would be most amenable to the assembly of the nuclear lamina from its individual subunits in vitro. Which of the following conditions do you predict would be most likely to enhance the assembly of the nuclear lamina? (a) addition of phosphatase inhibitors (b) addition of ATP (c) addition of a concentrated salt solution that is 10 times the concentration normally found in the nucleoplasm (d) addition of protein kinase inhibitors

(d) addition of protein kinase inhibitors

After isolating the rough endoplasmic reticulum from the rest of the cytoplasm, you purify the RNAs attached to it. Which of the following proteins do you expect the RNA from the rough endoplasmic reticulum to encode? (a) soluble secreted proteins (b) ER membrane proteins (c) plasma membrane proteins (d) all of the above

(d) all of the above

The hydrolysis of GTP to GDP carried out by tubulin molecules _________. (a) provides the energy needed for tubulin to polymerize. (b) occurs because the pool of free GDP has run out. (c) tips the balance in favor of microtubule assembly. (d) allows the behavior of microtubules called dynamic instability.

(d) allows the behavior of microtubules called dynamic instability

When introduced into mitotic cells, which of the following is expected to impair anaphase B but not anaphase A? (a) an antibody against myosin (b) ATPγS, a nonhydrolyzable ATP analog that binds to and inhibits ATPases (c) an antibody against the motor proteins that move from the plus end of microtubules to the minus end (d) an antibody against the motor proteins that move from the minus end of microtubules toward the plus end

(d) an antibody against the motor proteins that move from the minus end of microtubules toward the plus end

In which phase of the cell cycle do cells check to determine whether the DNA is fully and correctly replicated? (a) at the transition between G1 and S (b) when cells enter G0 (c) during M (d) at the end of G2

(d) at the end of G2

During nervous-system development in Drosophila, the membrane-bound protein Delta acts as an inhibitory signal to prevent neighboring cells from developing into neuronal cells. Delta is involved in _______ signaling. (a) endocrine (b) paracrine (c) neuronal (d) contact-dependent

(d) contact-dependent

Levels of Cdk activity change during the cell cycle, in part because _________. (a) the Cdks phosphorylate each other. (b) the Cdks activate the cyclins. (c) Cdk degradation precedes entry into the next phase of the cell cycle. (d) cyclin levels change during the cycle.

(d) cyclin levels change during the cycle

For both actin and microtubule polymerization, nucleotide hydrolysis is important for ______. (a) stabilizing the filaments once they are formed. (b) increasing the rate at which subunits are added to the filaments. (c) promoting nucleation of filaments. (d) decreasing the binding strength between subunits on filaments.

(d) decreasing the binding strength between subunits on filaments

During sexual reproduction, novel mixtures of alleles are generated. This is because ______. (a) in all diploid species, two alleles exist for every gene. (b) a diploid individual has two different alleles for every gene. (c) every gamete produced by a diploid individual has several different alleles of a single gene. (d) during meiosis, the segregation of homologs is random such that different gametes end up with different alleles of each gene.

(d) during meiosis, the segregation of homologs is random such that different gametes end up with different alleles of each gene

Where are proteins in the chloroplast synthesized? (a) in the cytosol (b) in the chloroplast (c) on the endoplasmic reticulum (d) in both the cytosol and the chloroplast

(d) in both the cytosol and the chloroplast

All members of the steroid hormone receptor family _________. (a) are cell-surface receptors. (b) do not undergo conformational changes. (c) are found only in the cytoplasm. (d) interact with signal molecules that diffuse through the plasma membrane.

(d) interact with signal molecules that diffuse through the plasma membrane

The G1 DNA damage checkpoint ________. (a) causes cells to proceed through S phase more quickly. (b) involves the degradation of p53. (c) is activated by errors caused during DNA replication. (d) involves the inhibition of cyclin-Cdk complexes by p21.

(d) involves the inhibition of cyclin-Cdk complexes by p21

Disassembly of the nuclear envelope ________. (a) causes the inner nuclear membrane to separate from the outer nuclear membrane. (b) results in the conversion of the nuclear envelope into protein-free membrane vesicles. (c) is triggered by the phosphorylation of integrins. (d) must occur for kinetochore microtubules to form in animal cells.

(d) must occur for kinetochore microtubules to form in animal cells

Your friend works in a biotech company that has just discovered a drug that seems to promote lamellipodia formation in cells. Which of the following molecules is unlikely to be involved in the pathway that this drug affects? (a) Rac (b) ARP (c) actin (d) myosin

(d) myosin

The length of time a G protein will signal is determined by _______. (a) the activity of phosphatases that turn off G proteins by dephosphorylating Gα. (b) the activity of phosphatases that turn GTP into GDP. (c) the degradation of the G protein after Gα separates from Gβγ (d) the GTPase activity of Gα

(d) the GTPase activity of Gα

N-linked oligosaccharides on secreted glycoproteins are attached to ________. (a) nitrogen atoms in the polypeptide backbone. (b) the serine or threonine in the sequence Asn-X-Ser/Thr. (c) the N-terminus of the protein. (d) the asparagine in the sequence Asn-X-Ser/Thr.

(d) the asparagine in the sequence Asn-X-Ser/Thr

Proteins that are fully translated in the cytosol do not end up in _______. (a) the cytosol. (b) the mitochondria. (c) the interior of the nucleus. (d) transport vesicles.

(d) transport vesicles

Organisms that reproduce sexually ________. (a) must be haploid, unlike organisms that reproduce asexually. (b) can reproduce only with a partner that carries the same alleles. (c) create zygotes that are genetically identical to each other. (d) undergo a sexual reproductive cycle that involves an alternation of haploid cells with the generation of diploid cells.

(d) undergo a sexual reproductive cycle that involves an alternation of haploid cells with the generation of diploid cells

A single nondisjunction event during meiosis _________. (a) will block recombination. (b) will occur only during meiosis II. (c) cannot occur with sex chromosomes. (d) will involve the production of two normal gametes if it occurs during meiosis II.

(d) will involve the production of two normal gametes if it occurs during meiosis II

Which of the following statements about the structure of microtubules is false? (a) Microtubules are built from protofilaments that come together to make a hollow structure. (b) The two ends of a protofilament are chemically distinct, with α-tubulin exposed at one end and β-tubulin exposed at the other end. (c) Within a microtubule, all protofilaments are arranged in the same orientation, giving the microtubule structural polarity. (d) α-Tubulin and β-tubulin are covalently bound to make the tubulin dimer that then assembles into protofilaments.

(d) α-Tubulin and β-tubulin are covalently bound to make the tubulin dimer that then assembles into protofilaments

Match the components involved with ER transport with the appropriate cellular location. Locations can be used more than once, or not at all. 1. signal-recognition particle _____ 2. protein translocator _____ 3. mRNA _____ 4. SRP receptor _____ 5. active site of signal peptidase ____ A. cytosol, B. ER lumen, C. ER membrane

1—A; 2—C; 3—A; 4—C; 5—B

Rank the following cytoskeletal filaments from smallest to largest in diameter (1 = smallest in diameter, 4 = largest) ______ intermediate filaments ______ microtubules ______ actin filament ______ myofibril

2, 3, 1, 4

Rank the following types of cell signaling from 1 to 4, with 1 representing the type of signaling in which the signal molecule travels the least distance and 4 the type of signaling in which the signal molecule travels the largest distance. ______ paracrine signaling ______ contact-dependent signaling ______ neuronal signaling ______ endocrine signaling

3, 1, 2, 4

Meiosis is a highly specialized cell division in which several events occur in a precisely defined order. Please order the meiotic events listed below. 1. loss of cohesins near centromeres 2. chromatid pairing 3. chromosome condensation 4. chromosome replication 5. degradation of cohesins bound to chromosome arms 6. formation of chiasmata (chiasmata = plural of chiasma) 7. homolog pairing 8. alignment of chromosomes at the metaphase plate

4, 2, 7, 6, 3, 8, 5, 1

Place the numbers 1-8 next to the letter headings to indicate the normal order of events. A. alignment of the chromosomes at the spindle equator B. attachment of spindle microtubules to chromosomes C. breakdown of nuclear envelope D. pinching of cell in two E. separation of two centrosomes and initiation of mitotic spindle assembly F. re-formation of the nuclear envelope G. condensation of the chromosomes H. separation of sister chromatids

5, 4, 3, 8, 2, 7, 1, 6

Circle the phrase in each pair that is likely to occur more rapidly in response to an extracellular signal. A. changes in cell secretion / increased cell division B. changes in protein phosphorylation / changes in proteins being synthesized C. changes in mRNA levels / changes in membrane potential

A. changes in cell secretion B. changes in protein phosphorylation C. changes in membrane potential

An extracellular signal molecule can act to change a cell's behavior by acting through cell-surface ________ that control intracellular signaling proteins. These intracellular signaling proteins ultimately change the activity of _______ proteins that bring about cell responses. Intracellular signaling proteins can _______ the signal received to evoke a strong response from just a few extracellular signal molecules. A cell that receives more than one extracellular signal at the same time can _______ this information using intracellular signaling proteins. ______ proteins can act as molecular switches, letting a cell know that a signal has been received. Enzymes that phosphorylate proteins, termed _______, can also serve as molecular switches; the actions of these enzymes are countered by the activity of _______. Acetylase, decouple, GTP-binding, AMP-binding, decrease, neurotransmitter, amplify, effector, protein kinases, autocrine, esterases, protein phosphatases, cleavage, integrate, receptors, convolute, GMP-binding, sterols

An extracellular signal molecule can act to change a cell's behavior by acting through cell-surface receptors that control intracellular signaling proteins. These intracellular signaling proteins ultimately change the activity of effector proteins that bring about cell responses. Intracellular signaling proteins can amplify the signal received to evoke a strong response from just a few extracellular signal molecules. A cell that receives more than one extracellular signal at the same time can integrate this information using intracellular signaling proteins. GTP-binding proteins can act as molecular switches, letting a cell know that a signal has been received. Enzymes that phosphorylate proteins, termed protein kinases, can also serve as molecular switches; the actions of these enzymes are countered by the activity of protein phosphatases.

Before mitosis, the number of centrosomes must [increase/decrease]. At the beginning of [anaphase/prophase] in animal cells, the centrosomes separate in a process driven partly by interactions between the [plus/minus] ends of microtubules arising from the two centrosomes. Centrosome separation initiates the assembly of the bipolar mitotic spindle and is associated with a sudden [increase/decrease] in the dynamic instability of microtubules. In comparison with an interphase microtubule array, a mitotic aster contains a [smaller/larger] number of [longer/shorter] microtubules. Extracts from M-phase cells exhibit [increased/decreased/unchanged] rates of microtubule polymerization and increased frequencies of microtubule [shrinkage/growth]. The changes in microtubule dynamics are largely due to [enhanced/reduced] activity of microtubule-associated proteins and [increased/decreased] activity of catastrophins. The new balance between polymerization and depolymerization of microtubules is necessary for the mitotic spindle to move the [replicated chromosomes/daughter chromosomes] to the metaphase plate.

Before mitosis, the number of centrosomes must increase. At the beginning of prophase in animal cells, the centrosomes separate in a process driven partly by interactions between the plus ends of microtubules arising from the two centrosomes. Centrosome separation initiates the assembly of the bipolar mitotic spindle and is associated with a sudden increase in the dynamic instability of microtubules. In comparison with an interphase microtubule array, a mitotic aster contains a larger number of shorter microtubules. Extracts from M-phase cells exhibit unchanged rates of microtubule polymerization and increased frequencies of microtubule shrinkage. The changes in microtubule dynamics are largely due to reduced activity of microtubule-associated proteins and increased activity of catastrophins. The new balance between polymerization and depolymerization of microtubules is necessary for the mitotic spindle to move the replicated chromosomes to the metaphase plate.

Match the type of intermediate filament with its appropriate location. lamins _________ neurofilaments _________ vimentins _________ keratins _________ A. nerve cells, B. epithelia, C. nucleus, D. connective tissue

C, A, D, B

Place the following in order of size, from the smallest to the largest. A. protofilament B. microtubule C. α-tubulin D. tubulin dimer E. mitotic spindle

C, D, A, B, E

Ca2+ can trigger biological effects in cells because an unstimulated cell has an extremely ______ concentration of free Ca2+ in the cytosol, compared with its concentration in the ________ space and in the ______, creating a steep electrochemical gradient. When Ca2+ enters the cytosol, it interacts with Ca2+-responsive proteins such as ______, which also binds diacylglycerol, and ______, which activates CaM-kinases. adenylyl cyclase, endoplasmic reticulum, nuclear, average, extracellular, peroxisome, Ca2+, high, phospholipase C, calmodulin, intracellular, protein kinase A, colorful, low, protein kinase C

Ca2+ can trigger biological effects in cells because an unstimulated cell has an extremely low concentration of free Ca2+ in the cytosol, compared with its concentration in the extracellular space and in the endoplasmic reticulum, creating a steep electrochemical gradient. When Ca2+ enters the cytosol, it interacts with Ca2+-responsive proteins such as protein kinase C, which also binds diacylglycerol, and calmodulin, which activates CaM-kinases

Cells can signal to each other in various ways. A signal that must be relayed to the entire body is most efficiently sent by ______ cells, which produce hormones that are carried throughout the body through the bloodstream. On the other hand, ______ methods of cell signaling do not require the release of a secreted molecule and are used for very localized signaling events. During ______ signaling, the signal remains in the neighborhood of the secreting cell and thus acts as a local mediator on nearby cells. Finally, ______ signaling involves the conversion of electrical impulses into a chemical signal. Cells receive signals through a _______, which can be an integral membrane protein or can reside inside the cell. Amplification, G protein, phosphorylation, contact-dependent, K+ channel, receptor, endocrine, neuronal, target, epithelial, paracrine

Cells can signal to each other in various ways. A signal that must be relayed to the entire body is most efficiently sent by endocrine cells, which produce hormones that are carried throughout the body through the bloodstream. On the other hand, contact-dependent methods of cell signaling do not require the release of a secreted molecule and are used for very localized signaling events. During paracrine signaling, the signal remains in the neighborhood of the secreting cell and thus acts as a local mediator on nearby cells. Finally, neuronal signaling involves the conversion of electrical impulses into a chemical signal. Cells receive signals through a receptor, which can be an integral membrane protein or can reside inside the cell.

Cells signal to one another in various ways. Some use extracellular signal molecules that are dissolved gases, such as ______, which can diffuse easily into cells. Others use cytokines, which bind to cytokine receptors. Cytokine receptors have no intrinsic enzyme activity but are associated with cytoplasmic tyrosine kinases called ______s, which become activated on the binding of cytokine to its receptor and go on to phosphorylate and activate cytoplasmic transcriptional regulators called ______s. Some intracellular signaling pathways involve chains of protein kinases that phosphorylate each other, as seen in the ______ signaling module. Lipids can also relay signals in the cell, as we observe when phospholipase C cleaves the sugar-phosphate head off a lipid molecule to generate the two small messenger molecules ______ (which remains embedded in the plasma membrane) and ______ (which diffuses into the cytosol). cyclic GMP, MAP kinase, STAT, diacylglycerol, NO, TGFβ, IP3, Ras, JAK, SMAD

Cells signal to one another in various ways. Some use extracellular signal molecules that are dissolved gases, such as NO, which can diffuse easily into cells. Others use cytokines, which bind to cytokine receptors. Cytokine receptors have no intrinsic enzyme activity but are associated with cytoplasmic tyrosine kinases called JAKs, which become activated on the binding of cytokine to its receptor and go on to phosphorylate and activate cytoplasmic transcriptional regulators called STATs. Some intracellular signaling pathways involve chains of protein kinases that phosphorylate each other, as seen in the MAP kinase signaling module. Lipids can also relay signals in the cell, as we observe when phospholipase C cleaves the sugar-phosphate head off a lipid molecule to generate the two small messenger molecules diacylglycerol (which remains embedded in the plasma membrane) and IP3 (which diffuses into the cytosol).

Indicate whether each of the following conditions would increase or decrease the effect of acetylcholine. A. addition of a drug that stimulates the GTPase activity of the Gα subunit B. mutations in the K+ channel that keep it closed all the time C. modification of the Gα subunit by cholera toxin D. a mutation that decreases the affinity of the βγ complex of the G protein for the K+ channel E. a mutation in the acetylcholine receptor that prevents its localization on the cell surface F. adding acetylcholinesterase to the external environment of the cell

Decrease, decrease, increase, decrease, decrease, decrease

Eukaryotic cells are continually taking up materials from the extracellular space by the process of endocytosis. One type of endocytosis is ________, which uses ______ proteins to form small vesicles containing fluids and molecules. After these vesicles have pinched off from the plasma membrane, they will fuse with the ______, where materials that are taken into the vesicle are sorted. A second type of endocytosis is ______, which is used to take up large vesicles that can contain microorganisms and cellular debris. Macrophages are especially suited for this process, as they extend ________ (sheetlike projections of their plasma membrane) to surround the invading microorganisms. Chaperone, Golgi apparatus, pseudopods, cholesterol, mycobacterium, rough ER, clathrin, phagocytosis, SNARE, endosome, pinocytosis, transcytosis

Eukaryotic cells are continually taking up materials from the extracellular space by the process of endocytosis. One type of endocytosis is pinocytosis, which uses clathrin proteins to form small vesicles containing fluids and molecules. After these vesicles have pinched off from the plasma membrane, they will fuse with the endosome, where materials that are taken into the vesicle are sorted. A second type of endocytosis is phagocytosis, which is used to take up large vesicles that can contain microorganisms and cellular debris. Macrophages are especially suited for this process, as they extend pseudopods (sheetlike projections of their plasma membrane) to surround the invading microorganisms

Before chromosomes segregate in M phase, they and the segregation machinery must be appropriately prepared. Indicate whether the following statements are true or false. If false, change a single noun to make the statement true. A. Sister chromatids are held together by condensins from the time they arise by DNA replication until the time they separate at anaphase. B. Cohesins are required to make the chromosomes more compact and thus to prevent tangling between different chromosomes. C. The mitotic spindle is composed of actin filaments and myosin filaments. D. Microtubule-dependent motor proteins and microtubule polymerization and depolymerization are mainly responsible for the organized movements of chromosomes during mitosis. E. The centromere nucleates a radial array of microtubules called an aster, and its duplication is triggered by S-Cdk. F. Each centrosome contains a pair of centrioles and hundreds of γ-tubulin rings that nucleate the growth of microtubules.

False, False, False, True, False, True

G-protein-coupled receptors (GPCRs) all have a similar structure with _______ transmembrane domains. When a GPCR binds an extracellular signal, an intracellular G protein, composed of ______ subunits, becomes activated. _____ of the G-protein subunits are tethered to the plasma membrane by short lipid tails. When unstimulated, the α subunit is bound to _______, which is exchanged for _______ on stimulation. The intrinsic _______ activity of the α subunit is important for inactivating the G protein. ______ inhibits this activity of the α subunit, thereby keeping the subunit in an active state. adenylyl cyclase, cholera toxin, GTPase, AMP, diacylglycerol, phosphodiesterase, ATP, five, seven, ATPase, four, three, Ca2+, GDP, twelve, cAMP, GTP, two,

G-protein-coupled receptors (GPCRs) all have a similar structure with seven transmembrane domains. When a GPCR binds an extracellular signal, an intracellular G protein, composed of three subunits, becomes activated. Two of the G-protein subunits are tethered to the plasma membrane by short lipid tails. When unstimulated, the α subunit is bound to GDP, which is exchanged for GTP on stimulation. The intrinsic GTPase activity of the α subunit is important for inactivating the G protein. Cholera toxin inhibits this activity of the α subunit, thereby keeping the subunit in an active state.

Intermediate filaments are elongated fibrous proteins with an N-terminal globular ______ region and a C-terminal globular _______ region; these regions flank the elongated rod domain. The α-helical region of the rod interacts with the α-helical region of another monomer in a _______ configuration to form a dimer. _______ dimers will line up to form a staggered tetramer. _____ strands of tetramers come together and twist together to form the _____ nm filament. The ______ domains are exposed on the surface of the intermediate filament, allowing for interaction with cytoplasmic components. Antiparallel, four, tail, β barrel, globular, ten, coiled-coil, head, trimeric, covalent, rod, twenty-five, eight, seven, two

Intermediate filaments are elongated fibrous proteins with an N-terminal globular head region and a C-terminal globular tail region; these regions flank the elongated rod domain. The α-helical region of the rod interacts with the α-helical region of another monomer in a coiled-coil configuration to form a dimer. Two dimers will line up to form a staggered tetramer. Eight strands of tetramers come together and twist together to form the ten nm filament. The globular domains are exposed on the surface of the intermediate filament, allowing for interaction with cytoplasmic components

Intermediate filaments are found mainly in cells that are subject to mechanical stress. Gene mutations that disrupt intermediate filaments cause some rare human genetic diseases. For example, the skin of people with epidermolysis bullosa simplex is very susceptible to mechanical injury; people with this disorder have mutations in their ______ genes, which code for the intermediate filament found in epithelial cells. These filaments are usually connected from cell to cell through junctions called ______s. The main filaments found in muscle cells belong to the _____ family; people with disruptions in these intermediate filaments can have muscular dystrophy. In the nervous system, ______s help strengthen the extremely long extensions often present in nerve cell axons; disruptions in these intermediate filaments can lead to neurodegeneration. People who carry mutations in the gene for _____, an important protein for cross-linking intermediate filaments, have a disease that combines symptoms of epidermolysis bullosa simplex, muscular dystrophy, and neurodegeneration. Humans with progeria, a disease that causes premature aging, carry mutations in a nuclear _______. Desmosome, lamin, synapse, keratin, neurofilament, vimentin, kinase, plectin

Intermediate filaments are found mainly in cells that are subject to mechanical stress. Gene mutations that disrupt intermediate filaments cause some rare human genetic diseases. For example, the skin of people with epidermolysis bullosa simplex is very susceptible to mechanical injury; people with this disorder have mutations in their keratin genes, the intermediate filament found in epithelial cells. These filaments are usually connected from cell to cell through junctions called desmosomes. The main filaments found in muscle cells belong to the vimentin family; people with disruptions in these intermediate filaments can have muscular dystrophy. In the nervous system, neurofilaments help strengthen the extremely long extensions often present in nerve cell axons; disruptions in these intermediate filaments can lead to neurodegeneration. People who carry mutations in the gene for plectin, an important protein for cross-linking intermediate filaments, have a disease that combines symptoms of epidermolysis bullosa simplex, muscular dystrophy, and neurodegeneration. Humans with progeria, a disease that causes premature aging, carry mutations in a nuclear lamin.

Many features of _______ cells make them suitable for biochemical studies of the cell-cycle control system. For example, the cells are unusually large and are arrested in a _______-like phase. When the cells are triggered to resume cycling, the cell divisions have especially _______ G1 and G2 phases and occur _______. Studies with Xenopus eggs identified a partly purified activity called _______ that drives a resting Xenopus oocyte into M phase. MPF activity was found to _______ during the cell cycle, although the amount of its kinase component, called _______, remained constant. The regulatory component of MPF, called ________, has a ______ effect on MPF activity and plays a part in regulating interactions with its _______s. The components of MPF are evolutionarily ______ from yeast to humans, so that the corresponding human genes are _______ to function in yeast. Able, hexokinase, short, asynchronously, inhibitory, sperm, Cdk, long, steady, conserved, M, stimulatory, cyclin, maturation promoting factor, substrate, divergent, oscillate, synchronously, egg, PI 3-kinase, ubiquitin, fibroblast, regulin, unable, G1, S, uniform, G2

Many features of egg cells make them suitable for biochemical studies of the cell-cycle control system. For example, the cells are unusually large and are arrested in a G2-like phase. When the cells are triggered to resume cycling, the cell divisions have especially short G1 and G2 phases and occur synchronously. Studies with Xenopus eggs identified a partly purified activity called maturation promoting factor that drives a resting Xenopus oocyte into M phase. MPF activity was found to be oscillate during the cell cycle, although the amount of its kinase component, called Cdk, remained constant. The regulatory component of MPF, called cyclin, has a stimulatory effect on MPF activity and plays a part in regulating interactions with its substrates. The components of MPF are evolutionarily conserved from yeast to humans, so that the corresponding human genes are able to function in yeast.

Microtubules are formed from the tubulin heterodimer, which is composed of the nucleotide-binding ______ protein and the ______ protein. Tubulin dimers are stacked together into protofilaments; ______ parallel protofilaments form the tubelike structure of a microtubule. _______ rings are important for microtubule nucleation and are found in the _______ , which is usually found near the cell's nucleus in cells that are not undergoing mitosis. A microtubule that is quickly growing will have a _______ cap that helps prevent the loss of subunits from its growing end. Stable microtubules are used in cilia and flagella; these microtubules are nucleated from a ______ and involve a "_______ plus two" array of microtubules. The motor protein _______ generates the bending motion in cilia; the lack of this protein can cause Kartagener's syndrome in humans. α-tubulin, dynein, nine, ATP, four, thirteen, basal body, γ-tubulin, twenty-one, β-tubulin, GTP, UTP, centrosome, kinesin two, vimentin, δ-tubulin, myosin

Microtubules are formed from the tubulin heterodimer, which is composed of the nucleotide-binding β-tubulin protein and the α-tubulin protein. Tubulin dimers are stacked together into protofilaments; thirteen parallel protofilaments form the tubelike structure of a microtubule. γ-Tubulin rings are important for microtubule nucleation and are found in the centrosome, which is usually found near the cell's nucleus in cells that are not undergoing mitosis. A microtubule that is quickly growing will have a GTP cap that helps prevent the loss of subunits from its growing end. Stable microtubules are used in cilia and flagella; these microtubules are nucleated from a basal body and involve a "nine plus two" array of microtubules. The motor protein dynein generates the bending motion in cilia; the lack of this protein can cause Kartagener's syndrome in humans

Indicate by writing "yes" or "no" whether amplification of a signal could occur at the particular steps described below. A. An extracellular signaling molecule binds and activates a GPCR. B. The activated GPCRs cause Gα to separate from Gβ and Gγ. C. Adenylyl cyclase produces cyclic AMP. D. cAMP activates protein kinase A. E. Protein kinase A phosphorylates target proteins.

No, Yes, Yes, No, Yes

Plasma membrane proteins are inserted into the membrane in the __________. The address information for protein sorting in a eukaryotic cell is contained in the ________ of the proteins. Proteins enter the nucleus in their _______ form. Proteins that remain in the cytosol do not contain a _______. Proteins are transported into the Golgi apparatus via ________. The proteins transported into the endoplasmic reticulum by ________ are in their _______ form. amino acid sequence, Golgi apparatus, sorting signal, endoplasmic reticulum, plasma membrane, transport vesicles, folded protein, translocators, unfolded

Plasma membrane proteins are inserted into the membrane in the endoplasmic reticulum. The address information for protein sorting in a eukaryotic cell is contained in the amino acid sequence of the proteins. Proteins enter the nucleus in their folded form. Proteins that remain in the cytosol do not contain a sorting signal. Proteins are transported into the Golgi apparatus via transport vesicles. The proteins transported into the endoplasmic reticulum by protein translocators are in their unfolded form.

Proteins are transported out of a cell via the _______ or ______ pathway. Fluids and macromolecules are transported into the cell via the ______ pathway. All proteins being transported out of the cell pass through the _______ and the _______. Transport vesicles link organelles of the ______ system. The formation of _______ in the endoplasmic reticulum stabilizes protein structure. Carbohydrate, Golgi apparatus, disulfide bonds, hydrogen bonds, endocytic, ionic bonds, endomembrane, lysosome, endoplasmic reticulum, protein, endosome, secretory, exocytic

Proteins are transported out of a cell via the secretory or exocytic pathway. Fluid and macromolecules are transported into the cell via the endocytic pathway. All proteins being transported out of the cell pass through the endoplasmic reticulum and the Golgi apparatus. Transport vesicles link organelles of the endomembrane system. The formation of disulfide bonds in the endoplasmic reticulum stabilizes protein structure

Predict whether you would expect the cell's size to be bigger or smaller than normal cells if cells were treated in the following fashion. A. You change threonine 42 on TFS to an alanine residue. B. You create a version of the receptor that is constitutively active. C. You add a drug that inhibits adenylyl cyclase. D. You add a drug that increases the activity of cyclic AMP phosphodiesterase. E. You mutate the cAMP-binding sites in the regulatory subunits of PKA, so that the complex binds cAMP more tightly.

Smaller, bigger, smaller, smaller, bigger

Starting with a single diploid cell, mitosis produces [two/four] [identical/different] [haploid/diploid] cells, whereas meiosis yields [two/four] [identical/different] [haploid/diploid] cells. This is accomplished in meiosis because a single round of chromosome [replication/segregation] is followed by two sequential rounds of [replication/segregation]. Mitosis is more like meiosis [I/II] than meiosis [I/II]. In meiosis I, the kinetochores on sister chromatids behave [independently/coordinately] and thus attach to microtubules from the [same/opposite] spindle. The cohesin-mediated glue between [chromatids/homologs] is regulated differently near the centromeres than along the chromosome arms. Cohesion is lost first at the [centromeres/arms] to allow segregation of [chromatids/homologs] and is lost later at the [centromeres/arms] to trigger segregation of [chromatids/homologs].

Starting with a single diploid cell, mitosis produces two identical diploid cells, whereas meiosis yields four different haploid cells. This is accomplished in meiosis because a single round of chromosome replication is followed by two sequential rounds of segregation. Mitosis is more like meiosis II than meiosis I. In meiosis I, the kinetochores on sister chromatids behave coordinately and thus attach to microtubules from the same spindle. The cohesin-mediated glue between chromatids is regulated differently near the centromeres than along the chromosome arms. Cohesion is lost first at the arms to allow segregation of homologs and is lost later at the centromeres to trigger segregation of chromatids

The cell cycle consists of an alternation between _______, which appears as a period of dramatic activity under the microscope, and a preparative period called ______, which consists of three phases called _______, ______, and _______. During M phase, the nucleus divides in a process called _______, and the cytoplasm splits in two in a process called _______. The cell-cycle control system relies on sharp increases in the activities of regulatory proteins called _______, or ______, to trigger S phase and M phase. Inactivation of _______ is required to exit from M phase after chromosome segregation. APC, G2 phase, metaphase, Cdks, interphase, microtubules, condensation, intraphase, mitosis, cyclin-dependent kinases, kinesins, myosins, cytokinesis, M phase, S phase, G1 phase, M-Cdk, S-Cdk, G1-Cdk, meiosis

The cell cycle consists of an alternation between M phase, which appears as a period of dramatic activity under the microscope, and a preparative period called interphase, which consists of three phases called G1 phase, S phase, and G2 phase. During M phase, the nucleus divides in a process called mitosis, and the cytoplasm splits in two in a process called cytokinesis. The cell-cycle control system relies on sharp increases in the activities of regulatory proteins called cyclin-dependent kinases, or Cdks, to trigger S phase and M phase. Inactivation of M-Cdk is required to exit from M phase after chromosome segregation.

The _______ makes up about half of the total cell volume of a typical eukaryotic cell. Ingested materials within the cell will pass through a series of compartments called _______ on their way to the _______, which contains digestive enzymes and will ultimately degrade the particles and macromolecules taken into the cell and will also degrade worn-out organelles. The ________ has a cis and trans face and receives proteins and lipids from the _______, a system of interconnected sacs and tubes of membranes that typically extends throughout the cell. Cytosol, Golgi apparatus, nucleus, endoplasmic reticulum, lysosome, peroxisomes, endosomes, mitochondria, plasma membrane

The cytosol makes up about half of the total cell volume of a typical eukaryotic cell. Ingested materials within the cell will pass through a series of compartments called endosomes on their way to the lysosome, which contains digestive enzymes and will ultimately degrade the particles and macromolecules taken into the cell and will also degrade worn-out organelles. The Golgi apparatus has a cis and trans face and receives proteins and lipids from the endoplasmic reticulum, a system of interconnected sacs and tubes of membranes that typically extends throughout the cell.

The four phases of the cell cycle, in order, are G1, _______, _______, and ______. A cell contains the most DNA after ______ phase of the cell cycle. A cell is smallest in size after ______ phase of the cell cycle. Growth occurs in ______, ______, and ______ phases of the cell cycle. A cell does not enter mitosis until it has completed _______ synthesis. DNA, M, protein, G1, nucleotide, S, G2, organelle

The four phases of the cell cycle, in order, are G1, S, G2, and M. A cell contains the most DNA after S phase of the cell cycle. A cell is smallest in size after M phase of the cell cycle. Growth occurs in G1, S, and G2 phases of the cell cycle. A cell does not enter mitosis until it has completed DNA synthesis

The survival, _______, and size of each cell in an animal are controlled by extracellular signal molecules secreted by neighboring and distant cells. Many of these signal molecules bind to a cell-surface ______ and trigger various intracellular signaling pathways. One class of signal molecules, called _______, stimulates cell division by releasing the molecular brakes that keep cells in the _______ or ______ phase of the cell cycle. Members of a second class of signal molecules are called _______, because they stimulate cell growth and an increase in cell mass. The third class of signal molecules, called _______, inhibits _______ by regulating members of the ______ family of proteins. In addition to such stimulatory factors, some signal proteins such as ______ act negatively on other cells, inhibiting their survival, growth, or proliferation. Anaphase, differentiation, myostatin, annihilation, G0, nourishment, apoptosis, G1, nutrition, arrestase, G2, phosphatases, Bcl2, growth factors, proliferation, biosynthetic, interphase, receptor, cascades, ligand, S, caspase, M, survival factors, Cdk, mitogens, transcription, cyclin

The survival, proliferation, and size of each cell in an animal are controlled by extracellular signal molecules secreted by neighboring and distant cells. Many of these signal molecules bind to a cell-surface receptor and trigger various intracellular signaling pathways. One class of signal molecules, called mitogens, stimulates cell division by releasing the molecular brakes that keep cells in the G0 or G1 phase of the cell cycle. Members of a second class of signal molecules are called growth factors, because they stimulate cell growth and an increase in cell mass. The third class of signal molecules, called survival factors, inhibits apoptosis by regulating members of the Bcl2 family of proteins. In addition to such stimulatory factors, some signal proteins such as myostatin act negatively on other cells, inhibiting their survival, growth, or proliferation

To reproduce sexually, an organism must create haploid ______ cells, or ______, from diploid cells via a specialized cell division called _______. During mating, the father's haploid cells, called ______ in animals, fuse with the mother's haploid cells, called ______. Cell fusion produces a diploid cell called a ________, which undergoes many rounds of cell division to create the entire body of the new individual. The cells produced from the initial fusion event include _______ cells that form most of the tissues of the body as well as the _______-line cells that give rise to the next generation of progeny. Allele, germ, pollen, bivalent, meiosis, somatic, eggs, mitosis, sperm, gametes, pedigree, zygote

To reproduce sexually, an organism must create haploid germ cells, or gametes, from diploid cells via a specialized cell division called meiosis. During mating, the father's haploid cells, called sperm in animals, fuse with the mother's haploid cells, called eggs. Cell fusion produces a diploid cell called a zygote, which undergoes many rounds of cell division to create the entire body of the new individual. The cells produced from the initial fusion event include somatic cells that form most of the tissues of the body as well as the germ-line cells that give rise to the next generation of progeny

Indicate whether each of the following statements refers to a ciliary microtubule, a microtubule of the mitotic spindle, both types of microtubule, or neither type of microtubule. A. The basal body is the organizing center. B. The monomer is sequestered by profilin. C. It is arranged in a "9 + 2" array. D. It is nucleated at the centrosome. E. It uses dynein motors. F. It is involved in sperm motility. G. It is involved in moving fluid over the surface of cells.

ciliary, neither, ciliary, mitotic, both, neither, ciliary

Would they be higher or lower than in normal cells treated with adrenaline? A. cells that lack adenylyl cyclase B. cells that lack the GPCR C. cells that lack cAMP phosphodiesterase D. cells that have an α subunit that cannot hydrolyze GTP but can interact properly with the β and γ subunits

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