Obesity: Biochemical Aspects — MCQs
Which protein secreted by adipocytes prevents obesity?
Which of the following is not the criteria for diagnosis of Metabolic syndrome?
Which of the following statements about adiponectin is incorrect?
Which of the following is NOT true about ghrelin?
A 45-year-old man with a recent history of bizarre behavior is seen by a psychiatrist. On physical examination, the patient appears moderately obese with mild hypertension, facial acne, and fat accumulation in the supraclavicular fossae. Laboratory studies demonstrate neutrophilic leukocytosis, decreased lymphocytes, and absence of eosinophils, along with mild hypokalemia and mild metabolic alkalosis. The fasting serum glucose is within the reference range, but the OGTT shows glucose concentrations > 200 mg/dL. Laboratory studies also show a free urinary cortisol of 156 mg/24 hours. Which of the following questions would be of most help in establishing a diagnosis?
Which of the following is a lipotropic factor?
Consider the following statements with reference to 'trans fatty acids' : 1. They are geometrical isomers of cis-unsaturated fatty acids. 2. Though atherogenic, being unsaturated they are less so than saturated fatty acids. 3. It takes years for trans fatty acids to be flushed from the body. 4. They lower both LDL cholesterol and HDL cholesterol in the body. Which of the statements given above are correct ?
Which amino acid is common to both the urea cycle and the TCA cycle?
A 26-year-old woman undertakes a prolonged fast for religious reasons. Which of the following metabolites will be most elevated in her blood plasma after 3 days?
Acetyl CoA is used for the synthesis of the following, except:
Obesity: Biochemical Aspects Indian Medical PG Practice Questions and MCQs
Question 1: Which protein secreted by adipocytes prevents obesity?
- A. Galanin
- B. Neuropeptide Y
- C. Cathepsin
- D. Leptin (Correct Answer)
Explanation: ***Leptin*** - **Leptin** is a hormone secreted by **adipocytes** (fat cells) that plays a crucial role in long-term energy balance and appetite suppression. - It signals the brain about the body's energy stores, leading to decreased food intake and increased energy expenditure, and thus **preventing obesity**. *Galanin* - **Galanin** is a neuropeptide that has been shown to **stimulate food intake**, particularly fat consumption. - It is associated with **increased appetite** and **obesity**, rather than its prevention. *Neuropeptide Y* - **Neuropeptide Y (NPY)** is a potent **orexigenic** (appetite-stimulating) peptide primarily found in the hypothalamus. - Its activation leads to **increased food intake** and **decreased energy expenditure**, promoting weight gain and obesity. *Cathepsin* - **Cathepsins** are a family of **proteolytic enzymes** found in lysosomes. - They are involved in protein degradation and other cellular processes, but they are not directly involved in the prevention of obesity through appetite regulation or energy balance.
Question 2: Which of the following is not the criteria for diagnosis of Metabolic syndrome?
- A. High LDL (Correct Answer)
- B. Hyperiglyceridemia
- C. Hypertension
- D. Central obesity
Explanation: ***High LDL*** - While **high LDL (low-density lipoprotein)** is a risk factor for cardiovascular disease [1], it is **not** one of the specific diagnostic criteria for metabolic syndrome. - The criteria for metabolic syndrome focus on a cluster of metabolic abnormalities associated with insulin resistance. *Hypertriglyceridemia* - **Elevated triglycerides** (typically ≥ 150 mg/dL or on drug treatment for elevated triglycerides) is one of the key diagnostic criteria for metabolic syndrome. - It reflects impaired lipid metabolism often associated with insulin resistance [2]. *Hypertension* - **Elevated blood pressure** (systolic ≥ 130 mmHg or diastolic ≥ 85 mmHg, or on antihypertensive drug treatment) is a core component of metabolic syndrome. - Hypertension in this context is often linked to underlying insulin resistance. *Central obesity* - **Increased waist circumference** (varying by ethnicity and sex, e.g., >102 cm in men and >88 cm in women for adults of European descent) is a primary criterion for metabolic syndrome. - It is a strong indicator of visceral fat accumulation, which is closely linked to insulin resistance [3].
Question 3: Which of the following statements about adiponectin is incorrect?
- A. Secreted by adipose tissue
- B. Increases FFA oxidation
- C. Lowers glucose
- D. Positive Correlation with BMI (Correct Answer)
Explanation: ***Positive Correlation with BMI (INCORRECT STATEMENT)*** - Adiponectin levels are **inversely correlated with BMI**, NOT positively correlated; as BMI increases, adiponectin levels generally decrease. - This inverse relationship is significant because lower adiponectin levels are associated with increased insulin resistance and **metabolic syndrome**. - This statement is **false**, making it the correct answer to this question. *Secreted by adipose tissue (Correct statement)* - Adiponectin is a **hormone primarily secreted by adipocytes** (fat cells). - It plays a crucial role in regulating glucose and lipid metabolism, and its secretion is altered in conditions like obesity. - This statement is **true**. *Lowers glucose (Correct statement)* - Adiponectin **enhances insulin sensitivity** in peripheral tissues like skeletal muscle and liver, leading to increased glucose uptake and utilization. - This action helps to **lower blood glucose levels** and improve glycemic control. - This statement is **true**. *Increases FFA oxidation (Correct statement)* - Adiponectin **promotes fatty acid oxidation** in muscle and liver, reducing intracellular lipid accumulation. - By increasing fatty acid burning, it helps to **decrease circulating free fatty acid (FFA) levels**, which can contribute to insulin resistance if elevated. - This statement is **true**.
Question 4: Which of the following is NOT true about ghrelin?
- A. Has anorexic effect (Correct Answer)
- B. Stimulates growth hormone release
- C. Secreted by gastric fundus cells
- D. Increases gastric motility
Explanation: ***Has anorexic effect*** - Ghrelin is known as the **"hunger hormone"** because it stimulates appetite and has an **orexigenic effect**, meaning it increases food intake. - Therefore, stating that it has an **anorexic effect** (reduces appetite) is incorrect. *Stimulates growth hormone release* - Ghrelin is a **natural ligand** for the **growth hormone secretagogue receptor (GHSR)**. - This binding leads to the stimulation of **growth hormone (GH)** release from the pituitary gland. *Secreted by gastric fundus cells* - The primary source of ghrelin in the body is the **P/D1 cells** found in the mucosa of the **gastric fundus**. - Smaller amounts are also produced in the small intestine, pancreas, and hypothalamus. *Increases gastric motility* - Ghrelin is involved in regulating stomach function and can **increase gastric motility** and acid secretion. - This action helps to prepare the digestive system for incoming food.
Question 5: A 45-year-old man with a recent history of bizarre behavior is seen by a psychiatrist. On physical examination, the patient appears moderately obese with mild hypertension, facial acne, and fat accumulation in the supraclavicular fossae. Laboratory studies demonstrate neutrophilic leukocytosis, decreased lymphocytes, and absence of eosinophils, along with mild hypokalemia and mild metabolic alkalosis. The fasting serum glucose is within the reference range, but the OGTT shows glucose concentrations > 200 mg/dL. Laboratory studies also show a free urinary cortisol of 156 mg/24 hours. Which of the following questions would be of most help in establishing a diagnosis?
- A. Are you experiencing muscle weakness?
- B. Do you have a family history of endocrine neoplasia?
- C. Are you experiencing shortness of breath?
- D. Are you receiving corticosteroids for some other disease? (Correct Answer)
Explanation: ***Are you receiving corticosteroids for some other disease?*** - The patient's presentation including **obesity**, **hypertension**, **facial acne**, **supraclavicular fat accumulation** (buffalo hump), **neutrophilic leukocytosis**, **lymphopenia**, **eosinopenia**, **hypokalemia**, **metabolic alkalosis**, and **impaired glucose tolerance** with **elevated urinary free cortisol** are all highly suggestive of **Cushing's syndrome** [1]. - Exogenous corticosteroid use is the most common cause of Cushing's syndrome (iatrogenic Cushing's syndrome), and directly asking about it is crucial to differentiate it from endogenous causes [2]. *Are you experiencing muscle weakness?* - **Proximal muscle weakness** is a common symptom in Cushing's syndrome due to the catabolic effects of excess cortisol on muscle protein [1]. - While it's a helpful diagnostic symptom, it describes a manifestation of the disease rather than helping to determine its etiology, especially when differentiating between endogenous and exogenous causes. *Are you experiencing shortness of breath?* - **Shortness of breath** is not a direct or common symptom of Cushing's syndrome itself. - While hypertension and obesity associated with Cushing's can contribute to cardiovascular or respiratory issues in some cases, it's not a primary or specific finding. *Do you have a family history of endocrine neoplasia?* - A family history of **endocrine neoplasia** (e.g., Multiple Endocrine Neoplasia type 1 or 2, or familial isolated pituitary adenoma) might suggest an inherited predisposition to certain endocrine tumors, some of which could potentially cause endogenous Cushing's syndrome (e.g., pituitary adenoma leading to ACTH-dependent Cushing's disease) [3]. - However, considering the overall clinical picture, the initial step should be to rule out the most common cause of Cushing's symptoms, which is exogenous corticosteroid use, before delving into rare genetic causes of endogenous Cushing's.
Question 6: Which of the following is a lipotropic factor?
- A. Sphingomyelin
- B. Histidine
- C. Bilirubin
- D. Methionine (Correct Answer)
Explanation: ***Methionine*** - **Methionine** is an essential amino acid that serves as a precursor for **choline** and **creatine**, both of which play crucial roles in lipid metabolism and transport. - Lipotropic factors prevent or reverse the accumulation of **fat in the liver** by promoting the synthesis of **lipoproteins**, which package and transport fats from the liver to other tissues. *Sphingomyelin* - **Sphingomyelin** is a type of **sphingolipid**, a component of cell membranes and myelin sheaths, but it does not directly act as a lipotropic factor to prevent fatty liver. - While it's involved in cellular signaling and membrane structure, it does not directly facilitate the metabolism or transport of **hepatic triglycerides** in the same way as lipotropic agents. *Histidine* - **Histidine** is an essential amino acid involved in protein synthesis and the production of **histamine**, but it is not considered a primary lipotropic factor. - Its main roles are in **immune response** and **neurotransmission**, not in preventing fat accumulation in the liver. *Bilirubin* - **Bilirubin** is a waste product from the breakdown of **heme**, primarily from red blood cells. It is excreted by the liver. - It is known for its **antioxidant properties** but does not play a direct role as a lipotropic factor in lipid metabolism or in preventing **fatty liver**.
Question 7: Consider the following statements with reference to 'trans fatty acids' : 1. They are geometrical isomers of cis-unsaturated fatty acids. 2. Though atherogenic, being unsaturated they are less so than saturated fatty acids. 3. It takes years for trans fatty acids to be flushed from the body. 4. They lower both LDL cholesterol and HDL cholesterol in the body. Which of the statements given above are correct ?
- A. 1 and 3 only
- B. 2, 3 and 4
- C. 1 only (Correct Answer)
- D. 1, 3 and 4
Explanation: ***1 only*** - **Statement 1 is CORRECT**: Trans fatty acids are **geometrical isomers of cis-unsaturated fatty acids**, differing in the spatial arrangement of hydrogen atoms around the carbon-carbon double bond. This structural difference gives them physical and biological properties more similar to saturated fats. - **Statement 2 is INCORRECT**: Trans fatty acids are **MORE atherogenic** than saturated fatty acids, not less. They raise LDL cholesterol and lower HDL cholesterol more significantly than saturated fats. - **Statement 3 is INCORRECT**: Trans fatty acids are metabolized and eliminated from the body within **days to weeks**, not years. Long-term cardiovascular damage results from chronic dietary exposure, not slow elimination kinetics. - **Statement 4 is INCORRECT**: Trans fatty acids **raise LDL cholesterol** ("bad" cholesterol) and **lower HDL cholesterol** ("good" cholesterol). They do not lower both as stated. *1 and 3 only* - Statement 1 is correct, but statement 3 is **incorrect**. The body processes and eliminates trans fatty acids relatively quickly (days to weeks), not years. The detrimental cardiovascular effects accumulate due to chronic dietary exposure, not slow metabolism of individual molecules. *2, 3 and 4* - All three statements are **incorrect**. Statement 2 is wrong because trans fats are **more atherogenic** than saturated fats. Statement 3 is wrong because trans fats are metabolized within weeks, not years. Statement 4 is wrong because trans fats **raise LDL** (not lower it) while lowering HDL. *1, 3 and 4* - Only statement 1 is correct. Statement 3 is **incorrect** as trans fatty acids are metabolized within weeks, not years. Statement 4 is **incorrect** because trans fatty acids **increase LDL cholesterol** and **decrease HDL cholesterol** - they do not lower both.
Question 8: Which amino acid is common to both the urea cycle and the TCA cycle?
- A. Aspartate (Correct Answer)
- B. Alanine
- C. Asparagine
- D. Glutamate
Explanation: ### Explanation The correct answer is **Aspartate**. **Why Aspartate is the Correct Answer:** The Urea cycle and the TCA cycle are interconnected through what is known as the **"Kreb’s Bicycle"** or the **Aspartate-Argininosuccinate Shunt**. 1. **In the Urea Cycle:** Aspartate enters the cycle by reacting with citrulline to form argininosuccinate (catalyzed by argininosuccinate synthetase). It provides the second nitrogen atom required for urea synthesis. 2. **In the TCA Cycle:** Oxaloacetate (a TCA intermediate) can be converted into Aspartate via **transamination** (catalyzed by AST/GOT). Conversely, the fumarate produced in the urea cycle can be recycled back into oxaloacetate to regenerate aspartate. **Why the Other Options are Incorrect:** * **Alanine:** Primarily involved in the **Cahill cycle** (Glucose-Alanine cycle) for transporting nitrogen from muscles to the liver. It is not a direct intermediate or substrate in the urea cycle. * **Asparagine:** While structurally related to aspartate, it must first be hydrolyzed to aspartate by asparaginase to enter these metabolic pathways. * **Glutamate:** Although glutamate provides the first nitrogen (via oxidative deamination to produce ammonia) and is the donor for transamination to form aspartate, it is not a direct component of the TCA cycle itself (its keto-acid, **α-ketoglutarate**, is). **High-Yield NEET-PG Pearls:** * **Fumarate** is the other molecule connecting the two cycles; it is produced in the urea cycle and enters the TCA cycle. * **ATP Requirement:** The synthesis of one molecule of urea consumes **4 high-energy phosphates** (3 ATP are used, but one is cleaved to AMP + PPi). * **Rate-limiting step:** Carbamoyl phosphate synthetase I (CPS-I) is the rate-limiting enzyme of the urea cycle, activated by **N-acetylglutamate (NAG)**.
Question 9: A 26-year-old woman undertakes a prolonged fast for religious reasons. Which of the following metabolites will be most elevated in her blood plasma after 3 days?
- A. Glucose
- B. Glycogen
- C. Ketone bodies (Correct Answer)
- D. Non-esterified fatty acids
Explanation: **Explanation:** The metabolic response to fasting occurs in distinct phases to maintain energy homeostasis. After approximately 24–48 hours of fasting, hepatic glycogen stores are completely exhausted. To provide an alternative fuel source for the brain and conserve muscle protein, the liver shifts into intensive **ketogenesis**. **Why Ketone Bodies are the Correct Answer:** By day 3 of a fast (prolonged fasting/early starvation), the body enters a state of "glucose sparing." Low insulin and high glucagon levels stimulate the release of fatty acids from adipose tissue. These fatty acids undergo $\beta$-oxidation in the liver, producing excess Acetyl-CoA, which is converted into **ketone bodies** (acetoacetate and $\beta$-hydroxybutyrate). Their plasma concentration rises exponentially during this period, eventually becoming the primary fuel for the brain. **Analysis of Incorrect Options:** * **A. Glucose:** Plasma glucose levels are maintained at a low-normal range via gluconeogenesis but do not "elevate." * **B. Glycogen:** This is an intracellular storage polymer (liver/muscle), not a plasma metabolite. Furthermore, hepatic glycogen is depleted within the first 24 hours. * **D. Non-esterified fatty acids (NEFAs):** While NEFAs do increase due to lipolysis, their rise is modest compared to the massive, several-fold increase seen in ketone bodies. **NEET-PG High-Yield Pearls:** * **Order of Fuel Use:** Exogenous $\rightarrow$ Glycogenolysis $\rightarrow$ Gluconeogenesis $\rightarrow$ Ketosis. * **Ketogenesis Rate-Limiting Enzyme:** HMG-CoA Synthase (Mitochondrial). * **Brain Adaptation:** The brain cannot use fatty acids (cannot cross BBB) but can adapt to use ketone bodies during prolonged starvation. * **Organ Specificity:** The liver **produces** ketone bodies but cannot **utilize** them because it lacks the enzyme **Thiophorase** (Succinyl-CoA:3-ketoacid CoA transferase).
Question 10: Acetyl CoA is used for the synthesis of the following, except:
- A. Carbohydrates
- B. Ketone bodies
- C. Cholesterol
- D. Non-ketogenic amino acids only (Correct Answer)
Explanation: **Explanation:** The core concept tested here is the **irreversibility of the Pyruvate Dehydrogenase (PDH) complex** and the metabolic fate of Acetyl CoA. **Why Option D is Correct:** In humans, Acetyl CoA cannot be converted back into glucose or non-ketogenic (glucogenic) amino acids. This is because the conversion of Pyruvate to Acetyl CoA by the PDH complex is a one-way, irreversible reaction. Furthermore, while Acetyl CoA enters the TCA cycle, the two carbons it contributes are lost as $CO_2$ before reaching Oxaloacetate, meaning there is no net gain of carbon atoms to support gluconeogenesis. Therefore, Acetyl CoA cannot synthesize non-ketogenic amino acids, which require a glucose-derived carbon skeleton. **Analysis of Incorrect Options:** * **A. Carbohydrates:** While Acetyl CoA cannot be converted to glucose in humans, it is often a "distractor" in such questions. However, compared to Option D, which specifies "only" non-ketogenic amino acids, Option D is the more precise biochemical "except." (Note: Plants/bacteria can do this via the Glyoxylate cycle, but humans cannot). * **B. Ketone Bodies:** Acetyl CoA is the primary precursor for ketogenesis (HMG-CoA pathway) in the liver during fasting. * **C. Cholesterol:** Acetyl CoA is the building block for cholesterol synthesis; two molecules condense to form Acetoacetyl CoA, eventually forming HMG-CoA and Mevalonate. **High-Yield NEET-PG Pearls:** * **PDH Complex:** Requires five cofactors (**T**iamine, **R**iboflavin, **N**iacin, **P**antothenic acid, **L**ipoic acid—Mnemonic: **T**ender **R**evolving **N**ew **P**arts **L**ubricated). * **Ketogenic Amino Acids:** Leucine and Lysine are purely ketogenic; they are metabolized directly to Acetyl CoA or Acetoacetate. * **The "No-Go" Route:** Fatty acids (which break down to Acetyl CoA) can never be used to maintain blood glucose levels in humans.
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