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UNE (University Of New England) Medical Biochemistry
Midterm Exam 2025 | Featuring Topics such as
Metabolic Pathways, Enzymatic Function, Bioenergetics,
Carbohydrate and Lipid Metabolism, Protein Structure,
and Clinical Correlations
A suspected mutation in the cortisol receptor is discovered. Cortisol can still bind its receptor but the dimerized complex remains in the cytosol. Based on this description which region on the receptor is most likely impacted? ---------CORRECT ANSWER-----------------Nuclear localization signal A patient is found to have a rare disease in which the secretory function of the alpha cells of the pancreas is impaired. As a consequence, glucagon cannot be secreted. Direct stimulation of which of the following pathways in liver will be impaired? ---------CORRECT ANSWER-----------------gluconeogenesis Caffeine is a natural inhibitor of phosphodiesterase. If you were to consume a large amount of coffee you would likely see a prolonged response to which of the following stimulants or hormones? ---------CORRECT ANSWER----------------- glucagon Which of the following statements is consistent with the actions of epinephrine? - --------CORRECT ANSWER-----------------Epinephrine enhances glucose output from the liver under stressful situations
Steroid hormones bind which of the following types of receptors? --------- CORRECT ANSWER-----------------intracellular receptors In the event that PI-3 kinase is not activated downstream of insulin, which of the following proteins would not be able to dock the membrane? ---------CORRECT ANSWER-----------------Protein kinase B 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? ---------CORRECT ANSWER-----------------Gluconeogenesis Newborn screening results show a biotinidase deficiency in a 2-day old infant. This deficiency impairs the infant's ability to reuse and recycle biotin. Due to this enzymatic deficiency, the activity of which of the following enzymes is likely impaired? ---------CORRECT ANSWER-----------------pyruvate carboxylase When insulin levels are high, which of the following is true? ---------CORRECT ANSWER-----------------glycogen synthase is dephosphorylated and active
A teenage female presenting with lack of menstruation (amenorrhea) is found to have dysfunctional steroid receptor characteristic of androgen insensitivity syndrome. Which of the following statements accurately describes steroid hormones? ---------CORRECT ANSWER-----------------The enhance transcription when bound to receptors. A deficiency in thiamine can reduce the activity of the pyruvate dehydrogenase complex. Under these conditions, you would expect to have a higher than normal blood concentration of which of the following metabolites? ---------CORRECT ANSWER-----------------Pyruvate Which of the following outlines the order of prosthetic groups as they are used for catalysis within the pyruvate dehydrogenase complex (PDC)? ---------CORRECT ANSWER-----------------Thiamine diphosphate-> lipoamide - > FAD After a meal, fructose 2,6-bisphosphate levels are elevated. This compound will allosterically iactivate which of the following glycolytic enzymes? ---------CORRECT ANSWER-----------------Phosphofructokinase - 1 (PFK1) In order for glucose to be retained within the cell, which of the following modifications must occur? ---------CORRECT ANSWER-----------------Phosphorylation
Which of the following reactions is commonly used to replenish intermediates of the TCA cycle? ---------CORRECT ANSWER-----------------Glutamate to alpha ketoglutarate Which of the following enzymes is correctly paired with its activator? --------- CORRECT ANSWER-----------------Pyruvate dehydrogenase complex; pyruvate Which of the following intermediates of the TCA cycle is required in the cytosol for fatty acid synthesis? ---------CORRECT ANSWER-----------------Citrate Pyruvate dehydrogenase kinase catalyzes a reaction that results in which of the following? ---------CORRECT ANSWER-----------------The phosphorylation and inactivation of E1 subunit of PDC A 1-month old boy is brought to the emergency department in a coma after sleeping through the night and failing to awaken in the morning. He is given intravenous glucose and awakens. Serum levels of pyruvate, lactate, and alanine are elevated, whereas oxaloacetate and aspartate levels are reduced. Which of the following is the most likely diagnosis in this patient? ---------CORRECT ANSWER-----------------Pyruvate carboxylase deficiency
Which of the following are two primary products of the pentose phosphate pathway? ---------CORRECT ANSWER-----------------Ribose- 5 - phosphate and NADPH 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 within the cell? ---------CORRECT ANSWER-----------------Oxidized glutathione Which of the following enzymes is involved in the non-oxidative portion of the pentose pathway? ---------CORRECT ANSWER-----------------transaldolase The major regulatory step of the pentose phosphate pathway is catalyzed by which enzyme? ---------CORRECT ANSWER-----------------Glucose 6-phosphate dehydrogenase Which of the following proteins is likely to have quaternary structure? --------- CORRECT ANSWER-----------------A multimeric protein that contains multiple peptide chains Prosthetic groups are complex nonprotein molecules that participate in catalysis by providing functional groups that form a covalent intermediate between the enzyme and the substrate. Which of the following is an example of a coenzyme or
cofactor that participates in a covalent catalysis reaction? ---------CORRECT ANSWER-----------------Pyridoxal phosphate Which of the following best describes a protein domain? ---------CORRECT ANSWER-----------------A section of a protein structure sufficient to perform a particular chemical or physical task Cleavage of fructose 1,6 bisphosphate to dihydroxyacetone and Glyceraldehyde 3- phosphate involves the breaking of a carbon-carbon bond through a process other than oxidation or hydrolysis. This is achieved by what class of enzymes? ----- ----CORRECT ANSWER-----------------Lyase A 55-year old man is brought to the emergency room with a chief complaint of chest pain and tingling in his left arm. Elevation of which of the following enzymes in circulation would be most indicative of myocardial infarction? ---------CORRECT ANSWER-----------------Troponin Allosteric activators of hemoglobin will increase substrate binding through which of the following mechanisms? ---------CORRECT ANSWER-----------------Binding the protein, and keeping it in the "R" conformation
activities? ---------CORRECT ANSWER-----------------Pump protons from the mitochondrial matrix into the inter membrane space. Succinate is a substrate for which complex in the electron transport chain? --------- CORRECT ANSWER-----------------Complex II (Succinate-Q reductase) The glycerophosphate shuttle is the major shuttle of most tissues. Which of the following best describes the transfer of electrons by this shuttle? ---------CORRECT ANSWER-----------------Electrons are directly transferred from glycerol 3-phosphate to an FAD containing glycerol phosphate dehydrogenase. 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? ---------CORRECT ANSWER-----------------Complex I (NADH Q- oxidoreductase) Which of the following components of the electron transport chain passes electrons to O2 causing it to be reduced to H2O? ---------CORRECT ANSWER--------- --------Cytochrome c oxidase
As electrons flow through complexes in the inner mitochondrial membrane, protons are pumped from the matrix into the inter membrane space. Which of the following statements is most reflective of the pH in the inter membrane space? ---------CORRECT ANSWER-----------------The pH is higher in the matrix when compared to the intermembrane space. The malate-aspartate shuttle is used to move reducing equivalents o cytosolic NADH into the mitochondria where it can be oxidized. Which of the following compounds is used to move the reducing equivalents from cytosolic NADH into the mitochondria? ---------CORRECT ANSWER-----------------Malate ATP is a high energy molecule that is often hydrolyzed during reactions. The energy within ATP is stored primarily in which of the following components of the molecule? ---------CORRECT ANSWER-----------------In the high energy phosphate bonds Which of the following is an example of enzyme regulation through covalent modification? ---------CORRECT 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? ---------CORRECT ANSWER-----------------Allosteric activation
which of the following? ---------CORRECT ANSWER-----------------Covalent modification An example of enzyme activation by cleavage is best illustrated by which of the following? ---------CORRECT ANSWER-----------------Activation of chymotrypsinogen to chymotrpysin Use the figure below to compare the activities of glucokinase and hexokinase. Based on this information, which of the following is a true statement? --------- CORRECT ANSWER-----------------Glucokinase has a higher Km than hexokinase 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 enzyme kinetics? --------- CORRECT ANSWER-----------------The enzyme will require a lower substrate concentration to reach 1/2 Vmax. Which of the following pathways directly provides oxidizable substrate to red blood cells during the fasted state? ---------CORRECT ANSWER-----------------hepatic glycogenolysis Following insulin binding its receptor and autophosphorylation of the beta chain, what is ht initial step in this cascade of events? ---------CORRECT ANSWER------------ -----Recruitment of the insulin receptor substrate
Red blood cells lack mitochondria; therefore glucose is primarily oxidized to ribose and which of the following compounds? ---------CORRECT ANSWER------------ -----Lactate Within the red blood cell, NADPH is used for which of the following processes? ---- -----CORRECT ANSWER-----------------To re-reduce glutathione Galactose 1-phosphate is initially converted to glucose 1-phosphate and requires which of the following compounds? ---------CORRECT ANSWER-----------------UDP glucose A novel signaling cascade is discovered that you suspect activates a G-alpha subunit. Which of the following downstream events would be consistent with this discovery? ---------CORRECT ANSWER-----------------Activation of adenylyl cyclase Insulin stimulates fatty acid synthesis in the liver. These fatty acids are transported to the adipose tissue as which of the following? ---------CORRECT ANSWER-----------------VLDL particles
following serum enzymes would be consistent with this diagnosis? --------- CORRECT ANSWER-----------------Amylase and lipase Which of the following best describes the structure of heme? ---------CORRECT ANSWER-----------------A planar porphyrin ring that binds iron Alpha-helices and Beta-sheets are primary stabilized by which of the following interactions? ---------CORRECT ANSWER-----------------Hydrogen bonding 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? ---------CORRECT ANSWER----------------- 2 , bisphosphoglycerate (BPG) Which of the following best describes an enzyme inhibitor that increases the Km but does not change the Vmax? ---------CORRECT 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 likely impact to the rate of reaction? ---------CORRECT ANSWER------- ----------The rate of reaction is likely to decrease as the pH is out of optimal range
Dinitrophenol is an uncoupler of the electron transport chain. The addition of dinitrophenol will have which of the following effects? ---------CORRECT ANSWER-- ---------------Increase oxygen consumption Which of the following describes a correct and complete electron transfer pathway necessary for oxidative phosphorylation? ---------CORRECT ANSWER------- ----------NADH - > Complex I - > CoQ - > complex III - > cyt c - > complex IV Which of the following components of the electron transport chain is not bound to the mitochondrial membrane? ---------CORRECT ANSWER-----------------CoQ
