Medical Biochemistry Exam Study Guide — MCQs OmpathStudy

Continued from $1. Medical Biochemistry Exam Study Guide SECTION A: MULTIPLE CHOICE QUESTIONS Question 1 The probability that disease is present when a test result falls outside reference interval is called the test's: A. SpecificityB. SensitivityC. Positive predictive valueD. EfficiencyE. Negative predictive value Answer: C. Positive predictive value Explanation: Positive predictive value (PPV) represents the probability that a patient actually has the disease when the test result is positive (outside reference interval). It depends on both test characteristics and disease prevalence. --- Question 2 The molecule that serves as the major source of readily available fuel for neurons and blood cells is: A. FatB. GlucoseC. Acetyl CoAD. CelluloseE. Glycogen Answer: B. Glucose Explanation: Glucose is the primary energy source for neurons and red blood cells. Neurons have limited ability to use alternative fuels, and RBCs lack mitochondria, making glucose essential for their ATP production via glycolysis. --- Question 3 Ammonia is an effective and important urinary buffer for which of the following reasons: A. Its production in the kidney decreases during chronic acidosisB. The walls of the renal tubules are impermeable to NH3C. The walls of the renal tubules are impermeable to NH4+D. Its acid base reaction has a low pKaE. None of the above Answer: C. The walls of the renal tubules are impermeable to NH4+ Explanation: NH3 diffuses into tubular fluid where it combines with H+ to form NH4+. The tubular membrane is impermeable to NH4+, effectively trapping it in urine and facilitating acid excretion. --- Question 4 Which of the choices below is not a fate of carbohydrate taken into the body: A. ATP productionB. LipogenesisC. Amino acid synthesisD. Conversion to a nucleic acidE. Glycogenesis Answer: D. Conversion to a nucleic acid Explanation: While carbohydrates can provide ribose for nucleic acid synthesis, they are not directly converted to nucleic acids. The other options are all direct metabolic fates of carbohydrates. --- Question 5 The amount of potassium excreted by the kidney will decrease if: A. Distal tubular flow increasesB. Circulating aldosterone levels increaseC. Dietary intake of potassium increasesD. Na+ reabsorption by the distal nephron decreasesE. The excretion of organic ions increases Answer: B. Circulating aldosterone levels increase Explanation: Aldosterone promotes Na+ reabsorption and K+ secretion in the distal nephron. However, when aldosterone levels increase, it also enhances overall K+ conservation mechanisms, leading to decreased K+ excretion. --- Question 6 Dietary fats are important because they: A. Keep blood pressure normalB. Help the body absorb fat-soluble vitaminsC. Contribute significantly to the health of the skinD. Help prevent the common coldE. None of the above Answer: B. Help the body absorb fat-soluble vitamins Explanation: Dietary fats are essential for absorption of fat-soluble vitamins (A, D, E, K) in the intestine. These vitamins require lipid micelles for proper absorption. --- Question 7 An increase in the concentration of plasma potassium causes increases in: A. Release of reninB. Secretion of aldosteroneC. Secretion of ADHD. Release of natriuretic hormoneE. Production of angiotensin II Answer: B. Secretion of aldosterone Explanation: Hyperkalemia directly stimulates aldosterone secretion from the adrenal cortex, which promotes K+ excretion in the distal nephron to restore K+ homeostasis. --- Question 8 When proteins undergo deamination, the waste substance found in the urine is mostly: A. Acetyl CoAB. Ketone bodiesC. UreaD. CreatinineE. Ammonia Answer: C. Urea Explanation: Protein deamination produces ammonia, which is converted to urea in the liver via the urea cycle. Urea is the major nitrogenous waste product excreted in human urine. --- Question 9 Glomerular filtration rate would be increased by: A. Constriction of the afferent arterioleB. A decrease in afferent arteriolar pressureC. Compression of the renal capsuleD. A decrease in the concentration of plasma proteinE. A decrease in renal blood flow Answer: D. A decrease in the concentration of plasma protein Explanation: Decreased plasma protein concentration reduces oncotic pressure, decreasing the force opposing filtration and thereby increasing GFR. --- Question 10 Lipogenesis occurs when: A. There is a shortage of fatty acidsB. Glucose levels drop slightlyC. Excess proteins are transported through the cell membraneD. StarvationE. Cellular ATP and glucose levels are high Answer: E. Cellular ATP and glucose levels are high Explanation: Lipogenesis (fat synthesis) occurs during fed state when energy (ATP) and substrate (glucose) are abundant, allowing conversion of excess carbohydrates to fat for storage. --- Question 11 The greatest amount of hydrogen ion secreted by the proximal tubule is associated with: A. Excretion of potassium ionB. Excretion of hydrogen ionC. Reabsorption of calcium ionD. Reabsorption