CHEM 301/ CHEM301 Midterm Examination V2 | Biochemistry – 2026/2027 Academic Year – Questions with Verified Answers and Elaborated Solutions

CHEM 301/ CHEM301 Midterm Examination V2 | Biochemistry – 2026/2027 Academic Year – Questions with Verified Answers and Elaborated Solutions Q: Which ONE of the following pairs of functional groups can interact by forming a hydrogen bond at physiological pH? Answer - Two amides. - Two phenyl rings. - Two aldehydes. - Two esters. Q: What type of functional group links amino acids together to form a protein? Answer - thioester bond - hydrogen bond - glycosidic bond - amide bond Q: What role does the hydrophobic effect play in protein folding? Answer - It allows for proteins to fold when some amino acids avoid contact with water. - Proteins only fold when they become insoluble in water. - The second law of thermodynamics provides energy for protein to fold. - It causes an overall decrease in the entropy of water. Q: Proteins that catalyze chemical reactions are classified as: Answer - proteases - enzymes - hormones - catalases Q: Hormones can belong to which ONE of the following categories? Answer - Lipids - Nucleic Acids - Carbohydrates - Vitamins Q: What is the take home message for BCH210H? Answer - The structure of a molecule is essential for its function. - All proteins require vitamins for their function and are essential for human health. - Biochemistry is all about the chemical reactions in the cell. - Cells rely primarily on proteins for structural support. Q: Which ONE of the following biomolecules has the most complex structure? Answer - An amino acid - A polysaccharide - A molecule of water - A nucleotide Q: Q: Which ONE of the following non-covalent forces can contribute the MOST to a molecule (eg. drug or cofactor) that interacts with a soluble protein? Answer - A disulfide bond - Van der Waals forces - The hydrophobic effect - Ionic interactions Q: In biochemistry, PDB stands for: Answer - Protein Data Bank - Platform to Deduce Binding partners - Polypeptide Data Base - Program for Documenting Biomolecules Q: Which ONE of the following pairs of amino acids (represented by 3 letter codes) have side chains that can form a salt bridge? Answer - Cys - Cys - Lys - Asn - Arg - Ser - His - Glu Q: Which ONE of the following tri-peptides (amino acids represented by their 1-letter code) would have a titration curve with 4 buffering regions? Answer - F-A-R - S-A-D - P-E-P - M-I-N Q: Which ONE of the following statements is CORRECT regarding amino acids? Answer - They can form covalent and non-covalent interactions. - They are considered essential if they are found in every protein. - They join together to form polypeptides via amine bonds. - They only contain carbon, hydrogen, oxygen and nitrogen. Q: What is the approximate isoelectric point (pI) of Cysteine (pKas = 1.7, 8.3, 10.8)? Answer - 5.0 - 6.9 - 9.6 - 8.3 Q: How many of the 20 standard amino acids are zwitterions at physiological pH=7.4? Answer - 11 - 16 - 15 - 5 Q: Which ONE of the following polypeptides only contains letters that represent the one letter codes for the 20 standard amino acids? Answer - J-U-N-E - F-E-B-R-U-A-R-Y - D-E-C-E-M-B-E-R - A-P-R-I-L Q: What is the correct 3 letter code for Glutamine? Answer - Gln - Glq - Gla - Glu Which ONE of the following groups of amino acids (represented by their 3-letter codes) is least likely to be found on the surface of a soluble protein? Answer - Ala, Glu, Ser - Asp, His, Gln - Cys, Leu, Phe - Asn, Lys, Thr Which ONE of the following statements is CORRECT regarding chirality and amino acids? Answer - Chirality arises due to the presence of 4 different carbons in the structure. - The 20 amino acids each contain a chiral alpha carbon. - Amino acids are chiral because they have different side chains. - A chiral amino acid will have an L and D isomer. While purifying your protein of interest from a crude extract, you forget to label the collection tubes and mix up which samples contain the void volume and which ones eluted from the column. Which ONE of the following techniques is the best choice to determine which fraction you should use for subsequent experiments? Answer - UV spectroscopy - Dialysis - Bradford assay - Western blotting Which ONE of the following is CORRECT regarding the differences between an alpha helix and beta strand/sheet? - They can be found in different motifs contributing to the level of tertiary structure. - Hydrogen bonds can form between amides in an alpha helix but not between amides in a beta sheet. - Amino acids can only exist in alpha helices or beta strands based on their properties. - A stretch of 20 amino acids would have a more extended structure in an alpha helix. Which ONE of the following types of secondary structure will the following polypeptide (amino acids represented by their 1-letter code) most likely form? W-A-V-T-F-K-I-G-Y-C - beta strand - beta turn - Amphipathic alpha helix - random coil Which ONE of the following statements is CORRECT regarding the amino acids found in a protein? - The composition of amino acids dictates the secondary structure that will form. - A protein's amino acid sequence doesn't necessarily tell you its function. - All proteins include the 20 basic amino acids in their primary structure. - Proteins in the same family of proteins have identical amino acid sequences. You are wish to study the structure of a brand new protein of unknown structure and function, but are having trouble purifying it from its endogenous source. Which ONE of the following would be useful to assist in its purification? - Co-immunoprecipitation with another protein. - The inclusion of a GST tag at the N-terminus. - Dialysis to change the pH of the buffer to the pI. - Treating the crude lysate with formaldehyde. Which ONE of the following statements is CORRECT regarding the role of hydrogen bonds for protein structure? - These covalent interactions are necessary for the formation of tertiary structure. - Hydrogen bonds between side chains allow for alpha helices to form. - Amino acids are joined by hydrogen bonds to form a polypeptide. - They can contribute to the formation of quaternary structure. You are monitoring the elution of your protein of interest from a size exclusion column and detect an absorbance of 0.45 at 415 nm in a 1 cm cuvette. Given a molar absorptivity of 15,000 L mol-1 cm-1 , what is the concentration of protein present in your fraction? - 30 uM - 6.75 uM - 67.5 nM - 3.0 mM Which ONE of the following statements is CORRECT regarding the methods used to determine a protein's sequence? - The chemical cleavage in Edman degradation limits how many amino acids can be sequenced. - Edman degradation is an effective way of detecting post-translational modifications. - Mass spec can only deduce the molecular weight of a polypeptide chain, not its identity. - Mass spec can only be done after larger chains are cleaved into smaller fragments. Protein X has a pI of 9.0 and is in a buffer with a pH = 7.4, along with a mixture of other proteins. You decide to try and purify it using a DEAE (diethylaminoethyl) column. Which ONE of the following statements is CORRECT regarding this experiment? - A buffer of pH 6.0 would be needed to elute Protein X from the column. - Since the pI is above the physiological range, it can't be purified from a mixture of proteins. - Once Protein X is bound to the column, a high salt buffer could be used to elute it. - The protein will elute in the void volume. Which ONE of the following enzymes or chemical reagents will not cleave the following polypeptide (amino acids represented by their 1-letter code)? P-A-R-T-Y-T-I-M-E - Cyanogen Bromide - Carboxypeptidase B - Trypsin - Chymotrypsin Which of the following is not true of the reaction catalyzed by the pyruvate dehydrogenase complex? Biotin participates in the decarboxylation. Both NAD+ and a flavin nucleotide act as electron carriers. The reaction occurs in the mitochondrial matrix. The substrate is held by the lipoyl-lysine "swinging arm." Two different cofactors containing —SH groups participate. Biotin participates in the decarboxylation. Which of the below is not required for the oxidative decarboxylation of pyruvate to form acetyl CoA? ATP CoA-SH FAD Lipoic acid NAD+ ATP Which combination of cofactors is involved in the conversion of pyruvate to acetyl-CoA? TPP, lipoic acid, and NAD+ Which of the following statements about the oxidative decarboxylation of pyruvate in aerobic conditions in animal cells is correct? One of the products of the reactions of the pyruvate dehydrogenase complex is a thioester of acetate. The methyl (—CH3) group is eliminated as CO2. The process occurs in the cytosolic compartment of the cell. The pyruvate dehydrogenase complex uses all of the following as cofactors: NAD+, lipoic acid, pyridoxal phosphate (PLP), and FAD. The reaction is so important to energy production that pyruvate dehydrogenase operates at full speed under all conditions. One of the products of the reactions of the pyruvate dehydrogenase complex is a thioester of acetate. Glucose labeled with 14C in C-3 and C-4 is completely converted to acetyl-CoA via glycolysis and the pyruvate dehydrogenase complex. What percentage of the acetyl-CoA molecules formed will be labeled with 14C, and in which position of the acetyl moiety will the 14C label be found? No label will be found in the acetyl-CoA molecules. Which of the following is not true of the citric acid cycle? All enzymes of the cycle are located in the cytoplasm, except succinate dehydrogenase, which is bound to the inner mitochondrial membrane. In the presence of malonate, one would expect succinate to accumulate. Oxaloacetate is used as a substrate but is not consumed in the cycle. Succinate dehydrogenase channels electrons directly into the electron transfer chain. The condensing enzyme is subject to allosteric regulation by ATP and NADH. All enzymes of the cycle are located in the cytoplasm, except succinate dehydrogenase, which is bound to the inner mitochondrial membrane. Acetyl-CoA labeled with 14C in both of its acetate carbon atoms is incubated with unlabeled oxaloacetate and a crude tissue preparation capable of carrying out the reactions of the citric acid cycle. After one turn of the cycle, oxaloacetate would have 14C in: all four carbon atoms. Malonate is a competitive inhibitor of succinate dehydrogenase. If malonate is added to a mitochondrial preparation that is oxidizing pyruvate as a substrate, which of the following compounds would you expect to decrease in concentration? Citrate Fumarate Isocitrate Pyruvate Succinate Fumarate Which of the following is not an intermediate of the citric acid cycle? Acetyl-CoA Citrate Oxaloacetate Succinyl-CoA α-Ketoglutarate Acetyl-CoA In mammals, each of the following occurs during the citric acid cycle except: formation of α-ketoglutarate. generation of NADH and FADH2. metabolism of acetate to carbon dioxide and water. net synthesis of oxaloacetate from acetyl-CoA. oxidation of acetyl-CoA. net synthesis of oxaloacetate from acetyl-CoA. Oxaloacetate uniformly labeled with 14C (i.e., with equal amounts of 14C in each of its carbon atoms) is condensed with unlabeled acetyl-CoA. After a single pass through the citric acid cycle back to oxaloacetate, what fraction of the original radioactivity will be found in the oxaloacetate? 1/2 Conversion of 1 mol of acetyl-CoA to 2 mol of CO2 and CoA via the citric acid cycle results in the net production of: 1 mol of FADH2. Which one of the following is not associated with the oxidation of substrates by the citric acid cycle? All of the below are involved. CO2 production Flavin reduction Lipoic acid present in some of the enzyme systems Pyridine nucleotide oxidation Pyridine nucleotide oxidation The two moles of CO2 produced in the first turn of the citric acid cycle have their origin in the: two carboxyl groups derived from oxaloacetate. The oxidative decarboxylation of α-ketoglutarate proceeds by means of multistep reactions in which all but one of the following cofactors are required. Which one is not required? ATP Coenzyme A Lipoic acid NAD+ Thiamine pyrophosphate ATP 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: α-ketoglutarate to succinyl-CoA. Which one of the following enzymatic activities would be decreased by thiamine deficiency? 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: succinyl-CoA to succinate. The standard reduction potentials (E'°) for the following half reactions are given. Fumarate + 2H+ + 2e- → succinate E'° = +0.031 V FAD + 2H+ + 2e- → FADH2 E'° = -0.219 V If succinate, fumarate, FAD, and FADH2, all at l M concentrations, were mixed together in the presence of succinate dehydrogenase, which of the following would happen initially? Fumarate and succinate would become oxidized; FAD and FADH2 would become reduced. Fumarate would become reduced; FADH2 would become oxidized. No reaction would occur because all reactants and products are already at their standard concentrations. Succinate would become oxidized; FAD would become reduced. Succinate would become oxidized; FADH2 would be unchanged because it is a cofactor, not a substrate. Fumarate would become reduced; FADH2 would become oxidized. For the following reaction, ΔG'° = 29.7 kJ/mol. L-Malate + NAD+ → oxaloacetate + NADH + H+ The reaction as written: may occur in cells at certain concentrations of substrate and product. All of the oxidative steps of the citric acid cycle are linked to the reduction of NAD+ except the reaction catalyzed by: succinate dehydrogenase. Which of the following cofactors is required for the conversion of succinate to fumarate in the citric acid cycle? ATP Biotin FAD NAD+ NADP+ FAD In the citric acid cycle, a flavin coenzyme is required for: oxidation of succinate. Which of the following intermediates of the citric acid cycle is prochiral? Citrate Isocitrate Malate Oxaloacetate Succinate Citrate Anaplerotic reactions . produce oxaloacetate and malate to maintain constant levels of citric acid cycle intermediates produce biotin needed by pyruvate carboxylase recycle pantothenate used to make CoA produce pyruvate and citrate to maintain constant levels of citric acid cycle intermediates All of the above 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: amino acids. nucleotides. fatty acids. sterols. All of the above 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). 4; 1; 1 During the reaction of pyruvate carboxylase, CO2 is covalently attached to all the following except: phosphate. biotin. pyruvate. lysine. All of the above lysine Entry of acetyl-CoA into the citric acid cycle is decreased when: 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: ATP and/or NADH. During seed germination, the glyoxylate pathway is important to plants because it enables them to: carry out the net synthesis of glucose from acetyl-CoA. A function of the glyoxylate cycle, in conjunction with the citric acid cycle, is to accomplish the: A) complete oxidation of acetyl-CoA to CO2 plus reduced coenzymes. B) net conversion of lipid to carbohydrate. C) net synthesis of four-carbon dicarboxylic acids from acetyl-CoA. D) net synthesis of long-chain fatty acids from citric acid cycle intermediates. E) Both B and C are correct. E) Both B and C are correct. The glyoxylate cycle is: a means of using acetate for both energy and biosynthetic precursors. The citric acid cycle begins with the condensation of acetyl-CoA with oxaloacetate. Describe three possible sources for the acetyl-CoA. Acetyl-CoA is produced by (1) the pyruvate dehydrogenase complex, (2) β oxidation of fatty acids, or (3) degradation of certain amino acids. Briefly describe the relationship of the pyruvate dehydrogenase complex reaction to glycolysis and the citric acid cycle. The pyruvate dehydrogenase complex converts pyruvate, the product of glycolysis, into acetyl CoA, the starting material for the citric acid cycle. Describe the enzymes, cofactors, intermediates, and products the pyruvate dehydrogenase complex. The pyruvate dehydrogenase complex consists of multiple copies of each of three enzymes. The first enzyme to act is pyruvate dehydrogenase (E1), which converts pyruvate to CO2 and the hydroxyethyl derivative of thiamine pyrophosphate (TPP). The same enzyme then oxidizes the hydroxyethyl group to an acetyl group attached to enzyme-bound lipoate through a thioester linkage. The second enzyme, dihydrolipoyl transacetylase (E2), transfers the acetyl group to coenzyme A, forming acetyl-CoA. The third enzyme, dihydrolipoyl dehydrogenase (E3), oxidizes the dihydro-lipoate to its disulfide form, passing the electrons through FAD to NAD+. (See Fig. 16-6.) Suppose you found an overly high level of pyruvate in a patient's blood and urine. One possible cause is a genetic defect in the enzyme pyruvate dehydrogenase, but another plausible cause is a specific vitamin deficiency. Explain what vitamin might be deficient in the diet, and why that would account for high levels of pyruvate to be excreted in the urine. How would you determine which explanation is correct? The most likely explanation is that the patient has a deficiency of thiamine, without which the cell cannot make thiamine pyrophosphate, the cofactor for pyruvate dehydrogenase. The inability to oxidize pyruvate produced by glycolysis to acetyl-CoA would lead to accumulation of pyruvate in blood and urine. The most direct test for this deficiency is to feed a diet supplemented with thiamine and determine whether urinary pyruvate levels fall. Match the cofactors below with their roles in the pyruvate dehydrogenase complex reaction. Cofactors: A. Coenzyme A (CoA-SH) B. NAD+ C. Thiamine pyrophosphate (TPP) D. FAD E. Lipoic acid in oxidized form Roles: _______ Attacks and attaches to the central carbon in pyruvate _______ Oxidizes FADH2 _______ Accepts the acetyl group from reduced lipoic acid _______ Oxidizes the reduced form of lipoic acid _______ Initial electron acceptor in oxidation of pyruvate. C; B; A; D; E Two of the steps in the oxidative decarboxylation of pyruvate to acetyl-CoA do not involve the three carbons of pyruvate, yet are essential to the operation of the pyruvate dehydrogenase complex. Explain. The two steps catalyzed by dihydrolipoyl dehydrogenase (E3) are required to regenerate the oxidized form of lipoate, bound to dihydrolipoyl transacetylase, from the dihydrolipoyl (reduced) form produced in the oxidation of pyruvate. First, FAD is reduced to FADH2 to reoxidize the dihydrolipoate, then NAD+ is reduced to NADH to reoxidize the FADH2 to complete the reaction. What is the function of FAD in the pyruvate dehydrogenase complex? How is it regenerated? FAD serves as the electron acceptor in the re-oxidation of the cofactor dihydrolipoate. It is converted to FADH2 by this reaction and is regenerated by the passage of electrons to NAD+. The human disease beriberi is caused by a deficiency of thiamine in the diet. People with severe beriberi have higher than normal levels of pyruvate in their blood and urine. Explain this observation in terms of specific enzymatic reaction(s). Thiamine is essential for the synthesis of the cofactor thiamine pyrophosphate (TPP). Without this cofactor the pyruvate dehydrogenase complex cannot convert pyruvate into acetyl-CoA, so the pyruvate produced by glycolysis accumulates. There are few, if any, humans with defects in the enzymes of the citric acid cycle. Explain this observation in terms of the role of the citric acid cycle. The citric acid cycle is central to all aerobic energy-yielding metabolisms and also plays a critical role in biosynthetic reactions by providing precursors. Mutations in the enzymes of the citric acid cycle are likely to be lethal during fetal development. Preparation of an extract of muscle results in a dramatic decrease in the concentration of citric acid cycle intermediates compared to their concentrations in the tissue. However, in 1935, Szent-Gyorgi showed that the production of CO2 by the extract increased when succinate was added. In fact, for every mole of succinate added, many extra moles of CO2 were produced. Explain this effect in terms of the known catabolic pathways. Succinate is an intermediate in the citric acid cycle that is not consumed but is regenerated by the operation of the cycle. By adding succinate to an extract that is depleted in citric acid cycle intermediates, these intermediates are replenished and the cycle can resume operating, oxidizing acetyl-CoA to CO2. Draw the citric acid cycle from isocitrate to fumarate only, showing and naming each intermediate. Show where high-energy phosphate compounds or reduced electron carriers are produced or consumed, and name the enzyme that catalyzes each step. This part of the citric acid cycle includes the reactions catalyzed by isocitrate dehydrogenase, the α-ketoglutarate dehydrogenase complex, succinyl-CoA synthetase, and succinate dehydrogenase. (See Fig. 16-7.) Show the three reactions in the citric acid cycle in which NADH is produced, including the structures. None of these reactions involves molecular oxygen (O2), but all three reactions are strongly inhibited by anaerobic conditions; explain why. NADH is produced in the reactions catalyzed by isocitrate dehydrogenase, the α-ketoglutarate dehydrogenase complex, and malate dehydrogenase. These reactions are indirectly dependent on the presence of O2 because the NADH produced in the reactions is normally recycled to NAD+ by passage of electrons from NADH through the respiratory chain to O2. (See also Fig. 16-7.) At what point in the citric acid cycle do the methyl carbon from acetyl-CoA and the carbonyl carbon from oxaloacetate become chemically equivalent? This happens with the formation of succinate. Show the reactions by which α-ketoglutarate is converted to malate in the citric acid cycle. The reactions are those catalyzed by the α-ketoglutarate dehydrogenase complex, succinyl-CoA synthetase, succinate dehydrogenase, and fumarase. (See Fig. 16-7.) Show the steps of the citric acid cycle in which a six-carbon compound is converted into the first four-carbon intermediate in the path. For each step, show structures of substrate and product, name the enzyme responsible, and show where cofactors participate. The reactions are those catalyzed by isocitrate dehydrogenase, the α-ketoglutarate dehydrogenase complex, and succinyl-CoA synthetase. (See Fig. 16-7.) Show the structures of the reactants and products for two of the four redox reactions in the citric acid cycle. Indicate where any cofactors participate, and label the reactants, products, and cofactors as oxidants or reductants in the reaction. The four oxidation-reduction reactions are those catalyzed by isocitrate dehydrogenase, the α ketoglutarate dehydrogenase complex, succinate dehydrogenase, and malate dehydrogenase. (See Fig. 16-7.) For isocitrate dehydrogenase, isocitrate is the reductant (i.e. it becomes oxidized), NAD+ is the oxidant (i.e. it becomes reduced), and a divalent metal is required for this reaction. For the α-ketoglutarate dehydrogenase complex, α-ketoglutarate is the reductant, NAD+ is the oxidant, and the enzyme requires the same menagerie of cofactors as does pyruvate dehydrogenase (TPP, lipoyllysine, FAD). For malate dehydrogenase, malate is the reductant, NAD+ is the oxidant, and no cofactors are required. Show the steps of the citric acid cycle from succinyl-CoA to oxaloacetate only. For each step, show structures of substrate and product, name the enzyme responsible, and show where cofactors participate. These are the steps catalyzed by succinyl-CoA synthetase, succinate dehydrogenase, fumarase, and malate dehydrogenase. (See Fig. 16-7) Explain why fluorocitrate, a potent inhibitor of the enzyme aconitase, is a deadly poison. By inhibiting aconitase, fluorocitrate prevents the citric acid cycle from operating. This prevents the oxidation of acetyl-CoA and dramatically reduces the yield of ATP from carbohydrate and lipid catabolism. The resulting drop in ATP levels is lethal. The citric acid cycle is frequently described as the major pathway of aerobic catabolism, which means that it is an oxygen-dependent degradative process. However, none of the reactions of the cycle directly involves oxygen as a reactant. Why is the pathway oxygen-dependent? The citric acid cycle produces NADH, which normally is recycled by passage of electrons from NADH to O2 via the respiratory chain. With no O2 to accept electrons from NADH, the accumulation of NADH effectively stops the citric acid cycle. In the citric acid cycle, a five-carbon compound is decarboxylated to yield an activated four carbon compound. Show the substrate and product in this step, and indicate where any cofactor(s) participate(s). The oxidation of α-ketoglutarate to succinyl-CoA involves five cofactors: lipoate, thiamine pyrophosphate (TPP), FAD, NAD+, and CoA-SH. CO2 is produced in two reactions in the citric acid cycle. For each of these reactions, name and show the structures of reactant and product, name the enzyme, and show how any cofactors participate. See the isocitrate dehydrogenase and α-ketoglutarate dehydrogenase reactions. (See also Fig. 16 6.) In which reaction of the citric acid cycle does substrate-level phosphorylation occur? Substrate-level phosphorylation of GDP to GTP occurs in the succinyl-CoA synthetase reaction in which succinyl-CoA is converted to succinate during the citric acid cycle. Explain in quantitative terms the circumstances under which the following reaction can proceed. L-Malate + NAD+ → oxaloacetate + NADH + H+ ΔG'° = +29.7 kJ/mol A reaction for which ΔG'° is positive can proceed under conditions in which the actual ΔG is negative. From the relationship ΔG = ΔG'° + RT ln [product], [reactant] it is clear that if the concentration of product is kept very low (e.g., by its removal in a subsequent metabolic step), the logarithmic term becomes negative and the actual ΔG can then have a negative value. (See also Chapter 13.) You are in charge of genetically engineering a new bacterium that will derive all of its ATP from sunlight by photosynthesis. Will you put the enzymes of the citric acid cycle in this organism? Briefly explain why or why not. Yes; even though the citric acid cycle is not needed for catabolic reactions in this organism, the enzymes of the cycle are still essential. They produce precursors of amino acids (such as α-keto glutarate and oxaloacetate), of heme (succinyl-CoA), and of a variety of other essential products. Match the cofactor with its function in the citric acid cycle. A given function may be used more than once or not at all. Cofactor Function (a) NAD+/NADH (1) carries O2 (b) FAD/FADH2 (2) carries small carbon-containing molecules (c) CoA (3) carries e- (d) thiamine (4) carries small nitrogen-containing molecules (e) biotin (a)-(3); (b)-(3); (c)-(2); (d)-(2); (e)-(2) Germinating plant seeds can convert stored fatty acids into oxaloacetate and a variety of carbohydrates. Animals cannot synthesize significant quantities of oxaloacetate or glucose from fatty acids. What accounts for this difference? Plants use the glyoxylate cycle to convert two molecules of acetyl-CoA into one four-carbon compound (such as oxaloacetate), then use this compound to make glucose (gluconeogenesis). In animals that lack the glyoxylate cycle, each acetyl group that enters the citric acid cycle yields two CO2, allowing no net conversion of acetyl groups into oxaloacetate. 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