Microbial Metabolism

Microbiology with Diseases by Taxonomy Microbial Metabolism Multiple Choice Questions 1) Which of the following statements concerning cellular metabolism is FALSE? A) Energy obtained from nutrients or light is stored in the bonds of ATP. B) Enzymes are used in both catabolic and anabolic reactions. C) Macromolecules are converted into cell structures via catabolism. D) The goal of metabolism is reproduction of the organism. E) ATP is used in the formation of macromolecules. Answer: C 2) Anabolic reactions may be characterized as A) exergonic. B) breaking large molecules into smaller molecules. C) forming large molecules from smaller molecules. D) producing ATP. E) breaking large molecules into smaller molecules to produce ATP. Answer: C 3) An organic compound gains an electron from another molecule. The organic compound A) has been oxidized. B) is an electron donor. C) has been reduced. D) has become more positively charged. E) has lost a hydrogen atom. Answer: C 4) The molecule that an enzyme acts upon is known as its A) substrate. B) coenzyme. C) apoenzyme. D) product. E) catalyst. Answer: A 5) Which of the following statements concerning enzymes is FALSE? A) They are usually, but not always, proteins. B) They always function best at 37°C. C) They can be denatured if the pH of their environment is too high or too low. D) They form a temporary intermediate compound with a substrate. E) They can be used to catalyze a chemical reaction over and over again. Answer: B 6) Sulfanilamide is an antimicrobial drug that mimics the shape of an important substrate for a particular bacterial enzyme, thereby inhibiting the enzyme. This type of inhibition is known as A) allosteric inhibition. B) competitive inhibition. C) allosteric activation. D) noncompetitive inhibition. E) feedback inhibition. Answer: B 7) Which of the following produces NADPH? A) the pentose phosphate pathway only B) the Calvin-Benson cycle only C) the Embden-Meyerhof pathway only D) both the Embden-Meyerhof and Calvin-Benson cycle pathways E) both the pentose phosphate and Entner-Doudoroff pathways Answer: E 8) Which of the following statements concerning glycolysis is TRUE? A) The first step of glycolysis involves substrate level phosphorylation. B) The glycolytic pathway has a net gain of two ATP molecules. C) Glucose is activated by substrate-level phosphorylation. D) Glyceraldehyde 3-phosphate (G3P) is the end-product of glycolysis. E) Two NADH molecules are used during glycolysis. Answer: B 9) Many vitamins are important ________ of enzymes. A) protein cofactors B) coenzymes C) allosteric inhibitors D) competitive inhibitors E) activators Answer: B 10) Pyruvic acid is a product of A) the Citric acid cycle. B) fermentation. C) glycolysis. D) the pentose phosphate pathway. E) both fermentation and the Citric acid cycle. Answer: C Bloom's Taxonomy: Remembering 11) All of the following are forms of oxidation EXCEPT A) loss of an electron. B) loss of hydrogen atom. C) a dehydrogenation event. D) substrate-level phosphorylation. E) gain of an oxygen atom and its electrons. Answer: D 12) Anaerobic bacteria may use ________ as the final electron acceptor during anaerobic respiration. A) nitrate only B) carbon dioxide only C) sulfate only D) either nitrate and sulfate E) carbon dioxide, nitrate and sulfate Answer: D 13) Which of the following is a non-protein carrier found in some electron transport chains? A) flavoproteins B) metal-containing proteins C) ribozymes D) cytochromes E) ubiquinone Answer: E 14) The electron transport chain provides the energy for A) oxidative phosphorylation. B) substrate-level phosphorylation. C) beta-oxidation. D) photophosphorylation. E) anabolic reactions. Answer: A 15) Which of the following is a by-product of the catabolism of proteins? A) lactic acid B) acetyl-CoA C) proteases D) ammonia E) carbon dioxide Answer: D 16) An apoenzyme requires ________ to be active. A) substrate-level phosphorylation B) a cofactor C) an allosteric inhibitor D) a holoenzyme E) substrate Answer: B 17) Which of the following is/are common to chemiosmosis and the light-dependent reactions of photosynthesis? A) reduction of NADP+ only B) electron transport only C) a proton gradient only D) both electron transport and a proton gradient E) electron transport, a proton gradient, and reduction of NADP+ Answer: D 18) Which of the following is a by-product of both Swiss cheese and beer production? A) acetic acid B) carbon dioxide C) ethanol D) lactic acid E) pyruvic acid Answer: B 19) How many ATP molecules can theoretically be produced from the NADH generated by the catabolism of a molecule of glucose during aerobic respiration? A) 34 B) 30 C) 38 D) 36 E) 4 Answer: B 20) The various types of chlorophyll differ in the A) amount of light they can absorb. B) amount of ATP they produce. C) number of electrons they release. D) amount of oxygen they utilize. E) wavelengths of light they absorb. Answer: E 21) Which of the following metabolic processes is commonly used to identify bacteria? A) carbohydrate fermentation B) lipid catabolism C) Citric acid cycle products D) lipid synthesis E) pentose phosphate pathway products Answer: A 22) Glycerol from triglycerides can be converted to a substrate for the A) pentose phosphate pathway. B) glycolytic pathway. C) Embden-Meyerhof pathway. D) Citric acid cycle. E) Calvin-Benson cycle. Answer: B 23) Which of the following is associated with the Calvin-Benson cycle? A) acetyl-CoA B) TMAO C) RuBP D) FADH2 E) PABA Answer: C 24) The energy captured by photophosphorylation is used to produce glucose A) through the Calvin-Benson cycle. B) through the Citric acid cycle. C) by cyclic phosphorylation. D) through the pentose-phosphate pathway. E) by beta-oxidation. Answer: A 25) Chemical reactions that can proceed toward either anabolism or catabolism are called A) glycolytic. B) light-independent. C) synthetic. D) cyclic. E) amphibolic. Answer: E 26) If a cell reverses the process of beta-oxidation, which of the following molecules will it make? A) glycerol B) amino acids C) fatty acids D) nucleotides E) starch Answer: C 27) When a cell forms an amino acid by adding an amine group derived from ammonia to a precursor metabolite, this process is called A) amination. B) transamination. C) reduction. D) polymerization. E) deamination. Answer: A 28) The conversion of amino acids to carbohydrates is an example of A) amination. B) gluconeogenesis. C) substrate-level phosphorylation. D) beta-oxidation. E) electron transport. Answer: B 29) Noncyclic photophosphorylation produces A) ATP only. B) oxygen. C) NADPH only. D) ATP and NADPH. E) water and ATP. Answer: D 30) The metabolic processes called fermentation A) produce substrates for the Citric acid cycle. B) are alternatives for the pentose phosphate pathway. C) use an organic molecule as a final electron acceptor. D) occur only when oxygen is readily available. E) produce substrates for glycolysis. Answer: C 31) Which of the following is TRUE concerning the structure and function of enzymes? A) All enzymes bind cofactors necessary for their function. B) An apoenzyme is a combination of a cofactor bound to a holoenzyme. C) Enzymes can function at a wide range of pH. D) Competitive inhibition of an enzyme occurs when an inhibitor binds to an allosteric site on the enzyme. E) After an enzyme has catalyzed a reaction, it resumes its original shape and can interact with a new substrate molecule. Answer: E 32) Bacteriochlorophyll a absorbs ________ light. A) 350 nm, ultraviolet B) 425 nm, violet C) 660 nm, red D) both 425 & 660 nm (violet and red) E) all visible Answer: A 33) Prokaryotes produce the majority of their ATP A) on the cytoplasmic membrane. B) in the cytosol. C) on the thylakoids. D) on the inner mitochondrial membrane. E) on ribosomes. Answer: A 34) The conversion of pyruvic acid to acetyl-CoA can be described as ________, because a molecule of CO2 is produced as a by-product. A) decarboxylation B) amination C) respiration D) oxidation E) phosphorylation Answer: A 35) Although glycolysis requires an input of ATP, this pathway results in a net gain of two ATP; therefore it is a(n) ________ pathway. A) exergonic B) endergonic C) oxidative D) reductive E) neither exergonic nor endergonic Answer: A 36) Reactions in which atoms are rearranged within a molecule are catalyzed by A) hydrolases. B) isomerases. C) transferases. D) ligases. E) polymerases. Answer: B 37) Prokaryotes use folds of their cytoplasmic membrane called ________ for photosynthesis. A) thylakoids B) grana C) nucleoid D) cristae E) outer membrane Answer: A 38) During the synthesis of acetyl-CoA from pyruvic acid, ________ is produced. A) ATP B) NADH C) FADH2 D) H2O E) acetic acid Answer: B 39) During reactions catalyzed by oxidoreductases an electron donor is A) oxidized. B) reduced. C) synthesized. D) degraded. E) unaltered. Answer: A 40) Hydrolases are generally involved in ________ reactions. A) anabolic B) catabolic C) both anabolic and catabolic D) neither anabolic nor catabolic E) oxidation-reduction Answer: B 41) Reactions involving ligases are typically ________ reactions. A) anabolic B) catabolic C) both anabolic and catabolic D) neither anabolic nor catabolic E) exergonic Answer: A 42) Substrate-level phosphorylation occurs during which of the following stage(s) of glucose catabolism? A) formation of acetyl-CoA B) lysis stage of glycolysis C) energy-conservation stage of glycolysis D) Citric acid cycle E) formation of acetyl-CoA and the cycle Answer: C 43) Which of the following metabolic pathways is found only in prokaryotes? A) Embden-Meyerhof-Parnas (EMP) B) Entner-Doudoroff (ED) C) Pentose phosphate pathway D) Non-cyclic photophosphorylation E) Calvin-Benson Answer: B 44) Which of the following is the CORRECT sequence of stages in glycolysis? A) energy-conservation, energy-investment, lysis B) lysis, energy-investment, energy-conservation C) energy-investment, lysis, energy-conservation D) lysis, energy-conservation, energy-investment E) energy-investment, energy-conservation, lysis Answer: C 45) Identify the processes of glucose metabolism represented in Figure 5.1. A) A = electron transport chain, B = Citric acid cycle, C = glycolysis, D = fermentation B) A = glycolysis, B = fermentation, C = Citric acid cycle, D = electron transport chain C) A = fermentation, B = glycolysis, C = Citric acid cycle, D = electron transport chain D) A = glycolysis, B = Citric acid cycle, C = fermentation, D = electron transport chain E) A = glycolysis, B = Citric acid cycle, C = electron transport chain, D = fermentation F) Answer: B 46) The process illustrated in the figure above is an example of a(n) ________ reaction. A) amination B) reduction C) oxidation D) transamination E) transferase Answer: A 5.2 True/False Questions 1) Reactions that are both catabolic and anabolic are amphibolic. Answer: TRUE 2) The amount of energy required for a reaction to occur is its activation energy. Answer: TRUE 3) Accumulation of a metabolic pathway product may result in decreased activity of the pathway enzymes. Answer: TRUE 4) As the concentration of substrate increases, the activity of the enzyme decreases. Answer: FALSE 5) Coenzyme Q is a type of flavoprotein found in all organisms. Answer: FALSE 6) During chemiosmosis, electrons are pumped across a membrane to produce ATP. 7) Glyceraldehyde 3-phosphate is an intermediate in the Calvin-Benson cycle. Answer: TRUE 8) All the precursors of amino acids are intermediates of glycolytic and fermentation pathways. Answer: FALSE 9) Essential amino acids are amino acids that cannot be synthesized by an organism and so must be provided as nutrients. Answer: TRUE 10) The pentose phosphate pathway generates all the necessary precursors for nucleotide biosynthesis. Answer: FALSE 5.3 Short Answer Questions 1) The conversion of phosphoenol pyruvic acid (PEP) to pyruvic acid results in the production of an ATP. This reaction is an example of (substrate-level/oxidative/reductive) phosphorylation. Answer: substrate-level 2) Ribosomes are a type of (apoenzyme/enzyme/ribozyme). Answer: ribozyme 3) A(n) (oxidation/reduction/transport) reaction is one in which a molecule accepts an electron. Answer: reduction 4) A holoenzyme is composed of an apoenzyme one or more (cofactors/inhibitors/substrates). Answer: cofactors 5) Another name for the Citric acid cycle is (Entner-Doudoroff/Krebs/Calvin-Benson) cycle. Answer: Krebs 6) Beta-oxidation of fatty acids produces (acetic acid/acetyl-CoA/glycerol). Answer: acetyl-CoA 7) Electrons are transferred in the Citric acid cycle in the form of (carbon/oxygen/hydrogen) atoms to NAD+ and FAD. Answer: hydrogen 8) Both chemiosmosis and photophosphorylation involve (electron/proton/hydroxyl) gradients. Answer: proton 9) Anaerobic respiration involves the use of molecules other than oxygen as the final electron (acceptor/donor) in an electron transport chain. Answer: acceptor 10) Laboratory fermentation tests often include a pH indicator because many bacteria produce (O2/bases/acids) as they ferment carbohydrates. Answer: acids 11) Amino acids are converted to substrates of the Citric acid cycle by (betaoxidation/deamination/transamination). Answer: deamination 12) Some bacteria use (acetyl-CoA/DHAP/TMAO) as a final electron receptor, resulting in a detectable odor. Answer: TMAO 13) Anoxygenic photosynthesis typically results in the production of (oxygen/sulfur/ ammonia) as a waste product. Answer: sulfur 14) The (active/allosteric/substrate) sites of an enzyme can be used to regulate enzyme activity within a cell, and thereby control their metabolism. Answer: allosteric 15) Significant amounts of the NADPH required for the Calvin-Benson cycle are produced during the (cyclic/noncyclic) photophosphorylation reactions of photosynthesis. Answer: noncyclic 16) Only Photosystem I is required for (anoxygenic/cyclic/noncyclic) photophosphorylation to occur. Answer: cyclic Essay Questions 1) Describe the mechanism of feedback inhibition and the role this process plays in controlling enzyme activity. Answer: Feedback inhibition is also known as negative feedback and end-product inhibition. In this mechanism, the product of a particular metabolic pathway inhibits an enzyme that catalyzes a reaction earlier in the pathway. For example, the end-product might be an allosteric inhibitor of that enzyme, binding to a location on the enzyme outside the active site. When the allosteric inhibitor binds, it changes the shape of the enzyme and prevents the enzyme from binding to its substrate. This "shuts off" the enzyme, and because the product of one reaction is the substrate for another, it shuts down the pathway. The inhibition is released as the amount of the endproduct decreases. When this occurs, the pathway will be turned on again, because the cell again needs the end-product. Feedback inhibition controls enzyme activity so that energy and metabolites are not wasted. 2) The discussion of carbohydrate catabolism includes some of the many metabolic variations microbes are capable of. Devise a set of biochemical tests to identify the Gram-negative bacteria mentioned. Assume you can detect various organic compounds. Prepare a dichotomous key of your identification scheme. Answer: Many answers are possible. Figure 5.3 shown below is one example, based on glucose and lactose fermentation. Test for ability to ferment glucose and lactose. If glucose is fermented, test for the presence of 6-phosphogluconic acid and 2,3-butandiol. 3) Explain why the ATP yield from processes such as cellular respiration is generally given as a theoretical number. Answer: The maximum yield of ATP from a single molecule of glucose is 38 ATP molecules. However, any given glucose molecule may produce fewer than this number of ATP molecules for a variety of reasons. A eukaryotic cell spends 2 ATP molecules in transporting NADH produced during glycolysis into the mitochondrion; this reduces the theoretical yield to 36 ATP. The yield might be even lower, because in chemiosmosis there is no direct relationship between the number of electrons used to create a proton gradient and the number of ATP molecules produced from that proton gradient. Proton gradients are used to drive other processes and activities in the cell besides ATP production, so some of the energy that is represented by the proton gradient can be "siphoned off" before it is used to make ATP. Some of the intermediates of glycolysis and the Citric acid cycle can be used as substrates for other metabolic processes, and when the intermediates are diverted, the theoretical ATP yield is not realized. 4) Compare and contrast cyclic and noncyclic photophosphorylation. Answer: Both cyclic photophosphorylation and noncyclic photophosphorylation are aspects of the light-dependent reactions of photosynthesis. They both involve the excitation of electrons by light energy; these excited electrons then participate in an electron transport pathway to create a proton gradient that can be used to produce ATP through chemiosmosis. However, as its name implies, cyclic photophosphorylation occurs when electrons return to the chlorophyll molecules whence they came. Excited electrons in noncyclic photophosphorylation are also used in the same way to produce ATP; however, these electrons are donated to an NADP+ molecule at the end of their transport chain, producing NADPH as a product of the system. Because electrons are constantly leaving the chlorophyll molecules where they are being excited, and not returning, there must also be a steady source of electrons for the photosystem. These electrons can come from molecules such as water or hydrogen sulfide. 5) Discuss the interrelationships between anabolic and catabolic pathways. Provide specific examples in your answer. Answer: Catabolic pathways generate the energy required for anabolic reactions. Catabolic pathways produce intermediates for other pathways, and some intermediates and products of anabolic pathways provide intermediates for catabolic pathways. The Citric acid cycle produces energy to drive amino acid synthesis, and several Citric acid cycle intermediates are substrates for amino acid biosynthesis. For example, oxaloacetic acid is a precursor for half a dozen amino acids, and α-ketoglutaric acid is a precursor for about four additional amino acids. The pentose phosphate pathway produces the five-carbon sugar required for nucleotide synthesis, and various amino acids are metabolized to produce the nitrogenous bases in nucleotides. The Citric acid cycle produces intermediates and substrates for lipid biosynthesis. Catabolism of amino acids produces a variety of molecules that are intermediates of glycolysis and the Citric acid cycle, and the same is true of lipid catabolism.