Biochemistry MCQs with Answer and Explanations | Chapter 5

Answer: Cyanmethemoglobin

The Cyanmethemoglobin method is the recommended standard for hemoglobin determination due to its accuracy and reliability.

The other options are incorrect:

• Methemoglobin: This is an abnormal form of hemoglobin that cannot carry oxygen. While it can be measured in some tests, it’s not the recommended method for determining total hemoglobin concentration.
• Oxyhemoglobin: This is the form of hemoglobin that carries oxygen in red blood cells. Similar to methemoglobin, it’s not directly measured for total hemoglobin concentration.
• Sulfhemoglobin: Another abnormal form of hemoglobin that cannot carry oxygen. It’s not used for routine hemoglobin determination.

Answer: 3-hydroxy butyric acid

Ketone bodies are a group of three molecules produced by the liver during periods of low blood sugar:

• Acetoacetic acid
• Acetone
• 3-hydroxy butyric acid (This is the main ketone body)

The other options are incorrect:

• Lactic acid: Lactic acid is produced by muscles during exercise and is not a ketone body.
• Acetic acid: While somewhat similar to acetoacetic acid, acetic acid is not a primary ketone body.
• Oxaloacetic acid: This is an intermediate molecule in the citric acid cycle, not a ketone body produced for energy.

Answer: Prehepatic bilirubin

Unconjugated bilirubin is the form produced from the breakdown of red blood cells before being processed by the liver. Prehepatic bilirubin is another term for unconjugated bilirubin.

The other options are incorrect:

• Conjugated bilirubin: This is the opposite of unconjugated bilirubin. It’s the form processed by the liver and ready for excretion.
• Biliverdin: Biliverdin is a green pigment that precedes bilirubin in the heme breakdown pathway.
• Total bilirubin: This refers to the sum of both conjugated and unconjugated bilirubin.

Answer: Peptide bonds

The biuret reaction specifically detects the presence of peptide bonds, which are the chemical linkages between amino acids in proteins. The number of peptide bonds directly correlates with the amount of protein present.

The other options are incorrect:

• Free amino acids: These are individual amino acids not yet linked into proteins and wouldn’t react in the biuret test.
• Free carboxyl groups: These functional groups exist in some amino acids but are not specific to proteins and wouldn’t be the target of the biuret reaction.
• Tyrosine residues: Tyrosine is a specific amino acid, but the biuret reaction doesn’t rely on individual amino acid types, just the presence of peptide bonds.

Answer: Parathyroid hormone

Parathyroid hormone (PTH) is the primary regulator of calcium concentration in the serum. It acts on bones, kidneys, and intestines to maintain calcium balance.

The other options are incorrect:

• Insulin: Insulin is primarily involved in regulating blood sugar levels, not calcium.
• Thyroxin: While thyroxin can indirectly affect calcium metabolism, it’s not the main regulator.
• Vitamin C: Vitamin C has various functions but doesn’t directly regulate calcium concentration.

Answer: Bilirubin diglucuronide

In the liver, bilirubin undergoes a process called conjugation where it binds with glucuronic acid. This makes bilirubin more water-soluble and allows it to be excreted in bile. Bilirubin diglucuronide is the main conjugated form of bilirubin.

The other options are incorrect:

• Urobilinogen: This is a breakdown product of bilirubin that occurs in the intestines, not the liver.
• Urobilin: Similar to urobilinogen, urobilin is another breakdown product formed further down the digestive tract.
• Bilirubin-albumin complex: This complex is how unconjugated bilirubin travels in the bloodstream before reaching the liver for processing. It’s not the final converted form.

Answer: Freezing point

Osmolality of a solution reflects the concentration of particles that contribute to osmotic pressure. A common method for measuring osmolality relies on the principle of freezing point depression. The more solutes (particles) present, the lower the temperature at which the solution freezes. By measuring this change in freezing point, osmolality can be determined.

The other options are incorrect:

• Sediment point: This doesn’t directly relate to osmolality. Sedimentation refers to the settling of particles, not a measure of solute concentration.
• Midpoint: There’s no specific “midpoint” relevant to osmolality measurement in this context.
• Osmotic pressure: While osmolality is related to osmotic pressure, it’s the freezing point change that’s directly measured in this technique.

Answer: Corticosterone

Corticosterone is a type of corticosteroid hormone produced by the adrenal cortex, a region of the adrenal gland. It plays a role in regulating various bodily functions, including stress response and metabolism.

The other options are incorrect:

• Angiotensinogen: This is a protein produced by the liver and is a precursor to angiotensin, a hormone involved in blood pressure regulation. It’s not a steroid hormone from the adrenal cortex.
• Progesterone: Primarily produced by the ovaries, progesterone is a sex hormone involved in the menstrual cycle and pregnancy. While the adrenal glands can produce small amounts, it’s not their main function.
• Pregnanetriol: This is a metabolite (breakdown product) of progesterone. While it can be measured in some tests, it’s not a primary hormone produced by the adrenal cortex.

Answer: Growth, third trimester of pregnancy

These two conditions lead to a natural increase in alkaline phosphatase due to:

• Growth: During bone growth in children and adolescents, there’s an increased production of alkaline phosphatase by osteoblasts (bone-forming cells).
• Third trimester of pregnancy: The placenta produces an alkaline phosphatase isoenzyme during pregnancy, leading to a physiological rise in serum levels.

The other options are incorrect:

• Rickets, hyperparathyroidism: These are pathological conditions that can cause abnormally high alkaline phosphatase levels, but they’re not considered “physiological” elevations.
• Obstructive jaundice: This condition can also elevate alkaline phosphatase due to bile duct blockage, but it’s not a physiological process.
• Viral hepatitis, infectious mononucleosis: These are viral infections that can damage the liver, leading to abnormal liver enzyme levels, including alkaline phosphatase. They’re not physiological increases.

Answer: Act as a carrier for ions

Act as carrier for ions: Buffer molecules contain charged particles (ions) that move freely in the electric field, carrying the current through the gel.

The other options are incorrect:

• Stabilize electrolytes: While buffers can indirectly influence electrolyte stability by maintaining a constant pH, their primary function is not directly stabilizing electrolytes.
• Maintain basic pH: Buffers can maintain a specific pH range, but this isn’t always basic. The appropriate pH depends on the type of electrophoresis being performed.
• Produce an effect on protein configuration: While the electrical field in electrophoresis can affect protein conformation to some extent, it’s not the buffer’s primary function. Buffers primarily act as ion carriers.

Answer: Calculations of blood PH and total CO2 concentration

Blood PCO2 is commonly measured by using the Henderson-Hasselbalch equation, which requires knowing the blood pH and total CO2 concentration.

The other options are incorrect:

• Direct colorimetric measurement of dissolved CO2: This method is not specific for CO2 and can be affected by other dissolved gases in the blood.
• Measurement of CO2-saturated hemoglobin: This only measures the amount of CO2 bound to hemoglobin, not the free PCO2 level in the blood.
• Measurement of CO2 consumed at the cathode: This is not a standard method for measuring PCO2 in blood gas analysis.

Answer: Glucose

Glucose is a relatively unstable molecule at room temperature. When left unprocessed for extended periods, blood cells in the sample can continue to consume glucose for energy, leading to a decrease in the measured blood glucose concentration.

The other options are incorrect:

• Cholesterol: Cholesterol is a fairly stable molecule and remains relatively unchanged at room temperature for 8 hours.
• Triglyceride: Similar to cholesterol, triglycerides are also relatively stable at room temperature for this timeframe.
• Creatinine: Creatinine is a waste product produced at a constant rate by muscles. It’s not significantly affected by storage time at room temperature for 8 hours.

Answer: Bicarbonate ion

Most of the carbon dioxide in the blood is transported in the form of bicarbonate ions (HCO3^-), which is formed when CO2 reacts with water in red blood cells.

The other options are incorrect:

• Dissolve CO2: While a small amount of CO2 dissolves directly in blood plasma, it’s not the major form of transport.
• Carbonate: Carbonate ions (CO3^2-) are present in much lower concentrations compared to bicarbonate ions in blood.
• Carbonic acid: Although formed as an intermediate step, carbonic acid quickly converts to bicarbonate and hydrogen ions.

Answer: Inhibits glycolysis

Sodium fluoride is an anticoagulant that inhibits glycolysis, thus preserving glucose levels in blood specimens by preventing the breakdown of glucose by enzymes in the blood cells.

The other options are incorrect:

• Serves as a coenzyme of hexokinase: Hexokinase is an enzyme involved in the initial step of glycolysis. Sodium fluoride does not act as a coenzyme for this enzyme.
• Prevents reactivity of non-glucose reducing substances: While sodium fluoride may have some minor effects on other substances in the blood, its primary function is to inhibit glycolysis of glucose.
• Precipitates proteins: Sodium fluoride does not significantly precipitate proteins at the concentrations used in blood collection tubes.

Answer: Estrogens

Estrogens are characterized by an unsaturated A ring, which is a distinguishing feature of their chemical structure.

The other options are incorrect:

• Progestins Progestins do not have an unsaturated A ring; they have a different chemical structure primarily involved in regulating the menstrual cycle and pregnancy.
• Androgens Androgens, like testosterone, do not have an unsaturated A ring; they are primarily involved in male traits and reproductive activity.
• Glucocorticoids Glucocorticoids, such as cortisol, do not have an unsaturated A ring; they are involved in the metabolism of carbohydrates, proteins, and fats and have anti-inflammatory properties.

Answer: Sodium

Sodium (Na+) is the major contributor to serum osmolality. It’s the most abundant electrolyte in the blood plasma and plays a significant role in maintaining the balance of water in and out of cells.\

The other options are incorrect:

• Glucose: While glucose can contribute to osmolality, its concentration is typically much lower than sodium and has a smaller overall impact.
• Chloride (Cl-): Chloride is the major anion balancing sodium, but it exists in a 1:1 ratio with sodium. So, its contribution is inherently linked to sodium.
• Urea: Urea is another molecule that can affect osmolality, but its concentration is generally lower than both sodium and glucose.

Answer: Lactic acidosis

Lactic acidosis increases the serum anion gap because it introduces an excess of lactate, an anion, into the blood, leading to a higher concentration of unmeasured anions.

The other options are incorrect:

• Renal tubular acidosis: This is a type of acidosis where the kidneys have difficulty excreting acid or reabsorbing bicarbonate. It can sometimes cause a normal or even decreased anion gap depending on the specific type.
• Diabetic alkalosis: This condition is characterized by a loss of bicarbonate and an increase in blood pH (alkalosis). It would not typically cause an increased anion gap.
• Metabolic acidosis due to diarrhea: While diarrhea can lead to electrolyte imbalances and acidosis, it doesn’t usually cause a significant increase in unmeasured anions and the anion gap may be normal or even slightly decreased.

Answer: Hyperventilation

Hyperventilation refers to abnormally rapid or deep breathing that leads to a decrease in carbon dioxide (CO2) levels in the blood. This disrupts the blood’s pH balance, causing respiratory alkalosis (blood pH becomes too alkaline).

The other options are incorrect:

• Vomiting: While vomiting can sometimes lead to a temporary respiratory alkalosis due to expulsion of acidic stomach contents, it’s not a common cause.
• Starvation: Starvation can lead to metabolic changes that might influence acid-base balance, but it’s not a typical cause of respiratory alkalosis.
• Asthma: Asthma is a chronic respiratory condition that can cause difficulty breathing, but it doesn’t directly lead to hyperventilation or respiratory alkalosis unless there’s severe airflow obstruction.

Answer: Sodium, potassium, chloride, and total CO2

The anion gap is a calculation based on the concentrations of routinely measured electrolytes (sodium, potassium, chloride) and an estimate of bicarbonate derived from total CO2. It helps identify potential errors or inconsistencies in these core electrolyte measurements.

The other options are incorrect:

• Amino acids and proteins: The anion gap calculation doesn’t involve these components.
• Blood gas analyses: While blood gas analysis includes CO2 measurement, the anion gap specifically focuses on electrolytes and their relationship.
• Calcium, phosphorus, and magnesium: These electrolytes are not directly involved in the anion gap calculation.

Answer: Sodium

Sodium is the chief plasma cation responsible for maintaining osmotic pressure and fluid balance in the body. It plays a crucial role in regulating water distribution and maintaining cellular integrity.

The other options are incorrect:

• Chloride Chloride is an important electrolyte for maintaining electrolyte balance and acid-base equilibrium but is not the primary cation responsible for osmotic pressure regulation.
• Calcium Calcium is essential for bone health, muscle contraction, and nerve function but does not primarily regulate osmotic pressure in the blood plasma.
• Potassium Potassium is crucial for muscle function, nerve transmission, and maintaining cellular function but is not the chief plasma cation responsible for osmotic pressure maintenance

Answer: 0.5

Here’s how to calculate the molarity (M) of the solution:

1. Convert grams of KCl to moles:
   • Moles of KCl = mass (g) / molar mass (g/mol)
   • Moles of KCl = 18.7 g / 74.5 g/mol = 0.25 moles
2. Convert volume of water to liters:
   • Volume (L) = Volume (mL) / 1000 mL/L
   • Volume (L) = 500 mL / 1000 mL/L = 0.5 L
3. Calculate Molarity:
   • Molarity (M) = Moles / Volume (L)
   • Molarity (M) = 0.25 moles / 0.5 L = 0.5 M

Therefore, the molarity of the solution is 0.5 M.

The other options are incorrect:

• 0.1 M and 1.0 M: These values are too low or high based on the concentration of KCl and the volume of water.
• 5.0 M: This value is significantly too high, likely due to a miscalculation in the conversion or unit factors.

Answer: Bicarbonate buffer

Acidosis and alkalosis are defined by changes in blood pH and CO2 content primarily due to alterations in the bicarbonate buffer system. This system involves the reversible exchange of CO2 and bicarbonate ions (HCO3^-) regulated by the lungs and kidneys to maintain acid-base balance.

The other options are incorrect:

• Bohr’s effect: The Bohr effect describes how changes in blood pH and CO2 levels can affect hemoglobin’s affinity for oxygen. While it can indirectly influence acid-base balance, it’s not the primary cause of acidosis or alkalosis.
• O2 content: Changes in oxygen content primarily affect oxygen delivery to tissues and cellular respiration. It doesn’t directly cause significant fluctuations in blood pH on its own.
• Carbonic anhydrase: This enzyme facilitates the conversion of CO2 and water into carbonic acid in red blood cells. While crucial for the bicarbonate buffer system to function, changes in carbonic anhydrase activity itself wouldn’t be the primary driver of acidosis or alkalosis.

Answer: Increase in CO2 content and PCO2 with a decreased pH

Metabolic acidosis is characterized by a primary decrease in bicarbonate (HCO3^-) levels or an increase in non-carbonic acids in the body fluids, leading to a decreased pH. This condition does not directly affect CO2 levels in the blood.

The other options are incorrect:

Answer: 7.35-7.45

The normal range for the pH of arterial blood measured at 37 degrees Celsius is 7.35-7.45. This range reflects a healthy balance between acids and bases in the blood, which is crucial for many physiological processes.

The other options are incorrect:

• 7.28-7.34 This range indicates acidosis, specifically metabolic acidosis, where the pH is lower than normal.
• 7.33-7.37 This range is slightly below the normal physiological pH range and would suggest a mild acidosis if consistently measured in arterial blood.
• 7.45-7.50 This range indicates alkalosis, where the pH is higher than normal. Alkalosis can result from conditions such as hyperventilation or excessive bicarbonate intake.

Answer: Glass

The pH in blood is most commonly measured using a glass electrode. This type of electrode has a special glass membrane that is permeable to hydrogen ions (H+). The concentration of H+ ions in the blood solution affects the electrical potential across the membrane, which is then measured to determine the pH.

The other options are incorrect:

• Silver and Platinum: These electrodes are not typically used for pH measurement in biological samples like blood. They might be used for other types of electrochemical measurements.
• Platinum-lactate: This is not a standard electrode for blood pH measurement. While lactate sensors exist, they are separate from pH electrodes and measure blood lactate concentration, not hydrogen ion concentration.

Answer: Glycolysis

Glycolysis is the metabolic pathway that breaks down glucose (a hexose sugar) or other six-carbon sugars into pyruvate or lactate. It’s the primary pathway for cellular energy production in the absence of sufficient oxygen (anaerobic conditions).

The other options are incorrect:

• Glycogenesis: This process refers to the synthesis of glycogen (storage form of glucose) from glucose or other precursors. It’s the opposite of glycolysis.
• Glycogenolysis: This is the breakdown of glycogen back into glucose, which can then be used for energy. While it can indirectly lead to pyruvate or lactate formation through subsequent glycolysis, it’s not the direct conversion process.
• Gluconeogenesis: This pathway creates new glucose molecules from non-carbohydrate precursors like amino acids or lactate

Answer: Sodium and potassium

Sodium and potassium have a reciprocal relationship in cellular ion exchange mechanisms, where sodium ions (Na+) are actively pumped out of cells, and potassium ions (K+) are pumped in, maintaining cellular osmotic balance and membrane potential.

The other options are incorrect:

• Calcium and phosphorus: While calcium (Ca2+) and phosphorus (PO43-) work together in bone health and other functions, their transport mechanisms across cell membranes are not directly reciprocal.
• Chloride (Cl-) and CO2: These are not directly involved in a reciprocal transport relationship. Chloride primarily balances the charge of cations like Na+ and K+, while CO2 has a separate transport system.
• Calcium and magnesium: Similar to calcium and phosphorus, these electrolytes have important roles but don’t exhibit a well-defined reciprocal transport relationship across cell membranes.

Answer: Increase in CO2 content and PCO2 with a decreased pH

Respiratory acidosis occurs when there is an increase in the partial pressure of carbon dioxide (PCO2) in the blood, leading to an increase in CO2 content, which subsequently lowers the blood pH.

The other options are incorrect:

• Decrease in CO2 content with an increased pH: This scenario describes respiratory alkalosis, the opposite condition where excessive CO2 is removed, leading to a decrease in CO2 content, PCO2, and a rise in blood pH (more alkaline).
• Increase in CO2 content with an increased pH: This is not a typical acid-base imbalance. An increase in CO2 content would tend to drive the pH down, not up.
• Decrease in CO2 content and PCO2 with a decreased pH: This could be caused by metabolic acidosis, where an unrelated acid buildup (not due to CO2) lowers pH. However, respiratory acidosis specifically involves CO2 retention.

Answer: LDL

LDL, also known as “bad cholesterol,” is the primary carrier of cholesterol in the blood, transporting 60-75% of plasma cholesterol. It delivers cholesterol to peripheral tissues for various functions. High LDL levels are associated with increased risk of atherosclerosis and cardiovascular disease.

The other options are incorrect:

• Chylomicrons: These are large lipoproteins that transport dietary fat (triglycerides) from the intestines to tissues. They carry a smaller amount of cholesterol compared to LDL.
• VLDL (Very-low-density lipoprotein): VLDL transports triglycerides synthesized in the liver to peripheral tissues. It also carries some cholesterol but to a lesser extent than LDL. As VLDL gets metabolized, it contributes to the formation of LDL.
• HDL (High-Density Lipoprotein): HDL is known as “good cholesterol” because it helps remove excess cholesterol from peripheral tissues and transports it back to the liver for excretion. It carries a much smaller percentage of total cholesterol compared to LDL.

Answer: Thyroxine-binding globulin

The measurement of total T4 (thyroxine) by competitive protein binding or displacement assays relies on the specific binding properties of thyroxine-binding globulin (TBG), a protein that binds and transports thyroid hormones in the bloodstream.

The other options are incorrect:

• Thyroxine-binding prealbumin (TBPA): While TBPA can bind T4, its binding affinity is significantly lower compared to TBG. It plays a less prominent role in competitive protein binding assays for total T4 measurement.
• Albumin: Albumin also binds T4, but to a much lesser extent than TBG or TBPA. Its contribution is usually considered negligible in this context.
• Thyroid-stimulating hormone (TSH): TSH is a hormone produced by the pituitary gland that regulates thyroid hormone production. It doesn’t bind to T4 in this assay.

Answer: T4 by RIA

T4 by RIA (Radioimmunoassay) employs a highly specific antibody to thyroxine (T4) to measure the concentration of T4 in a sample. This method uses radioactive isotopes to detect the binding of T4 to its specific antibody.

The other options are incorrect:

• Total T4 by competitive protein binding: As mentioned previously, competitive protein binding assays can have various formats, and not all involve a specific T4 antibody.
• T4 by column: Column chromatography separates molecules based on their interaction with the stationary phase in the column. Antibodies are not typically involved.
• T4 by equilibrium dialysis: This technique separates molecules based on their ability to diffuse across a semipermeable membrane. Antibodies are not used in this method.

Answer: CK

Creatine Kinase (CK) is the first enzyme to become elevated in the blood following a myocardial infarction (heart attack). This occurs because CK is abundant in heart muscle cells, and when these cells are damaged due to a heart attack, CK leaks into the bloodstream.

The other options are incorrect:

• LD (Lactate Dehydrogenase): LD levels also rise after a heart attack, but the increase occurs slightly later than CK.
• AST (Aspartate Aminotransferase): Similar to LD, AST levels increase after a heart attack but with a slower rise compared to CK.
• ALT (Alanine Aminotransferase): ALT is primarily found in the liver and is not a specific marker for heart muscle damage. While it can be elevated in some liver diseases that may co-occur with heart problems, it wouldn’t be the first enzyme to rise solely due to a myocardial infarction.

Answer: Alkaline picrate solution to yield and orange-red complex

In the Jaffe reaction, creatinine reacts with alkaline picrate solution to form a colored complex that is measured photometrically. This reaction is used for the quantitative determination of creatinine in clinical laboratory testing.

The other options are incorrect:

• Alkaline sulfasalazine solution: Sulfasalazine is not typically used in the Jaffe reaction.
• Potassium iodide: Potassium iodide can be used in some other colorimetric reactions, but it doesn’t form a complex with creatinine in the Jaffe reaction.
• Sodium nitroferricyanide: Similar to potassium iodide, sodium nitroferricyanide is not a reagent used in the Jaffe reaction for creatinine measurement.

Answer: Uric acid

Humans lack the enzyme uricase, which is necessary to further convert uric acid into allantoin, a more soluble waste product. Therefore, uric acid becomes the final product of purine metabolism in our bodies.

The other options are incorrect:

• AMP and GMP: These are nucleotides, the building blocks of RNA and DNA, but they are not the end products of purine metabolism. They can be further broken down.
• DNA and RNA: These are nucleic acids formed from nucleotides, not the end products of purine breakdown.
• Allantoin: This is the final product of purine catabolism in many mammals, but humans lack the enzyme to convert uric acid to allantoin.

Answer: Hepatobiliary disease

Bile acid concentrations are useful for assessing hepatobiliary disease because they can indicate impaired liver function or obstruction of the bile ducts, leading to changes in bile acid metabolism and excretion.

The other options are incorrect:

• Diabetes mellitus: While diabetes can affect various aspects of metabolism, it doesn’t directly impact bile acid production or metabolism. Bile acid concentrations are not typically used to diagnose diabetes.
• Intestinal Malabsorption: Intestinal malabsorption problems can affect nutrient uptake from food, but they don’t directly involve bile acid metabolism. Bile acids might be indirectly affected if fat malabsorption is present, but it’s not a primary use of the test.
• Kidney function: The kidneys are not majorly involved in bile acid metabolism. Bile acids are primarily eliminated through bile excretion, not the kidneys. Kidney function tests typically assess blood urea nitrogen, creatinine, and other markers related to kidney function.

Answer: Human Chorionic gonadotropin (HCG)

Human Chorionic Gonadotropin (HCG) is a hormone produced by the placenta during pregnancy. It is used for the early detection of pregnancy in urine and blood tests because its levels rise rapidly in the early weeks of pregnancy.

The other options are incorrect:

• Follicle-stimulating hormone (FSH) and Luteinizing hormone (LH): These hormones are produced by the pituitary gland and are involved in ovulation and early follicle development. Their levels are not typically used for pregnancy detection.
• Progesterone: Progesterone is produced by the corpus luteum in the ovary during the menstrual cycle and early pregnancy. While it’s important for pregnancy, it’s not a placental hormone and not the primary marker used for early detection.

Answer: Iron deficiency anemia

Decreased serum iron levels combined with an increased Total Iron Binding Capacity (TIBC) is indicative of iron deficiency anemia. In this condition, the body lacks sufficient iron to produce hemoglobin, leading to decreased serum iron levels, while TIBC increases as the body attempts to bind more iron.

The other options are incorrect:

• Anemia of chronic infection Anemia of chronic infection (also known as anemia of chronic disease) is characterized by decreased serum iron but typically with a normal or decreased TIBC due to impaired iron release from stores.
• Chronic liver disease Chronic liver disease can lead to disturbances in iron metabolism but does not typically result in increased TIBC. Iron levels may vary depending on the specific liver condition.
• Nephrosis Nephrotic syndrome can lead to loss of proteins, including iron-binding proteins, but it usually results in decreased TIBC due to protein loss, not increased TIBC.

Answer: Urea

Urea is the primary excretory form of nitrogen in humans. It is formed in the liver from ammonia produced by the breakdown of amino acids and is excreted by the kidneys in urine.

The other options are incorrect:

• Amino acids: While amino acids contain nitrogen, they are the building blocks of proteins and are not typically excreted in large amounts.
• Creatinine: Creatinine is a waste product from muscle breakdown, but it’s a much smaller contributor to overall nitrogen excretion compared to urea.
• Uric acid: Uric acid is another nitrogenous waste product, but it’s the main form excreted by some animals like birds and reptiles. Humans excrete a smaller amount of uric acid compared to urea.

Answer: Cholesterol

Cholesterol is the precursor molecule for the biosynthesis of all steroid hormones, including androgens (male sex hormones) and estrogens (female sex hormones). The body modifies cholesterol through a series of enzymatic reactions to produce these specific hormones.

The other options are incorrect:

• Cortisol: Cortisol is a steroid hormone itself, but it belongs to the glucocorticoid class and is derived from cholesterol, not the other way around.
• Catecholamines: These are signaling molecules derived from the amino acid tyrosine, not cholesterol.
• Progesterone: Progesterone is a specific steroid hormone involved in the menstrual cycle and pregnancy. While it’s part of the steroid hormone pathway, it’s further downstream from cholesterol in the biosynthesis process.

Answer: Diazotized sulfanilic acid

The Malloy and Evelyn method for bilirubin determination relies on the reaction between bilirubin and diazotized sulfanilic acid to form a colored azobilirubin complex. This colored complex can then be measured spectrophotometrically to quantify bilirubin levels in the sample.

The other options are incorrect:

• Dilute sulfuric acid: This acid solution might be used in the preparation of reagents or to adjust the pH of the reaction mixture, but it doesn’t directly react with bilirubin to form the colored complex.
• Diazonium sulfate: This is a general term for a type of diazonium salt. While diazotized sulfanilic acid is a specific type of diazonium salt used in the Malloy and Evelyn method, just “diazonium sulfate” wouldn’t be a precise description of the reagent.
• Sulfobromophthalein (BSP): This is a different compound used in some liver function tests, but it’s not the reagent that reacts with bilirubin in the Malloy and Evelyn method.

Answer: Valine, leucine, and isoleucine

Maple syrup urine disease (MSUD) is characterized by an increase in the urinary excretion of branched-chain amino acids (BCAAs): valine, leucine, and isoleucine. This occurs due to a deficiency in the enzyme complex responsible for their metabolism.

The other options are incorrect:

• Phenylalanine and Tyrosine: These are aromatic amino acids, not branched-chain amino acids. They are not primarily affected in Maple Syrup Urine Disease.
• Cystine and cysteine: These are sulfur-containing amino acids and are not specifically involved in MSUD.

Answer: Amylase (AMS)

Amylase is the enzyme that catalyzes the hydrolysis of starch into simpler sugars such as glucose and maltose. It is produced in the salivary glands and pancreas and aids in the digestion of carbohydrates in the digestive system.

The other options are incorrect:

• Malate dehydrogenase (MD): This enzyme participates in the citric acid cycle (Krebs cycle) for energy production and doesn’t directly convert starch.
• Creatine kinase (CK): This enzyme plays a role in energy transfer within muscle cells and doesn’t break down starch.
• Isocitric dehydrogenase (ICD): Similar to malate dehydrogenase, this enzyme is involved in the citric acid cycle and doesn’t act on starch.

Answer: Acute hepatitis

The greatest activities of serum AST (Aspartate Aminotransferase) and ALT (Alanine Aminotransferase) are typically seen in acute hepatitis. These enzymes are released into the bloodstream when liver cells are damaged or destroyed, as is common in acute hepatitis.

The other options are incorrect:

• Primary Biliary Cirrhosis In primary biliary cirrhosis, liver damage is chronic and progressive. While AST and ALT levels may be elevated, the highest activities are generally observed in acute conditions like acute hepatitis.
• Metastatic Hepatic Carcinoma Metastatic hepatic carcinoma involves the spread of cancer to the liver. While liver enzymes may be elevated, the pattern of elevation and enzyme activity levels differ from those typically seen in acute hepatitis.
• Alcoholic Cirrhosis In alcoholic cirrhosis, liver damage occurs due to chronic alcohol abuse. While AST and ALT levels may be elevated, they are typically not as markedly elevated as in acute hepatitis, where there is rapid and severe liver cell damage.

Answer: Dehydration

Increased serum albumin concentrations are seen in dehydration. Dehydration leads to a relative increase in the concentration of albumin in the blood due to a decrease in plasma volume, rather than an actual increase in albumin production.

The other options are incorrect:

• Nephrotic syndrome Nephrotic syndrome is characterized by increased urinary loss of albumin, leading to hypoalbuminemia (low serum albumin levels), not increased levels.
• Acute hepatitis In acute hepatitis, liver damage can lead to leakage of albumin into the extracellular space, resulting in decreased serum albumin levels, not increased levels.
• Chronic inflammation Chronic inflammation can affect liver function and lead to decreased synthesis of albumin, resulting in hypoalbuminemia, not increased levels.

Answer: Cysteine

Cysteine (symbol Cys or C) is the only amino acid among the listed options that contains a sulfhydryl group (also called a thiol group). This group consists of a sulfur atom bonded to a hydrogen atom (SH). The sulfhydryl group plays a crucial role in protein structure and function due to its ability to form disulfide bonds with other cysteine residues or to participate in various chemical reactions.

The other options are incorrect:

• Glycine: Glycine is the simplest amino acid and has a hydrogen atom as its side chain. It doesn’t contain a sulfhydryl group.
• Serine: Serine has a hydroxyl group (OH) attached to its side chain. While it has an oxygen atom, it lacks the characteristic sulfur atom of a sulfhydryl group.
• Tyrosine: Tyrosine has an aromatic ring structure with a hydroxyl group attached to its side chain. Similar to serine, it doesn’t have a sulfhydryl group.

Answer: Triglyceride

Triglyceride levels are significantly affected by recent food intake, so they are expected to be falsely elevated in a nonfasting patient. Postprandial triglycerides can increase due to the absorption of dietary fats.

The other options are incorrect:

• Cholesterol Cholesterol levels are less affected by recent food intake compared to triglycerides. They may show minor fluctuations but are not typically considered falsely elevated in a nonfasting state.
• HDL (High-Density Lipoprotein) HDL cholesterol levels are generally not significantly affected by recent food intake and are less likely to be falsely elevated in a nonfasting patient.
• LDL (Low-Density Lipoprotein) LDL cholesterol levels are also less influenced by recent food intake compared to triglycerides. They may vary slightly but are not expected to be falsely elevated in a nonfasting state to the same extent as triglycerides.

Answer: Chylomicrons

Turbidity in serum suggests the presence of chylomicrons, which are large lipoprotein particles containing dietary triglycerides. Chylomicrons can cause the serum to appear cloudy or turbid when viewed visually.

The other options are incorrect:

• Cholesterol Cholesterol does not cause turbidity in serum. It is a lipid molecule that is typically present in solution and does not affect the visual clarity of serum.
• Total protein Total protein, which includes albumin and globulins, does not cause turbidity in serum. Proteins are soluble molecules and do not contribute to the visual appearance of turbidity.
• Albumin Albumin is a major protein in serum and is soluble in water. It does not contribute to turbidity in serum.

Answer: Analyzed immediately

Cerebrospinal fluid (CSF) for glucose assay should be analyzed immediately after collection to obtain accurate results. Glucose levels in CSF can decrease rapidly if the sample is not processed promptly due to continued cellular metabolism.

The other options are incorrect:

• Refrigerated: While refrigeration might slow down some metabolic processes, it’s not the optimal approach for CSF glucose analysis. Delays due to cooling can still lead to some glucose degradation.Heated to 56 degrees Celsius: Heating the sample can denature enzymes and other proteins, potentially affecting the accuracy of the glucose assay.Stored at room temperature after centrifugation: Similar to refrigeration, room temperature storage can still allow for some glucose degradation, compromising the test’s reliability. Centrifugation might be a preliminary step to separate cells from the fluid, but the analysis should be performed on the cell-free supernatant as soon as possible.

Answer: True

Isozymes of the cytochrome P450 enzyme family, particularly CYP2C9, can significantly affect the metabolism of warfarin. Variations in CYP2C9 enzyme activity can lead to differences in how individuals metabolize and respond to warfarin therapy, influencing its efficacy and risk of adverse effects.

The other options are incorrect:

• False The metabolism of warfarin is indeed influenced by isozymes of the cytochrome P450 enzyme family, particularly CYP2C9.
• None there is no effect of isozymes on warfarin, which is incorrect. The presence and activity of specific isozymes like CYP2C9 are crucial in determining the pharmacokinetics and pharmacodynamics of warfarin.

Answer: Paul Ehrlich

Paul Ehrlich, a German scientist, proposed modern concepts of chemotherapy. He coined the term “magic bullet” and developed the concept of targeting specific pathogens or diseased cells with chemical substances, leading to the development of chemotherapy as a treatment for infectious diseases and cancer.

The other options are incorrect:

• Joseph Lister Joseph Lister is known for his contributions to antiseptic surgery and infection control, particularly through the use of carbolic acid (phenol) to disinfect surgical instruments and wounds. His work focused on preventing infections rather than chemotherapy.
• Elie Metchnikoff Elie Metchnikoff: was a Russian scientist known for his work on immunology and the discovery of phagocytes. His research focused on the immune system’s role in fighting infections and did not directly contribute to the development of chemotherapy.
• None of these: Paul Ehrlich is recognized for his significant contributions to the development of modern chemotherapy.