Hemoglobin and Iron Metabolism — MCQs

Hemoglobin and Iron Metabolism Indian Medical PG Practice Questions and MCQs

Question 201: The shown pattern in electrophoresis is due to:

A. Charges (Correct Answer)
B. Molecular weight
C. Bound oxygen
D. Hydrophobicity

Explanation: ***Charges*** - Electrophoresis separates molecules, such as **hemoglobin variants**, based on their **electrical charge** when placed in an electric field. - Different amino acid substitutions in hemoglobin lead to changes in net charge, causing them to migrate at different rates in the gel, as seen by the distinct bands for Hb A, Hb S/D, and Hb A2. *Molecular weight* - While molecular weight can influence migration in some electrophoretic techniques (e.g., SDS-PAGE), standard hemoglobin electrophoresis primarily separates based on **charge differences**, not molecular size. - All common hemoglobin variants have a very similar **molecular weight** (approximately 64,500 Da), so this factor would not effectively separate them into distinct bands. *Bound oxygen* - The amount of **bound oxygen** to hemoglobin does not significantly alter its overall electrical charge or molecular weight to cause distinct bands in electrophoresis. - Oxygen binding is a dynamic process and does not account for the **structural differences** in hemoglobin variants that lead to their electrophoretic separation. *Hydrophobicity* - Hydrophobicity is a characteristic of molecules, but it is not the primary principle by which standard **gel electrophoresis** separates hemoglobin variants. - Techniques like **hydrophobic interaction chromatography** would exploit hydrophobicity, not the electrophoretic gel shown.

Question 202: The single most sensitive tool for evaluating the iron status in an individual is

A. serum iron concentration
B. haemoglobin concentration
C. serum ferritin value (Correct Answer)
D. serum transferrin saturation

Explanation: ***serum ferritin value*** - **Serum ferritin** directly reflects the size of the body's iron stores and is the most sensitive indicator of **iron deficiency** in the preclinical stage. - A low serum ferritin value is highly specific for diagnosing **iron deficiency** before anemia develops. *serum iron concentration* - **Serum iron concentration** fluctuates throughout the day and is affected by many factors, making it a poor sole indicator of overall **iron status**. - It can be normal even in early stages of **iron deficiency** due to compensatory mechanisms. *haemoglobin concentration* - **Hemoglobin concentration** only falls in the late stages of **iron deficiency**, once **iron deficiency anemia** has developed. - It does not reflect early **iron depletion** or iron-deficient erythropoiesis. *serum transferrin saturation* - **Serum transferrin saturation** (TSAT) measures the amount of iron bound to transferrin and transporting iron, but it is less sensitive than ferritin for detecting early **iron deficiency**. - TSAT can be influenced by inflammation and other medical conditions, potentially masking true iron status.

Question 203: Which of the following interfere with iron absorption?

A. Myoglobin
B. Vitamin C
C. Phytates (Correct Answer)
D. Oxalate

Explanation: ***Phytates*** - **Phytates** (phytic acid), found in plant-based foods like whole grains, legumes, nuts, and seeds, are **potent inhibitors of non-heme iron absorption**. - They **chelate non-heme iron** and form insoluble complexes in the gastrointestinal tract, making it unavailable for absorption. - Phytates are considered **the most significant dietary inhibitor** of iron absorption among the options listed. *Myoglobin* - **Myoglobin is a heme-containing protein** found in muscle tissue and serves as an excellent dietary source of readily absorbable **heme iron**. - It does **not interfere** with iron absorption; instead, it provides bioavailable heme iron. *Vitamin C* - **Vitamin C** (ascorbic acid) significantly **enhances the absorption of non-heme iron** by reducing ferric iron (Fe³⁺) to ferrous iron (Fe²⁺), which is more soluble and bioavailable. - It counteracts the inhibitory effects of phytates and other dietary inhibitors. - This is an **absorption enhancer, not an inhibitor**. *Oxalate* - **Oxalate** (oxalic acid), found in foods like spinach, rhubarb, and beet greens, can also **interfere with iron absorption** by forming insoluble complexes with iron and other minerals. - However, oxalate is a **less potent inhibitor** compared to phytates, and its primary effect is on calcium absorption. - While it does reduce iron bioavailability, **phytates remain the more clinically significant inhibitor** of iron absorption.

Question 204: Reagent used in Apt test

A. Sodium bicarbonate
B. Sodium hydroxide (Correct Answer)
C. Potassium Chloride
D. Sodium chloride

Explanation: ***Sodium hydroxide*** - In the **Apt test**, a small amount of **fecal or vomitus sample** is mixed with water, and then **sodium hydroxide (NaOH)** is added. - **Fetal hemoglobin** (HbF) is resistant to denaturation by alkali, while **adult hemoglobin** (HbA) is denatured by alkali, turning the solution brown. *Sodium bicarbonate* - **Sodium bicarbonate** is primarily used as an antacid or in metabolic acidosis management. - It is not a component of the **Apt test**, which differentiates between fetal and maternal blood in infant stools or vomit. *Potassium Chloride* - **Potassium chloride** is an electrolyte used to treat or prevent low potassium levels. - It plays no role in the **Apt test** for detecting hemoglobin type. *Sodium chloride* - **Sodium chloride** (table salt) is used as an isotonic solution or electrolyte replacement. - It does not have the alkaline properties necessary for the denaturation of adult hemoglobin in the **Apt test**.

Question 205: A useful screening test for lead is measurement of which of the following?

A. Coproporphyrin in urine
B. Free erythrocyte protoporphyrin (FEP) (Correct Answer)
C. Aminolevulinic acid in urine
D. Lead in morning urine sample

Explanation: ***Free erythrocyte protoporphyrin (FEP)*** - **FEP (or Zinc Protoporphyrin - ZPP)** is the **most widely used screening test** for lead poisoning, particularly in occupational health and community screening programs. - Lead inhibits **ferrochelatase**, the enzyme that incorporates iron into protoporphyrin IX to form heme, resulting in accumulation of **protoporphyrin** in erythrocytes. - FEP levels reflect **chronic lead exposure** and remain elevated for the lifespan of the red blood cell (~120 days), making it an excellent screening tool. - It is **non-invasive** (can use capillary blood), **cost-effective**, and **widely available**. - Note: FEP is also elevated in **iron deficiency**, so elevated values should be followed up with blood lead levels for confirmation. *Coproporphyrin in urine* - Urinary coproporphyrin is elevated in lead poisoning due to inhibition of **coproporphyrinogen oxidase** in the heme synthesis pathway. - While it can be used as a **confirmatory test**, it is **less specific** than FEP and not the primary screening test. - It is also elevated in other conditions like liver disease and alcoholism. *Aminolevulinic acid in urine* - Urinary **δ-aminolevulinic acid (ALA)** is elevated in lead poisoning because lead inhibits **ALA dehydratase**, the second enzyme in heme synthesis. - This is a **sensitive indicator** of lead exposure and is often used as a **supplementary screening test** alongside FEP. - However, FEP remains the more commonly used initial screening test in practice. *Lead in morning urine sample* - Urine lead measurement has significant **day-to-day variability** and is not a reliable screening test. - Most lead is stored in **bone** (90% in adults), not excreted in urine. - **Blood lead levels (BLL)** are the gold standard for diagnosis, not urinary lead measurements.

Question 206: All are involved in bilirubin metabolism except?

A. Biliverdin reductase
B. Heme oxygenase
C. Glucuronyl transferase
D. ALA synthase (Correct Answer)

Explanation: ***ALA synthase*** - **ALA synthase** is the enzyme responsible for the first committed step in **heme synthesis**, not bilirubin metabolism. - It catalyzes the condensation of **succinyl CoA** and **glycine** to form δ-aminolevulinic acid (ALA). *Biliverdin reductase* - This enzyme catalyzes the conversion of **biliverdin**, a green pigment, into **unconjugated bilirubin**, a yellow pigment. - It is an essential step in the breakdown pathway of **heme** into bilirubin. *Heme oxygenase* - **Heme oxygenase** is the enzyme that cleaves the **heme ring** to form **biliverdin**, releasing carbon monoxide and iron. - This is the initial and rate-limiting step in **heme catabolism**, leading to bilirubin formation. *Glucuronyl transferase* - **UDP-glucuronyl transferase** (UGT) conjugates unconjugated bilirubin with **glucuronic acid** in the liver. - This conjugation process makes bilirubin water-soluble, allowing its excretion into the **bile**.

Question 207: Hepcidin inhibits which of the following?

A. Ferroportin (Correct Answer)
B. Ceruloplasmin
C. Hepheastin
D. DMT-1

Explanation: ***Ferroportin*** - **Hepcidin** is a key regulator of iron homeostasis, primarily by binding to and inhibiting **ferroportin**, the sole known iron export channel from cells. - This binding leads to the **internalization and degradation** of ferroportin, thereby reducing iron release from cells (enterocytes, macrophages, hepatocytes) into the bloodstream and consequently decreasing plasma iron levels. *Ceruloplasmin* - **Ceruloplasmin** is a copper-containing enzyme that acts as a ferroxidase, oxidizing Fe2+ to Fe3+, which is necessary for iron loading onto transferrin. - Hepcidin does not directly inhibit ceruloplasmin; instead, a deficiency in ceruloplasmin can lead to iron accumulation in tissues. *Hepheastin* - **Hephaestin** is a ferroxidase enzyme similar to ceruloplasmin, predominantly found in the intestinal enterocytes, which facilitates iron export from enterocytes. - While hephaestin is involved in iron metabolism, hepcidin directly regulates ferroportin, not hephaestin itself. *DMT-1* - **DMT-1 (Divalent Metal Transporter 1)** is responsible for the uptake of non-heme iron (Fe2+) from the intestinal lumen into the enterocyte. - Hepcidin primarily acts on iron export from cells via ferroportin, rather than on the initial uptake of iron into the enterocytes via DMT-1.

Question 208: Which TCA intermediate is used in haem synthesis?

A. Succinyl CoA (Correct Answer)
B. Malate
C. Fumarate
D. Alpha keto glutarate

Explanation: ***Succinyl CoA*** - **Succinyl CoA** combines with **glycine** to form **δ-aminolevulinic acid (δ-ALA)**, the first committed step in **heme synthesis** catalyzed by **ALA synthase**. - This intermediate from the **TCA cycle** provides the carbon backbone for the initial steps of **porphyrin ring** formation. - ALA synthase is the **rate-limiting enzyme** of heme synthesis and requires **pyridoxal phosphate (vitamin B6)** as a cofactor. *Malate* - **Malate** is an intermediate in the TCA cycle but is not directly incorporated into the **heme synthesis pathway**. - Its primary role in the TCA cycle is to be oxidized to **oxaloacetate**, which then condenses with **acetyl CoA**. *Fumarate* - **Fumarate** is a product of the oxidation of succinate in the TCA cycle and is converted to malate. - It does not serve as a direct precursor or essential component in the biosynthesis of **heme**. *Alpha keto glutarate* - **Alpha-ketoglutarate** is an important TCA cycle intermediate involved in amino acid metabolism, but it does not directly contribute to the **heme synthetic pathway**. - It is primarily involved in transamination reactions and is a precursor for **glutamate** synthesis.

Question 209: Which factor controls the release of iron from macrophages?

A. Transferrin
B. Ferritin
C. Hepcidin (Correct Answer)
D. Ceruloplasmin

Explanation: ***Hepcidin*** - **Hepcidin** is a key regulator of iron homeostasis, primarily by controlling the activity of **ferroportin**, the iron export channel on macrophages and enterocytes. - High hepcidin levels lead to the internalization and degradation of ferroportin, thereby **trapping iron within macrophages** and reducing its release into the circulation. *Transferrin* - **Transferrin** is an iron-binding protein responsible for transporting iron in the blood, but it does not directly control the release of iron from cells. - It binds to **ferric iron (Fe3+)** and delivers it to cells expressing transferrin receptors. *Ferritin* - **Ferritin** is an intracellular protein that stores iron in a non-toxic form within cells, primarily to prevent iron overload and oxidative damage. - While it stores iron, it does not regulate the release of iron from macrophages; rather, it is a marker of **iron stores**. *Ceruloplasmin* - **Ceruloplasmin** is a copper-carrying protein with ferroxidase activity, meaning it oxidizes ferrous iron (Fe2+) to ferric iron (Fe3+). - This oxidation is necessary for iron to bind to transferrin, but ceruloplasmin does not directly control the **release of iron** from macrophages.

Question 210: Which is not a product of heme catabolism?

A. Aminolevulinic acid (Correct Answer)
B. Ferrous ion
C. Biliverdin
D. Carbon monoxide

Explanation: ***Aminolevulinic acid*** - **Aminolevulinic acid (ALA)** is a precursor in the **heme biosynthetic pathway**, not a product of its degradation. - The formation of ALA is the **rate-limiting step** in heme synthesis, catalyzed by ALA synthase. *Ferrous ion* - During heme catabolism, the **iron atom (Fe2+)** is released from the porphyrin ring. - This **ferrous ion** is then recycled or stored, as it is a product of heme degradation. *Biliverdin* - **Biliverdin** is the first green-colored product formed when heme oxygenase cleaves the **porphyrin ring** of heme. - It is an intermediate in the conversion of heme to **bilirubin**, making it a direct product of heme catabolism. *Carbon monoxide* - The oxidative cleavage of the heme ring by **heme oxygenase** liberates one molecule of **carbon monoxide (CO)**. - This CO is an important signaling molecule and has vasodilatory effects, making it a product of heme degradation.

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