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UNE BIOCHEMISTRY MIDTERM STUDY
GUIDE QUESTIONS FULLY SOLVED &
UPDATED 2023
A 19-year-old boy is diagnosed with Creutzfeldt-Jakob disease which is caused by the introduction of an amyloid fold in the disease-causing protein. The introduction of this fold causes the protein to transition from a primarily alpha helical structure to an aggregate of mostly beta sheets. This change in protein structure (leading to disease) is best attributed to changes in which of the following? - answer folding of the secondary structures Which of the following is the best description of primary protein structure? - answer a newly synthesized strand of amino acids How do most enzymes reduce the activation energy needed to move a reaction forward? - answer providing an active site most complementary the transition state Movement of ammonia from an amino acid to an a-keto acid involves a family of enzymes best categorized as which of the following? - answer transferases Hemoglobin has the ability to display cooperative binding while myoglobin does not display this binding kinetic pattern. Which of the following differences between the two proteins accounts for this difference in binding kinetics? - answer the presence of quaternary structure Changes in the physiological variables listed below can alter the affinity of hemoglobin for oxygen. Which of the following will lower the affinity of hemoglobin for oxygen? - answer increase in 2,3 bisphosphoglycerate (BPG) An enzyme has a mutation within the substrate binding site that reduces the binding of the coenzyme needed for covalent catalysis. Which of the following is likely to result as a consequence of this mutation? - answer the enzyme will not be able to form the transition state complex
Chymotrypsin is a protease that cleaves peptide bonds. It is characterized as which of the following classes of enzymes? - answer hydrolases If a mutation is made within the active site of an enzyme resulting in a decrease in Km, which of the following will be true with respect to the enzyme kinetics? - answer the enzyme will require a lower substrate concentration to reach 1/2 Vmax Which of the following best describes an enzyme inhibitor that increases the Km but does not change the Vmax? - answer a competitive inhibitor An enzyme is participating in a general acid-base catalysis reaction with an optimal reaction pH of 6.0. If acid is added to the environment reducing the pH to 3, what is the Iikely impact to the rate of the reaction? - answer the rate of the reaction is likely to decrease as the pH is out of optimal catalytic range A new enzyme is discovered that increases in activity when it is phosphorylated on an exposed tyrosine residue. Phosphorylation of this amino acid is classified as which of the following? - answer covalent modification In the image below the blue line indicates enzyme kinetics with no inhibitor present. Based on this information, which of the following is true? - answer the green line shows enzyme kinetics with the addition of a noncompetitive inhibitor An example of enzyme activation by cleavage is best illustrated by which of the following? - answer activation of chymotrypsinogen to chymotrypsin Use the figure below to compare the activities of glucokinase and hexokinase. Based on this information, which of the following is a true statement? - answer glucokinase has a higher Km than hexokinase
Complex II (Succinate Q-reductase) is not considered to be part of the process of oxidative phosphorylation because it is unable to do which of the following activities? - answer pump protons from the mitochondrial matrix to the intermembrane space Dinitrophenol is an uncoupler of the electron transport chain. The addition of dinitrophenol will have which of the following impacts? - answer increase oxygen consumption A 19-year-old male is being evaluated for muscle weakness. Evaluation of a muscle biopsy revealed normal rates of succinate oxidation but very low rates of pyruvate oxidation. Further testing determined normal levels of enzymatic activity in both malate dehydrogenase and pyruvate dehydrogenase. Based on this data, the patient may have a mutation in a gene encoding for which mitochondrial protein? - answer Complex I (NADH Q-oxidoreductase) The malate-asparate shuttle is used to move reducing equivalents of cystolic NADH into the mitochondria where it can be oxidized. Which of the following compounds is used to move the reducing equivalents from cystolic NADH into the mitochondria? - answer malate A series of reaction have the following delta G: A+B--> G=-1; C+D--> E G=+3 and E+F-->G G=-5.... the overall delta G for this series of reactions is determined to be which of the following values?
- answer - An alpha-helical arrangement of amino acids is considered to be what level of protein structure?
- answer secondary structure of the protein Which amino acid would not be commonly found in the middle of an alpha-helical domain? - answer proline Which of the following best describes a protein domain? - answer a section of protein structure sufficient to perform a particular chemical or physical task Allosteric activators of hemoglobin will increase substrate binding through which of the following mechanisms? - answer binding the protein, and keeping it in the "R" conformation
Which of the following best describes the structure of heme? - answer a planar porphyrin ring that binds iron Which of the following is an example of enzyme regulation through covalent modifcation? - answer phosphorylation of muscle glycogen phosphorylase Under low energy conditions, AMP will bind to phosphofructokinase I and glycogen phosphorylase at site unique to the active site. This enhances the activity of these enzymes. This is an example of which of the following types of enzyme regulation? - answer allosteric activation A 28-year-old male is recently diagnosed with HIV. As part of his treatment he is prescribed Nevirapine which interferes with retroviral reverse transcriptase enzyme. Using the graph below, which of the following best describes the impact of this drug on its target? - answer It reduces the catalytic activity of the enzyme Children with cystinosis have growth delay and both renal and ocular issues due to accumulation of cysteine in cellular lysosomes. The defect involves a specific lysosomal membrane receptor that facilitates cysteine removal from the cell. An effective therapy has been administration of a drug with a similar structure to cysteine. This therapy reflects the general principle that competitive inhibitors typically resemble the structure of which of the following? - answer substrates or ligands that bind the active site The association of DNA and histones can be modified by histone acetylation. A decrease in histone acetylation will have which of the following impacts on the association of DNA and histones? - answer increase DNA: histone association What is the primary oxidized fuel for skeletal muscle in the fasted state? - answer free fatty acids Following insulin binding its receptor and autophosphorylation of the B-chain, what is the initial step in this cascade of events? - answer recruitment of the insulin receptor substrate (IRS)
Certain metabolic conditions will reduce flux through the TCA cycle due to an increase in the TCA cycle inhibitors. Elevation of which of the following would be an example of a compound that will reduce activity through the TCA? - answer NADH A 10-year-old boy is playing soccer and is sprinting after the ball. Under these anaerobic conditions, glucose oxidation primarily results in an increase in which of the following compounds? - answer lactate A farmer finds a cow dead in his field and notices an unusual plant nearby. Autopsy results show an elevated level of citrate present in the cow's mitochondria. This data collectively suggest inhibition of which of the following enzymes? - answer aconitase Pyruvate dehydrogenase kinase catalyzes a reaction that results in which of the following? - answer The phosphorylation and inactivation of E1 subunit of PDC (pyruvate dehydrogenase complex) Which of the following enzymes is correctly paired with its activator? - answer pyruvate dehydrogenase complex; pyruvate Alanine can be shuttled from the skeletal muscle to the liver where it is deaminated to generate pyruvate. When glucagon is high, pyruvate is primarily used as a substrate for which of the following pathways? - answer gluconeogenesis When insulin levels are high, which of the following is true? - answer glycogen synthase is dephosphorylated and active When the insulin to glucagon ratio is low, glycogenoylsis is activated in the liver. Which of the following is the primary fate of the glucose 6-phosphate released under these conditions? - answer dephosphorylated and released into the blood to maintain blood glucose
What sequence of enzymes allows for the synthesis of glycogen from glucose-6-phosphate? - answer phosphoglucomutase, UDP-glucose pyrophosphorylase, glycogen synthase, amylo- (1,4a1,6)-transglycosylase Which of the following events occurs during the formation of phosphoenolpyruvate from pyruvate during gluconeogenisis? - answer CO2 is required Which of the following best describes the role of the Cori cycle? - answer the process using lactate from skeletal muscle and red blood cells to generate glucose When cortisol binds to its receptor, which of the following events occur to stimulate gluceoneogenesis? - answer enhanced transcription of regulatory enzymes The skeletal muscle primarily provides substrate for glucongeogenesis through which of the following processes? - answer protein catabolism The major regulatory step of the pentose phosphate pathway is catalyzed by which enzyme? - answer glucose 6-phosphate dehydrogenase Which of the following are the two primary products of the pentose phosphate pathway? - answer ribose-5-phosphate and NADPH Cleavage of fructose 1-phosphate into dihydroxyacetone-phosphate and glyceraldehyde is facilitated by which enzyme? - answer aldolase High levels of activity of the non-oxidative portion of the pentose phosphate pathway will directly produce intermediates of which of the following pathways? - answer glycolysis A deficiency in glucose 6-phosphate dehydrogenase reduces the levels of NADPH in the red blood cell. This leads to an increase in which of the following compounds with the cell? - answer oxidized gluthathione
Glycolysis provides intermediates that can be used to make other necessary substrates. One example of this is the direct conversion of pyruvate to which of the following amino acids? - answer Alanine Which of the following correctly pairs amino acid with the TCA cycle intermediate it can be transaminated to? - answer glutamate: a-ketoglutarate Red blood cells lack mitochondria; therefore glucose is primarily oxidized to ribose and which of the following compounds? - answer lactate A patient presents to the emergency department with lactic acidosis. A deficiency in thiamine (TPP) is suspected and this will be consistent with a decrease in the activity of following enzymes? - answer transketolase A patient is newly diagnose with a deficiency in fructokinase. Which of the following will not be a metabolic consequence of this deficiency? - answer hypoglycemia A family presents for genetic counseling. The couple has two female children who are alive and well; however, their infant son recently died in the nursery with severe hemolysis (lysis of the blood cells) and jaundice. The wife recalls she a lost a brother in infancy with severe hemolysis, induced after a viral infection. The physician suspects a glucose-6-phosphate dehydrogenase deficiency. this would result in a deficiency in which of the following compounds in the red blood cells? - answer ribose and NADPH In the non-oxidative portion of the pentose phosphate pathway, 2-carbon fragments of keto- sugars can be transferred to other sugars to generate a larger sugar molecule. This reaction is catalyzed by which of the following enzymes? - answer transketolase Galactose 1-phosphate is initially converted to glucose 1-phosphate and requires which of the following compounds? - answer UDP-glucose
Which of the following pathways is not stimulated by high levels of insulin? - answer amino acid catabolism Which of the following pathways provides the primary oxidizable fuel for skeletal muscle in the fasted state? - answer lipolysis from adipose tissue A young women goes to work without eating breakfast and skips lunch. In this scenario, which of the following pathways is providing substrates used to generate ATP in the liver? - answer free fatty acids Which of the following hormones is best described as anabolic? - answer insulin Which of the following events occurs during the formation of phosphoenolpyruvate from pyruvate during gluconeogenesis? - answer CO2 is required An individual is recently diagnosed with Type 2 diabetes. In this individual, hyperglycemia may in part be due to inactivity of which of the following glucose transporters on skeletal muscle? - answer GLUT When the insulin to glucagon ratio is low, glycogenolysis is activated in the liver. Which of the following is primary fate of the glucose 6-phosphate released under these conditions? - answer dephosphorylated and released into the blood to maintain blood glucose Which of the following would occur in the lover when glucose levels are high (think insulin is elecated)? - answer generation of glucose 1-phosphate to be used for glyvogen synthesis During an overnight fast, which of the following is the major source of blood glucose? - answer hepatic glycogenolysis If unregulated, which of the following pairs of enzymes would represent a futile cycle? - answer fructose 1,6-bisphosphatase and phosphofructokinase-
