Biochemistry of obesity, metabolic syndrome and free radicals

17 NEET-PG practice questions on Biochemistry of obesity, metabolic syndrome and free radicals, part of Biochemistry. The first 17 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

1. Question 1 · Hard

   Notes prepared for a seminar on the genetics of obesity: 1. Most people with common obesity have a high serum leptin. 2. Congenital leptin deficiency responds to recombinant leptin (metreleptin). 3. MC4R variants are the commonest cause of monogenic obesity. 4. Adiponectin rises with visceral fat mass. Which of these are correct?

   1. A2, 3 and 4 only
   2. B1, 2 and 3 only
   3. C1, 2, 3 and 4
   4. D1 and 4 only

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   Answer: B · 1, 2 and 3 only

   Common obesity shows high leptin and leptin resistance. Rare congenital leptin deficiency, often in consanguineous families, causes extreme hyperphagia from infancy and responds dramatically to metreleptin. Heterozygous MC4R variants are the commonest monogenic cause, found in a few percent of severe early-onset obesity, and setmelanotide acts on this pathway. Adiponectin falls, not rises, with visceral fat. Key point: High leptin in common obesity; leptin replacement only for congenital deficiency; MC4R is the commonest monogenic cause; adiponectin falls with visceral fat.

   • A: Statement 4 is false: adiponectin falls with visceral fat.
   • C: Statement 4 is false, so all four cannot be correct.
   • D: Statement 4 is false, and statements 2 and 3 are true.

2. Question 2 · Easy

   Which hormone, secreted by adipocytes in proportion to fat mass, acts on the hypothalamus to suppress appetite?

   1. ANeuropeptide Y
   2. BAdiponectin
   3. CLeptin
   4. DGhrelin

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   Answer: C · Leptin

   Leptin is made by adipocytes, and its level rises with fat mass. It acts on receptors in the arcuate nucleus, stimulating POMC neurons (alpha-MSH acting on MC4R) and inhibiting NPY/AgRP neurons, which lowers food intake and raises energy expenditure. Most obese people have high leptin with leptin resistance. Key point: Leptin from fat cells signals satiety through the arcuate nucleus; common obesity shows high leptin and leptin resistance.

   • A: Neuropeptide Y is a hypothalamic peptide that increases appetite.
   • B: Adiponectin improves insulin sensitivity and falls in obesity; it is not the main satiety signal.
   • D: Ghrelin comes from the stomach and increases appetite.

3. Question 3 · Medium

   A college student with polycystic ovary syndrome, acanthosis nigricans on the neck and a BMI of 31 kg/m2 has a fasting glucose of 99 mg/dL and fasting insulin of 24 µU/mL. Her HOMA-IR is calculated as (glucose in mg/dL x insulin in µU/mL) / 405. How is the result best interpreted?

   1. AAbout 59, showing beta-cell failure
   2. BAbout 2.4, at the upper normal limit
   3. CAbout 0.6, showing normal sensitivity
   4. DAbout 5.9, showing insulin resistance

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   Answer: D · About 5.9, showing insulin resistance

   HOMA-IR = 99 x 24 / 405, about 5.9. Values above about 2.5 (cut-offs vary by population) suggest insulin resistance, which fits acanthosis nigricans and PCOS; her normal fasting glucose shows that high insulin is still compensating. Insulin resistance drives ovarian androgen production and lowers SHBG, worsening hyperandrogenism. Key point: HOMA-IR = fasting glucose (mg/dL) x fasting insulin (µU/mL) / 405; above about 2.5 suggests insulin resistance.

   • A: 59 is a tenfold error, and HOMA-IR does not diagnose beta-cell failure on its own.
   • B: 2.4 is a miscalculation and would be near normal.
   • C: 0.6 comes from a wrong calculation; the true value is about 5.9.

4. Question 4 · Medium

   Genetic testing finds an SOD1 mutation in a man with progressive limb weakness, fasciculations, brisk reflexes and wasting of the small hand muscles, whose father died of the same illness. Sensation and bladder function are normal, and EMG shows widespread denervation. What is the normal function of the enzyme coded by this gene?

   1. AReduces oxidised glutathione using NADPH
   2. BConverts hydrogen peroxide to water and oxygen
   3. CConverts hypoxanthine to xanthine
   4. DConverts superoxide to hydrogen peroxide

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   Answer: D · Converts superoxide to hydrogen peroxide

   Upper and lower motor neuron signs with a family history suggest familial amyotrophic lateral sclerosis. SOD1 codes cytosolic copper-zinc superoxide dismutase, which turns superoxide into hydrogen peroxide and oxygen. Mutant SOD1 damages motor neurons mainly through a toxic gain of function with protein misfolding and aggregation, not simply through lost activity. Key point: SOD1 (Cu-Zn superoxide dismutase) converts superoxide to H2O2; its mutations cause familial ALS.

   • A: This is the reaction of glutathione reductase.
   • B: This is the reaction of catalase.
   • C: This is the reaction of xanthine oxidase.

5. Question 5 · Easy

   After a sleeve gastrectomy at a bariatric centre in Hyderabad, a woman notices that her hunger has fallen sharply, even before she has lost much weight. Removal of the gastric fundus has lowered which hormone?

   1. ACholecystokinin
   2. BGhrelin
   3. CPeptide YY
   4. DLeptin

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   Answer: B · Ghrelin

   Ghrelin is produced mainly by the oxyntic mucosa of the gastric fundus; it rises before meals and stimulates hunger through the hypothalamus. Sleeve gastrectomy removes most of the fundus, so ghrelin falls and appetite drops early, independent of weight loss. Peptide YY and GLP-1, which reduce appetite, also rise after bariatric surgery. Key point: Ghrelin, the hunger hormone from the gastric fundus, falls after sleeve gastrectomy.

   • A: CCK is from the duodenum and is not removed by a sleeve gastrectomy.
   • C: Peptide YY suppresses appetite and rises after bariatric surgery.
   • D: Leptin falls with fat loss and would increase hunger, not reduce it.

6. Question 6 · Medium

   Fasting results of a sedentary bank manager with a waist of 104 cm: glucose 112 mg/dL, triglycerides 240 mg/dL, HDL 34 mg/dL; BP 142/90 mmHg. Adipokine assays show a low level of one hormone that normally activates AMP-kinase in liver and muscle, increases fatty acid oxidation and improves insulin sensitivity. Which hormone is this?

   1. AResistin
   2. BLeptin
   3. CTNF-alpha
   4. DAdiponectin

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7. Question 7 · Medium

   A teenager with cystic fibrosis who often skips his pancreatic enzymes and passes bulky, greasy stools develops an unsteady gait, loss of vibration and position sense, absent ankle reflexes and limited upward gaze; his blood film shows haemolysis. Serum B12 is normal. Deficiency of which vitamin best explains these features?

   1. AVitamin E
   2. BVitamin B1
   3. CVitamin A
   4. DVitamin C

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8. Question 8 · Medium

   Lipid results in a man with central obesity, fatty liver and a fasting glucose of 118 mg/dL: total cholesterol 196 mg/dL, LDL 118 mg/dL, HDL 32 mg/dL, triglycerides 290 mg/dL. Despite the near-normal LDL value, his cardiologist calls the profile atherogenic. Which effect of insulin resistance best explains this?

   1. ARaised lipoprotein(a) synthesis
   2. BAbsent lipoprotein lipase activity
   3. CDeficiency of LDL receptors on hepatocytes
   4. DMore VLDL output and small dense LDL

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9. Question 9 · Medium

   Four hours after swallowing 40 tablets of paracetamol 500 mg, a nursing student has a plasma level above the treatment line, and N-acetylcysteine is started in the casualty. How does it protect her liver?

   1. AIt binds paracetamol in the gut
   2. BIt inhibits CYP2E1 formation of NAPQI
   3. CIt speeds renal excretion of paracetamol
   4. DIt replenishes glutathione to detoxify NAPQI

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10. Question 10 · Medium

    Serum ferritin is 4,800 ng/mL in a transfusion-dependent boy with beta-thalassaemia major who is poorly compliant with chelation; he now has heart failure and raised liver enzymes. Which reaction produces the most damaging free radical in his tissues?

    1. ASuperoxide dismutase, forming H2O2
    2. BCatalase, splitting H2O2 to water
    3. CFe2+ with H2O2, forming hydroxyl radical
    4. DMyeloperoxidase, forming hypochlorous acid

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11. Question 11 · Medium

    Carotid endarterectomy is done on a smoker with diabetes and metabolic syndrome after a transient ischaemic attack. Histology of the plaque shows many lipid-laden macrophages (foam cells) beneath the endothelium. LDL entering the intima is first modified by free radicals. How do macrophages take up this modified LDL in such large amounts?

    1. AUptake of HDL through SR-B1
    2. BScavenger receptors that are not down-regulated
    3. CLDL receptors up-regulated by cholesterol
    4. DPinocytosis of native LDL via apo B-100

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12. Question 12 · Medium

    Ultrasound shows a fatty liver in a woman of 52 with type 2 diabetes and obesity; ALT is 68 U/L, AST 54 U/L and platelets 1.9 lakh/µL. Viral markers are negative, and she drinks no alcohol. Which is the best first step to assess her risk of advanced fibrosis?

    1. ARefer for liver biopsy
    2. BRepeat ultrasound in 6 months
    3. CMeasure serum ferritin
    4. DCalculate the FIB-4 index

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13. Question 13 · Easy

    Lipofuscin, the yellow-brown 'wear and tear' pigment in the heart and liver of elderly people, is formed mainly by which process?

    1. APeroxidation of membrane lipids
    2. BGlycation of tissue proteins
    3. COxidation of tyrosine to melanin
    4. DBreakdown of haemoglobin

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14. Question 14 · Hard

    Soon after successful thrombolysis of an anterior STEMI, a patient develops accelerated idioventricular rhythm, and the final infarct is larger than the ischaemic time alone would predict. The registrar explains reperfusion injury. During ischaemia, ATP is degraded to hypoxanthine; when oxygen returns, an enzyme converted in ischaemic tissue from its dehydrogenase form makes a burst of superoxide. Which enzyme is this?

    1. ANitric oxide synthase
    2. BMyeloperoxidase
    3. CNADPH oxidase
    4. DXanthine oxidase

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15. Question 15 · Hard

    Severe obesity from the first months of life, constant hunger and red hair mark a toddler admitted with hypoglycaemia and collapse during a febrile illness. Serum cortisol is low and plasma ACTH undetectable; serum leptin is high for his fat mass. His parents, who are first cousins, have dark hair. What is the most likely diagnosis?

    1. APrader-Willi syndrome
    2. BPOMC deficiency
    3. CMC4R deficiency
    4. DCongenital leptin deficiency

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16. Question 16 · Medium

    In obesity, excess free fatty acids and diacylglycerol in muscle and liver activate novel protein kinase C isoforms. Which change in insulin signalling follows?

    1. ALoss of insulin receptors from the muscle genome
    2. BSerine phosphorylation of IRS-1 blocks signalling
    3. CAntibodies form against the insulin receptor
    4. DExcess tyrosine phosphorylation of GLUT4

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17. Question 17 · Medium

    On home parenteral nutrition for 3 years after massive small bowel resection, a man develops dilated cardiomyopathy, muscle pain and whitened nail beds. Serum selenium is very low. Reduced activity of which antioxidant enzyme is most likely?

    1. AGlutathione peroxidase
    2. BCatalase
    3. CGlucose-6-phosphate dehydrogenase
    4. DSuperoxide dismutase

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