Category: Metabolism of Carbohydrates

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Starvation induced metabolic alterations

A 23 –year- old female was brought for consultation by her mother who was troubled by her daughter’s continuous fatigue, dizziness and loss of weight. The patient was 6 feet 2 inches tall and weighed 100 pounds. Further questioning revealed that the young woman had been virtually fasting for 4 months hoping to obtain a ‘skinny figure’ as a prelude to a career in modeling. Physical examination revealed dehydration and a fruity odor in her breath. Laboratory results revealed – Blood glucose 50 mg%. Which substance would most likely be detected in abnormally high concentration upon patient’s urine test? A)...

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Carbohydrates induced obesity

An 18-year-old female is diagnosed as obese. She maintains a sedentary life style and eats a high-fat, high-sugar diet. Maintenance of this diet and lifestyle has led to lipogenesis and obesity. Which of the following best explains carbohydrates induced obesity? A) Excess glycerol is obtained through glycolysis B) Fatty acids are excessively synthesized from Acetyl co A C) NADPH is excessively obtained through HMP pathway D) Triglycerides are excessively synthesized E) All of the above. The correct answer is E- All of the above. Excess carbohydrate ingestion is a major cause of obesity. Obesity is a state of excess adipose...

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Role of Thiamine in HMP pathway

Case details A 50 -year-old alcoholic male presents with pain, numbness, tingling and weakness in his feet. He is diagnosed with thiamine deficiency. Thiamine and ATP condense together to form   thiamine pyrophosphate, a cofactor important for the enzymes that catalyze oxidative decarboxylation of (α-keto acids) in the TCA cycle and also at one of the steps in pentose phosphate pathway, which out of the following enzymes requires TPP as a coenzyme ? A) Glucose-6-P dehydrogenase B) Transaldolase C) Transketolase D) 6-P-Gluconate dehydrogenase E) Gluconolactone hydrolase The correct answer is- C) – Transketolase. Two reactions are catalyzed by Transketolase in HMP...

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Implications of suppressed TCA cycle in Diabetes Mellitus

A 22- year-old diabetic comes to the Accident and Emergency department. She gives a 2-day history of vomiting and abdominal pain. She is drowsy and her breathing is deep and rapid. There is distinctive smell from her breath. She has been diagnosed with Diabetic ketoacidosis. Diabetic ketoacidosis is a complication of uncontrolled diabetes mellitus. The TCA cycle in diabetes mellitus is suppressed and the excess Acetyl co A, resulting from fatty acid oxidation is channeled towards the pathway of ketogenesis. Which of the following intermediates of TCA cycle is depleted in Type 1 Diabetes mellitus to suppress TCA cycle? A)...

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Glycerol kinase deficiency in adipose tissue

A 50-year-old, alcoholic male presents with a swollen face, distended abdomen, and an enlarged fatty liver. Fatty acids react with glycerol-3-P to form triglycerides, which accumulate to cause fatty liver. The liver has glycerol kinase, while adipose tissue lacks glycerol kinase. As a result, in adipose tissue, which of the following occurs? A) Glucose cannot be converted to DHAP (dihydroxyacetone phosphate) B) Glycerol cannot be converted to Glycerol-3-P C) DHAP cannot be converted to Glycerol-3-P D) Diacylglycerol cannot be converted to Triacylglycerol E) Triacylglycerols cannot be stored. The correct answer is- B) – Glycerol cannot be converted to Glycerol-3-P. Glycerol...

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Components of Sucrose

A 7-month-old baby girl, the second child born to unrelated parents was brought to Pediatrics outdoor department. History revealed that she did not respond well to breast-feeding and was changed entirely to a formula based on cow’s milk at 4 weeks. Between 7 and 12 weeks of age, she was admitted to the hospital twice with a history of screaming after feeding, but was discharged after observation without a specific diagnosis. Elimination of cow’s milk from her diet did not relieve her symptoms; her mother reported that the screaming bouts were worse after the child drank juice and that she...

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Lactate to glucose conversion

Lactate is oxidized to pyruvate in a reaction catalyzed by Lactate dehydrogenase. The patients with genetic deficiency of lactate dehydrogenase present with muscle cramping and myoglobinuria after intense exercise. The sources of lactate include muscle and red blood cells. Lactate is a waste product in such cells; it is transported to liver and can be converted to glucose through pathway of gluconeogenesis. The energy requirements for conversion of lactate to glucose are: A. 2 ATP B. 4 ATP C. 6 ATP D. 8 ATP E. 38 ATP. The correct answer is C- 6 ATP. Lactate produced by active skeletal muscle...

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Energy output per Acetyl co A by one round of TCA cycle

The total energy generated by one round of TCA cycle starting with 1 Acetyl co A is approximately 12 ATP. Of this total energy output, what percentage is contributed by oxidation of niacin dependent coenzymes in the electron transport chain? A. 38% B. 42% C. 86% D.75 % E. 100% The correct answer is D- 75%. The citric acid cycle (Krebs cycle, tricarboxylic acid cycle) includes a series of oxidation-reduction reactions in mitochondria that result in the oxidation of an acetyl group to two molecules of carbon dioxide and reduce the coenzymes that are reoxidized through the electron transport chain,...

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Glucose transporter-1(GLUT-1)

Glucose travels across the cell membrane on a transport protein. Hereditary deficiency of GLUT-1, insulin -independent transporter, results in decreased glucose transport. Patients manifest with intractable seizures in infancy and a developmental delay. GLUT-1 transporter is expressed in which of the following cell types? A. Liver, kidney and pancreatic β cells B. Brain (neurons) C. Adipose tissue, skeletal muscle and cardiac muscle D. Erythrocytes, Blood -brain barrier, blood-retinal barrier E. Intestinal epithelium, Spermatozoa. The correct answer is- D, Erythrocytes, Blood -brain barrier, blood-retinal barrier. Basic concept Glucose transport across the cell membrane is a facilitated transport, a carrier mediated transport....

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Question of the day-Enzyme catalyzing Carbon-Carbon bond cleavage in Glycolysis

Which of the following enzymes cleaves a carbon-carbon bond in glycolysis? A. Phospho triose isomerase B. Aldolase C. Phospho glycerate kinase D. Enolase E. Pyruvate Kinase The correct answer is B- Aldolase. The Aldolase cleaves fructose-1,6-bisphosphate (the product of 2nd glycolytic reaction catalyzed by Phospho fructo kinase -1) between the C-3 and C-4 carbons to yield two triose phosphates. The products are dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate (figure). Figure- Reactions of glycolysis. Phospho triose isomerase Of the two products of the Aldolase reaction, only glyceraldehyde-3-phosphate goes directly into the second phase of glycolysis. The other triose phosphate, dihydroxyacetone phosphate, must be...

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Case study- Glycogen storage disease

Case details A female infant appeared normal at birth but developed signs of liver disease and muscular weakness at 3 months. She had periods of hypoglycemia, particularly on awakening. Examination revealed an enlarged liver. Laboratory analyses following fasting revealed ketoacidosis, blood pH 7.25, and elevations in both alanine transaminase (ALT) and aspartate transaminase (AST). Administration of glucagon following a carbohydrate meal elicited a normal rise in blood glucose, but glucose levels did not rise when glucagon was administered following an overnight fast. Liver biopsy revealed an increase in the glycogen content (6 percent of wet weight). In which of the...

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Low body fat mass and hormone levels ?

An 11-year-old girl is presented at the clinic with reports of frequent fainting and lethargy. The girl is 5 ft tall and weighs 80 lb. Skin fold tests show an abnormally low percentage of body fat mass. Which of the following hormones is likely to be severely diminished in this patient? A. Cortisol B. Epinephrine C. Glucagon D. Insulin E. Thyroid Answer- The correct answer is D. The patient has low body weight and fat mass and there are frequent fainting attacks. Apparently her condition is consistent with a low energy state that might be due to poor diet or...

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Galactosemia and impaired interconversions ?

A newborn infant presents with poor feeding, vomiting, jaundice and an enlarged liver. The urine test is positive for a reducing substance. Which of the following conversions is most likely to be normal? A. Glucose to Galactose B. Activated galactose to activated Glucose C. Lactose to galactose D. Excretion of galactose by kidney E. Excretion of glucose by kidney Answer- The correct answer is- B- Conversion of activated galactose to activate glucose. As evident from the clinical features, the child is suffering from Galactosemia. Galactosemia is associated with the following 3 enzyme deficiencies; 1) Classical galactosemia is a major symptom...

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Question of the day- Energy required for conversion of glycerol to glucose?

A 45-year-old obese male presents for a routine examination. He has a sedentary life style and eats a high-fat diet. His triglyceride level is abnormally elevated. When glycerol derived from adipose triglycerides is converted to glucose, how many moles of high- energy phosphates are required? A. 1 B. 2 C. 3 D. 4 E. 6 Answer- The correct answer is B- 2 ATP. Glycerol is phosphorylated at the expense of ATP to form Glycerol-3-P; the reaction is catalyzed by glycerol Kinase. Glycerol-3-P enters the main pathway of Gluconeogenesis at the level of Dihydroxy acetone-P (Figure-1). Since glycerol is a three...

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Source of glycerol-3-P in adipose tissue?

Glycerol produced from hydrolysis of triglycerides in adipose tissue is a waste product, since it has to be in glycerol-3-P form and the enzyme for phosphorylation, glycerol kinase is absent in the adipose tissue. Glycerol -3-P can still be produced in the adipose tissue through interconversion of one of the glycolytic intermediates. Which of the following glycolytic intermediates can be used for the synthesis of glycerol-3-P? A. Phosphoenol pyruvate B. 1, 3 Bisphosphoglycerate C. Dihydroxyacetone phosphate D. Fructose 1, 6 bisphosphate E. 2-Phosphoglycerate The correct answer is C- Dihydroxy acetone phosphate. In adipose tissue glycerol-3-p is obtained through glycolysis from...

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Prolonged fasting and gluconeogenesis…

A 14-year-old high school girl who is extremely conscious about her appearance has gone a full day fasting to fit in to a dress she intentionally brought a size smaller than her actual size for a dance party. Which of the following organs/tissues contribute to the glucose that is being synthesized through gluconeogenesis during periods of prolonged fasting? A. Spleen B. Red blood cells C. Skeletal muscle D. Liver E. Brain D-Liver is the correct answer. Gluconeogenesis is the process of converting noncarbohydrate precursors to glucose or glycogen. The major substrates are the glucogenic amino acids, lactate, glycerol, and propionate....

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Case study- Starvation

Case details A 25 –year-old woman living alone became severely depressed after the termination of her engagement. Two months later, she was brought to the emergency room by a friend because of weakness and lethargy. She appeared thin and pale. Questioning revealed that she had not eaten for several weeks. Analysis of a plasma sample indicated elevated levels of acetoacetate, β hydroxybutyrate, and blood urea nitrogen (BUN). However her plasma glucose concentration was within normal limits. She was hospitalized, given intravenous feeding and antidepressant medications and subsequently shifted to an 1800 Cal (7500 kJ) diet. Her recovery was uneventful. During...

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Fructose 2, 6 Bis phosphate and regulation of glycolysis

Case details A patient presents with dizziness, fatigue and tremors. A finger stick test indicates blood glucose of 36mmol/L. Of the allosteric activators of glycolysis in the liver, which of the following is the most important in maintaining a normal blood glucose level? A. Citrate B. ATP C. Fructose 2, 6 bisphosphate D. Glucose-6-Phosphate E. Acetyl Co A The correct answer is- C- Fructose 2,6 bisphosphate Generally, enzymes that catalyze essentially irreversible steps in metabolic pathways are potential sites for regulatory control.  Although most of the reactions of glycolysis are reversible, three are markedly exergonic and must therefore be considered...

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Muscle glycogen synthesis in the resting phase…

A 28- year-old professional cyclist has been training for a race. His coach strongly suggests the intake of carbohydrates after his workout to ensure a muscle glycogen storage that can endure the 28-day race. The activity of muscle Glycogen synthase in the resting muscles is increased by the action of which of the following? A. Epinephrine B. Glucagon C. Insulin D. Cortisol E. Thyroid hormone The correct answer is- C- Insulin. Glucose homeostasis reflects a balance between hepatic glucose production and peripheral glucose uptake and utilization. Insulin is the most important regulator of this metabolic equilibrium, but neural input, metabolic signals,...

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Case study- Wernicke-Korsakoff syndrome

Case details A 58-year-old man with a history of heavy drinking presents with confusion, unstable gait, and nystagmus. A provisional diagnosis of Wernicke’s- Korsakoff syndrome is made. Which of the patient’s enzymes of the pentose phosphate pathway is inhibited due to vitamin deficiency in this case? A. Transaldolase B. Transketolase C. Glucose-6-P- dehydrogenase D. Epimerase E. Phosphogluconate dehydrogenase The correct answer is B. – Transketolase. Wernicke-Korsakoff syndrome (thiamine deficiency) is often associated with chronic alcoholics. Thiamine deficiency is uncommon except in alcoholics as a result of nutritional deficiencies and malabsorption. The term Wernicke’s encephalopathy is used to describe the clinical...

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Answer- Case study- Hypoglycemia and Hepatomegaly

A female infant appeared normal at birth but developed signs of liver disease and muscular weakness at 3 months. She had periods of hypoglycemia, particularly on awakening. Examination revealed an enlarged liver. Laboratory analyses following fasting revealed ketoacidosis, blood pH 7.25, and elevations in both alanine transaminase (ALT) and aspartate transaminase (AST). Administration of glucagon following a carbohydrate meal elicited a normal rise in blood glucose, but glucose levels did not rise when glucagon was administered following an overnight fast. Liver biopsy revealed an increase in the glycogen content (6 percent of wet weight). In which of the following enzymes...

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Case study- Hypoglycemia and Hepatomegaly

QUESTION OF THE DAY A female infant appeared normal at birth but developed signs of liver disease and muscular weakness at 3 months. She had periods of hypoglycemia, particularly on awakening. Examination revealed an enlarged liver. Laboratory analyses following fasting revealed ketoacidosis, blood pH 7.25, and elevations in both alanine transaminase (ALT) and aspartate transaminase (AST). Administration of glucagon following a carbohydrate meal elicited a normal rise in blood glucose, but glucose levels did not rise when glucagon was administered following an overnight fast. Liver biopsy revealed an increase in the glycogen content (6 percent of wet weight). In which...

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Case study- Lactose Intolerance

Case details A 30- year-old Asian male presents with bloating, abdominal cramps, and diarrhea. He states that he develops these symptoms whenever he drinks milk or eat dairy products. He is diagnosed with lactose intolerance, a common condition in which lactose is not digested normally and accumulates in the gut. Lactase converts lactose into : A. Two glucose molecules B. Glucose and Fructose C. Glucose and Galactose D. Fructose and Galactose E. Sucrose and Maltose Answer- The correct answer is C- Glucose and galactose. Lactose is a disaccharide made up of Galactose and glucose residues  linked together by beta 1-4...

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Case study- Lactose intolerance

QUESTION OF THE DAY A 30- year-old Asian male presents with bloating, abdominal cramps, and diarrhea. He states that he develops these symptoms whenever he drinks milk or eat dairy products. He is diagnosed with lactose intolerance, a common condition in which lactose is not digested normally and accumulates in the gut. Lactase converts lactose into : A. Two glucose molecules B. Glucose and Fructose C. Glucose and Galactose D. Fructose and Galactose E. Sucrose and Maltose For answer- follow the link http://usmle.biochemistryformedics.com/answer-case-study-lactose-intolerance/   Please help Biochemistry for Medics by “CLICKING ON THE ADVERTISEMENTS” every time you visit us. Thank...

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Case study- Primaquine induced hemolytic anemia

Question of the day A 20-year-old, African-American male military recruit is about to be sent on his assignment. In preparation for his tour of duty, he is given a prophylactic dose of primaquine to prevent malaria. Several days after he begins taking the drug, he develops fatigue and hemolytic anemia. Which of the following enzymes is likely deficient? A. Galactokinase B. Fructokinase C. Glucose-6-P dehydrogenase D. Pyruvate kinase E. Aldolase B Answer- The correct answer is- C-Glucose-6-P dehydrogenase deficiency The patient has presented with primaquine induced hemolytic anemia. Primaquine is an antimalarial drug known to trigger an attack of hemolysis...

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Case study- Primaquine induced hemolytic anemia

Question of the day A 20-year-old, African-American male military recruit is about to be sent on his assignment. In preparation for his tour of duty, he is given a prophylactic dose of primaquine to prevent malaria. Several days after he begins taking the drug, he develops fatigue and hemolytic anemia. Which of the following enzymes is likely deficient? A. Galactokinase B. Fructokinase C. Glucose-6-P dehydrogenase D. Pyruvate kinase E. Aldolase B For answer follow the link http://usmle.biochemistryformedics.com/answer-case-study-primaquine-induced-hemolytic-anemia/ Please help Biochemistry for Medics by “CLICKING ON THE ADVERTISEMENTS” every time you visit us. Thank you!

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‘Hereditary fructose Intolerance’- Case discussion

QUESTION OF THE DAY A 3-month-old girl is brought to the pediatrician due to fussiness and lethargy. According to the parents, the baby was just fine until the mother needed to return to work, and the baby was being switched from breast milk to baby foods, formula, and fruit juices. At that time, the child cried while feeding, sometimes vomited, and had been lethargic. The baby’s appetite seemed to have worsened. The parents thought that if only formula was used, the baby was better, but they really could not remember. Which possible enzyme defect might lead to this case presentation?...

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Case study- Metabolic disorder- A 3-month-old girl is brought to the pediatrician due to fussiness and lethargy….

QUESTION OF THE DAY A 3-month-old girl is brought to the pediatrician due to fussiness and lethargy. According to the parents, the baby was just fine until the mother needed to return to work, and the baby was being switched from breast milk to baby foods, formula, and fruit juices. At that time, the child cried while feeding, sometimes vomited, and had been lethargic. The baby’s appetite seemed to have worsened. The parents thought that if only formula was used, the baby was better, but they really could not remember. Which possible enzyme defect might lead to this case presentation?...

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