Cell Biology and Biochemistry Review, Exams of Biochemistry

Download Cell Biology and Biochemistry Review and more Exams Biochemistry in PDF only on Docsity! Biochemistry Final Exam (Multiple Choice) The theory of evolution includes which of the following principles? A) Evolution is not directed toward a specific goal. B) Evolution is ongoing, and is constrained by its past. C) Evolution requires some sloppiness for adaptation to changes. D) A and B. E) A, B, and C. - E) A, B, and C. Which three cellular components are present in both prokaryotes and eukaryotes? A) ribosomes, chloroplasts, mitochondria. B) nucleus, ribosomes, RNA. C) RNA, DNA, ribosomes. D) endoplasmic reticulum, DNA, RNA. E) mitochondria, DNA, RNA. - C) RNA, DNA, ribosomes. Which cellular compartment or organelle is involved in the synthesis of proteins and lipids? A) endoplasmic reticulum. B) lysosomes. C) peroxisomes. D) vacuoles. E) all of the above. - A) endoplasmic reticulum. Lyn Margi's Theory of Endosymbiosis is an explanation for the origin of... A) the endoplasmic reticulum. B) the nucleus. C) the mitochondria. D) peroxisomes. E) the Golgi apparatus. - C) the mitochondria. The second law of thermodynamics states: A) that spontaneous processes are characterized by the overall conversion of order to disorder. B) that spontaneous processes are characterized by the conversion of work to force. C) that non-spontatneous processes are characterized by the conversion of order to disorder. D) that spontaneous processes are characterized by the conversion of heat to pressure. E) none of the above. - A) that spontaneous processes are characterized by the overall conversion of order to disorder. Consider the reaction A+B <--> C+D> After reaching equilibrium at 25°C, the following concentrations of reactants and products were measured: [A] = 10 μM, [B] = 15 μM, [C] = 10 μM, and [D] = 10 μM. Calculate ΔG°' for this reaction. A) 1000 J/mol. B) 10 kJ/mol. C) 1 J/mol. D) insufficient data to determine answer. E) none of the above. - A) 1000 J/mol. A reaction with a ________ ΔH and a ________ΔS, will never be spontaneous. A) positive, positive. B) positive, negative. C) negative, positive. D) negative, negative. E) none of the above. - B) positive, negative. For a reaction with ΔH = 23 kJ/mol and ΔS = 22 J/K・mol, at 2°C, the reaction is: A) spontaneous. B) non-spontaneous. C) at equilibrium. D) impossible to determine reactivity. E) none of the above. - B) non-spontaneous. Rank the following interactions in order of increasing strength (start with the weakest interaction). A) ionic interactions, hydrogen bonds, London dispersion forces, covalent bonds. B) London dispersion forces, hydrogen bonds, ionic interactions, covalent bonds. C) London dispersion forces, ionic interactions, hydrogen bonds, covalent bonds. D) covalent bonds, London dispersion forces, ionic interactions, hydrogen bonds. E) hydrogen bonds, London dispersion forces, ionic interactions, covalent bonds. - B) London dispersion forces, hydrogen bonds, ionic interactions, covalent bonds. In a hydrogen bond between a water molecule and another biomolecule... A) a hydrogen ion on the water molecule forms an ionic bond with a hydride ion on the other molecule. B) the partial charge on a hydrogen of the water molecule interacts with the partial charge on a hydrogen of the other molecule. C) the hydrogen bond will typically form between a hydrogen atom of the water molecule and either a nitrogen, sulfur, or oxygen atom of the other molecule. D) a hydrogen on the water molecule forms a covalent bond with a hydrogen atom on the other molecule. E) the hydrogen atom is located between an oxygen atom of the water and a carbon atom of the other molecule. - C) the hydrogen bond will typically form between a hydrogen atom of the water molecule and either a nitrogen, sulfur, or oxygen atom of the other molecule. _______ is exceptionally soluble in water due to the formation of hydrogen bonds. A) NaCl. B) Benzene. C) Sodium palmitate. D) Ethanol. C) the decrease of the blood pH due to the production of hydronium ions. D) the excretion of bicarbonate and ammonium ions from the kidneys. E) all of the above. - E) all of the above. Use the terms a) chemoautotrophs, b) chemoheterotrophs, c) photoautotrophs, and d) photoheterotrophs and identify the answer that correctly finishes the statement: Carnivores are_________and herbivores are___________. A) b, c. B) b, d. C) b, b. D) a, b. E) a, a. - C) b, b. Humans maintain a nearly constant level of hemoglobin by continually synthesizing and degrading it. This is an example of a(n): A) dynamic steady state. B) equilibrium state. C) exergonic change. D) free-energy change. E) waste of energy. - A) dynamic steady state. Enzymes are biological catalysts that enhance the rate of a reaction by: A) decreasing the activation energy. B) decreasing the amount of free energy released. C) increasing the activation energy. D) increasing the amount of free energy released. E) increasing the energy of the transition state. - A) decreasing the activation energy. The three-dimensional structure of a protein is determined primarily by: A) electrostatic guidance from nucleic acid structure. B) how many amino acids are in the protein. C) hydrophobic interact with lipids that provide a folding framework. D) modification during interactions with ribosomes. E) the sequence of amino acids in the protein. - E) the sequence of amino acids in the protein. If the ΔG'° of the reaction A → B is -40 kJ/mol, under standard conditions the reaction: A) is at equilibrium. B) will never reach equilibrium. C) will not occur spontaneously. D) will proceed at a rapid rate. E) will proceed spontaneously from A to B. - E) will proceed spontaneously from A to B. Hydrolysis of 1 M glucose 6-phosphate catalyzed by glucose 6-phosphatase is 99% complete at equilibrium (i.e., only 1% of the substrate remains). Which of the following statements is most nearly correct? (R = 8.315 J/mol·K; T = 298 K). A) ΔG'° is -11 kJ/mol. B) ΔG'° is -5 kJ/mol. C) ΔG'° is 0 kJ/mol. D) ΔG'° is +11 kJ/mol. E) ΔG'° cannot be determined from the information given. - A) ΔG'° is -11 kJ/mol. For the reaction A → B, the Keq' is 104. If a reaction mixture originally contains 1 mmol of A and no B, which one of the following must be true? A) At equilibrium, there will be far more B than A. B) The rate of the reaction is very slow. C) The reaction requires coupling to an exergonic reaction in order to proceed. D) The reaction will proceed toward B at a very high rate. E) ΔG'° for the reaction will be large and positive. - A) At equilibrium, there will be far more B than A. Hydrophobic interactions make important energetic contributions to: A) binding of a hormone to its receptor protein. B) enzyme-substrate interactions. C) membrane structure. D) three-dimensional folding of a polypeptide chain. E) All of the above are true. - E) All of the above are true. The Henderson-Hasselbalch equation: A) allows the graphic determination of the molecular weight of a weak acid from its pH alone. B) does not explain the behavior of di- or tri-basic weak acids. C) employs the same value for pKa for all weak acids. D) is equally useful with solutions of acetic acid and of hydrochloric acid. E) relates the pH of a solution to the pKa and the concentrations of acid and conjugate base. - E) relates the pH of a solution to the pKa and the concentrations of acid and conjugate base. Three buffers are made by combining a 1 M solution of acetic acid with a 1 M solution of sodium acetate in the ratios shown below. 1 M acetic acid/1 M sodium acetate Buffer 1: 10 mL 90 mL Buffer 2: 50 mL 50 mL Buffer 3: 90 mL 10 mL A) pH of buffer 1 < pH of buffer 2 < pH of buffer 3. B) pH of buffer 1 = pH of buffer 2 = pH of buffer 3. C) pH of buffer 1 > pH of buffer 2 > pH of buffer 3. D) The problem cannot be solved without knowing the value of pKa. E) None of the above. - C) pH of buffer 1 > pH of buffer 2 > pH of buffer 3. Two amino acids of the standard 20 contain sulfur atoms. They are: A) cysteine and serine. B) cysteine and threonine. C) methionine and cysteine. D) methionine and serine. E) threonine and serine. - C) methionine and cysteine. Which two amino acids differ from each other by only one atom? A) Ser and Thr. B) Leu and Ile. C) Ala and Ser. D) Asp and Asn. E) Ser and Cys. - E) Ser and Cys. The peptide alanylglutamylglycylalanylleucine has: A) a disulfide bridge. B) five peptide bonds. C) four peptide bonds. D) no free carboxyl group. E) two free amino groups. - C) four peptide bonds. In a mixture of the five proteins listed below, which should elute last in size-exclusion (gel-filtration) chromatography. A) cytochrome c Mr = 13,000 B) immunoglobulin G Mr = 145,000 C) ribonuclease A Mr = 13,700 D) RNA polymerase Mr = 450,000 E) serum albumin Mr = 68,500 - A) cytochrome c Mr = 13,000 The first step in two-dimensional gel electrophoresis generates a series of protein bands by isoelectric focusing. In a second step, a strip of this gel is turned 90 degrees, placed on another gel containing SDS, and electric current is again applied. In this second step: A) the individual bands become stained so that the isoelectric focus pattern can be visualized. B) the individual bands become visualized by interacting with protein-specific antibodies in the second gel. C) the individual bands undergo a second, more intense isoelectric focusing. D) proteins with similar isoelectric points become further separated according to their molecular weights. B) generally near each other in sequence. Which of the following statements is false? A) Collagen is a protein in which the polypeptides are mainly in the α-helix conformation. B) Disulfide linkages are important for keratin structure. C) Gly residues are particularly abundant in collagen. D) Silk fibroin is a protein in which the polypeptide is almost entirely in the β conformation. E) α-keratin is a protein in which the polypeptides are mainly in the α-helix conformation. - A) Collagen is a protein in which the polypeptides are mainly in the α-helix conformation. Experiments on denaturation and renaturation after the reduction and reoxidation of the —S—S— bonds in the enzyme ribonuclease (RNase) have shown that: A) folding of denatured RNase into the native, active conformation, requires the input of energy in the form of heat. B) native ribonuclease does not have a unique secondary and tertiary structure. C) the completely unfolded enzyme, with all —S—S— bonds broken, is still enzymatically active. D) the enzyme, dissolved in water, is thermodynamically stable relative to the mixture of amino acids whose residues are contained in RNase. E) the primary sequence of RNase is sufficient to determine its specific secondary and tertiary structure. - E) the primary sequence of RNase is sufficient to determine its specific secondary and tertiary structure. Which of the following statements concerning the process of spontaneous folding of proteins is false? A) It may involve initial formation of a highly compact state. B) It may be defective in some human diseases. C) It may involve a gradually decreasing range of conformational species. D) It may be an essentially random process. E) It may involve initial formation of local secondary structure. - D) It may be an essentially random process. Protein S will fold into its native conformation only when protein Q is also present in the solution. However, protein Q can fold into its native conformation without protein S. Protein Q, therefore, may function as a ____________ for protein S. A) proteasome. B) molecular chaperone. C) protein precursor. D) structural motif. E) supersecondary structural unit. - B) molecular chaperone. In the binding of oxygen to myoglobin, the relationship between the concentration of oxygen and the fraction of binding sites occupied can best be described as: A) hyperbolic. B) linear with a negative slope. C) linear with a positive slope. D) random. E) sigmoidal. - A) hyperbolic. An allosteric interaction between a ligand and a protein is one in which: A) binding of a molecule to a binding site affects binding of additional molecules to the same site. B) binding of a molecule to a binding site affects binding properties of another site on the protein. C) binding of the ligand to the protein is covalent. D) multiple molecules of the same ligand can bind to the same binding site. E) two different ligands can bind to the same binding site. - B) binding of a molecule to a binding site affects binding properties of another site on the protein. In hemoglobin, the transition from T state to R state (low to high affinity) is triggered by: A) Fe2+ binding. B) heme binding. C) oxygen binding. D) subunit association. E) subunit dissociation. - C) oxygen binding. Which of the following is not correct concerning 2,3-bisphosphoglycerate (BPG)? A) It binds at a distance from the heme groups of hemoglobin. B) It binds with lower affinity to fetal hemoglobin than to adult hemoglobin. C) It is an allosteric modulator. D) It is normally found associated with the hemoglobin extracted from red blood cells. E) It increases the affinity of hemoglobin for oxygen. - E) It increases the affinity of hemoglobin for oxygen. Carbon monoxide (CO) is toxic to humans because: A) it binds to myoglobin and causes it to denature. B) it is rapidly converted to toxic CO2. C) it binds to the globin portion of hemoglobin and prevents the binding of O2. D) it binds to the Fe in hemoglobin and prevents the binding of O2. E) it binds to the heme portion of hemoglobin and causes heme to unbind from hemoglobin. - D) it binds to the Fe in hemoglobin and prevents the binding of O2. The fundamental cause of sickle-cell disease is a change in the structure of: A) blood. B) capillaries. C) hemoglobin. D) red cells. E) the heart. - C) hemoglobin. Patients with chronic hypoxia (low O2 levels) due to decreased lung function may adapt by increasing their circulating BPG levels. Predict which of the following will be true for such a patient. A) p50 for O2 will be decreased. B) p50 for O2 will be increased. C) The R-state of hemoglobin will be favored. D) O2 binding to hemoglobin will be hyperbolic. E) None of the above. - B) p50 for O2 will be increased. One of the enzymes involved in glycolysis, aldolase, requires Zn2+ for catalysis. Under conditions of zinc deficiency, when the enzyme may lack zinc, it would be referred to as the: A) apoenzyme. B) coenzyme. C) holoenzyme. D) prosthetic group. E) substrate. - A) apoenzyme. Enzymes are potent catalysts because they: A) are consumed in the reactions they catalyze. B) are very specific and can prevent the conversion of products back to substrates. C) drive reactions to completion while other catalysts drive reactions to equilibrium. D) increase the equilibrium constants for the reactions they catalyze. E) lower the activation energy for the reactions they catalyze. - E) lower the activation energy for the reactions they catalyze. Which of the following statements about a plot of V0 vs. [S] for an enzyme that follows Michaelis- Menten kinetics is false? A) As [S] increases, the initial velocity of reaction V0 also increases. B) At very high [S], the velocity curve becomes a horizontal line that intersects the y-axis at Km. C) Km is the [S] at which V0 = 1/2 Vmax. D) The shape of the curve is a hyperbola. E) The y-axis is a rate term with units of μm/min. - B) At very high [S], the velocity curve becomes a horizontal line that intersects the y-axis at Km. The number of substrate molecules converted to product in a given unit of time by a single enzyme molecule at saturation is referred to as the: A) dissociation constant. B) half-saturation constant. C) maximum velocity. D) Michaelis-Menten number. E) turnover number. - E) turnover number. In competitive inhibition, an inhibitor: A) binds at several different sites on an enzyme. B) binds covalently to the enzyme. C) binds only to the ES complex. D) binds reversibly at the active site. E) lowers the characteristic Vmax of the enzyme. - D) binds reversibly at the active site. A good transition-state analog: A) binds covalently to the enzyme. B) binds to the enzyme more tightly than the substrate. D) glycine, alanine, or aspartate. E) tryptophan, aspartate, or cysteine. - A) asparagine, serine, or threonine. Which of the following techniques is not commonly used to study oligosaccharide structures? A) X-ray crystallography. B) Matrix-assisted laser desorption/ionization mass spectroscopy (MALDI-MS). C) Nuclear magnetic resonance (NMR). D) Complete chemical synthesis. E) Oligosaccharide microarrays. - A) X-ray crystallography. Sphingosine is not a component of: A) cardiolipin. B) ceramide. C) cerebrosides. D) gangliosides. E) sphingomyelin. - A) cardiolipin. Which of the following statements about membrane lipids is true? A) Glycerophospholipids are found only in the membranes of plant cells. B) Glycerophospholipids contain fatty acids linked to glycerol through amide bonds. C) Lecithin (phosphatidylcholine), which is used as an emulsifier in margarine and chocolate, is a sphingolipid. D) Some sphingolipids include oligosaccharides in their structure. E) Triacylglycerols are the principal components of erythrocyte membranes. - D) Some sphingolipids include oligosaccharides in their structure. Which of the following is not a glycerophospholipid? A) Phosphatidylcholine. B) Phosphatidylethanolamine. C) Phosphatidylserine. D) Cardiolipin. E) Ceramide. - E) Ceramide. Which of the following is true of sphingolipids? A) Cerebrosides and gangliosides are sphingolipids. B) Phosphatidylcholine is a typical sphingolipid. C) They always contain glycerol and fatty acids. D) They contain two esterified fatty acids. E) They may be charged, but are never amphipathic. - A) Cerebrosides and gangliosides are sphingolipids. Which of the following statements about sterols is true? A) All sterols share a fused-ring structure with four rings. B) Sterols are found in the membranes of all living cells. C) Sterols are soluble in water, but less so in organic solvents such as chloroform. D) Cholesterol is the principal sterol in fungi. E) The principal sterol of animal cells is ergosterol. - A) All sterols share a fused-ring structure with four rings. Fatty acids are a component of: A) carotenes. B) cerebrosides. C) sterols. D) vitamin D. E) vitamin K. - B) cerebrosides. Which of the following is not true of sterols? A) Cholesterol is a sterol that is commonly found in mammals. B) Sterols are commonly found in bacterial membranes. C) Sterols are more common in plasma membranes than in intracellular membranes (mitochondria, lysosomes, etc.). D) Sterols are precursors of steroid hormones. E) Sterols have a structure that includes four fused rings. - B) Sterols are commonly found in bacterial membranes. Which of the following techniques is not commonly used to analyze lipid composition? A) Selective extraction using apolar solvents. B) Adsorption chromatography. C) X-ray crystallography. D) Hydrolysis using enzymes with specificity for certain linkages. E) Mass spectroscopy. - C) X-ray crystallography. Which of these statements about the composition of biological membranes is false? A) In a given eukaryotic cell type (e.g., a hepatocyte), all intracellular membranes have essentially the same complement of lipids and proteins. B) The carbohydrate found in membranes is virtually all part of either glycolipids or glycoproteins. C) The plasma membranes of the cells of vertebrate animals contain more cholesterol than the mitochondrial membranes. D) The ratio of lipid to protein varies widely among cell types in a single organism. E) Triacylglycerols are not commonly found in membranes. - A) In a given eukaryotic cell type (e.g., a hepatocyte), all intracellular membranes have essentially the same complement of lipids and proteins. Which of these statements about the composition of membranes is true? A) All biological membranes contain cholesterol. B) Free fatty acids are major components of all membranes. C) The inner and outer membranes of mitochondria have different protein compositions. D) The lipid composition of all membranes of eukaryotic cells is essentially the same. E) The lipid:protein ratio varies from about 1:4 to 4:1 - C) The inner and outer membranes of mitochondria have different protein compositions. Membrane proteins: A) are sometimes covalently attached to lipid moieties. B) are sometimes covalently attached to carbohydrate moieties. C) are composed of the same 20 amino acids found in soluble proteins. D) diffuse laterally in the membrane unless they are anchored E) have all of the properties listed above. - E) have all of the properties listed above. Peripheral membrane proteins: A) are generally noncovalently bound to membrane lipids. B) are usually denatured when released from membranes. C) can be released from membranes only by treatment with detergent(s). D) may have functional units on both sides of the membrane. E) penetrate deeply into the lipid bilayer. - A) are generally noncovalently bound to membrane lipids. A hydropathy plot is used to: A) determine the water-solubility of a protein. B) deduce the quaternary structure of a membrane protein. C) determine the water content of a native protein. D) extrapolate for the true molecular weight of a membrane protein. E) predict whether a given protein sequence contains membrane-spanning segments. - E) predict whether a given protein sequence contains membrane-spanning segments. Which of the following are not enzymes involved in moving phospholipids from one leaflet to another? A) Flippases that move phosphatidylethanolamine and phosphatidylserine. B) Floppases that move phospholipids from the cytosolic leaflet to the extracellular leaflet. C) Flip-floppases that allow phospholipids to move back and forth between the inner and outer leaflets. D) Scramblases that allow phospholipids to move down their concentration gradient. E) Phosphatidylinositol transfer proteins that play a role in lipid signaling. - C) Flip-floppases that allow phospholipids to move back and forth between the inner and outer leaflets. The fluidity of a lipid bilayer will be increased by: A) decreasing the number of unsaturated fatty acids. B) decreasing the temperature. C) increasing the length of the alkyl chains. D) increasing the temperature. E) substituting 18:0 (stearic acid) in place of 18:2 (linoleic acid). - D) increasing the temperature. Which of the following statements about caveolin is false? A) Caveolin is an integral membrane protein. B) Caveolin induces outward membrane curvature. C) Caveolin is palmitoylated. D) Caveolin associates with cholesterol rich regions. E) Caveolin is involved in membrane trafficking and cellular signaling. - B) Caveolin induces outward membrane curvature. Membrane fusion leading to neurotransmitter release requires the action of: C) GTP-binding protein D) Protein kinase E) All of the above are involved. - E) All of the above are involved. Calmodulin is a(n): A) allosteric activator of calcium-dependent enzymes. B) allosteric inhibitor of calcium-dependent enzymes. C) calcium-dependent enzyme. D) cell surface calcium receptor. E) regulatory subunit of calcium-dependent enzymes. - E) regulatory subunit of calcium-dependent enzymes. Autophosphorylation of receptor tyrosine kinases depends on which of the following? A) Dimerization of the receptor. B) ATP. C) Ligand binding D) Transmission of conformational changes through the membrane. E) All of the above. - E) All of the above. Guanyl cyclase receptor enzymes: A) are all membrane-spanning proteins. B) are examples of ligand-gated ion channels. C) catalyze synthesis of a phosphate ester. D) catalyze synthesis of a phosphoric acid anhydride. E) require hydrolysis of ATP in addition to GTP. - C) catalyze synthesis of a phosphate ester. The specificity of signaling pathways includes all of the following except: A) flippase-catalyzed movement of phospholipids from the inner to the outer leaflet. B) migration of signal proteins into membrane rafts. C) phosphorylation of target proteins at Ser, Thr, or Tyr residues. D) the ability to be switched off instantly by hydrolysis of a single phosphate-ester bond. E) the assembly of large multiprotein complexes. - A) flippase-catalyzed movement of phospholipids from the inner to the outer leaflet. The force that drives an ion through a membrane channel depends on the: A) charge on the membrane. B) difference in electrical potential across the membrane. C) size of the channel. D) size of the ion. E) size of the membrane. - B) difference in electrical potential across the membrane. Which of the following is true of gated ion channels? A) Each channel can allow 10 million ions per second through the membrane. B) The gating mechanism involves piston-like movement of the transmembrane helices. C) Each channel lets both positive and negative ions flow through the pore. D) Closing of the gate requires phosphorylation of the channel protein. E) Gated channels only respond to intracellular ligands. - A) Each channel can allow 10 million ions per second through the membrane. Most transduction systems for hormones and sensory stimuli that involve trimeric G proteins have in common all of the following except: A) cyclic nucleotides. B) nuclear receptors. C) receptors that interact with a G protein. D) receptors with multiple transmembrane segments. E) self-inactivation. - B) nuclear receptors. Which of the following is not a shared feature of signaling by mammalian vision and gustatory receptor pathways? A) Changes in cAMP levels. B) GDP/GTP exchange. C) Heterotrimeric G proteins. D) Open/closing of ion channels. E) Transmembrane receptors. - A) Changes in cAMP levels. Which of the following statements concerning cyclin-dependent protein kinases is not correct? A) Each type of cell contains one specific form (isozyme). B) Their activity fluctuates during the cell cycle. C) Their activity is regulated by changes in gene expression, protein phosphorylation, and proteolysis. D) Their activity is regulated by cyclins. E) They can alter the activity of proteins involved in the progression of cells through the cell cycle. - A) Each type of cell contains one specific form (isozyme). Oncogenes are known that encode all of the following except: A) cytoplasmic G proteins and protein kinases. B) DNA-dependent RNA polymerases. C) growth factors. D) secreted proteins. E) transmembrane protein receptors. - B) DNA-dependent RNA polymerases. Programmed cell death is called: A) metastasis. B) apoptosis. C) mitotic termination. D) oncogenic transformation. E) ubiquitination. - B) apoptosis. Which of the following would be responsible for decreasing cGMP A) Nitric Oxide synthase is decreased. B) cGmp phosphodiesterase is inhibited. C) The heart, due to increased blood volume, releases ANF. E) The intestinal peptide guanylin bind to guanylyl cyclase receptor. - A) Nitric Oxide synthase is decreased. All the following statements about guanylyl cyclase are true except.... A) Nitric Oxide binds to the heme group of soluble guanylyl cyclase. B) Soluble guanylyl cyclase is cytosolic and associated with a heme group. C) Membrane-spanning guanylyl cyclase are specific to smooth muscle of the heart and blood vessels. D) Guanylyl cyclase catalyzes the cyclization of GTP associated with the removal of two phosphate groups. - C) Membrane-spanning guanylyl cyclase are specific to smooth muscle of the heart and blood vessels. The conversion of 1 mol of fructose 1,6-bisphosphate to 2 mol of pyruvate by the glycolytic pathway results in a net formation of: A) 1 mol of NAD+ and 2 mol of ATP. B) 1 mol of NADH and 1 mol of ATP. C) 2 mol of NAD+ and 4 mol of ATP. D) 2 mol of NADH and 2 mol of ATP. E) 2 mol of NADH and 4 mol of ATP. - E) 2 mol of NADH and 4 mol of ATP. In glycolysis, fructose 1,6-bisphosphate is converted to two products with a standard free-energy change (ΔG'°) of 23.8 kJ/mol. Under what conditions (encountered in a normal cell) will the free- energy change (ΔG) be negative, enabling the reaction to proceed to the right? A) If the concentrations of the two products are high relative to that of fructose 1,6-bisphosphate. B) The reaction will not go to the right spontaneously under any conditions because the ΔG'° is positive. C) Under standard conditions, enough energy is released to drive the reaction to the right. D) When there is a high concentration of fructose 1,6-bisphosphate relative to the concentration of products. E) When there is a high concentration of products relative to the concentration of fructose 1,6- bisphosphate. - D) When there is a high concentration of fructose 1,6-bisphosphate relative to the concentration of products. Which of the following reactions in glycolysis requires ATP as a substrate? A) Hexokinase. B) Glyceraldehyde-3-phosphate dehydrogenase. C) Pyruvate kinase. D) Aldolase. E) Phosphoglycerate kinase. - A) Hexokinase. Which of the following reactions in glycolysis produces ATP as a product? A) Hexokinase. B) Glyceraldehyde-3-phosphate dehydrogenase. C) Pyruvate kinase. D) Aldolase. A) aldolase. B) hexokinase. C) lactate dehydrogenase. D) pyruvate decarboxylase. E) transaldolase. - D) pyruvate decarboxylase. Which of the following compounds cannot serve as the starting material for the synthesis of glucose via gluconeogenesis? A) acetate B) glycerol C) lactate D) oxaloacetate E) α-ketoglutarate - A) acetate Which one of the following statements about gluconeogenesis is false? A) For starting materials, it can use carbon skeletons derived from certain amino acids. B) It consists entirely of the reactions of glycolysis, operating in the reverse direction. C) It employs the enzyme glucose 6-phosphatase. D) It is one of the ways that mammals maintain normal blood glucose levels between meals. E) It requires metabolic energy (ATP or GTP). - B) It consists entirely of the reactions of glycolysis, operating in the reverse direction. In humans, gluconeogenesis: A) can result in the conversion of protein into blood glucose. B) helps to reduce blood glucose after a carbohydrate-rich meal. C) is activated by the hormone insulin D) is essential in the conversion of fatty acids to glucose. E) requires the enzyme hexokinase. - A) can result in the conversion of protein into blood glucose. Which of the following substrates cannot contribute to net gluconeogenesis in mammalian liver? A) Alanine B) Glutamate C) Palmitate D) Pyruvate E) α-ketoglutarate - C) Palmitate For an enzyme to effectively change its activity in response to a change in substrate concentration, it is most favorable for: A) Km to be less than cellular substrate concentrations. B) Km to be equal to cellular substrate concentrations. C) Km to be greater than cellular substrate concentrations. D) Vmax to be at the diffusion limit. E) The substrate to also be an allosteric effector. - E) The substrate to also be an allosteric effector. Reaction steps that are far from equilibrium are good control points in metabolic pathways because A) the net flux through those steps is easily reversed. B) the rate differences between the forward and reverse steps are often small. C) these reactions occur most frequently in the cell. D) these reactions are highly endergonic. E) these reactions are highly exergonic. - E) these reactions are highly exergonic. Aside from maintaining the integrity of its hereditary material, the most important general metabolic concern of a cell is: A) keeping its glucose levels high. B) maintaining a constant supply and concentration of ATP. C) preserving its ability to carry out oxidative phosphorylation. D) protecting its enzymes from rapid degradation. E) running all its major metabolic pathways at maximum efficiency. - B) maintaining a constant supply and concentration of ATP. If the mass action ratio, Q, for a reaction under cellular conditions is larger than the equilibrium constant, Keq, then: A) the reaction will be at equilibrium. B) the reaction will go backward and be endergonic. C) the reaction will go backward and be exergonic. D) the reaction will go forward and be endergonic. E) the reaction will go forward and be exergonic. - C) the reaction will go backward and be exergonic. The flux control coefficient for an enzyme in a multistep pathway depends on: A) the concentration of the enzyme itself. B) the concentration of other enzymes in the pathway. C) the levels of regulatory molecules. D) the amounts of substrate molecules present at each step. E) All of the above - E) All of the above The elasticity coefficient for an enzyme in a multistep pathway depends on: A) the concentration of the enzyme itself. B) the levels of regulatory molecules. C) the amounts of substrate molecules present at each step. D) both A and C. E) both B and C. - E) both B and C. Gluconeogenesis must use "bypass reactions" to circumvent three reactions in the glycolytic pathway that are highly exergonic and essentially irreversible. Reactions carried out by which three of the enzymes listed must be bypassed in the gluconeogenic pathway? 1) Hexokinase 2) Phosphoglycerate kinase 3) Phosphofructokinase-1 4) Pyruvate kinase 5) Triosephosphate isomerase A) 1, 2, 3 B) 1, 2, 4 C) 1, 4, 5 D) 1, 3, 4 E) 2, 3, 4 - D) 1, 3, 4 Cellular isozymes of pyruvate kinase are allosterically inhibited by: A) high concentrations of AMP. B) high concentrations of ATP. C) high concentrations of citrate. D) low concentrations of acetyl-CoA. E) low concentrations of ATP. - B) high concentrations of ATP. Which of the following statements about gluconeogenesis in animal cells is true? A) A rise in the cellular level of fructose-2,6-bisphosphate stimulates the rate of gluconeogenesis. B) An animal fed a large excess of fat in the diet will convert any fat not needed for energy production into glycogen to be stored for later use. C) The conversion of fructose 1,6-bisphosphate to fructose 6-phosphate is not catalyzed by phosphofructokinase-1, the enzyme involved in glycolysis. D) The conversion of glucose 6-phosphate to glucose is catalyzed by hexokinase, the same enzyme involved in glycolysis. E) The conversion of phosphoenol pyruvate to 2-phosphoglycerate occurs in two steps, including a carboxylation. - C) The conversion of fructose 1,6-bisphosphate to fructose 6-phosphate is not catalyzed by phosphofructokinase-1, the enzyme involved in glycolysis. The enzyme glycogen phosphorylase: A) catalyzes a cleavage of β (1 → 4) bonds. B) catalyzes a hydrolytic cleavage of α (1 → 4) bonds. C) is a substrate for a kinase. D) uses glucose 6-phosphate as a substrate. E) uses glucose as a substrate. - B) catalyzes a hydrolytic cleavage of α (1 → 4) bonds. Which one of the following statements about mammalian glycogen synthase is not correct? A) It is especially predominant in liver and muscle. B) The donor molecule is a sugar nucleotide. C) The phosphorylated form of this enzyme is inactive. D) This enzyme adds glucose units to the nonreducing end of glycogen branches. E) This enzyme adds the initial glucose unit to a tyrosine residue in glycogenin. - E) This enzyme adds the initial glucose unit to a tyrosine residue in glycogenin. Glycogenin: A) catalyzes the conversion of starch into glycogen. B) is the enzyme responsible for forming branches in glycogen. C) Isocitrate D) Pyruvate E) Succinate - B) Fumarate Which of the following is not an intermediate of the citric acid cycle? A) Acetyl-CoA B) Citrate C) Oxaloacetate D) Succinyl-CoA E) α-Ketoglutarate - A) Acetyl-CoA The reaction of the citric acid cycle that is most similar to the pyruvate dehydrogenase complex- catalyzed conversion of pyruvate to acetyl-CoA is the conversion of: A) citrate to isocitrate. B) fumarate to malate. C) malate to oxaloacetate. D) succinyl-CoA to succinate. E) α-ketoglutarate to succinyl-CoA. - E) α-ketoglutarate to succinyl-CoA. Which one of the following enzymatic activities would be decreased by thiamine deficiency? A) Fumarase B) Isocitrate dehydrogenase C) Malate dehydrogenase D) Succinate dehydrogenase E) α-Ketoglutarate dehydrogenase complex - E) α-Ketoglutarate dehydrogenase complex The reaction of the citric acid cycle that produces an ATP equivalent (in the form of GTP) by substrate level phosphorylation is the conversion of: A) citrate to isocitrate. B) fumarate to malate. C) malate to oxaloacetate. D) succinate to fumarate. E) succinyl-CoA to succinate. - E) succinyl-CoA to succinate All of the oxidative steps of the citric acid cycle are linked to the reduction of NAD+ except the reaction catalyzed by: A) isocitrate dehydrogenase. B) malate dehydrogenase. C) pyruvate dehydrogenase D) succinate dehydrogenase. E) the α-ketoglutarate dehydrogenase complex. - D) succinate dehydrogenase. Which of the following cofactors is required for the conversion of succinate to fumarate in the citric acid cycle? A) ATP B) Biotin C) FAD D) NAD+ E) NADP+ - C) FAD In the citric acid cycle, a flavin coenzyme is required for: A) condensation of acetyl-CoA and oxaloacetate. B) oxidation of fumarate. C) oxidation of isocitrate. D) oxidation of malate. E) oxidation of succinate. - E) oxidation of succinate. Which of the following intermediates of the citric acid cycle is prochiral? A) Citrate B) Isocitrate C) Malate D) Oxaloacetate D) Succinate - A) Citrate Anaplerotic reactions________. A) produce oxaloacetate and malate to maintain constant levels of citric acid cycle intermediates B) produce biotin needed by pyruvate carboxylase C) recycle pantothenate used to make CoA D) produce pyruvate and citrate to maintain constant levels of citric acid cycle intermediates E) All of the above - A) produce oxaloacetate and malate to maintain constant levels of citric acid cycle intermediates Intermediates in the citric acid cycle are used as precursors in the biosynthesis of: A) amino acids. B) nucleotides. C) fatty acids. D) sterols. E) All of the above - E) All of the above The conversion of 1 mol of pyruvate to 3 mol of CO2 via pyruvate dehydrogenase and the citric acid cycle also yields _____ mol of NADH, _____ mol of FADH2, and _____ mol of ATP (or GTP). A) 2; 2; 2 B) 3; 1; 1 C) 3; 2; 0 D) 4; 1; 1 E) 4; 2; 1 - D) 4; 1; 1 Entry of acetyl-CoA into the citric acid cycle is decreased when: A) [AMP] is high. B) NADH is rapidly oxidized through the respiratory chain. C) the ratio of [ATP]/[ADP is low D) the ratio of [ATP]/[ADP] is high. E) the ratio of [NAD+]/[NADH] is high. - D) the ratio of [ATP]/[ADP] is high. Citrate synthase and the NAD+-specific isocitrate dehydrogenase are two key regulatory enzymes of the citric acid cycle. These enzymes are inhibited by: A) acetyl-CoA and fructose 6-phosphate. B) AMP and/or NAD+. C) AMP and/or NADH. D) ATP and/or NAD+. D) ATP and/or NAD+. E) ATP and/or NADH. - E) ATP and/or NADH.