Carbohydrate Metabolism Indian Medical PG Practice Questions and MCQs
Practice Indian Medical PG questions for Carbohydrate Metabolism. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Carbohydrate Metabolism Indian Medical PG Question 1: The diagnosis of diabetes mellitus is certain in which of the following situations?
- A. Abnormal oral glucose tolerance in a 24-yrs-old woman who has been dieting
- B. A serum glucose level >7.8 mmol/L in a woman in her twenty-fifth week of gestation after a 50-g oral glucose load
- C. Persistent asymptomatic glycosuria in a 30-yrs-old woman
- D. Successive fasting plasma glucose concentrations of 8, 9, and 8.5 mmol/L in an asymptomatic, otherwise healthy individual. (Correct Answer)
Carbohydrate Metabolism Explanation: ***Successive fasting plasma glucose concentrations of 8, 9, and 8.5 mmol/L in an asymptomatic, otherwise healthy individual.***
- A definitive diagnosis of **diabetes mellitus** requires two separate fasting plasma glucose (FPG) levels of **≥7.0 mmol/L** (126 mg/dL) or higher [1]. The given values (8, 9, 8.5 mmol/L) meet this criterion.
- Since the individual is **asymptomatic**, two abnormal tests are typically needed to confirm the diagnosis, which is satisfied by the successive elevated fasting glucose levels.
*Abnormal oral glucose tolerance in a 24-yrs-old woman who has been dieting*
- **Dieting** can affect glucose metabolism and potentially lead to an abnormal oral glucose tolerance test (OGTT) result that does not accurately reflect diabetes.
- A single abnormal OGTT in a dieting individual without confirmatory tests or symptoms is not sufficient for a definitive diagnosis of diabetes.
*A serum glucose level >7.8 mmol/L in a woman in her twenty-fifth week of gestation after a 50-g oral glucose load*
- A serum glucose level >7.8 mmol/L after a **50-g glucose challenge** is a positive screening test for **gestational diabetes mellitus**, but it is not diagnostic [2].
- A positive screening test requires further confirmation with a **100-g or 75-g oral glucose tolerance test** to diagnose gestational diabetes.
*Persistent asymptomatic glycosuria in a 30-yrs-old woman*
- **Glycosuria** (glucose in the urine) without hyperglycemia (elevated blood glucose) can be due to a low **renal threshold for glucose**, a benign condition called renal glycosuria.
- While it warrants investigation for diabetes, persistent asymptomatic glycosuria alone is **not diagnostic** of diabetes unless accompanied by elevated blood glucose levels.
Carbohydrate Metabolism Indian Medical PG Question 2: A patient with diabetes mellitus for the past 5 years presents with vomiting and abdominal pain. She is non-compliant with medication and appears dehydrated. Investigations revealed a blood sugar value of 500 mg/dl and the presence of ketone bodies. What is the next best step in management of this patient?
- A. Intravenous fluids
- B. Intravenous insulin
- C. Intravenous fluids with regular insulin (Correct Answer)
- D. Intravenous fluids with long-acting insulin
Carbohydrate Metabolism Explanation: Detailed management of diabetic ketoacidosis (DKA) requires both fluid resuscitation and insulin therapy.
***Intravenous fluids with regular insulin***
- The patient presents with classic signs of **diabetic ketoacidosis (DKA)**: hyperglycemia (blood sugar 500 mg/dl), ketone bodies, dehydration, and a history of diabetes non-compliance [1].
- Initial management for DKA involves aggressive **intravenous fluid resuscitation** to correct dehydration and then **intravenous regular insulin** to lower blood glucose and resolve ketosis [2].
*Intravenous fluids with long-acting insulin*
- While fluids are essential, **long-acting insulin** is not appropriate for the acute management of DKA because its slow onset of action makes it inefficient for rapidly correcting hyperglycemia and ketosis.
- **Regular insulin** is preferred as it has a quicker onset and shorter duration, allowing for more precise titration in an acute setting [2].
*Intravenous fluids*
- Although crucial for correcting **dehydration** and improving renal perfusion, fluids alone will not address the underlying **insulin deficiency** and **ketosis** that define DKA.
- Without insulin, the body will continue to produce ketones, exacerbating acidosis [3].
*Intravenous insulin*
- Giving intravenous insulin without prior or concomitant **fluid resuscitation** can be dangerous, as it can worsen **hypovolemia** and potentially lead to circulatory collapse by shifting glucose and potassium into cells.
- It is critical to first restore **circulating volume** before initiating insulin therapy [2].
Carbohydrate Metabolism Indian Medical PG Question 3: Which of the following metabolites is involved in glycogenolysis, glycolysis and gluconeogenesis ?
- A. Glucose-6-phosphate (Correct Answer)
- B. Uridine diphosphoglucose
- C. Fructose-6-phosphate
- D. Galactose-1-phosphate
Carbohydrate Metabolism Explanation: ***Glucose-6-phosphate***
- In **glycogenolysis**, **glycogen phosphorylase** breaks down glycogen into **glucose-1-phosphate**, which is then converted into **glucose-6-phosphate** by **phosphoglucomutase**.
- In **glycolysis**, **glucose-6-phosphate** is isomerized to **fructose-6-phosphate** by **phosphoglucose isomerase**, committing it to the glycolytic pathway.
- In **gluconeogenesis**, **glucose-6-phosphate** is the final product formed from other precursors; it can then be dephosphorylated to free glucose by **glucose-6-phosphatase**.
*Galactose-1-phosphate*
- This is an intermediate specifically in **galactose metabolism**, not directly involved in the central common pathways of glycogenolysis, glycolysis, or gluconeogenesis.
- It is converted to **glucose-1-phosphate** via the **Leloir pathway** (involving **galactose-1-phosphate uridylyltransferase**), which can then enter glycogen metabolism.
*Uridine diphosphoglucose*
- **UDP-glucose** is crucial for **glycogen synthesis** (**glycogenesis**), serving as the activated glucose donor.
- It is not directly a metabolite in the catabolic process of glycogenolysis, nor is it a direct intermediate in glycolysis or gluconeogenesis.
*Fructose-6-phosphate*
- **Fructose-6-phosphate** is a key intermediate in **glycolysis** and **gluconeogenesis**, specifically downstream from **glucose-6-phosphate**.
- However, it is not directly produced from glycogenolysis; **glucose-6-phosphate** is the direct link between glycogenolysis and glycolysis.
Carbohydrate Metabolism Indian Medical PG Question 4: Which of the following is not a substrate for gluconeogenesis?
- A. Leucine (Correct Answer)
- B. Lactate
- C. Propionate
- D. Glycerol
Carbohydrate Metabolism Explanation: ***Leucine***
- **Leucine** is an exclusively **ketogenic amino acid**, meaning its breakdown products can only be converted into **ketone bodies** or fatty acids, not glucose.
- It does not have a carbon skeleton that can be directly converted into **pyruvate** or **oxaloacetate**, which are key intermediates in gluconeogenesis.
*Lactate*
- **Lactate** is a major substrate for gluconeogenesis, particularly during exercise or fasting.
- It is converted to **pyruvate** by **lactate dehydrogenase**, and pyruvate can then enter the gluconeogenic pathway.
*Propionate*
- **Propionate** is a fatty acid with an odd number of carbon atoms, primarily derived from the catabolism of odd-chain fatty acids or from bacterial fermentation in the colon.
- It can be converted into **succinyl CoA**, an intermediate of the citric acid cycle, which can then be used for gluconeogenesis.
*Glycerol*
- **Glycerol**, released during the breakdown of triglycerides, is an important substrate for gluconeogenesis.
- It is phosphorylated to **glycerol-3-phosphate**, which is then oxidized to **dihydroxyacetone phosphate (DHAP)**, an intermediate in glycolysis and gluconeogenesis.
Carbohydrate Metabolism Indian Medical PG Question 5: In glycolysis, which of the following enzymes is not involved?
- A. Pyruvate dehydrogenase (Correct Answer)
- B. Phosphofructokinase
- C. Glucokinase
- D. Pyruvate kinase
Carbohydrate Metabolism Explanation: ***Pyruvate dehydrogenase***
- **Pyruvate dehydrogenase** is a mitochondrial enzyme complex that converts **pyruvate** to **acetyl-CoA** in the link reaction, which occurs after glycolysis and prepares for the citric acid cycle.
- It is not directly involved in the ten-step glycolytic pathway itself, which converts glucose to pyruvate.
*Phosphofructokinase*
- **Phosphofructokinase-1 (PFK-1)** is a key regulatory enzyme in glycolysis, catalyzing the phosphorylation of **fructose-6-phosphate** to **fructose-1,6-bisphosphate**.
- This step is often considered the **rate-limiting step** of glycolysis.
*Glucokinase*
- **Glucokinase**, located primarily in the liver and pancreatic beta cells, phosphorylates glucose to **glucose-6-phosphate** in the first step of glycolysis.
- It has a high **Km** (low affinity) for glucose, allowing it to respond to high glucose concentrations.
*Pyruvate kinase*
- **Pyruvate kinase** catalyzes the final step of glycolysis, transferring a phosphate group from **phosphoenolpyruvate (PEP)** to ADP to form **ATP** and **pyruvate**.
- This is one of the **irreversible** steps in glycolysis and a point of regulation.
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