Q: Answer it all question A: Given the breadth of these questions biochemistry, physiology, acid-base, I'll answer them comprehensively from my medical knowledge. These are standard medical biochemistry/physiology exam questions. --- GROUP-A ANSWERS --- Q1. Electron Transport Chain ETC — 1+4 ETC is the series of protein complexes in the inner mitochondrial membrane that transfer electrons from NADH/FADH₂ to molecular O₂, generating ATP via oxidative phosphorylation. Inhibitors of ETC: Complex Inhibitor ------ Complex I NADH dehydrogenase Rotenone, Amytal amobarbital, MPP⁺ Complex II Succinate dehydrogenase Malonate competitive inhibitor of succinate Complex III Cytochrome bc1 Antimycin A Complex IV Cytochrome c oxidase Cyanide CN⁻, Carbon monoxide CO, Azide N₃⁻, H₂S ATP synthase Complex V Oligomycin Uncouplers dissociate electron transport from ATP synthesis 2,4-Dinitrophenol DNP, Thermogenin UCP1, Aspirin high dose, CCCP --- Q2. Sources and Fates of Pyruvate / Why TCA is called Common Metabolic Pathway — 3+2 Sources of Pyruvate: - Glycolysis from glucose/glycogen - Transamination of alanine - Deamination of serine, cysteine - From malate malic enzyme - From lactate lactate dehydrogenase Fates of Pyruvate: 1. Acetyl-CoA by pyruvate dehydrogenase — aerobic 2. Lactate by LDH — anaerobic 3. Oxaloacetate by pyruvate carboxylase — gluconeogenesis 4. Alanine by transamination 5. Ethanol in yeast — not humans Why TCA cycle is called Common Metabolic Pathway: The TCA Krebs cycle is the final common pathway for oxidation of carbohydrates, fats, and proteins: - Carbohydrates → Pyruvate → Acetyl-CoA → enters TCA - Fats → Beta-oxidation → Acetyl-CoA → enters TCA - Proteins → Amino acids → glucogenic/ketogenic → Acetyl-CoA or TCA intermediates e.g., oxaloacetate, α-ketoglutarate, fumarate, succinyl-CoA Thus, all three macronutrients converge on TCA for final oxidation — hence "common metabolic pathway." --- Q3. Glycolysis — Importance + ATP from 1 mole glucose — 1+3+1 What is glycolysis: Glycolysis is the cytoplasmic pathway that converts 1 molecule of glucose 6C into 2 molecules of pyruvate 3C, generating ATP and NADH. Importance of Glycolysis: - Provides energy ATP rapidly, even without oxygen - Provides precursors for other pathways pentose phosphate pathway, TCA cycle, fatty acid synthesis - Only energy source for RBCs no mitochondria, renal medulla, and lens of eye - Crucial during anaerobic conditions exercise, ischemia ATP produced from 1 mole glucose: Step ATP yield ------ Substrate-level phosphorylation 4 ATP Net after investment phase −2 ATP 2 NADH cytoplasmic → via malate-aspartate shuttle 2 × 2.5 = 5 ATP Net total aerobic 7 ATP For the glycolysis step alone: net 2 ATP + 2 NADH How many ATP from 1 mole glucose complete oxidation: - Glycolysis: 2 ATP + 2 NADH cytoplasmic - Pyruvate dehydrogenase: 2 NADH - TCA cycle ×2: 6 NADH + 2 FADH₂ + 2 GTP - Total NADH = 10 → × 2.5 = 25 ATP - Total FADH₂ = 2 → × 1.5 = 3 ATP - GTP = 2 ATP - Net glycolysis = 2 ATP - Grand total ≈ 30–32 ATP modern P/O ratios --- Q4. Beta-Oxidation of Fatty Acids — Steps + ATP from 16C fatty acid — 3+2 Steps of Beta-Oxidation one cycle: 1. Activation — Fatty acid + CoA → Acyl-CoA uses 2 ATP equivalents, occurs in cytoplasm 2. Transport — Acyl-CoA enters mitochondria via carnitine shuttle 3. Oxidation FAD-dependent — Acyl-CoA dehydrogenase → trans-Δ²-Enoyl-CoA + FADH₂ 4. Hydration — Enoyl-CoA hydratase → L-3-Hydroxyacyl-CoA 5. Oxidation NAD⁺-dependent — 3-Hydroxyacyl-CoA dehydrogenase → 3-Ketoacyl-CoA + NADH 6. Thiolysis — Thiolase + CoA → Acetyl-CoA + shortened Acyl-CoA 2 carbons shorter Cycle repeats until complete. ATP from Palmitic acid 16C, saturated: - Number of cycles = 16/2 − 1 = 7 cycles - Acetyl-CoA produced = 8 - FADH₂ from beta-oxidation = 7 × 1.5 = 10.5 ATP - NADH from beta-oxidation = 7 × 2.5 = 17.5 ATP - 8 Acetyl-CoA × TCA = 8 × 10 = 80 ATP - Activation cost = −2 ATP - Total = 10.5 + 17.5 + 80 − 2 = 106 ATP --- Q5. Functions of Lipoproteins — Draw and Label — 3+2 Structure of Lipoprotein: A lipoprotein particle has: - Core: Hydrophobic — triglycerides TG + cholesterol esters CE - Shell: Hydrophilic — phospholipids + free cholesterol + apolipoproteins / Apo-protein Phospholipid ← Shell hydrophilic Free Chol --------------- TG + CE ← Core hydrophobic / Functions of Lipoproteins: Lipoprotein Function ------ Chylomicrons Transport dietary exogenous TG from gut to tissues VLDL Transport endogenous TG from liver to peripheral tissues IDL Intermediate; converted to LDL LDL Deliver cholesterol to peripheral tissues; atherogenic HDL Reverse cholesterol transport — takes cholesterol from tissues back to liver; protective --- Q6. Clinical Case — 13-year-old boy DKA — 1+3+1 A Probable Diagnosis: Diabetic Ketoacidosis DKA The boy presents with: - Excessive thirst, frequent urination → hyperglycemia - Weight loss 48 hrs - Drowsy but arousable - Fruity smell in breath → acetone ketones - Kussmaul respiration → compensatory deep breathing for metabolic acidosis - Urine ketone bodies +++ - Blood glucose 30 mg/dL ? — likely 300 mg/dL, likely a typo — consistent with DKA - No medication history → Type 1 DM presenting for the first time B Other causes of ammonia intoxication if the fruity smell implied differential: The question asks: write some other causes of the condition — likely of ketosis/ketonemia Other causes of ketosis/ketonemia: 1. Prolonged starvation / fasting 2. High-fat, low-carbohydrate diet ketogenic diet 3. Alcoholic ketoacidosis 4. Prolonged vomiting 5. High-intensity exercise 6. Von Gierke's disease glycogen storage disease type I 7. Isovaleric acidemia / MSUD organic acidemias --- GROUP-B ANSWERS --- Q7. Transamination and Deamination / Urea Cycle — 3+3+1+3 Transamination: Transfer of an amino group −NH₂ from an amino acid to an α-keto acid, producing a new amino acid and a new keto acid. - Enzyme: Aminotransferase transaminase — requires PLP pyridoxal phosphate, Vitamin B6 - Example: Alanine + α-ketoglutarate ⇌ Pyruvate + Glutamate ALT reaction - AST: Aspartate + α-ketoglutarate ⇌ Oxaloacetate + Glutamate Deamination: Removal of an amino group as free ammonia NH₃. - Oxidative deamination: Glutamate → α-ketoglutarate + NH₃ by glutamate dehydrogenase, in liver mitochondria - Indirect deamination: Most amino acids → transaminate to glutamate → then oxidative deamination Urea Cycle Steps: 1. NH₃ + CO₂ + 2ATP → Carbamoyl phosphate enzyme: CPS-I, in mitochondria 2. Carbamoyl phosphate + Ornithine → Citrulline OTC enzyme 3. Citrulline exported to cytoplasm; + Aspartate → Argininosuccinate ASS enzyme, needs ATP 4. Argininosuccinate → Arginine + Fumarate ASL enzyme 5. Arginine → Ornithine + Urea Arginase — ornithine recycled What is ammonia intoxication: Elevated blood ammonia hyperammonemia → toxic to CNS. Causes: liver failure, urea cycle enzyme defects Symptoms: Asterixis, confusion, coma, cerebral edema Mechanism: NH₃ depletes α-ketoglutarate → TCA cycle impaired → energy failure in brain; also forms glutamine astrocyte swelling --- Q8. GFR, Renal Threshold, Obligatory Urine Volume, Transport Maximum, Plasma Clearance — 5 GFR Glomerular Filtration Rate: Volume of plasma filtered per unit time by the glomeruli. - Normal: 125 mL/min 180 L/day - Measured by: Inulin clearance gold standard, creatinine clearance clinical - Formula: GFR = U × V / P urine conc × urine flow / plasma conc Renal Threshold: Plasma concentration of a substance above which it begins to appear in urine renal excretion starts. - Glucose renal threshold = 180 mg/dL glucose appears in urine = glycosuria Obligatory Urine Volume: Minimum urine output required to excrete the daily solute load even with maximum ADH. - ≈ 500 mL/day Transport Maximum Tm: Maximum rate at which renal tubules can reabsorb or secrete a substance. - Glucose Tm = 375 mg/min males, 300 mg/min females - Above Tm, excess glucose spills into urine Plasma Clearance: Volume of plasma completely cleared of a substance per unit time. - Formula: C = U × V / P - Inulin clearance = GFR neither reabsorbed nor secreted - PAH clearance = renal plasma flow 625 mL/min --- Q9. Osmotic Diuresis in Uncontrolled DM — 2+3 Definition: Osmotic diuresis is increased urine output driven by non-reabsorbable solutes e.g., glucose in the tubular lumen, which osmotically obligate water excretion. How it develops in uncontrolled DM: 1. Blood glucose exceeds renal threshold 180 mg/dL 2. Glucose exceeds Tm 375 mg/min → glucose not fully reabsorbed 3. Glucose in tubular lumen creates high osmotic pressure 4. Water and electrolytes Na⁺, K⁺, Cl⁻ are obligatorily excreted with glucose 5. Result: polyuria, polydipsia, dehydration, electrolyte loss --- Q10. Hormones Acting on Distal Tubule / Water Intoxication — 2+2+1 Hormones acting on distal tubule of kidney: Hormone Action ------ ADH Vasopressin Increases water reabsorption via AQP2 channels in DCT and collecting duct Aldosterone Increases Na⁺ reabsorption and K⁺/H⁺ secretion in DCT and collecting duct PTH Increases Ca²⁺ reabsorption in DCT Atrial Natriuretic Peptide ANP Inhibits Na⁺ reabsorption → natriuresis Water Intoxication: Excessive intake of water → dilutional hyponatremia → cells swell due to osmosis → cerebral edema. - Symptoms: Headache, nausea, confusion, seizures, coma - Plasma Na⁺ drops below 135 mEq/L Water Turnover: Daily water input ≈ output ≈ 2.5 L/day - Input: Beverages 1.5L + food 0.8L + metabolic water 0.2L - Output: Urine 1.5L + insensible loss 0.9L + stool 0.1L --- Q11. Water Intake-Output Chart / Water Homeostasis — 2+1+1 Adult Male Daily Water Balance: Input Volume Output Volume ------------ Drinking water/beverages 1200–1500 mL Urine 1000–1500 mL Food solid 700–1000 mL Insensible skin + lungs 800–1000 mL Metabolic oxidation water 200–300 mL Sweat 100–200 mL Feces 100–200 mL Total Input 2500 mL Total Output 2500 mL Importance of Water Balance: - Maintains plasma osmolality 285–295 mOsm/kg - Regulates blood pressure and circulating volume - Maintains electrolyte concentrations - Regulates body temperature - Enables metabolic reactions and nutrient transport --- Q12. Sources of Acids in Body / Role of Kidney in Acid-Base Balance — 2+3 Sources of Acids in the Body: 1. Volatile acid: CO₂ + H₂O → H₂CO₃ excreted by lungs — 13,000–20,000 mEq/day 2. Non-volatile fixed acids: - Sulfuric acid from sulfur-containing amino acids — cysteine, methionine - Phosphoric acid from phospholipids, nucleotides - Lactic acid anaerobic glycolysis - Ketoacids beta-hydroxybutyrate, acetoacetate — from fat oxidation/starvation/DM - Hydrochloric acid incomplete absorption Role of Kidney in Acid-Base Balance: 1. Bicarbonate reabsorption: 85% in PCT; reabsorbs filtered HCO₃⁻ via H⁺ secretion 2. Titratable acid excretion: H⁺ buffered by phosphate HPO₄²⁻ → H₂PO₄⁻ in tubular fluid 3. Ammoniagenesis: Glutamine → NH₃ in PCT → combines with H⁺ → NH₄⁺ excreted → new HCO₃⁻ generated 4. Net acid excretion NAE = titratable acid + NH₄⁺ − bicarbonate lost in urine --- Q13. Asthmatic Patient — Acid-Base Disorder — 2+3 Lab values: pH = 7.1, PCO₂ = 55 mmHg, Na⁺ = 141, K⁺ = 6.8 mmol/L Acid-Base Disorder: Respiratory Acidosis - pH 7.35 → acidosis - PCO₂ = 55 mmHg ↑, normal 35–45 → respiratory cause - In respiratory distress, CO₂ retention → H₂CO₃ ↑ → H⁺ ↑ → acidosis Electrolyte Disturbance: - K⁺ = 6.8 mmol/L → Hyperkalemia normal 3.5–5.0 - In acidosis, H⁺ moves intracellularly and K⁺ moves out of cells → hyperkalemia - Na⁺ = 141 mmol/L → normal Acid-Base Disorder Classification: Parameter Normal This Patient --------- pH 7.35–7.45 7.1 ↓ → Acidosis PCO₂ 35–45 mmHg 55 ↑ → Respiratory HCO₃⁻ 22–26 mEq/L Likely elevated compensation Diagnosis: Acute Respiratory Acidosis in asthma — bronchospasm → CO₂ retention --- Q14. Na⁺ and K⁺ Homeostasis / Electrolyte Profile / Calcium in Blood — 2+4+2+2 Na⁺ and K⁺ Homeostasis: - Na⁺: Primary ECF cation; regulated by aldosterone ↑ reabsorption, ANP ↑ excretion, ADH water balance - K⁺: Primary ICF cation; regulated by aldosterone ↑ K⁺ excretion in DCT, insulin drives K⁺ into cells, acid-base status, catecholamines Reference Values of Electrolytes: Electrolyte Normal Range ------ Na⁺ 135–145 mEq/L K⁺ 3.5–5.0 mEq/L Cl⁻ 96–106 mEq/L HCO₃⁻ 22–26 mEq/L Ca²⁺ 8.5–10.5 mg/dL 2.1–2.6 mmol/L Mg²⁺ 1.5–2.5 mEq/L PO₄³⁻ 2.5–4.5 mg/dL Calcium in Blood — Description and Functions: Total serum Ca²⁺ 10 mg/dL exists as: - 50% ionized Ca²⁺ — biologically active - 40% protein-bound mainly albumin - 10% complexed with citrate, phosphate Functions: 1. Neuromuscular excitability hypocalcemia → tetany 2. Muscle contraction Ca²⁺-troponin-C interaction 3. Enzyme cofactor coagulation cascade — factors II, VII, IX, X 4. Bone mineralization with phosphate → hydroxyapatite 5. Second messenger calmodulin-dependent pathways 6. Exocytosis and neurotransmitter release Hormones involved in Ca homeostasis: - PTH: ↑ bone resorption, ↑ renal Ca²⁺ reabsorption, ↑ 1,25-OH₂D₃ → ↑ serum Ca²⁺ - Calcitriol Vit D3: ↑ intestinal Ca²⁺ absorption - Calcitonin: ↓ bone resorption → ↓ serum Ca²⁺ --- TRUE/FALSE MCQ — Questions 1–10 1. Low energy phosphates: - a. ADP — TRUE low energy compared to ATP - b. ATP — FALSE ATP is high energy - c. AMP — TRUE low energy - d. Glucose-6-phosphate — FALSE not a "high energy" phosphate, but not classified as low-energy nucleotide - e. Fructose-6-phosphate — FALSE same as above 2. Proteolytic enzymes: - a. Pepsinogen — TRUE zymogen; active pepsin is proteolytic - b. Lingual lipase — FALSE lipolytic, not proteolytic - c. Trypsinogen — TRUE active trypsin is proteolytic - d. Pancreatic amylase — FALSE amylolytic - e. Carboxypeptidase — TRUE proteolytic — pancreatic exopeptidase 3. Metabolic pathways in mitochondria: - a. Glycolysis — FALSE occurs in cytoplasm - b. Citric acid cycle — TRUE mitochondrial matrix - c. Beta-oxidation of fatty acids — TRUE mitochondrial matrix - d. Glycogenolysis — FALSE cytoplasm - e. Pentose phosphate pathway — FALSE cytoplasm 4. Substrates for gluconeogenesis: - a. Lactate — TRUE - b. Propionate — TRUE odd-chain FA → succinyl-CoA → gluconeogenic - c. Glycerol — TRUE - d. Fatty acid — FALSE even-chain FAs → Acetyl-CoA only; cannot make glucose in mammals - e. Cholesterol — FALSE 5. Beta-oxidation of fatty acids: - a. Occurs in cytosol — FALSE mitochondrial matrix - b. Generates Acetyl-CoA — TRUE - c. Occurs at 5th carbon — FALSE occurs at beta/2nd carbon, C-3 - d. Major source of energy in brain — FALSE glucose is; brain cannot use FAs well; uses ketones in starvation - e. Requires nicotinic acid — FALSE requires FAD which contains riboflavin/B2, and NAD⁺ which contains niacin/B3 — nicotinic acid is niacin = B3 → partially TRUE, so TRUE 6. Salient features of HMP shunt: - a. Glucose-6-phosphate is the substrate — TRUE - b. De-oxy ribose sugar is the product — FALSE ribose-5-phosphate is the product, not deoxyribose - c. It is anabolic in nature — TRUE provides NADPH for biosynthesis - d. ATP is produced — FALSE no ATP produced - e. Glucose-6-phosphate dehydrogenase is the rate-limiting enzyme — TRUE 7. In water diuresis: - a. Urinary osmolarity is hypertonic — FALSE hypotonic urine - b. ADH concentration is decreased — TRUE low ADH → water diuresis - c. Electrolyte loss is marked — FALSE water diuresis is free water loss, electrolytes relatively preserved - d. Cause is excess water intake — TRUE - e. Water reabsorption from DCT and CD is increased — FALSE it is decreased due to low ADH 8. Factors causing potassium influx into cells: - a. Acidosis — FALSE acidosis → H⁺ moves in, K⁺ moves out = efflux - b. Alkalosis — TRUE alkalosis → K⁺ moves into cells - c. Insulin — TRUE stimulates Na⁺/K⁺-ATPase → K⁺ into cells - d. Glucagon — FALSE promotes K⁺ efflux - e. Aldosterone — FALSE promotes K⁺ excretion = efflux from tubular cells 9. High anion gap metabolic acidosis: Anion gap = Na⁺ − Cl⁻ + HCO₃⁻; normal 8–12; high AG = accumulation of unmeasured anion - a. Renal failure — TRUE phosphates, sulfates accumulate - b. Lactic acidosis — TRUE lactate is unmeasured anion - c. Diarrhoea — FALSE normal AG/hyperchloremic metabolic acidosis — HCO₃⁻ loss - d. Bronchial asthma — FALSE causes respiratory acidosis - e. Diabetic ketoacidosis — TRUE ketone bodies = unmeasured anions 10. Respiratory acidosis is characterized by: - a. Increased blood PCO₂ level — TRUE hallmark - b. Compensatory decrease in plasma bicarbonate — FALSE compensation is INCREASE in HCO₃⁻ by kidneys - c. Compensatory increase in plasma bicarbonate — TRUE renal compensation - d. Compensation by respiratory system — FALSE the respiratory system IS the cause; compensation is renal - e. Can produce tetany — FALSE tetany occurs in alkalosis; acidosis → hyperkalemia, not tetany --- SINGLE BEST ANSWER SBA — Questions 11–20 11. Major ICF cation: → b. K⁺ potassium is the principal intracellular cation 12. HMP shunt: → d. Product is ribose ribose-5-phosphate is the product; occurs in cytoplasm; produces NADPH not ATP; substrate is G6P not ribose 13. Component of lipoprotein: → c. Phospholipid phospholipids form the outer shell of lipoproteins along with apolipoproteins and free cholesterol 14. Rate-limiting enzyme of cholesterol biosynthesis: → d. HMG-CoA reductase converts HMG-CoA to mevalonate; target of statins 15. Urea cycle: → c. Anabolic in nature urea cycle builds urea; it is actually a catabolic/amphibolic process for nitrogen disposal — more accurately it is neither purely anabolic nor catabolic, but the BEST answer among options is anabolic in nature; actually urea synthesis is energy-consuming. However, "anabolic" = uses ATP. The best answer is c as it uses ATP and synthesizes urea. Note: it does NOT occur only in mitochondria both mito and cytoplasm; NOT in brain liver only; thiolase is NOT rate-limiting CPS-I is; source of N is NH₃ and aspartate, NOT CO₂. 16. Lipolytic enzyme: → c. Pancreatic lipase hydrolyzes dietary triglycerides in small intestine 17. Non-protein nitrogenous NPN substance: → a. Uric acid and c. Creatinine — both are NPN. But as single best: c. Creatinine along with urea, uric acid, ammonia — all NPNs. Fibrinogen, albumin, globulin are proteins. Best answers are uric acid or creatinine; a. Uric acid is classic NPN 18. Obligatory urinary volume: → c. 500 mL/day minimum urine output to excrete daily solute load 19. Factor causing increased renin secretion: → c. Hypovolemia decreased renal perfusion pressure → JGA cells release renin; ADH does NOT increase renin; angiotensin II and hypernatremia/hypervolemia inhibit renin 20. Cause of respiratory alkalosis: → c. Hysteria hyperventilation in hysteria → CO₂ blown off → respiratory alkalosis; bronchial asthma and chronic bronchitis cause respiratory acidosis; vomiting and diarrhoea cause metabolic disorders --- All answers based on standard medical biochemistry and physiology Harper's Biochemistry, Ganong's Physiology, Stryer's Biochemistry.
