Biochemistry Questions and Answers PDF

BIOCHEMISTRY QUESTIONS ANSWER & EXPLANATIONS 1) An uncoupler is a molecule that disrupts oxidative phosphorylation, which among the following is an example of physiological uncoupler ? 1. 2,4-Dinitrophenol 2. Dinitrocresol 3. Aspirin 4. Unconjugated bilirubin Explanation: Unconjugated bilirubi...

BIOCHEMISTRY QUESTIONS ANSWER & EXPLANATIONS 1) An uncoupler is a molecule that disrupts oxidative phosphorylation, which among the following is an example of physiological uncoupler ? 1. 2,4-Dinitrophenol 2. Dinitrocresol 3. Aspirin 4. Unconjugated bilirubin Explanation: Unconjugated bilirubin Uncouplers inhibit oxidative phosphorylation. They are hydrophobic molecules with a dissociable protein. They uncouple the ETC form oxidative phosphorylationPhysiological uncouplers act only at high doses. Physiological Uncouplers  Thyroid hormones.  Long chain fatty acids.  Unconjugated Bilirubin. These act as Uncouplers only at high concentration 2) A patient presents with fatigue, tiredness and dizziness, on examination hepatosplenomegaly is noted. On doing further investigations a diagnosis of hemolytic anemia is made. Which of the following if deficient can lead to this? 1. Glucose-6-phosphate dehydrogenase 2. Glucose- 3- phosphate dehydrogenase 3. Branched chain alpha keto acid decarboxylase 4. None of the above Explanation: Glucose-6-phosphate dehydrogenase 3) A disorder that is mild and it probably remains undiagnosed in many people, characterized by the presence of fructose in the urine after ingesting fructose. Which of the following enzymes is deficient in this condition? 1. Aldolase A 2. Aldolase B 3. Fructokinase 4. Glucokinase Explanation: FructokinaseDeficiencies in the enzymes of fructose and galactose metabolism lead to essential fructosuria and galactosemias.Lack of hepatic fructokinase causes essential fructosuria, and absence of hepatic aldolase B, which cleaves fructose 1-phosphate, leads to hereditary fructose intolerance. 4) Identify among the following a glycogen storage disorder that is asap with exercise induced myoglobinuria? 1. McArdle"s disease 2. Pompe"s disease 3. Von gierke disease 4. Anderson disease Explanation: McArdle"s diseaseGlycogen storage diseases are a group of inherited disorders characterized by deficient mobilization of glycogen or deposition of abnormal forms of glycogen, leading to muscular weakness or even death.Approximately 50% patients withGSD type V, report burgundy colored urine after exercise, which is a consequence of exercise-induced myoglobinuria secondary to rhabdomyolysis. 5) Insulin is considered to be the main anabolic hormone of the body, insulin is vital for the entry of glucose in which of the following tissues mentioned below? 1. Most neurons in cerebral cortex 2. Renal tubular cells 3. Skeletal muscles 4. Mucosa of small intestine Explanation: Skeletal musclesInsulin increases the number and activity of GLUT 4 receptors. Thereby facilitating the entry of glucose in tissues having GLUT4 receptors.Tissues with abundant GLUT4 receptor are: Skeletal muscles, Heart and Adipose tissueThus among the given choices, skeletal muscle is the one which is required for the entry of glucose. 6) Which of the following substrate shuttles contributes in the transport of extramitochondrial (cytoplasm) to mitochondria? 1. Glycerophosphate shuttle 2. Malate shuttle 3. Phosphoenol pyruvate 4. Oxaloacetate Explanation: Malate shuttleThere are certain shuttle systems that operate for transport of reducing equivalents from cytosol. into mitochondria.These shuttle systems operate because mitochondrial membrane is impermeable to cytosolic NADH produced during glycolysis. In order to gain entry of NADH into mitochondrial electron transport chain, these shuttle systems are helpful. 7) Nitric oxide is an essential molecule required for vasodilation, to relax blood vessels allowing them to expand, nitric oxide is synthesized from? 1. L- arginine 2. L- citrulline 3. Lysine 4. Tryptophan Explanation: L- arginineNitric oxide, known as the endothelium-derived relaxing factor, is biosynthesized endogenously from L-arginine, oxygen and NADPH by various nitric oxide synthase (NOS) enzymes. Reduction of inorganic nitrate may also serve to make nitric oxide.The endothelium of blood vessels uses nitric oxide to signal the surrounding smooth muscle to relax, thus resulting in vasodilation and increasing blood flow. 8) Creatinine is formed from which of the following amino acids ? 1. Aspartate, glycine, leucine 2. Alanine ,glutamate ,methionine 3. Aspartate ,lysine , glutamate 4. Arginine ,glycine, methionine Explanation: Creatinine is formed in muscle from creatine phosphate by irreversible, nonenzymatic dehydration and loss of phosphate. Glycine, arginine and methionine all participate in creatine biosynthesis. Synthesis of creatine is completed by methylationof guanidinoacetate by S- adenosyl methionine. 9) Site of gluconeogenesis is? 1. Muscle 2. Liver 3. Heart 4. Intestine Explanation: Gluconeogenesis is the synthesis of glucose from non-carbohydrate compounds. It takes place in liver and kidney. The liver accounts for 90% of gluconeogenesis in the body and the remaining 10% occurs in kidney and other tissues of the body. It takes place in both cytoplasm and mitochondria of liver. 10) Match the following: Select the correct answer from the given below code: 1. 1-A, 2-B, 3-C, 4-D 2. 1-A, 2-C, 3-B, 4-D 3. 1-D, 2-C, 3-B, 4-A 4. 1-D, 2-C, 3-A, 4-B Explanation: Minor Pathway for Glucose Oxidation: Hexose Monophosphate Pathway (HMP). Major Pathway for Glucose Oxidation: Glycolysis, also known as the Embden-Meyerhof-Parnas (EMP) pathway. Pathway Active During Fasting/Starvation: Gluconeogenesis, which generates glucose from non-carbohydrate sources. Amphibolic Pathway (Both Catabolic and Anabolic): Tricarboxylic Acid (TCA) Cycle, integral to both breaking down and synthesizing molecules. Pathway Occurring in Both Aerobic and Anaerobic Conditions: Glycolysis/EMP pathway, which can function with or without oxygen. In aerobic conditions, the pyruvate produced by glycolysis can enter the mitochondria and be used in the TCA cycle and oxidative phosphorylation for further energy production. In contrast, under anaerobic conditions, such as in muscle cells during intense exercise where oxygen supply is limited, the pyruvate is typically converted into lactate. 11) In order to keep ion gradients across their membrane, red blood cells need ATP in the absence of which they will enlarge and burst causing hemolytic anemia. The main process by which RBCs generate their energy is: 1. Substrate-level phosphorylation 2. TCA cycle 3. Oxidative phosphorylation 4. Electron transfer to oxygen Explanation: Red blood cells do not contain mitochondria and can only generate energy via anaerobic glycolysis with the production of lactate and production of ATP by substrate-level phosphorylation. 12) A variety of dietary plans and exercise regimen are recommended and used by dietitians and trainers for weight management. One of them among is Atkins diet which is a: 1. Low-calorie diet 2. Low carbohydrate die 3. Low-fat diet 4. Low calorie, low carbohydrate diet Explanation: Atkin"s diet is a weight-loss diet that is low in calorie and also low in carbohydrates. It was originally promoted by the physician Dr. Robert C. Atkins.For weight reduction, the amount of carbohydrates taken in the diet should be less as carbohydrate gets converted to fats in the body, which is called endogenous fat and it gets transported in the form of VLDL 13) Mitochondria are involved in all of the following EXCEPT: 1. ATP production 2. Apoptosis 3. Tricarboxylic acid cycle 4. Cholesterol synthesis Explanation: The primary functions of mitochondria include: ATP Production: Mitochondria are known as the powerhouse of the cell, mainly because they produce ATP through oxidative phosphorylation. Apoptosis: Mitochondria play a critical role in apoptosis or programmed cell death by releasing factors that trigger this process. Tricarboxylic Acid Cycle: Also known as the Krebs cycle or citric acid cycle, it takes place in the matrix of mitochondria and is a vital part of cellular respiration. However, Cholesterol Synthesis primarily occurs in the cytoplasm and endoplasmic reticulum of cells, not in mitochondria. 14) Glucuronic acid and lduronic acid are oxidation products of glucose and idose sugar and are structural components of glycosaminoglycans (GAGs). They are which of the following kind of isomers? 1. Anomers 2. Enantiomers 3. Functional isomers 4. Epimers Explanation: Epimers: Stereoisomers differing at only one chiral carbon. Example: Glucuronic acid and Iduronic acid (C-5 epimers). Key glucose epimers: Mannose (C-2), Allose (C-3), Galactose (C-4), Idose (C-5). Anomerism: Isomerism in cyclic sugars due to different orientations of H and OH groups around the anomeric carbon. Examples: α-glucose (OH down) and β-glucose (OH up). Enantiomerism (D-L Isomerism): Mirror image isomerism, differing at the second-to-last carbon. Humans primarily use D- sugars and L-amino acids. Functional Isomerism: Isomerism due to different functional groups, like aldose (glucose) and ketose (fructose). Ketoses have one fewer asymmetric carbon than their aldose counterparts. 15) A patient of 24-year of age presents symptoms of polyuria, polydipsia, and polyphagia. The urine sample of the patient was tested with Benedict's test. Brick red precipitate developed in the urine sample. The principle of the test involves a reaction: 1. Oxidation of Cu+ ions 2. Reduction of Cu++ ions 3. Reduction of sugars in urine 4. Bothaand Explanation: The reducing sugars like glucose in urine catalyzes the reduction of cupric ions in Benedict's solution into cuprous ions to form red-colored.The reducing sugars are oxidized in the reaction. Benedict's test can also be used to check for the presence of glucose in a urine Since this test detects any aldehydes and a- hydroxy ketones and glucose is an aldose whose open-chain forms an aldehyde group, the test yields a positive result when glucose is present in the analyte. 16) A 54-year-old woman who was bed bound in a nursing home began to develop swelling in her left leg. She was diagnosed with a Venous Doppler ultrasound and was found to have a deep vein thrombosis. She should be treated with which chemical to prevent the clot from enlarging? 1. Heparin Sulfate 2. Clopidogrel 3. Heparin 4. Aspirin Explanation: Heparin is an anticoagulant that helps to prevent existing clots from growing larger and new clots from forming, making it the standard treatment for DVT. Heparan sulfate is a naturally occurring glycosaminoglycan but not used as a medication for DVT. Clopidogrel: Primarily an antiplatelet agent, more commonly used for arterial clots rather than venous thrombosis like DVT. Aspirin: An antiplatelet drug, not typically used as the primary treatment for DVT. 17) Which enzyme is the rate-limiting step in the beta-oxidation of fatty acids? 1. Acyl CoA dehydrogenase 2. Thiokinase 3. Thiolase 4. Carnitine palmitoyl transferase-1 Explanation: Carnitine palmitoyl transferase-1 (CPT-1): The rate-limiting enzyme in beta-oxidation of fatty acids. Transfers acyl group from CoA to carnitine, forming acylcarnitine. Enables acyl group to enter mitochondria from cytoplasm. Regulation of CPT-I: Inhibited by Malonyl CoA. Fed State (High insulin: glucagon ratio): Malonyl CoA is produced, inhibiting beta-oxidation. Fasting State (Low insulin: glucagon ratio): Less Malonyl CoA, allowing beta-oxidation 18) A male infant who is failing to thrive showed hepatomegaly and splenomegaly, among other findings on examination. Dermatan sulfate and heparan sulfate were also present in urine. The patient is suspected to have Hurler syndrome. The enzyme you would select to be assayed to support your diagnosis is: 1. 13-Glucuronidase 2. Neuraminidase 3. 13-Galactosidase 4. α -L-lduronidase Explanation: α-L-Iduronidase Hurler syndrome, also known as Mucopolysaccharidosis type I (MPS I), is caused by a deficiency in the enzyme α-L- Iduronidase. This enzyme"s deficiency leads to the accumulation of glycosaminoglycans like dermatan sulfate and heparan sulfate in the body, contributing to the symptoms observed. 19) GLUTs and SGLTs are two types of sugar transporter present in the intestine and kidneys. Which of the following transporters is defective in renal glycosuria? 1. GLUT-1 2. GLUT-2 3. SGLT-1 4. SGLT-2 Explanation: In this disease, blood glucose is normal, but still Glucose appears in the urine.It is due to a defect/mutation in SGLT- 2, which is major glucose transporter (90% glucose reabsorption) present in kidneys for the reabsorption and transport of Glucose (see fig below). SGLT-1 is major transporter in the intestine for the absorption of glucose and galactose and is also responsible for 10% glucose reabsorption in the kidneys.So, the mutation in SGLT-1 leads to glucose-galactose malabsorption 20) Which enzyme is activated by a decrease in the insulin:glucagon ratio? 1. Hexokinase 2. Glucose 6-phosphatase 3. Phosphofructokinase 4. Glucokinase Explanation: Decrease in Insulin:Glucagon Ratio: Typically occurs in a fasting state. Metabolic Changes: Activation of gluconeogenesis and inhibition of glycolysis. Relevant Enzyme:Glucose 6-phosphatase is activated in this scenario. Role of Glucose 6-Phosphatase: A gluconeogenesis enzyme, contrasts with glycolysis enzymes that are inhibited during fasting. Other Enzymes: Glucokinase, Hexokinase, and Phosphofructokinase are irreversible enzymes of glycolysis and are inhibited in fasting conditions. 21) ATP acts as a sensor of the energy status of the cells and acts by binding as an allosteric regulator to the regulatory enzymes. ATP is an allosteric regulator of which of the following enzyme? 1. Hexokinase and PFK 1 2. PFK 1 and PFK 2 3. PFK 1 and Pyruvate kinase 4. Glyceraldehyde 3 phosphate dehydrogenase and PFK 1 Explanation: PFK 1 (Phosphofructokinase-1): This is the Rate limiting enzyme of glycolysis with ATP as its substrate. It is inhibited by high levels of ATP, indicating a sufficient energy supply and reducing the need for further glycolysis. Pyruvate kinase: It is the last enzyme of glycolysis. Also regulated by ATP, with high levels of ATP signaling sufficient energy, thus inhibiting this enzyme. Based on this, the enzymes regulated by ATP as an allosteric regulator are: PFK 1 and Pyruvate kinase Fructose 2,6-bisphosphate and Fructose 1,6- bisphosphate are allosteric activators of PFK-1 and Pyruvate kinase respectively. 22) In the absence or shortage of oxygen certain cells or tissue resort to anaerobic glycolysis. The end product of anaerobic glycolysis are: 1. 2ATP+2NAD 2. 2ATP 3. 2ATP + 2 NADH 4. 4 ATP+ 2 FADH2 Explanation: Anaerobic Glycolysis ETC is not working hence NADH cannot enter ETC to form ATP. NADH is used to regenerate NAD by LDH Lactate is a dead end as it cannot be further metabolized under anaerobic conditions. So, 2 Lactate and 2 NAD are end products of anaerobic glycolysis.Net gain of ATP:4 ATP produced (substrate level phosphorylation)- 2 ATP used (one by Hexokinase, other used by PFK-1) = 2 ATP (net gain).Here, they are asking about the end-product, and at the end of anaerobic glycolysis, 2 ATP and 2 NAD are obtained.So, when asked about end-product then you have to mark 2ATP + 2NAD. 23) Person of age 23 years was employed on the horticulture farm where he performed pesticide spray on the plants. Accidentally, he inhaled pesticide spray and was taken to the hospital with restlessness, seizure, vomiting, and abdominal cramps. The label of pesticide shows that it has a high content of arsenic. Select the reaction which is affected by arsenic in this patient? 1. G-3-P to 1,3 BPG 2. 3-PG to 2-PG 3. 2-PG to PEP 4. Pyruvate to Iactate Explanation: Arsenate poisoning Arsenate inhibits the Glyceraldehyde-3-P dehydrogenase as a result, instead of G-3-P to 1,3 BPG, 1-arseno-3-PG will be formed.But glycolysis continues even in the presence of arsenite but with no net ATP production. 2-PG to PEP is catalyzed by enolase which is inhibited by fluorocitrate 2-PG to PEP conversion will be normal in this patient Pyruvate to lactate is catalyzed by LDH which is inhibited by oxamate 24) Reduced coenzymes NADH and FADH2 are formed in reactions catalyzed by dehydrogenases in the oxidative metabolism of carbohydrates. Which of the following is the FAD-linked dehydrogenase of the TCA cycle? 1. lsocitrate dehydrogenase 2. Malate dehydrogenase 3. Succinate dehydrogenase 4. Glyceraldehyde 3-P dehydrogenase Explanation: Succinate dehydrogenase is the only FAD-linked dehydrogenase in the TCA cycle.The reaction catalyzed by this enzyme is as: 25) The TCA cycle is a common link between various metabolic pathways and plays a vital role in cell metabolism. The unavailability of which of the following will most adversely affect the TCA cycle: 1. Acetyl CoA 2. Oxaloacetate 3. Insulin 4. Glucagon Explanation: The most critical components for the TCA cycle"s functioning are Acetyl CoA and Oxaloacetate. Without either, the cycle cannot proceed. Between the two, Oxaloacetate"s unavailability would be more critical as it would halt the cycle entirely, preventing the combination with Acetyl CoA to form citrate and continue the cycle. Acetyl CoA: Essential for the entry into the TCA cycle. It combines with oxaloacetate to form citrate, starting the cycle. Oxaloacetate: Also crucial as it not only combines with Acetyl CoA to initiate the cycle but also gets regenerated at the end of the cycle for continued functioning. Insulin and Glucagon: These hormones regulate glucose metabolism but do not directly participate in the TCA cycle. 26) ETC complexes are formed of protein, enzymes, and a number of metal ions as well as vitamin-derived cofactors. Which of the following vitamin is a component of ETC? 1. Vitamin B12 2. Riboflavin 3. Cobalamine 4. Thiamine Explanation: Riboflavin Riboflavin, or Vitamin B2, is a component of the ETC as it is a precursor for the formation of flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). Both FMN and FAD are essential cofactors in the ETC, particularly in Complexes I and II. 27) What step of the mitochondrial respiratory chain is affected by Rotenone during ATP synthesis? 1. Complex I to Co-enzyme Q 2. Coenzyme Q to Complex Ill 3. Complex II to Coenzyme Q 4. Cytochrome C to Complex IV Explanation: Complex I to Coenzyme Q Rotenone"s Mechanism of Action: Acts as an inhibitor in the Electron Transport Chain (ETC). Specifically targets and blocks Complex I. Effect on ETC: Prevents electron transfer from Complex I to Coenzyme Q (ubiquinone). This inhibition disrupts the proton gradient formation needed for ATP synthesis. Implications: Inhibiting Complex I leads to a reduction in ATP production, affecting cellular energy metabolism. 28) Arrange the following 4 enzymes of gluconeogenesis in sequence: A. Pyruvate carboxylase B. Glucose-6-phosphatase C. Phosphoenol pyruvate carboxykinase D. Fructose 1,6 Bisphosphatase Select the correct answer from given below code 1. D→C→A→B 2. A→C→D→B 3. B→A→D→C 4. C→D→B→A Explanation: To arrange the gluconeogenesis enzymes in the correct sequence: Pyruvate Carboxylase (A): Converts pyruvate into oxaloacetate. Phosphoenolpyruvate Carboxykinase (C): Converts oxaloacetate to phosphoenolpyruvate. Fructose-1,6-Bisphosphatase (D): Converts fructose-1,6-bisphosphate to fructose-6-phosphate. Glucose-6-Phosphatase (B): Converts glucose-6-phosphate into glucose. Therefore, the correct sequence is: A→C→D→B 29) Glycogen phosphorylase catalyzes the phosphorolysis of glycogen, producing glucose-1-phosphate. Which of the following vitamin acts as a cofactor for this enzyme: 1. Thiamine pyrophosphate 2. Riboflavin 3. Pyridoxal phosphate 4. Methylcobalamin Explanation: Glycogen Phosphorylase is the rate-limiting enzyme of glycogenolysis and uses PLP (the active form of vitamin B6) as its coenzyme.Pyridoxal phosphate is also a cofactor for transamination and decarboxylation 30) A young person of age 23 years presented intense muscle ache, cramps, and fatigue after a session of strenuous physical exercise. The person complained of passing blood in the urine. The patient was diagnosed with Mc Ardle"s disease. He was advised mild aerobic exercise like walking and cycling. Select the cause of Mc Ardle"s disease. 1. Deficiency of Fructokinase 2. Deficiency of Glucose 6-Phosphatase 3. Deficiency of Glucose 6-Phosphate Dehydrogenase 4. Deficiency of Glycogen Phosphorylase Explanation: Deficiency of Glycogen Phosphorylase McArdle's Disease: A glycogen storage disease affecting muscle metabolism. Key Symptom: Muscle cramps and fatigue triggered by exercise. Biochemical Cause: Deficiency of Glycogen Phosphorylase in muscle tissue. Function of Glycogen Phosphorylase: Breaks down glycogen into glucose-1-phosphate, providing energy during muscle activity. Impact of Deficiency: Impairs glycogen breakdown, leading to energy shortage in muscles during exercise, causing cramps and fatigue. Blood in Urine: Due to muscle breakdown (rhabdomyolysis) and release of myoglobin. Deficiency of Fructokinase: Leads to Essential Fructosuria, a benign condition characterized by the presence of fructose in the urine Deficiency of Glucose 6-Phosphatase:Causes Von Gierke"s Disease (Glycogen Storage Disease Type I), leading to symptoms like hypoglycemia, lactic acidosis, and growth retardation. Deficiency of Glucose 6-Phosphate Dehydrogenase (G6PD): Results in G6PD Deficiency, which can lead to hemolytic anemia, particularly after eating certain foods or taking certain medications. 31) In the 1920s, Otto Warburg observed that cancerous cells consume a lot of glucose and produce a lot of lactate even in the presence of sufficient oxygen. This effect observed in cancerous cells is also referred to as: 1. Aerobic glycolysis 2. Anaerobic glycolysis 3. Inhibition of glycolysis by oxygen 4. Inhibition of oxygen uptake by glycolysis Explanation: Aerobic glycolysis In cancer cells, pyruvate is converted to lactate even in the presence of 02. This is known as the Warburg effect or aerobic glycolysis. Lactic acid makes the local environment acidic helping in metastasis.Energy derived from the conversion of pyruvate to lactate is just 2 ATPs, so, cancer cells take up a large amount of glucose compared to normal cells. This leads to glucose wastage by cells and weight loss (cachexia). 32) Snowflake cataract is produced because of: 1. Aldose reductase 2. Galactose reductase 3. Fructose dehydrogenase 4. Alcohol dehydrogenase Explanation: Aldose reductase This enzyme is involved in the polyol pathway, where it catalyzes the reduction of glucose to sorbitol. In individuals with diabetes, high glucose levels lead to increased activity of aldose reductase in the lenses of the eyes, resulting in an accumulation of sorbitol. This accumulation can cause osmotic stress, leading to changes in the lens fibers and the development of the characteristic "snowflake" cataracts. 33) Biological dehydrogenation reactions are enzymecatalyzed oxidation-reduction reactions where one molecule loses hydrogen or electrons and other molecule accept it. Most of the time the cofactor of the enzyme plays a role as an electron acceptor or donor.Which vitamin as a coenzyme is required for glucose 6 phosphate dehydrogenase? 1. Riboflavin 2. Thiamine 3. Niacin 4. Biotin Explanation: Niacin Niacin is a pyridine derivative. Coenzyme forms: NADP+, NAD+. These coenzyme forms are involved in a variety of oxidation-reduction reactions as a part of oxidoreductases enzymes e.g. (see table below) 34) An infant of age 8 months was taken to the clinic of a pediatrician. The infant was restless and crying. Vomitus was noted on the clothes of the infant. Parents gave a history of periodic abdominal pain, vomiting, and diarrhea that started after the weaning of the infant with fruit juices and corn syrup past month. Upon physical examination, hepatomegaly was evident. Laboratory investigation revealed the presence of reducing sugar upon analysis by the Seliwanoff reagent. Select the deficient enzyme in the body of the infant under the above-mentioned clinical manifestations? 1. Fructokinase deficiency 2. Aldolase B deficiency 3. Galactokinase deficiency 4. Glucose 6-phosphatase deficiency Explanation: Aldolase B Deficiency: Results in the failure to split fructose-1-phosphate into dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3- phosphate. Causes accumulation of fructose-1-phosphate in tissues. Leads to irreversible liver damage (hepatomegaly). This condition is known as Hereditary Fructose Intolerance. Seliwanoff Test: Detects ketohexoses like fructose in urine, supporting the diagnosis. 35) Identify A and B enzymes in the given figure: 1. Glutathione peroxidase and Glutathione reductase 2. Glutathione oxidase and Glutathione reductase 3. Glutathione reductase and Glutathione peroxidase 4. Glutathione reductase and Glutathione oxidase Explanation: Glutathione peroxidase and Glutathione reductase In RBCs, HMP forms NADPH. It is used to reduce oxidized glutathione and, in the process, itself gets oxidized (removal of hydrogen) to NADP. The enzyme involved is glutathione reductase, which requires FAD (or Vit B2).So, the function of HMP in RBCs is to produce this reduced glutathione which is used to destroy H202. Now glutathione gets oxidized again by the reduction of H202 to harmless water. The enzyme involved is glutathione peroxidase, which is a selenoprotein (requires selenocysteine, the 21st amino acid at its active site). 36) An infant of age 4 months is breastfeeding. Suddenly, the infant developed disliking to feed, vomiting, and restlessness. The body weight of infant started to decline. The parents brought the infant to the pediatrician for consultation. Upon examination, the physician observed hepatomegaly, jaundice, and bilateral cataract. Select the deficient enzyme responsible for the clinical manifestations in the infant? 1. Deficiency of galactose-1-phosphate uridyl transferase 2. Deficiency of fructokinase 3. Deficiency of aldolase B 4. Deficiency of glucose 6-P dehydrogenase Explanation: Galactose is produced in the intestine from the degradation of milk sugar lactose by the enzyme lactase.The patient"s symptoms suggest it to be a case of classic galactosemia which is due to a deficiency of enzyme Galactose I-phosphate uridyltransferase of galactose metabolism.Excess Galput accumulation occurs in this disease in the liver causing jaundice, vomiting, hepatomegaly, and in the brain causing mental retardation. 37) Cytochrome Oxidase is an enzyme carrying out the transfer of electrons to the final electron acceptor 02 in ETC. The presence of which of the following is required for the proper working of this enzyme? 1. Cu 2. Fe 3. Mo 4. Both A&B Explanation: Cytochrome Oxidase: Final enzyme in the ETC, crucial for electron transfer to oxygen. Essential Elements: Contains copper (Cu) ions. Also includes iron (Fe) in its heme groups. Role of Cu and Fe: These metals are integral for the enzyme"s ability to facilitate the reduction of oxygen to water. Given the requirement of both copper and iron for the catalytic activity of Cytochrome Oxidase, the correct answer is: Both A & B (Cu and Fe) 38) Argininosuccinate synthetase links aspartate and citrulline via the amino group of aspartate and provides the second nitrogen of urea. The reaction requires ATP and involves the intermediate formation of citrullyl-AMP. Subsequent displacement of AMP by aspartate then forms arginosuccinate. Select the class of enzyme that the enzyme belongs? 1. Transferases 2. Ligases 3. Lyases 4. Hydrolases Explanation: Argininosuccinate synthetase (EC 6.3.4.5) belongs to ligases. Argininosuccinate synthase or synthetase is an enzyme that catalyzes the synthesis of argininosuccinate from citrulline and aspartate. Transferases are enzymes transferring a group, e.g. a methyl group or a glycosyl group, from one compound (generally regarded as a donor) to another compound (generally regarded as an acceptor). Lyases are enzymes cleaving C-C, C-O, C-N, and other bonds by elimination, leaving double bonds or rings, or conversely groups to double bonds. Hydrolases:These enzymes catalyze the hydrolytic cleavage of C-O, C-N, C-C, and some other bonds, including phosphoric anhydride bonds 39) Match the following inhibitors with the enzyme inhibited:Select the correct from given below code: 1. 1 a, 2d, 3b, 4c 2. 1 a, 2b, 3c, 4d 3. 1d, 2a, 3b, 4c 4. None of the above Explanation: Oxamate: This inhibitor is structurally similar to pyruvate and competitively inhibits lactate dehydrogenase (LDH) by binding to the LDH active site, preventing the conversion of lactate to pyruvate. Malonate: It is a competitive inhibitor of succinate dehydrogenase (Complex II) in the TCA cycle. It resembles succinate structurally and competes for the active site. Fluorocitrate: This compound is a potent inhibitor of aconitase, an enzyme in the TCA cycle that catalyzes the isomerization of citrate to isocitrate. Methotrexate: This is a chemotherapeutic agent that inhibits dihydrofolate reductase (DHFR), an enzyme involved in the synthesis of tetrahydrofolate, a carrier of carbon groups that are essential for the synthesis of purines and the amino acid methionine. 40) A PhD student is studying the differences in glucose metabolism in hepatocytes and other body tissues. She isolated the same enzyme of glucose metabolism from myocytes and hepatocytes. She ran kinetics assays on these enzymes and got the following graphs in the image provided. A is the curve obtained for liver enzyme while B is for muscle enzyme using the same set of parameters. Which of the following is the correct statement regarding the relationship between these enzymes? 1. A is the same enzyme as B but in the presence of a competitive inhibitor 2. B has a greater affinity for glucose than A 3. At maximal substrate concentrations, both enzymes display first-order kinetics 4. B has a higher Michaelis-Menten constant (Km) than A Explanation: B has a higher Michaelis-Menten constant (Km) than A This conclusion is drawn from the observation that enzyme B (muscle enzyme) requires a higher substrate concentration to reach half of its maximum velocity compared to enzyme A (liver enzyme), indicating a lower affinity for the substrate. This characteristic is reflected in a higher Km value. 41) Most proteins in the cells are under continuous turnover by a well-designed cycle of synthesis and degradation. The mechanism of degradation of defective proteins involves their covalent attachment to: 1. Pepsin 2. Laminin 3. Clathrin 4. Ubiquitin Explanation: The Ubiquitin-Proteasome Pathway (UPP) is the main & highly regulated mechanism for protein degradation. It uses ATP.Ubiquitin protein:It is present in the cytoplasm and nucleus.It is a highly conserved, small, globular, nonenzymic protein and is recycled.It is used as part of the UPP pathway to degrade damaged, short-lived or misfolded proteins. 42) 6-year-old boy experienced episodes, where he develops patches of skin rashes the go away in a week to 10 days. A pediatrician told the boy's parents to give him niacin the next time this will occur, along with ahigh-protein diet. The rash resolved in a day or two when they did this. This child has which one of the following diseases based on this information? 1. Cystinuria 2. Hartnup's disease 3. HHH syndrome 4. Alkaptonuria Explanation: Based on the case of a 6-year-old boy who develops transient skin rashes that resolve with niacin supplementation and a high-protein diet, the most likely diagnosis is: Hartnup"s disease Hartnup"s Disease: An autosomal recessive metabolic disorder. Impairs the absorption and reabsorption of nonpolar amino acids, especially tryptophan. Defective Transporter: Caused by a defect in the neutral amino acid transporter SLC6A19. Aminoaciduria: Results in the excretion of large amounts of amino acids in urine, notably tryptophan. Niacin Deficiency: Tryptophan is a precursor for niacin (Vitamin B3); its deficiency can lead to pellagra-like symptoms. Supplementation with niacin can alleviate these symptoms. Impact on Neurotransmitter Synthesis: Tryptophan is also involved in the synthesis of serotonin and melatonin. Deficiency can affect these pathways. 43) A 6-month-old infant presents with developmental delay, hypopigmentation of hair and skin, and a musty odor. The infant"s diet consists mainly of normal baby formula. Which of the following is the most likely diagnosis? 1. Alkaptonuria 2. Tyrosinemia 3. Maple Syrup Urine Disease (MSUD) 4. Phenylketonuria Explanation: The clinical presentation is suggestive of Phenylketonuria (PKU), an autosomal recessive metabolic disorder characterized by a deficiency in the enzyme phenylalanine hydroxylase. This leads to the accumulation of phenylalanine in the body, causing developmental delay and other symptoms. The musty odor is due to the presence of phenylketones, which are produced from excess phenylalanine. 44) A 9-month-old infant presents with acute diarrhea, vomiting, a "cabbage"-like smell, failure to thrive, hepatomegaly, and elevated tyrosine levels. What is the defect in amino acid metabolism causing these symptoms, based on the catabolic end products? 1. Fumarate and succinate 2. Fumarate and acetoacetate 3. Fumarate and Malate 4. Fumarate and pyruvate Explanation: Fumarate and acetoacetate Diagnosis: Likely Hereditary tyrosinemia type I (Hepatorenal tyrosinemia). Enzymatic Deficiency: Caused by a lack of fumarylacetoacetate hydrolase (fumarylacetoacetase). End Products: Normally, tyrosine is broken down into Fumarate and acetoacetate. Metabolic Pathway: Phenylalanine is first converted to tyrosine, which should further break down into these end products. Impact of Deficiency: Disruption in this pathway leads to the accumulation of tyrosine and associated symptoms. 45) The catecholamines such as Epinephrine and Norepinephrine are important bioamines and are required for the body to adapt to a great variety of acute and chronic stresses. The biosynthesis of Epinephrine from Norepinephrine requires which of the following? 1. Pyridoxal phosphate 2. Biotin 3. Cytochrome P450 4. S-adenosyl methionine Explanation: S-adenosyl methionineSAM (s-adenosyl methionine) is the methyl donor for the conversion of Norepinephrine to Epinephrine.QID: 36038 46) A 50-year-old man with refractory hypertension, sporadic panic attacks, and a recent episode of a throbbing headache accompanied by excessive perspiration is suspected to have pheochromocytoma. To confirm this diagnosis, which urine test should be conducted? 1. VMA 2. Catecholamine 3. 5-HIAA 4. Serotonin Explanation: Pheochromocytoma Characteristics: Tumor of the adrenal gland. Secretes high levels of epinephrine and norepinephrine. Diagnostic Test: Measuring VMA (Vanillylmandelic Acid), a catabolic product of catecholamines, in a 24-hour urine sample. Clinical Features: Classic symptoms include palpitations, headaches, and sweating. Requires long-term follow-up due to recurrence risk. Catecholamine: Direct measurement of catecholamines is also indicative but less specific than VMA. 5-HIAA (5-Hydroxyindoleacetic Acid): A metabolite of serotonin, used to diagnose carcinoid syndrome, not pheochromocytoma. Serotonin: Involved in mood regulation and gastrointestinal function. 47) Which is not a biological derivative of tyrosine? 1. Melanin 2. Melatonin 3. Epinephrine 4. Dopamine Explanation: Melatonin is formed from tryptophan, not from tyrosine Phenylalanine is converted to tyrosine by the enzyme Phenylalanine Hydroxylase. The. tyrosine is non-essential as it can be synthesized inthe body from phenylalanine.Other uses of tryptophan are- Synthesis of vitamin B3 and serotonin 48) Albinism is a hereditary disorder. In humans, it is manifested as partial or complete loss of melanin pigment in the skin, eyes, and hair. Albinism is a recessive autosomal trait. It is mainly two types: ocular and Oculocutaneous. The absence of melanin in the skin renders it susceptible to sunburn and skin cancer conditions. Select the incorrect statements about Albinism? 1. Deficiency of tyrosinase enzyme that causes melanin deficiency in the skin 2. Deficiency of tryptophan in the body resulting in melanin deficiency in the skin 3. Hypopigmentation of the ocular fundus and red or grey pigmentation in the iris. There is nystagmus, photophobia, and reduced visual acuity 4. Hypopigmentation in skin. Hypersensitivity to UV rays. High predisposition to naevi and melanomas. white Explanation: Deficiency of tryptophan in the body resulting in melanin deficiency in the skin This statement is incorrect because albinism is not caused by a deficiency of tryptophan. Rather, it is typically caused by a deficiency of the enzyme tyrosinase or a disruption in one of the several other enzymes involved in the synthesis of melanin from tyrosine. Tryptophan is not directly involved in melanin production; it is a precursor for the synthesis of serotonin and niacin, not melanin. 49) A 6-year-old girl was taken to a pediatrician for a routine checkup. On long standing the change in the color of her urine is given below. This inborn error in the metabolism is due to a deficiency of which of the following? 1. Tyrosine Hydroxylase 2. Phenylalanine hydroxylase 3. Homogentisate oxidase 4. Xanthine oxidase Explanation: Homogentisate oxidase The diagnosis of this disorder is Alkaptonuria. Alkaptonuria:Defect in the catabolism of Tyrosine and Phenylalanine.Enzyme deficient is Homogentisate Dioxygenase (new name) or Homogentisate oxidase (old name)Urine turns black on exposure to air due to oxidation of homogentisic acid. Homogentisic acid is an intermediate in the catabolism of Tyrosine. 50) A 32-year-old man was admitted to the ER with a large amount of blood and protein in his urine. He also has misshaped lenses (anterior lenticonus) and sensorineural hearing loss in his teenage years. The physician suspected it to be a case of Alport syndrome and ordered a genetic test. The tests would most likely show a defect in which of the proteins? 1. a1-Antitrypsin 2. Collagen 3. Fibrillin 4. 13-Myosin heavy chain Explanation: In Alport syndrome, there is a defect in type IV collagen that changes the composition of the basement membrane kidney glomeruli. Due to the absence of a functional basement membrane, the kidneys are unable to properly filter waste products from the blood and both proteins and blood can enter the urine. Type IV collagen is also found in the inner ear so it is important for hearing and for the eye. A mutation in α1 -antitrypsin will lead to emphysema, mutations in fibrillin lead to Marfan syndrome, and mutations in the -myosin heavy chain can lead to FHC (Familial hypertrophic cardiomyopathy) 51) Certain amino acids are not part of the primary structure of proteins but are modified after translation. Such a modified amino acid that is present abundantly in bone is which of the following? 1. Hydroxytryptophan 2. Hydroxyproline 3. Hydroxy Alanine 4. Hydroxyglycine Explanation: Hydroxyproline The most abundant protein in bones is collagen.Collagen is formed from Glycine, Proline and lysine are hydroxylated to make OH proline and OH-lysine.So the most abundant modified amino acid in bone is hydroxyproline.OH-praline cause extensive hydrogen bonding and hence collagen provide strength to the bones. 52) Acquired porphyria is due to which of the following? 1. Mercury toxicity 2. Lead poisoning 3. Copper deficiency 4. Selenium toxicity Explanation: Lead poisoning Porphyria can be either inherited or acquired. Causes of acquired porphyria:Lead poisoning, AlcoholismHepatitis C infection, Plumboporphyria. 53) Multiple sclerosis is a disease characterized by chronic inflammation. Research data indicate that susceptibility to multiple sclerosis may be inherited. This disease is characterized by a loss of which of the following lipids? 1. Phospholipids and sphingolipids 2. Sphingolipids and ceramide 3. Phospholipids and ceramide 4. Sphingolipids and gangliosides Explanation:  Nature of Multiple Sclerosis: A chronic inflammatory disease, potentially hereditary, affecting the central nervous system.  Characteristic Feature:  Loss of myelin sheath around nerve fibers. Consequently, brain white matter eventually looks like gray matter  Myelin Composition:  Primarily made of lipids, including sphingolipids and gangliosides.  Loss in MS:  The degradation of myelin results in the loss of its constituent lipids. 54) Correct match of disease and enzyme defect: 1. Krabbe's -β Galactocerebrosidase 2. Gaucher's- Ceraminidase 3. Farber's disease - Alpha galactosidase A 4. Sandhoff's -Arylsulfatase A Explanation: Krabbe"s Disease: Caused by a deficiency in β Galactocerebrosidase. Affects the metabolism of sphingolipids. Gaucher"s Disease: Result of a deficiency in Glucocerebrosidase (not Ceraminidase). Impacts fat metabolism, specifically glucocerebrosides. Farber"s Disease: Due to a deficiency in Ceramidase (not Alpha galactosidase A). Involves the metabolism of ceramide. Sandhoff"s Disease:Caused by a deficiency in β-Hexosaminidase A and B (not Arylsulfatase A) Affects GM2 ganglioside metabolism 55) In a cerebrohepatorenal syndrome, which of the following accumulates in the brain? 1. Pyruvate 2. Short-chain fatty acid 3. Very long-chain fatty acid 4. Acetyl CoA Explanation: Very long-chain fatty acid Zellweger syndrome aka Cerebro-Hepato-Renal Syndrome.Impaired neuronal migration, hypomyelination, hepatomegaly, renal cysts. Absence of Peroxisomes in almost all tissues, peroxisomes are responsible for the oxidation of very long chain fatty acids, which contain more than 22 carbon. Accumulation of polyenoic acids in the brain, with carbon> 22 Severe neurological symptoms. Most patients die within 1st year of life. 56) The two strands of DNA have to separate for the replication machinery to work on single strands of DNA. The unwinding of DNA causes the creation of supercoils which are relieved by the action of: 1. Topoisomerase 2. Gyrase 3. Helicase 4. Polymerase Explanation: During the unwinding of DNA, relief of supercoil is made possible by Topoisomerase QID: 36055 57) A 10-year-old girl is brought to the dermatologist by her parents. She has many freckles on her face, neck, arms, and hands and her parents report that she is highly sensitive to sunlight. On examination, two basal cell carcinomas are observed on her face. The process which is most likely defective in this patient is? 1. Repair of double-stranded breaks 2. Removal of mismatched bases from the 3' end of Okazaki fragments 3. Removal of pyrimidine dimers from DNA 4. Removal of uracil from DNA. Explanation:. Removal of pyrimidine dimers from DNA. Clinical Presentation: The symptoms suggest a condition related to DNA damage from UV radiation.. Pyrimidine Dimers: UV light can cause the formation of pyrimidine dimers in DNA, particularly thymine dimers.. Defective Process: The inability to efficiently repair these dimers can lead to mutations and skin cancers, including basal cell carcinoma.. Nucleotide Excision Repair (NER): This pathway, responsible for removing pyrimidine dimers, is likely impaired in this patient. 58) An insertion mutation in a gene can be detected by comparison of Polymerase Chain Reaction {PCR) amplified product from a normal and patient DNA sample using primers that flank the given gene. What is the correct sequence of steps in a PCR reaction? 1. Annealing →Denaturation → Polymerisation 2. Polymerisation → Denaturation →Annealing 3. Denaturation→ Annealing →Polymerisation 4. Denaturation→ Polymerisation →annealing Explanation: The correct sequence of steps in a Polymerase Chain Reaction (PCR) is:. Denaturation → Annealing → Polymerization Explanation of Steps:. Denaturation: The double-stranded DNA is heated to separate it into two single strands.. Annealing: The temperature is lowered to allow primers to bind (anneal) to the complementary sequences on the single- stranded DNA.. Polymerization: DNA polymerase extends the primers to form a new strand of DNA, replicating the target sequence. 59) A 20-year-old alcoholic malnourished patient presented to the hospital with respiratory distress. His pulse was 112 / minute. The patient had edema, hypertension, and systolic murmur along the left sternal edge. Bilateral crepitations were felt in the lungs. A diagnosis of congestive high-output cardiac failure was made. The physician suspected thiamine deficiency. Which of the following test will most likely support the diagnosis: 1. Erythrocyte transketolase activity 2. RBS Glutathione reductase 3. RBC thiamine levels 4. Serum thiamine level Explanation: Chronic alcoholics are at risk for thiamine deficiency, this is a case of Wet/cardiac Beri-Beri, i.e., Vitamin B1 Deficiency. Vitamin B1 is mainly involved in Oxidative Decarboxylation reactions, so in B1deficiency, highly aerobic tissues, e.g., the heart and brain, fail first.Thiamine (vitamin Bl) DeficiencyIt is assessed by Erythrocyte transketolase activity.Thiamine (Vitamin B1) is the marker for transketolase enzyme which is involved in the HMP pathway (in RBCs) 60) While studying the structure of a small gene that was recently sequenced during the Human Genome Project, an investigator notices that one strand of the DNA molecule contains 20 As, 25 Gs, 30 Cs, and 22 TS. How many of each base is found in the complete double stranded molecule? 1. A = 42, G = 55, C = 55, T = 42 2. A = 44, G = 60, C = 50, T = 40 3. A = 45, G = 45, C = 52, T = 52 4. A= 50, G = 47, C = 50, T = 47 Explanation: To determine the number of each base in a complete double-stranded DNA molecule, it"s important to remember that DNA is complementary. Chargaff's rule: This means adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C). Given that one strand has 20 As, 25 Gs, 30 Cs, and 22 Ts, we can calculate the total for each base in the double-stranded molecule:  Adenine (A): Matches with thymine (T). Since there are 20 As on one strand, there must be 20 Ts on the other strand. Thus, total As = 20 + 22 (from Ts on the original strand) = 42.  Guanine (G): Pairs with cytosine (C). There are 25 Gs on one strand, so there must be 25 Cs on the other strand. Thus, total Gs = 25 + 30 (from Cs on the original strand) = 55.  Cytosine (C): Matches with guanine (G). There are 30 Cs on one strand, so there must be 30 Gs on the other strand. Thus, total Cs = 30 + 25 (from Gs on the original strand) = 55.  Thymine (T): Pairs with adenine (A). Since there are 22 Ts on one strand, there must be 22 As on the other strand. Thus, total Ts = 22 + 20 (from As on the original strand) = 42. Therefore, the correct number of each base in the complete double-stranded molecule is: A = 42, G = 55, C = 55, T = 42