Exam 4 Review
Rank the following types of cell signals in order from which signal molecule that travels the least distance to the type of signal molecule travels the largest distance. _____ paracrine signaling _____ contact-dependent signaling _____ neuronal signaling _____ endocrine signaling
2, 1, 3, 4
The receptor tyrosine kinases (RTK's) fall into which class of receptors? (a) ion-channel coupled receptor (b) G-protein coupled receptor (c) enzyme-coupled receptor (d) contact-dependent coupled receptor
C. enzyme-coupled receptor
Several different classes of enzymes are needed for the catabolism of carbohydrates. Which of the following descriptions best matches the function of an isomerase? (a) An enzyme that catalyzes the rearrangement of bonds within a single molecule. (b) An enzyme that catalyzes a change in the position of a specific chemical group within a single molecule. (c) An enzyme that catalyzes the oxidation of a molecule by removing a hydride ion. (d) An enzyme that catalyzes the addition of phosphate groups to other molecules.
a. An enzyme that catalyzes the rearrangement of bonds within a single molecule.
Which of the following statements about vesicle budding from the Golgi is false? (a) Clathrin molecules are unnecessary for vesicular transport from the Golgi (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 unnecessary for vesicular transport from the Golgi
Which of the following statements is true? (a) Extracellular signal molecules that are hydrophilic must bind to a cell-surface 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 cell-surface receptor so as to signal a target cell to change its behavior.
You have been assigned to identify a novel purified protein in your lab. You immediately notice this protein contains a polypeptide chain that traverses the membrane seven times and the transmembrane portion of the protein consist of alpha helices. What can you conclude about this protein? (a) It belongs to the family of G-protein coupled receptors (b) It belong to the cyclin dependent kinase family (c) It belongs to the receptor tyrosine kinase family (d) It belongs to the enzyme-coupled receptors family (e) It belongs to the integrin family of cell membrane proteins
a. It belongs to the family of G-protein coupled receptors
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 serine/threonine kinase can Akt activate in order to stimulate cellular growth? (a) bcl2 (b) tor (c) bad (d) protein kinase 1
b. tor
How many calcium ions must bind to calmodulin in order for it to be activated? (a) 2 (b) 3 (c) 4 (d) 6
c. 4
The "slow" response to an extracellular signal molecule involves... (a) an alteration in the transcription of genes (b) movement of a cell to a new location (c) an alteration of existing proteins (d) a downstream signaling cascade that does NOT enter the nucleus
a. an alteration in the transcription of genes
Most proteins destined to enter the endoplasmic reticulum _________. (a) begin to cross the membrane while still being synthesized. (b) are transported across the membrane after their synthesis is complete. (c) are synthesized on free ribosomes in the cytosol. (d) remain within the endoplasmic reticulum.
a. begin to cross the membrane while still being synthesized.
The local mediator nitric oxide stimulates the intracellular enzyme guanylyl cyclase by ________________. (a) diffusing into cells and stimulating the cyclase directly. (b) activating a G protein. (c) activating a receptor tyrosine kinase. (d) activating an intracellular protein kinase.
a. diffusing into cells and stimulating the cyclase directly
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.
In ________ feedback, a component that lies downstream in the pathway acts on an earlier component in the same pathway to enhance the response to the initial signal. (a) positive (b) negative (c) neutral (d) enhancing
a. positive
What molecule activates a certain class of GTP-binding proteins by catalyzing the removal of GDP and the addition of GTP? (a) GAP (b) GEF (c) phosphatase (d) kinase
b. GEF
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 are translated by cytosolic ribosomes and are targeted to the ER when a signal sequence emerges during translation. (c) Proteins destined for the ER translocate their associated mRNAs into the ER lumen where they are translated. (d) Proteins destined for the ER are transcribed by special ribosomes that spend their entire life attached to the ER membrane.
b. Proteins destined for the ER are translated by cytosolic ribosomes and are targeted to the ER when a signal sequence emerges during translation.
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.
In some cases, cells can respond to the local mediators that they themselves produce. This is an example of _____ signaling. (a) paracrine (b) autocrine (c) endocrine (d) neuronal
b. autocrine
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.
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
Knowing what you know about the cell membrane, which signal molecules would you expect to rely on cell surface receptor proteins to initiate intracellular signaling? (a) small and hydrophobic (b) large and hydrophilic
b. large and hydrophilic
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.
c. Nuclear transport receptors would be unable to release their cargo in the nucleus.
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.
c. The GTP hydrolysis of the Rab proteins provides the energy for membrane fusion.
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.
c. The α subunit exchanges its bound GDP for GTP.
After an activated phospholipase C cleaves the membrane-bound inositol phospholipid, it is split into IP3 (inositol 1,4,5-trisphospate) and DAG (diacylglycerol). What is the next step for IP3? (a) activates calcium channels in the cell membrane (b) activates protein kinase C (PKC) (c) activates calcium channels in the endoplasmic reticulum (d) activates adenylyl cyclase
c. activates calcium channels in the endoplasmic reticulum
Vesicles from the ER enter the Golgi at the ______. (a) medial cisternae. (b) trans Golgi network. (c) cis Golgi network. (d) trans cisternae.
c. cis Golgi network.
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) neuronal (c) contact-dependent (d) paracrine
c. contact dependent
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
c. dynamin
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.
c. encoded in the amino acid sequence and sufficient for targeting a protein to its correct destination.
What is the mechanism by which cholera toxins cause disease? (a) inhibition of cyclic GMP (b) blocking the signal transduction of an activated Gs (stimulatory) protein (c) preventing the Gs from hydrolyzing its bound GTP (d) causing uncontrolled intestinal cell growth
c. preventing the Gs from hydrolyzing its bound GTP
Which type of G-proteins have intrinsic GTPase activity? (ie do not need assistance to hydrolyze their bound GTP to GDP) (a) monomeric (b) dimeric (c) trimeric (d) that's RTK's (receptor tyrosine kinases) not G-proteins
c. trimeric
Several different classes of enzymes are needed for the catabolism of carbohydrates. Which of the following descriptions best matches the function of a kinase? (a) An enzyme that catalyzes the rearrangement of bonds within a single molecule. (b) An enzyme that catalyzes a change in the position of a specific chemical group within a single molecule. (c) An enzyme that catalyzes the oxidation of a molecule by removing a hydride ion. (d) An enzyme that catalyzes the addition of phosphate groups to other molecules.
d. An enzyme that catalyzes the addition of phosphate groups to other molecules.
Which of the following statements is true? (a) The signal sequences on mitochondrial proteins are usually unnecessary (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.
d. Chaperone proteins in the mitochondria facilitate the movement of proteins across the outer and inner mitochondrial membranes.
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
You are interested in a soluble protein that functions within the ER lumen named Fuzzy. 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.
Which of the following statements is true? (a) MAP kinase is important for phosphorylating MAP kinase kinase. (b) Ras becomes activated when an RTK phosphorylates its bound GDP to create GTP. (c) STAT proteins phosphorylate JAK proteins, which then enter the nucleus and activate gene transcription. (d) PI 3-kinase phosphorylates a lipid in the plasma membrane.
d. PI 3-kinase phosphorylates a lipid in the plasma membrane.
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
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
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.
