Test 1- (Chap 1-15) Flashcards
(48 cards)
Which one of the following statements concerning the regulation of enzyme activity in cells is INCORRECT?
A. Enzymes that show allosteric regulation typically have a single subunit to allow more rapid regulation of catalytic activity.
B. Enzymes catalyzing a connected series of chemical reactions (for example, a metabolic pathway) are sometimes arranged into a multienzyme complex.
C. In all cases of allosteric regulation, a regulatory molecule binds to a site on the enzyme molecule that is separate from the active site where catalysis occurs.
D. Regulated enzyme molecules can often switch between two different shapes that differ in catalytic activity.
A. Enzymes that show allosteric regulation typically have a single subunit to allow more rapid regulation of catalytic activity.
Which one of the following statements concerning enzymes is FALSE?
A. The rate of an enzyme-catalyzed reaction is partly dependent on the initial concentration of its substrate.
B. Many enzymes change shape during the chemical reaction they catalyze.
C. Enzymes speed up metabolic reactions by lowering energy barriers.
D. Enzymes determine the direction of the chemical reaction they catalyze.
D. Enzymes determine the direction of the chemical reaction they catalyze.
Which of the following statements concerning a polypeptide chain is FALSE?
A. Methionine (abbreviated M) is typically the first amino acid of each polypeptide synthesized.
B. The ribosome catalyzes synthesis of polypeptides in cells.
C. Each amino acid is connected to the other by a single covalent bond.
D. Polypeptides are synthesized by addition of amino acids to the amino (NH2)- or N-terminus of the polypeptide.
D. Polypeptides are synthesized by addition of amino acids to the amino (NH2)- or N-terminus of the polypeptide.
Which one of the following statements concerning the folding of polypeptides in cells is CORRECT?
A. The primary structure of polypeptides ensures that each one is guaranteed to spontaneously fold into its final, fully functional shape.
B. The energy of ATP (actually its hydrolysis) is coupled to shape changes of Hsp70 to allow it to bind and release an unfolded polypeptide.
C. A polypeptide will not start to fold until its synthesis is complete.
D. Hsp70, a chaperone (also known as a chaperonin), binds to hydrophilic stretches of unfolded polypeptides.
B. The energy of ATP (actually its hydrolysis) is coupled to shape changes of Hsp70 to allow it to bind and release an unfolded polypeptide.
Which one of the following statements concerning membrane structure and function is INCORRECT?
A. The lateral movement of phospholipids in biological membranes is very slow and allows formation of stable structures, but flipping of phospholipids transversely across the membrane is more rapid.
B. Carbohydrates in chains of sugars (polysaccharides) are covalently attached to proteins or lipids on the extracellular surface of the cell.
C. Some membrane proteins cross the lipid bilayer, others are attached to molecules on the periphery of the bilayer.
D. Cholesterol is found in the plasma membrane of animal cells.
A. The lateral movement of phospholipids in biological membranes is very slow and allows formation of stable structures, but flipping of phospholipids transversely across the membrane is more rapid.
Which one of the following statements concerning transport by proteins is FALSE?
A. Active transport by an ATP-driven pump allows cells to maintain a much higher internal concentration of potassium ions than that outside the cells.
B. Facilitated diffusion is never coupled by a protein to any process that creates a chemical gradient.
C. Ion pumps help create an electrical membrane potential across the plasma membrane, negative relative to the outside of the cell.
D. Water often enters or leaves cells through water channel proteins.
B. Facilitated diffusion is never coupled by a protein to any process that creates a chemical gradient.
Which one of the following molecules is not found at the active site of the Hsp70 enzyme when ATP is bound?
A. a mechanically strained conformation of ATP
B. water coming between the second and third (terminal) phosphate of ATP
C. magnesium ion (Mg2+) bound to ATP
D. inorganic phosphate
D. inorganic phosphate
Which one of the following statements about polypeptide folding and protein turnover in cells is FALSE?
A. A long polypeptide can be temporarily attached to both Hsp70 and Hsp60 at the same time.
B. Ubiquitin is a short polypeptide, covalent attachment to which can mark another polypeptide for breakdown by the proteosome.
C. In the typical double ring of the Hsp60 complex, the 14 Hsp60 subunits are attached to each other by covalent bonds.
D. ATP hydrolysis by each of the Hsp60 subunits is strongly correlated in time, i.e., happen at about the same time.
C. In the typical double ring of the Hsp60 complex, the 14 Hsp60 subunits are attached to each other by covalent bonds.
Which one of the following statements concerning mitochondria, chloroplasts, or peroxisomes is FALSE?
A. Mitochondria and chloroplasts are typically not part of the endomembrane system.
B. Like mitochondria, chloroplasts are static, rigid, relatively immobile organelles.
C. Peroxisomes perform oxidation reactions and increase in number by a fission reaction in which they split in two after growing to a certain size.
D. Mitochondria are found in most eukaryotic cells, includiing plant cells.
B. Like mitochondria, chloroplasts are static, rigid, relatively immobile organelles.
Which one of the following statements about transport proteins is INCORRECT?
A. Diffusion of solutes down a chemical gradient across a membrane is a dynamic process with solute molecules moving in both directions.
B. Proteins that transport hydrophilic solutes across the plasma membrane have folded structures in which hydrophillic side chains on the inside face away from the nonpolar part of the phospholipid bilayer.
C. Most hydrophilic solute molecules are transported across the plasma membrane by movements of a peripheral membrane protein from the outside surface of the phospholipid bilayer to the other surface.
D. Many transmembrane proteins contain alpha helices in the portion of the protein that spans the phospholipid bilayer.
C. Most hydrophilic solute molecules are transported across the plasma membrane by movements of a peripheral membrane protein from the outside surface of the phospholipid bilayer to the other surface.
Which one of the following statements about the endomembrane system is INCORRECT?
A. Almost all proteins in the lumen of the Golgi complex are glycoproteins, i.e., proteins with covalently attached polysaccharide(s).
B. Secretion of a protein from a cell to the extracellular fluid requires two targeting signals: one signal at the N-terminus to allow entry of the polypeptide into the rough ER, another signal in the primary structure to direct the polypeptide from the Golgi apparatus to the plasma membrane via a vesicle.
C. Protein synthesis at the rough ER is rapidly followed by folding of the protein in the lumen in a process facilitated by Hsp70.
D. Any protein that functions in the lumen of the rough ER is first made there, travels to the Golgi complex, then returns to the rough ER in a process requiring two targeting signals on that protein: one to be made in the ER and one to return there.
B. Secretion of a protein from a cell to the extracellular fluid requires two targeting signals: one signal at the N-terminus to allow entry of the polypeptide into the rough ER, another signal in the primary structure to direct the polypeptide from the Golgi apparatus to the plasma membrane via a vesicle.
Which one of the following statements concerning transport of glucose via the Na+/glucose co-transporter is FALSE?
A. The Na+/glucose co-transporter protein has highly specific binding sites for Na+ and glucose some which face the extracellular solution and others of which face the cytoplasm.
B. Accumulation of glucose into cells is due to the coupling of facilitated diffusion of Na+ down its chemical gradient to glucose transport against a chemical gradient of glucose; covalent attachment of phosphate to glucose in the cytoplasm also aids in glucose accumulation.
C. The Na+/glucose co-transporter is found in the plasma membrane of intestinal epithelial cells and faces an extracellular solution with high levels of Na+ and variable levels of glucose.
D. The Na+/glucose co-transporter protein changes shape when neither solute is bound to the protein or when both solutes are bound, but cannot change shape when just Na+ or just glucose is bound to the transporter.
A. The Na+/glucose co-transporter protein has highly specific binding sites for Na+ and glucose some which face the extracellular solution and others of which face the cytoplasm.
Which one of the following statements about the cytoskeleton is INCORRECT?
A. Only a few eukaryotic cells –typically just dividing cells - have microtubules.
B. Intermediate filaments are specialized for bearing tension and are more permanent fixtures of cells than microfilaments (actin filaments) and microtubules.
C. Many cilia are motile while others are generally nonmotile and allow cells to sense their environment through signaling proteins in the membrane.
D. Cell motility generally requires the interaction of the cytoskeleton with motor proteins.
A. Only a few eukaryotic cells –typically just dividing cells - have microtubules.
Which one of the following is NOT a part of a motile cilium
A. Flexible protein cross-links connecting microtubule doublets.
B. Bending of cilium generated by microtubule depolymerization.
C. Dynein motor proteins that move along microtubules.
D. ATP providing energy for bending of cilium.
B. Bending of cilium generated by microtubule depolymerization.
Which one of the following statements concerning protein targeting signals is FALSE?
A. Targeting of a polypeptide to the mitochondrion or the rough endoplasmic reticulum is mediated by a signal at the N-terminus of the polypeptide.
B. Not all targeting signals of organelle proteins are located at the N-terminus, e.g., the nuclear localization signal is in the middle of the polypeptide.
C. The Signal Recognition Particle (SRP) pauses synthesis of certain polypeptides until the ribosome doing the synthesis is attached to (docked onto) the rough endoplasmic reticulum (rough ER).
D. An organelle targeting signal is typically added to a polypeptide after the synthesis of the polypeptide is complete.
D. An organelle targeting signal is typically added to a polypeptide after the synthesis of the polypeptide is complete.
Which one of the following statements concerning the rough endoplasmic reticulum (ER) or Golgi apparatus (both parts of the endomembrane system) is INCORRECT?
A. Almost all water-soluble proteins in the lumen of the rough ER or Golgi have covalently attached polysaccharides.
B. Proteins that function in the rough ER are synthesized there and stay there without having to travel to other parts of the endomembrane system.
C. A newly formed polypeptide that functions in the lysosome needs two targeting signals to get there, one to enter the rough ER and another to leave the Golgi apparatus and go to the lysosome.
D. Within the endomembrane system, proteins leave the rough ER or Golgi apparatus via membrane-enclosed vesicles.
B. Proteins that function in the rough ER are synthesized there and stay there without having to travel to other parts of the endomembrane system.
Which one of the following statements concerning the microtubule cytoskeleton in cells is FALSE?
A. Increases in the length of a microtubule are mediated by covalent attachment of tubulin subunits to the end of that microtubule.
B. Nucleation (initial growth) of microtubules requires a ring of gamma-tubulin for each microtubule; such rings are found in the region of the cell called the centrosome or microtubule organizing center (MTOC).
C. Microtubule polymerize and depolymerize at the same end - called the (+) end.
D. Microtubules are made of the cytosolic protein tubulin.
A. Increases in the length of a microtubule are mediated by covalent attachment of tubulin subunits to the end of that microtubule.
Which one of the following statements about electron transport and oxidative phosphorylation is TRUE?
A. The final electron acceptor in mitochondrial electron transport is water (H2O).
B. Electron transport in mitochondria is normally coupled to proton (H+) movement from the cytosol to the mitochondrial matrix.
C. The electron transport chain of mitochondria resides in its inner membrane.
D. ATP synthesis is directly coupled to electron transport by the ATP synthase.
C. The electron transport chain of mitochondria resides in its inner membrane.
Which one of the following statements about respiration is INCORRECT?
A. Chemical products of glycolysis include NADH, ATP, and pyruvate.
B. Production of CO2 from pyruvate occurs inside the mitochondrion.
C. Glucose is reduced to carbon dioxide (CO2) in cells.
D. Most of the ATP produced by respiration results from oxidative phosphorylation.
C. Glucose is reduced to carbon dioxide (CO2) in cells.
Which one of the following statements concerning cytoplasmic organelle and vesicle movements is INCORRECT?
A. The (-) end-oriented microtubule-based motor protein called dynein typically has a single binding site for cargo (like a vesicle) and a single binding site for a microtubule.
B. Organelles such as the Golgi complex typically have both kinesins and dyneins on their surface.
C. Two vesicles moving in opposite directions (propelled by different motor proteins) can pass each other on the same microtubule.
D. The microtubule-based, (+) end-oriented motor protein kinesin catalyzes the hydrolysis of ATP.
B. Organelles such as the Golgi complex typically have both kinesins and dyneins on their surface.
Which one of the following statements concerning G-proteins and G protein-coupled receptors is INCORRECT?
A. G proteins act as a GTPase.
B. G protein-coupled receptors continuously bind a G protein.
C. G proteins bind either GDP or GTP.
D. Some G proteins regulate the production of second messengers such as cyclic AMP or IP3
B. G protein-coupled receptors continuously bind a G protein.
Which one of the following statements concerning glycolysis in cells is FALSE?
A. A major function of glycolysis is the synthesis of ATP from ADP and inorganic phosphate; chemical intermediates in glycolysis also serve as starting material for synthesis of other biomolecules.
B. The enzymes of glycolysis are located in the cytosol.
C. The coenzyme NAD+ is oxidized by the addition of two electrons.
D. Substrate oxidation is coupled to its phosphorylation.
D. Substrate oxidation is coupled to its phosphorylation.
Which one of the following statements concerning protein kinases and phosphatases is FALSE?
A. The substrate of a protein kinase is often another protein kinase, for example, in the case of receptor tyrosine kinases.
B. The substrates of protein phosphatases are always the products of protein kinase-catalyzed reactions.
C. Once active, each protein kinase is completely free to catalyze the phosphorylation of a variety of other proteins.
D. The “second messenger” called cyclic AMP is an allosteric ligand for a protein kinase.
C. Once active, each protein kinase is completely free to catalyze the phosphorylation of a variety of other proteins.
Which one of the following statements concerning mitochondrial respiration and ATP synthesis is INCORRECT?
A. The active site of the ATP synthase is located on the matrix side of the mitochondrial inner membrane.
B. Metal ions help mediate the electron transfer between different inner membrane proteins, from NADH or FADH2 to O2.
C. Electron transport chain-driven transport of protons across the inner membrane of the mitochondria into the cytosol results in a large decrease in the pH of the cytosol.
D. The mitochondria and cytosol have separate pools of NAD+/NADH; electrons move between these compartments via shuttle systems of carbohydrates.
A. The active site of the ATP synthase is located on the matrix side of the mitochondrial inner membrane.
