UIUC MCB 450 PRACTICE EXAM

Most of the enzymes are made of - ANS Amino acids A biological molecule can serve as a hydrogen bond donor if the hydrogen is attached to: - ANS O or N A weak acid can act as a buffer: - ANS At pH values = pK ±1 Which of the following amino acid is not preferred to adopt the α-helix secondary structure? - ANS Proline Which kind of amino acids would most likely be buried in the interior of a water-soluble, globular protein? - ANS Hydrophobic amino acids with nonpolar R groups A peptide bond: - ANS has a partial double-bond character Which of the following structural features is the most likely characteristic of at least one protein in the brain plaques of patients with Alzheimer disease? - ANS A high content of beta-pleated sheet structure The enzyme enteropeptidase is important in the intestinal digestion of dietary protein because it initiates the protease activation cascade by converting: - ANS trypsinogen to trypsin Which statement about protein digestion and absorption is most correct? - ANS Gastric acids released from parietal cells help denature the proteins and activate pepsinogen Hartnup disease results from the genetic defect in the transporter gene, SLC6A19, which is responsible for the absorption of which of the following amino acids? - ANS Tryptophan Which of the transporter is actively involved in the transport of glucose into the intestine epithelium? - ANS Sodium-glucose cotransporter 1 (SGLT1) What is the role of emulsification in lipid digestion? - ANS It increases the surface area of the hydrophobic lipid droplets so the digestive enzymes can act effectively Which of the following test could be used to determine the folic acid deficiency? - ANS FIGLU test Which of the following co-factor is involved in the resynthesis of Succinyl CoA from L-methylmalonyl CoA? - ANS Deoxyadenosylcobalamin Which of the following statements is false of the metabolic disease phenylketonuria? - ANS The disease is treated with a high phenylalanine diet. What enzyme is deficient in maple syrup urine disease (MSUD)? - ANS branch-chain α-keto acid dehydrogenase The end product of degradation of purine nucleotides is: - ANS Uric acid Which of the following chemicals can be used for the treatment of gout? - ANS Allopurinol An enzyme deficiency in which of the following metabolic pathways is responsible for Lesch-Nyhan syndrome? - ANS Purine salvage Which one of the following enzymes of nucleotide metabolism is correctly paired with its pharmacological inhibitor? - ANS Dihydrofolate reductase----methotrexate Of the electron transfer complexes, which complex is unable to pump protons across the mitochondrial membrane? - ANS Succinate-Q reductase (complex II) A diet pill that acts to increase oxygen consumption and a high amount of electron transport without ATP production is likely what kind of compound? - ANS uncoupler Which of the following compounds binds to complex I and inhibits the formation of proton-motive force? - ANS Rotenone In the malate-aspartate shuttle, electrons from NADH are transferred to _____________, forming malate. - ANS Oxaloacetate Which of the following determines a protein's primary structure? - ANS The protein's linear amino acid sequence Denature of proteins by gastric acids is due to the disruption of _____ by low pH. - ANS Ionic bonds and hydrogen bonds What is the function of ApoCII in the chylomicrons? - ANS It is necessary for the activation of lipoprotein lipase Which of the following enzyme(s) catalyzes the transamination reaction in the catabolism of amino acids? - ANS aspartate and alanine aminotransferases What is the nitrogen source of for the carbamoyl phosphate in pyrimidine synthesis? - ANS Glutamine During oxidative phosphorylation, the proton motive force that is generated by electron transport is used to: - ANS induce a conformational change in the ATP synthase What is NOT a function of amino acids? - ANS building blocks of lipids Formation of the linkages that join the amino acids in a polypeptides involves: - ANS Elimination of one water molecule per linkage formed Glycosidic bond is a type of covalent bond that could be carried out by which of the following enzymes? - ANS Glycogen synthase Water weakens the electrostatic interaction of ions due to its: - ANS dielectric constant What is the [A-]/[HA] ratio when the weak acid is in a solution two pH units above its pKa? - ANS 100:1 What amino acids are most likely to be found in the core of a water-soluble globular protein? - ANS nonpolar Consider a biochemical reaction that is taking place in a 0.1 M buffer. The initial pH is 7.4, and the pKa of the buffer is 7.2. If, in a final reaction volume of 1.0 mL, 10 micromol of protons are generated, what would be the final pH of the solution? - ANS 7.22 Which one of the following statements concerning the peptide shown below is correct?Gly-Cys-Glu-Ser-Asp-Arg-Cys - ANS The peptide is able to form an internal disulfide bond What is the hydroxyl ion concentration in a urine sample that has a pH of 6? - ANS 10^-8 M Which of the following characterize alpha-helix regions of proteins? - ANS They are formed principally by hydrogen bonds between a carbonyl oxygen atom in one peptide bond and the amide hydrogen from a different peptide bond 4 amino acids apart. In which part of a globular protein are Trp and Phe located and why? - ANS interior due to the hydrophobic effect The secondary structure that is stabilized by CO and NH hydrogen bonding within the peptide chain is called a(n): - ANS alpha helix Why is the peptide bond planar? - ANS It exhibits partial double-bond character, preventing rotation. What would be the interactions between side chains of aspartate and arginine at a neutral pH? - ANS ionic Your study group is trying to identify differences in the four levels of protein structure. The secondary structure but not the tertiary structure is stabilized by: - ANS H-bonding between the oxygen of the backbone carbonyl and the hydrogen of the backbone amine. Which statement about protein digestion is CORRECT? - ANS The polypeptide products of pepsin digestion stimulate the release of the cholecystokinin. The pancreas releases _________ to buffer the pH of the stomach juices. - ANS NaHCO3 What enzyme activates trypsin? - ANS enteropeptidase The result of lipase activity in digestion is: - ANS Monoacylgycerol and two free fatty acids. What is the structure of micelles? - ANS The polar head groups of fatty acids are outside the micelle and the carbon chains are inside. Which one of the following statements about the absorption of lipids from the intestine is correct? - ANS The TAG carried by chylomicrons is degraded to free fatty acids and glycerol by lipoprotein lipase on the endothelial surface of capillaries in muscle and adipose primarily. A young black man entered his physician's office complaining of bloating and diarrhea. His eyes were sunken and the physician noted additional signs of dehydration. The patient's temperature was normal. He explained that the episode had occurred following a birthday party at which he had participated in an ice cream eating contest. The patient reported prior episodes of a similar nature following ingestion of a significant amount of dairy products. This clinical picture is most probably due to a deficiency in: - ANS lactase What is the role of cholesterol in lipid digestion? - ANS Bile salts necessary for lipid digestion are synthesized from cholesterol. What compound is oxidatively deaminated to yield an ammonium ion? - ANS glutamate What form is an ammonium ion converted into in most terrestrial vertebrates? - ANS urea N-Acetylglutamate synthase is activated by: - ANS arginine Excessive alcohol consumption not only makes you overweight, it can also lead to ammonia poisoning. How is alcohol metabolism linked to increased levels of blood ammonia? - ANS Excessive alcohol consumption can cause liver damage, the primary site of urea formation. A loss of liver function can lead to increased ammonia in the blood A 19-year-old patient with classic PKU is fed radio-labeled phenylalanine, which contains a radioactive atom in the aromatic ring of phenylalanine, and a urine sample is collected 24-hours later. Which of the following compounds would you expect to contain the greatest amount of label in the urine sample? - ANS Phenylketone Essential amino acids differ from nonessential amino acids in that: - ANS nonessential amino acids are synthesized in simple reactions compared to most essential amino acids. What cofactor or prosthetic group serves as a carrier for activated one-carbon units during the synthesis of amino acids and other biological molecules? - ANS Tetrahydrofolate Methotrexate inhibits purine synthesis by targeting formation of: - ANS Tetrahydrofolate from dihydrofolate What enzyme catalyzes the first step of pyrimidine nucleotides synthesis? - ANS carbamoyl phosphate synthetase II What is NOT a nucleotide? - ANS adenosine Sulfa drugs are analogs of p-aminobenzoate, a compound necessary for the biosynthesis of N10-formyltetrahydrofolate. How should these drugs act upon bacterial infections and why are humans not susceptible? - ANS N10-Formyltetrahydrofolate transfers a formyl group twice during de novo synthesis of the purine ring. Bacteria synthesize their own folate, whereas humans get theirs from eating green plants. A patient who has Lesch-Nyhan syndrome is given allopurinol by his physician to treat symptoms the physician attributes to gout. In this patient, - ANS The drug should help in the control of his increased excretion of uric acid. What is the final product of purine catabolism? - ANS urate Which complex in the electron transport chain does not contribute to the proton gradient across the mitochondrial membrane? - ANS Complex II What conformation of β subunits contributes to form ATP? - ANS tight conformation A 25-year-old woman presents with chronic fatigue. A series of blood tests is ordered, and the results suggest that her red blood cell count is low because of iron deficiency anemia. Such a deficiency would lead to fatigue because of which of the following? - ANS Her decrease in Fe-S centers is impairing the transfer of electrons in the electron-transport chain. The mitochondrial electron transport chain is organized into four large protein complexes, Complex (I-IV). Two diffusible redox carriers mediate the electron transport among these complexes and they are: - ANS Cytochrome c and coenzyme Q Which compound does not cross the inner mitochondrial membrane due to lack of a specific transport protein? - ANS NADH Oligomycin inhibits ATP synthase. What effect will this have on the electron transport chain? - ANS Electron transport will halt. For the proton motive force to be able to synthesize ATP in a normal mitochondrion, there must be: - ANS More positive charge on the outside of the inner membrane than on the inside. What is the source of cellular energy? - ANS adenosine triphosphate Carbohydrates function as structural components of other molecules including all of the following except: - ANS Amino acids Lipid functions include all of the following except - ANS Forming the skeletal muscle fibers Transmembrane proteins in the plasma membrane are made up of hydrophilic and hydrophobic regions. Most amino acids embedded in the membrane are _______, while most amino acids facing the extracellular field are __________. - ANS hydrophobic, hydrophilic The unique cyclic structure of which of the following amino acids plays a central role in the formation of alpha helices and beta sheets? - ANS Proline What is the pH of a buffer solution made from 0.20 M HC2H3O2 and 0.50 M C2H3O2- that has an acid dissociation constant for HC2H3O2 of 1.8x10^-5? - ANS 5.1 A disulfide bridge is formed by - ANS 2 cysteine side chains What is the concentration of acetic acid in 250 ml of a 100 mM acetate buffer at pH 4.78? pKa of acetic acid is 4.76. - ANS 48.8 mM Which of the following amino acid residues would most likely be buried in the interior of a water-soluble, globular protein? - ANS phenylalanine When an egg is fried, what happens to the protein in the egg? - ANS Heat breaks the H bonds and the protein is denatured. Which of the following describes a universal property of buffers? - ANS Buffers work best at pH at which they are 50% dissociated. Which of the following might constitute a rational therapy for sickle cell disease? - ANS Administration of agents inhibiting intermolecular hydrophobic interactions Denaturing of proteins by gastric acids is due to the disruption of _______ by low pH. - ANS Ionic and H bonds What is the function of ApoE in the chylomicrons? - ANS It is recognized by hepatic receptors for the recycling of lipids Which of the following statements about the digestion of lipids is correct? - ANS The peptide hormone cholecystokinin (CKK) causes the gallbladder to contract and release bile. Which of the following statements about the micelle is correct? - ANS Micelles transport the products of lipase digestion, fatty acids and monoacylglycerol, to the intestinal cells for absorption. Digestion of which of the following involves hydrolases? - ANS carbohydrates, triacylglycerols, proteins, and nucleic acids What sort of sugar linkages can alpha-amylase break down? - ANS alpha-1,4-glycosidic bond The transport of lipids in the lymph is carried out by - ANS chylomicrons Of the electron transfer complexes associated with the inner mitochondrial membrane, which is not directly involved in generation of a protein gradient? - ANS succinate-Q reductase (complex II) The mitochondrial electron transport chain is organized into four large protein complexes, Complex (I-IV). Two diffusible electron carriers mediate the electron transport among these complexes and they are: - ANS coenzyme Q and cytochrome c Which of the following is an enzyme involved in the scavenge pathway for removing the toxic derivatives of molecular oxygen such as peroxide ion? - ANS catalase The rotation of the gamma subunit of the mitochondrial F1 ATPase requires the presence of: - ANS proton motive force There are three conformations of beta subunit of the F1 component of ATP synthase. ATP is synthesized when beta subunit is in _______ conformation. - ANS T (tight) form The glycerol phosphate shuttle ultimately transfers the electrons from NADH to ________, which is then oxidized by the ETC. - ANS FAD The presence of uncoupling proteins allows ______ energy from the mitochondrial electron transport chain to be used for ATP synthesis and ______ for the production of heat. - ANS less, more Which of the following compounds binds to complex IV and inhibits the formation of proton-motive force? - ANS Carbon monoxide N enters the urea cycle most directly as - ANS free ammonia and aspartate Oxidative deamination is the conversion of an amino - ANS acid to a keto acid plus ammonia A deficiency in which of the following enzymes would directly limit the ability of the body to fix and dispose of ammonia? - ANS Carbamoyl phosphate synthase I ( CPS-I) A person suffering from phenylketonuria on consumption food containing high phenylalanine may lead to the accumulation of - ANS high levels of phenylpyruvate in the urine Which of the following cofactors is involved in the conversion of L-methylmalonyl CoA into succinyl CoA? - ANS Deoxyadenosylcobalamin How do animals remove urea produced during hibernation? - ANS Bacteria in the intestine hydrolyze the urea to NH4+, which can be used to synthesize amino acid. Nitrogen fixation is a means by which what types of organisms convert nitrogen into ammonium ions? - ANS bacteria A patient with maple syrup urine disease should be put on a lifelong diet restricted in which of the following? - ANS Branched-chain amino acids (leucine, valine, and isoleucine) Which of the following answers completes the sentence correctly? Adenosine is a - ANS purine nucleoside Which is the biochemical deficiency that leads to severe combined immunodeficiency disease (SCID)? - ANS adenosine deaminase Colchicine can be used to treat gout because it - ANS decreases the movement of granulocytes into the affected area