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MEDICAL BIOCHEMISTRY FINAL, UNE BIOCHEMISTRY
FINAL EXAM || 2025 - 2026 ||ACTUAL EXAM WITH
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In glycolysis, is considered the committed step in the pathway.
- ANSWER PFK- 1 Phospholipids are made up of one or more fatty acids, a core, a phosphate, and which one of the following? - ANSWER alcohol cholesterol has a unique chemical structure with four fused rings that allows it to serve what critical role in our bodies - ANSWER regulating membrane 昀 氀 uidity Pyruvate plays a central role in intermediary metabolism. Which three chemical functional groups does it contain?
- ANSWER carboxylic acid, methyl, ketone The urea cycle takes place in which subcellular location(s)?
- ANSWER cytosol, mitochondria Which pathway below requires the use of NADPH?
- ANSWER cholesterol biosynthesis Individuals with Lesch-Nyhan would be expected to build up which compound due to their enzyme de昀椀ciency?
- ANSWER uric acid The urea cycle takes place in which of the following subcellular locations? - ANSWER the cytosol and the mitochondria Which of the following enzymes is regulated by N-acetylglutamate (NAGs)? - ANSWER CPS I
Which of the following enzymes is the regulatory step in the urea cycle? - ANSWER Carbamoyl phosphate synthetase I (CPS I) A comatose infant is brought to the ER. In the course of the examination, plasma ammonia was found to be elevated 20 - fold over normal values. Urine orotic acid and uracil were both greater than normal. A defect of which of the following enzymes is the most likely diagnosis?
- ANSWER Ornithine transcarbamoylase Your patient presents with a de昀椀ciency of the enzyme that catalyzes synthesis of N- acetylglutamate (NAGs). Which of the following would be a consequence of this de昀椀ciency in the patient?
- ANSWER Increased amino acids in the blood The cellular uptake of LDL increases intracellular cholesterol levels. This has which of the following impacts on de novo cholesterol synthesis? - ANSWER Increases degradation of HMG- CoA reductase Dietary cholesterol is primarily transported in the body by which of the following lipoproteins?
- ANSWER Chylomicron A 47 - year-old male is prescribed a statin (HMG-CoA reductase inhibitor) to manage his elevated LDL cholesterol. What is the initial mechanism of action for obtaining the desired e昀昀ect in this man?
- ANSWER Decreasing hepatic cholesterol biosynthesis A de昀椀ciency in the LDL receptor will result in an initial decrease in which of the following?
- ANSWER Intracellular cholesterol A 45-year-old man has a mild heart attack and a history of vascular disease. He is placed on a Mediterranean diet and statin drug therapy. Which of the following will be the most likely result of this drug therapy? - ANSWER Low blood LDLs
- ANSWER Conversion of methyl malonyl-Co A to succinyl-CoA A 15-year-old female presents to her pediatrician with concerns over her inability to sleep, increased feelings of depression and generalized fatigue. A full laboratory work-up is ordered and based on these 昀椀ndings she is diagnosed with a melatonin de 昀椀ciency. Based on this information, metabolism of which of the following amino acids is likely impaired? - answer Tryptophan A 52-year- old male sought medical help complaining about progressive appearance of hyperchromic (hyper pigmented) papules on the edge of the second 昀椀nger of both hands. He also complained about darkening of urine. Incisional biopsy of one of the spots on his hands and urine sample tested positive for or homogentisic acid. Based on these 昀椀ndings a diagnosis of alkaptonuria is made. This diagnosis is consistent with a de昀椀ciency in which of the following enzymes? - answer Homogentisate oxidase Methotrexate is a potent anticancer agent that starves dividing cells of deoxyribonucleotides through direct inhibition of which of the following processes?
- answer Metabolism of folic acid A 47 - year-old man complains of pain in the joints of his left big toe, which are obviously swollen and tender. The pain has been chronic but became intolerable the day after Thanksgiving when he had a large meal and several glasses of red wine. Based on this information a diagnosis of gout is made. Which of the following is involved in the pathophysiology of this patient's condition? - answer Elevated uric acid Which of the following is the common intermediate for purine synthesis? - answer Inosine monophosphate In pyrimidine synthesis, carbamoyl phosphate synthetase II (CPSII) can be allosterically activated by which of the following compounds? - answer 5 - phosphoribosyl 1 - pyrophosphate (PRPP)
Which of the following enzymes is used directly in the synthesis of dTMP (thymidine)? - answer Thymidylate synthase The regulation of PRPP synthetase is critical in the production of both purines and pyrimidines. This enzyme is inhibited under which of the following conditions? - answer When both GDP and ADP are elevated A 4-year-old girl presented to the clinic with megaloblastic anemia and failure to thrive. Urinalysis showed signi昀椀cant sediment with extremely high levels of orotic acid. A de昀椀ciency in which of the following enzymes would be consistent with this presentation? - answer Orotate phosphoribosyltransferase The transamination of all amino acids requires which of the following cofactors? - answer Pyridoxal phosphate (PLP) Ubiquitination is a means of targeting a protein for which of the following cellular processes? - answer Proteasomal degradation Which of the following reactions of the urea cycle takes place in the mitochondria? - answer The synthesis of carbamoyl phosphate Several amino acids are intermediates of the urea cycle, having side ammonia groups that join with free carbon dioxide (CO2) and ammonia to produce net excretion of ammonia as urea. Which of the following amino acids has a nitrogen in its side chain and is an intermediate of the urea cycle? - answer Arginine Homocystinuria can be caused by several di昀昀erent enzyme or vitamin de昀椀ciencies. An elevation of homocysteine and a decrease in cysteine would most likely present due to which of the following de昀椀ciencies? - answer Loss of function of cystathionine-β synthase
fatty acid metabolism will be impaired? - answer Acetyl-CoA carboxylase Which of the following compounds or substrates is required for the synthesis of tyrosine? (+ indicates the compound is required; - indicates the compound is not required) - answer 4 A 2 - day-old infant test positive for hyperphenylalaninemia. This is most likely caused by a heritable defect in which of the following enzymes? - answer Phenylalanine hydroxylase You and a friend are being chased by a bear. Under these conditions levels of epinephrine are increased due to metabolism of which of the following amino acids?
- answer Tyrosine In pyrimidine synthesis, uridine triphosphate (UTP) can feedback and inhibit which of the following enzymes? - answer Carbamoyl phosphate synthase II Which of the following characteristics distinguish most RNA molecules from DNA?
- answer Uridine base on RNA, whereas a thymidine base on DNA Which of the following lipoproteins distributes dietary lipids? - answer Chylomicron The interaction fo chylomicrons with lipoprotein lipase is stimulated by which of the following App proteins? - answer ApoCII Nascent chylomicrons are synthesized in which tissue? - answer Intestine Bile salts are synthesized from cholesterol and are used for the emulsi昀椀cation of dietary lipids. What is the primary fate of bile salts during digestion? - answer They are reabsorbed in the ileum Nascent chylomicrons interact with HDL particles and obtain which fo the following Apo proteins? - answer ApoCII and ApoE
The activity of pancreatic lipase is inhibited by which of the following compounds?
- answer Bile salts Which fo the following statements regarding liid digestion and absorption is true? - answer The products of lipid digestion are resynthesizes into triacylglycerols in intestinal epithelial cells. Under fasting conditions, elevated glucagon will activate which of the following enzymes? - answer Hormone sensitive lipase VLDL particles are characterized by which of the following apoproteins? - answer ApoB An increase in insulin leads to which of the following metabolic shifts? - answer Acetyl CoA carboxylase will become dephosphorylated and active. Biotin is a cofactor required for which of the following enzymes? - answer A and B (Acetyl CoA carboxylase and Pyruvate carboxylase) The 昀椀rst step in fatty acid synthesis is the formation of from acetyl CoA and carbon dioxide. - answer Malonyl CoA Insulin increases the activity of all of the following enzymes except - answer Hormone sensitive lipase Which fo the following is the regulatory enzyme for fatty acid synthesis? - answer Acetyl CoA carboxylase Which fo the following is the regulated step of fatty acid synthesis in eukaryotes? - answer Carboxylation of acetyl CoA
Which of the following compounds is the substrate for the synthesis of cortisol? - answer Cholesterol Under cellular conditions when cholesterol is low, which of the following is a true statement regarding the sterol response element binding protein? - answer It will be associated with the sterol response element (SRE) in the DNA HDL particles are characterized by the presence of which apoprotein? - answer ApoA Which of the following is the regulatory enzyme in cholesterol synthesis? - answer HMG CoA reductase Which of the following lipoproteins is responsible for the transport of cholesterol to peripheral tissue? - answer LDL Which of the following enzymes is responsible for moving cholesterol from HDL to VLDL? - answer Cholesterol esterase transfer protein (CETP) The uptake of LDL increases the intracellular cholesterol levels. This has which of the following impacts on bile salt solubility? - answer Decrease solubility The uptake of LDL increases intracellular cholesterol levels. This has which of the following impacts on de novo cholesterol synthesis? - answer Increases degradation of HMG CoA reductase LCAT esteri昀椀es cholesterol. This process is required for which of the following processes? - answer To trap cholesterol in HDL particles The de昀椀ciency in the LDL receptor will result in which of the following? - answer A decrease in intracellular cholesterol
Which of the following terms is used to de昀椀ne macrophages that are 昀椀lled with oxLDL? - answer Foam cells Which of the following is a true statement concerning HMG CoA reductase? - answer It catalyzes the 昀椀rst committed step in cholesterol biosynthesis The regulatory enzyme of the cholesterol synthetic pathway is - answer HMG CoA reductase When an LDL particle is taken up by the cell, what impact will this have on the regulation of the de novo cholesterol synthesis? - answer SREBP:SCAP will be bound to the endoplasmic reticulum Under fasted conditions, which of the following enzymes will be phosphorylated and inactive? - answer HMG CoA reductase In the reaction catalyzed by cholesterol ester transfer protein (CETP), the VLDL particle receives which fo the following compounds from HDL particles? - answer Cholesterol-ester Statins are drugs that inhibit cholesterol synthesis by inhibition of the regulatory enzyme for this process. Which of the following enzymes is the direct target of statins? - answer HMD CoA reductase Which lipoprotein is responsible for the process of reverse cholesterol transport (the movement of cholesterol from the peripheral tissues back tot he liver)? - answer HDL Cholesterol is a substitute for all of the following compounds except - answer Guanine The skeletal muscle primarily provides substrate for gluconeogenesis through which
answer Lactate The oxidation of ethanol increases the ratio of NADH/ NAD in both the mitochondria and the cytosol. This leads to the inhibition of which of the following enzymes in the TCA cycle? - answer Isocitrate dehydrogenase Several friends went out Saturday evening to celebrate an exam. They skipped dinner and decided to head straight to the bar. The next morning one of the individuals was found laying unconscious at the bottom of the stairs. He was rushed to the emergency department and blood glucose levels of 30mg/ dL (normal range 100 - 120mg/ dL). At the time of presentation, which of the following would be consistent with this individuals signs and symptoms (when compared to a normal individual)? - answer Increase lactate levels Which of the following is the primary metabolic fate of acetate generated from ethanol metabolism? - answer It is converted to acetyl CoA by peripheral tissues Both gluconeogenesis and fatty acid beta oxidation are required for homeostasis in the fasted state. Which of the following statements is false with regards to how these pathways interact? - answer Acetyl CoA is a substrate required for gluconeogenesis Which of the following hormones initiates skeletal muscle catabolism to provide substrate for gluconeogenesis? - answer Cortisol In a fasted individual, excessive alcohol consumption will contribute to all of the following except - answer Increased chylomicron secretion Ethanol metabolism increases the ratio of NADH/NAD+. This leads to all of the following metabolic consequences except - answer Inhibition of lipolysis Which of the following is the primary factor leading to the inhibition of gluconeogenesis when excessive alcohol is consumed? - answer Increase in the ratio of NADH/NAD+
All of the following are potential substrates for gluconeogenesis except - answer Acetyl CoA The oxidation of ethanol initially takes place in the and the enzyme alcohol dehydrogenase converts ethanol to. - answer Cytosol; Acetaldehyde During fatty acid synthesis, after the initial step involving acetyl CoA, the fatty acid chain is elongated by the addition of which of the following compounds? - answer Malonyl CoA Excessive alcohol consumption can lead to the presentation of hypoglycemia. This is primarily caused by which of the following? - answer A decrease in substrates required for gluconeogenesis What is the primary fuel oxidized in the liver (to generate ATP) in the fasted state? - answer Free fatty acids The elevated levels of NADH/NAD generated by alcohol metabolism inhibit all of the following except - answer Pyruvate dehydrogenase kinase Shortly after meal high in fat you would expect an elevation of which of the follow lipoproteins in circulation? - answer Chylomicrons Under fasting conditions, acetyl CoA carboxylase will be inhibited by an increase in which of the following compounds? - answer Palmitoyl CoA Which of the following is consistent with an insulin/glucagon ratio of >1? - answer glycogen phosphorylase, dephosphorylated, inacitve Pyruvate carboxylase is allosterically by which of the following compounds? - answer Acetyl CoA
Which of the following lipoproteins is responsible for carrying cholesterol from peripheral tissues (i.e skeletal muscle) back to the liver? - answer HDL Which of the following lipoproteins is responsible for the transport of dietary triacylglycerols in the blood? - answer Chylomicrons HMG CoA reductase is highly regulated within the cell. Which of the following will reduce the activity of HMGCoA reductase? - answer Phosphorylation by a protein kinase Which of the following molecules is not synthesized using cholesterol as a substrate? - answer Insulin The processes of beta-oxidation and fatty acid synthesis are regulated in such a manner that neither process is active at the same time. Which of the following enzymes required for β oxidation is paired with the correct inhibitor? - answer Carnitine palmitoyl transferase I (CPTI); malonylCoA Elevated levels of acetyl CoA can be converted into ketone bodies and can potentially be used as fuel by all of the following tissues except - answer Liver AcetylCoA Carboxylase will be active when which of the following hormones is elevated? - answer Insulin Which of the following compounds can inhibit the actions of pancreatic lipase? - answer Bile salts Nascent chylomicrons originate from which of the following tissues? - answer Intestine Which of the following enzymes generates NADPH? - answer Malic enzyme NADPH and glyceraldehyde 3-phosphate are essential for the synthesis of fatty
acids and triacylglycerols. Which of the following pathways can supply both of these products? - answer Pentose Phosphate Pathway Fatty acid beta oxidation generates several products. Which of the following are direct products of beta oxidation?
- NADH
- FADH
- AcetylCoA
- Pyruvate
- beta-hydroxybutarate A. all of the above B. 1 through 4 only C. 2, 3, 4, and 5 D. 1 through 3 - answer 1 through 3 Which of the following best de昀椀nes the role of a micelle? - answer A micro droplet that facilitates the transport of dietary fats out of the intestine during digestion Which of the following hormones is correctly described? - answer Adiponectin: produced in adipose tissue, stimulates fatty acid oxidation Excessive alcohol consumption can cause several metabolic disturbances. Which of the following is not a direct metabolic consequence of excessive alcohol oxidation? - answer Increased protein synthesis
proceses? - answer Proteasomal degradation The reaction of ammonia with α-ketoglutarate is catalyzed by and requires as a reactant. - answer Glutamate dehydrogenase, NADH or NADPH Most enzymes involved in protein digestion require cleavage for activation. These proteins are secreted as inactive protein forms called - answer Zymogens Which of the following enzymes is regulated by N-acetyl glutamate (NAGs)? - answer CPS I Which of the following enzymes will be active in both the fed and fasted states? - answer Glutaminase Which of the following enzymes is correctly paired with its activator? - answer N- acetylglutamate synthtase; arginine In the case of a urea cycle de昀椀ciency, which of the following amino acids may become essential?
- answer Arginine The glucose alanine cycle is a method of transferring ammonia from the skeletal muscle to the liver. In this process the non-toxic carrier of ammonia is which of the following compounds? - answer Alanine Pepsinogen is activated by which of the following mechanisms or enzymes? - answer A change in pH catalyzes the activation of pepsinogen to pepsin The process of autophagy is de昀椀ned as which of the following processes? - answer Recycling of proteins under conditions of cellular need or starvation When is the process of autophage most likely occurring within the cell? - answer
When there is low energy in the cell; ratio of AMP/ATP is > The pancreatic zymogen trypsinogen is activated by which of the following enzymes or compounds? - answer Enteropeptidase Which of the following reactions takes place in the mitochondria? - answer The synthesis of carbamoyl phosphate Unlike many of the other metabolic pathways the urea cycle can be active under which of the following conditions? - answer Both the fed an the fasted state Which of the following will contribute to elevated triglycerides in individuals with type 2 diabetes? - answer Reduced activity of lipoprotein lipase Which of the following GLUT transporters facilitates glucose uptake in skeletal muscle? - answer GLUT 4 Alanine can be shuttled from the skeletal muscle to the liver where it is deaminated by which of the following enzymes? - answer Alanine aminotransferase The primary role of glutamine in the brain is to provide substrate for the synthesis of which of the following compounds? - answer Neurotransmitters In the fed state which of the following metabolic process is active? - answer Hepatic glycogen synthesis In the case of an individual in a sedentary life style eating a diet consisting of 50% carbohydrates 30% protein and 20% fat, this individual would be in nitrogen balance. - answer Neutral Alanine can be shuttled from the skeletal muscle to the liver where it is deaminated to genernate pyruvate. When glucagon is high, Pyruvate is primarily used as substrate for which of the following pathways? - answer Gluconeogenesis
