Hemoglobin and Iron Metabolism Practice Questions

Q: Each milliliter of red blood cells contains how many mg of elemental iron?

1 mg. ### Explanation **Correct Answer: A. 1 mg** The concentration of iron in red blood cells (RBCs) is directly linked to hemoglobin content. Under normal physiological conditions, **1 mL of packed red blood cells contains approximately 1 mg of elemental iron.** This relationship is derived from the following calculation: 1. Hemoglobin contains approximately **0.34% iron** by weight. 2. 100 mL of packed RBCs contains roughly 30–34 grams of hemoglobin. 3. Therefore, 100 mL of RBCs contains ~100 mg of iron, which simplifies to **1 mg of iron per 1 mL of RBCs.** **Analysis of Incorrect Options:** * **B, C, and D (2 mg, 3 mg, 4 mg):** These values overestimate the iron-carrying capacity of hemoglobin. While a unit of whole blood (approx. 350–450 mL) contains about 200–250 mg of iron, the specific ratio for pure RBC volume remains 1:1. **Clinical Pearls & High-Yield Facts for NEET-PG:** * **Blood Donation:** Since 1 mL of RBCs contains 1 mg of iron, donating one unit of whole blood (which contains ~200–250 mL of RBCs) results in a loss of approximately **200–250 mg of iron.** * **Iron Storage:** Total body iron is roughly **3–4 grams**, with the majority (~65-70%) found in hemoglobin. * **Daily Requirement:** The average adult loses about 1 mg of iron daily (via shedding of skin and GI cells), which is balanced by the absorption of 1 mg from the diet. * **Transfusion Overload:** In patients with chronic transfusion requirements (e.g., Thalassemia), every 1 mL of packed RBCs transfused adds 1 mg of iron to the body. Since the body lacks an active excretory pathway for iron, this leads to **hemosiderosis** after approximately 10–20 units.

Q: A 27-year-old woman presents with severe abdominal pain, nausea, vomiting, and constipation. She has experienced similar, though less severe, episodes previously. During examination, she appears agitated and confused, making an accurate history difficult. An emergency laparotomy reveals no pathology. An older surgeon suggests the possibility of porphyria. The porphyrias are biochemical abnormalities in which of the following pathways?

Heme synthesis. The correct answer is **B. Heme synthesis.** **Pathophysiology:** Porphyrias are a group of metabolic disorders caused by deficiencies in specific enzymes within the **heme biosynthetic pathway** [2]. Heme is essential for hemoglobin, myoglobin, and cytochrome P450 enzymes. When an enzyme in this pathway is deficient, there is an accumulation of toxic heme precursors (like delta-aminolevulinic acid and porphobilinogen). In **Acute Intermittent Porphyria (AIP)**, the most common acute form, these precursors lead to neurovisceral symptoms [3]. **Analysis of Options:** * **A. Glycogen degradation:** Deficiencies here lead to Glycogen Storage Diseases (e.g., Von Gierke or Pompe disease), typically presenting with hypoglycemia or muscle weakness, not acute abdominal crises. * **C. Lipoprotein degradation:** Defects here cause dyslipidemias (e.g., Familial Hypercholesterolemia), leading to xanthomas or premature atherosclerosis. * **D. Nucleotide degradation:** Abnormalities in this pathway (e.g., purine breakdown) lead to conditions like Gout or Lesch-Nyhan syndrome. **Clinical Pearls for NEET-PG:** * **The "Porphyria Triad":** Abdominal pain (out of proportion to physical findings), neuropsychiatric symptoms (agitation, seizures, psychosis), and autonomic instability (tachycardia, hypertension) [1]. * **Surgical Mimicry:** AIP is often called the "little imitator" because it mimics a surgical acute abdomen, frequently leading to unnecessary laparotomies. * **Diagnosis:** The classic sign is urine that turns **"port-wine" colored** upon standing or exposure to sunlight. * **Triggers:** Attacks are often precipitated by drugs (Barbiturates, Sulfonamides), alcohol, or fasting [1]. * **Management:** Treatment involves IV Hemin and high-dose glucose to suppress the enzyme ALA synthase.

Q: In intermittent porphyria, what is present in the urine?

Porphobilinogens. **Explanation:** **Acute Intermittent Porphyria (AIP)** is an autosomal dominant metabolic disorder caused by a deficiency of the enzyme **Porphobilinogen (PBG) deaminase** (also known as HMB synthase). This enzyme is responsible for converting Porphobilinogen into Hydroxymethylbilane. When this enzyme is deficient, there is a proximal buildup of the precursors **Porphobilinogen (PBG)** and **Delta-aminolevulinic acid (ALA)**. These metabolites are excreted in the urine. A classic clinical sign is that the urine is normal in color when fresh but turns **dark/port-wine colored** upon standing or exposure to light, due to the spontaneous oxidation of PBG into porphobilin. **Analysis of Incorrect Options:** * **A & D (Biliverdin and Bilirubin):** These are bile pigments derived from the catabolism of heme (breakdown of old RBCs). They are associated with jaundice and hepatobiliary disorders, not primary defects in the heme synthesis pathway. * **B (Uroporphyrin):** While uroporphyrins are found in the urine of patients with *Porphyria Cutanea Tarda* (the most common porphyria), they are not the primary diagnostic marker for the acute phase of AIP. **High-Yield Clinical Pearls for NEET-PG:** * **The 5 P’s of AIP:** **P**ainful abdomen, **P**ort-wine urine, **P**olyneuropathy, **P**sychological disturbances, and **P**recipitated by drugs (e.g., Barbiturates, Sulfonamides). * **Diagnostic Test:** The **Ehrlich’s aldehyde test** is used to detect PBG in the urine. * **Key Enzyme:** AIP is caused by a deficiency in **PBG Deaminase**; it is unique because it does **not** present with photosensitivity (unlike other porphyrias). * **Management:** Treatment includes glucose infusion and intravenous **Hemin**, which inhibits ALA synthase via feedback inhibition to reduce precursor production.

Q: Which of the following is an allosteric protein?

Haemoglobin. **Explanation:** **Haemoglobin (Hb)** is the classic example of an **allosteric protein**. It exhibits **cooperativity**, where the binding of an effector molecule (like Oxygen) to one subunit induces a conformational change in the other subunits. This transition from the **T-state (Tense/Low affinity)** to the **R-state (Relaxed/High affinity)** results in the characteristic **sigmoidal oxygen dissociation curve**. Other allosteric effectors of Hb include 2,3-BPG, H⁺ ions (Bohr effect), and CO₂, which stabilize the T-state and promote oxygen unloading. **Why the other options are incorrect:** * **Transferrin:** This is a transport protein responsible for carrying ferric iron (Fe³⁺) in the plasma. It does not exhibit allosteric regulation or cooperativity. * **Ceruloplasmin:** This is an alpha-2 globulin that functions as a ferroxidase (converting Fe²⁺ to Fe³⁺) and carries copper. It is an enzyme/transport protein but not an allosteric one. * **Phosphofructokinase (PFK):** While PFK is indeed an **allosteric enzyme** (the rate-limiting step of glycolysis), the question asks for an allosteric **protein**. In medical biochemistry nomenclature, when both are present, Haemoglobin is the prototypical structural/transport protein used to demonstrate allosterism. (Note: In some contexts, PFK is also correct, but Hb is the "gold standard" example for this specific question type). **High-Yield Clinical Pearls for NEET-PG:** * **Myoglobin vs. Hb:** Myoglobin is a monomer, lacks quaternary structure, and thus **cannot** be allosteric (it has a hyperbolic curve). * **2,3-BPG:** It binds to the central cavity of the Hb tetramer, stabilizing the T-state and shifting the curve to the **right**. * **The Bohr Effect:** Increased CO₂ and decreased pH decrease Hb's affinity for O₂, facilitating delivery to metabolically active tissues.

Q: The Watson-Swartz test is primarily used to diagnose which of the following conditions?

Acute intermittent porphyria. **Explanation:** The **Watson-Schwartz test** is a classic biochemical screening test used to detect **Porphobilinogen (PBG)** in the urine, which is the hallmark finding in **Acute Intermittent Porphyria (AIP)**. 1. **Why Option B is Correct:** In AIP, a deficiency of the enzyme *PBG deaminase* leads to the accumulation of porphyrin precursors, specifically PBG and delta-aminolevulinic acid (ALA). In the Watson-Schwartz test, urine is mixed with **Ehrlich’s reagent** (p-dimethylaminobenzaldehyde). If PBG is present, a red-colored complex forms. To differentiate PBG from urobilinogen (which also reacts), chloroform or butanol is added. PBG is **insoluble in organic solvents** and remains in the aqueous (top) layer, confirming a positive result for AIP. 2. **Why Other Options are Incorrect:** * **Hemochromatosis (A):** Diagnosed via serum ferritin, transferrin saturation, and genetic testing (HFE gene) or liver biopsy (Prussian blue stain). * **Wilson’s Disease (C):** Diagnosed by low serum ceruloplasmin, increased 24-hour urinary copper excretion, and the presence of Kayser-Fleischer (KF) rings on slit-lamp exam. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Triad of AIP:** Abdominal pain (most common), Neuropsychiatric symptoms, and Peripheral neuropathy. * **Urine Characteristic:** In AIP, urine is initially normal but turns **"port-wine"** colored upon standing or exposure to sunlight due to the oxidation of PBG to porphobilin. * **Precipitating Factors:** Drugs (Barbiturates, Sulfonamides), alcohol, and fasting. * **Management:** Intravenous **Hemin** (suppresses ALA synthase) and high-carbohydrate (glucose) intake.

Q: Oral contraceptive pill intake can cause psychiatric symptoms and abdominal pain. What is the diagnosis?

Acute intermittent porphyria. **Explanation:** **Acute Intermittent Porphyria (AIP)** is an autosomal dominant metabolic disorder caused by a deficiency of the enzyme **Porphobilinogen (PBG) deaminase** [2]. This leads to the accumulation of toxic heme precursors, specifically delta-aminolevulinic acid (ALA) and PBG. **Why it is the correct answer:** The classic presentation of AIP is the **"5 Ps"**: **P**ainful abdomen, **P**sychiatric symptoms (anxiety, psychosis), **P**olyneuropathy, **P**ort-wine colored urine, and **P**recipitated by drugs [1]. Oral Contraceptive Pills (OCPs) contain progesterone, which induces the enzyme **ALA synthase** in the liver. This increases the production of porphyrins, thereby triggering an acute attack in susceptible individuals [1]. **Why incorrect options are wrong:** * **Systemic Lupus Erythematosus (SLE):** While SLE can cause abdominal pain (vasculitis) and psychiatric issues (lupus cerebritis), it is not typically triggered by OCPs; in fact, OCPs are more associated with flares of skin disease or thrombosis in SLE. * **Thrombosis:** OCPs are a major risk factor for venous thromboembolism (VTE), but this usually presents with localized limb swelling or chest pain (PE), not a combination of psychiatric symptoms and generalized abdominal pain. * **Anemia:** OCPs actually reduce menstrual blood loss and are often used to *treat* iron-deficiency anemia. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnosis:** Elevated urinary **PBG** levels during an attack (Screening test: Hoesch test/Watson-Schwartz test). * **Triggers:** Barbiturates, Sulfonamides, Alcohol, Fasting, and Progesterone [1]. * **Management:** Intravenous **Hemin** (suppresses ALA synthase) and high-dose **Glucose** (dextrose) to inhibit the heme pathway. * **Key Sign:** Urine turns dark/red upon standing or exposure to sunlight.

Q: The conversion of Fe+2 to Fe+3 is called which reaction?

Fenton's reaction. **Explanation:** The correct answer is **B. Fenton's reaction.** In biochemistry, the **Fenton reaction** describes the oxidation of ferrous iron ($Fe^{2+}$) to ferric iron ($Fe^{3+}$) in the presence of hydrogen peroxide ($H_2O_2$). This reaction is critical because it generates the **hydroxyl radical (•OH)**, the most reactive and damaging of all free radicals, which leads to lipid peroxidation and cellular damage. * **Reaction:** $Fe^{2+} + H_2O_2 \rightarrow Fe^{3+} + \bullet OH + OH^-$ **Analysis of Incorrect Options:** * **A. Haber-Weiss reaction:** This reaction generates hydroxyl radicals from $H_2O_2$ and superoxide ($O_2^{\bullet-}$). While it involves iron as a catalyst, the primary definition of $Fe^{2+}$ to $Fe^{3+}$ oxidation via peroxide is the Fenton reaction. * **C. Nernst reaction:** This relates to electrochemistry and the calculation of the reduction potential of an electrochemical cell or the equilibrium potential of an ion across a membrane. * **D. Donnan reaction (Gibbs-Donnan Effect):** This describes the behavior of charged particles near a semi-permeable membrane that fail to distribute evenly due to the presence of non-diffusible ions (like proteins). **Clinical Pearls for NEET-PG:** 1. **Hemochromatosis:** Iron overload is dangerous because excess free iron drives the Fenton reaction, leading to tissue damage in the liver, heart, and pancreas (Bronze Diabetes). 2. **Ceruloplasmin:** This enzyme acts as a **ferroxidase**, converting $Fe^{2+}$ to $Fe^{3+}$ to allow iron to bind to transferrin for safe transport, preventing the Fenton reaction. 3. **Hydroxyl Radical:** Remember that unlike superoxide or hydrogen peroxide, the body has no specific enzyme (like SOD or Catalase) to neutralize the hydroxyl radical; prevention of its formation is the primary defense.

Q: What is the most common enzyme deficiency leading to porphyria in humans?

Uroporphyrinogen decarboxylase. **Explanation:** The correct answer is **Uroporphyrinogen decarboxylase (UROD)**. Deficiency of UROD leads to **Porphyria Cutanea Tarda (PCT)**, which is statistically the **most common porphyria** worldwide. PCT is unique because it can be either inherited (Type II) or, more commonly, acquired (Type I) due to factors like alcohol consumption, Hepatitis C, or iron overload. The enzyme UROD is responsible for converting uroporphyrinogen III to coproporphyrinogen III in the heme synthesis pathway. **Analysis of Incorrect Options:** * **A. PBG deaminase:** Deficiency causes **Acute Intermittent Porphyria (AIP)**. While AIP is the most common *acute* (neurological) porphyria, it is less common overall than PCT. * **C. Ferrochelatase:** Deficiency leads to **Erythropoietic Protoporphyria (EPP)**. This is the most common porphyria in children but not the most common in the general human population. * **D. Coproporphyrinogen oxidase:** Deficiency causes **Hereditary Coproporphyria (HCP)**, which is a rare autosomal dominant acute porphyria. **High-Yield Clinical Pearls for NEET-PG:** * **Porphyria Cutanea Tarda (PCT):** Characterized by **photosensitivity** and blistering/vesicles on sun-exposed skin (dorsum of hands). It is associated with **Hepatitis C** and "tea-colored" urine. * **Acute Intermittent Porphyria (AIP):** Presents with the "5 Ps": **P**ainful abdomen, **P**ort-wine urine, **P**olyneuropathy, **P**sychological disturbances, and **P**recipitated by drugs (e.g., Barbiturates, Cytochrome P450 inducers). * **Key Enzyme Rule:** Deficiencies *after* the formation of uroporphyrinogen lead to photosensitivity; deficiencies *before* that step (like AIP) typically do not.

Q: Which substance is typically excreted in lead poisoning?

Coproporphyrin. **Explanation:** Lead poisoning (Plumbism) interferes with the heme biosynthetic pathway by inhibiting two key enzymes: **ALA Dehydratase** and **Ferrochelatase**. 1. **Why Coproporphyrin is correct:** Lead inhibits the enzyme **Coproporphyrinogen oxidase**, which normally converts Coproporphyrinogen III to Protoporphyrin IX. When this enzyme is inhibited, Coproporphyrinogen III accumulates and is spontaneously oxidized into **Coproporphyrin III**, which is then excreted in excess in the urine. This is a classic biochemical marker used for screening lead exposure. 2. **Why the other options are incorrect:** * **Urobilinogen:** This is a byproduct of bilirubin degradation by intestinal bacteria. Increased levels are seen in hemolytic anemias or liver disease, not specifically in lead poisoning. * **Bilirubin:** Elevated levels (jaundice) indicate hemolysis, biliary obstruction, or hepatic dysfunction. While lead can cause hemolytic anemia, bilirubin is not the characteristic substance excreted. * **Bile salts:** These are synthesized in the liver from cholesterol and aid in fat digestion. Their presence in urine (choluria) typically indicates obstructive jaundice. **High-Yield Clinical Pearls for NEET-PG:** * **Enzymes inhibited by Lead:** ALA Dehydratase (most sensitive) and Ferrochelatase (leads to elevated Free Erythrocyte Protoporphyrin). * **Diagnostic Marker:** Elevated **Urinary Delta-Aminolevulinic Acid (δ-ALA)** is also a hallmark of lead poisoning. * **Hematological finding:** **Basophilic stippling** of RBCs (due to inhibition of pyrimidine 5'-nucleotidase). * **Clinical Signs:** Burton’s lines (blue gums), wrist drop/foot drop, and abdominal colic.

Question 1

Each milliliter of red blood cells contains how many mg of elemental iron?

Accepted Answer

1 mg

Answer

2 mg

Answer

3 mg

Answer

4 mg

Question 2

A 27-year-old woman presents with severe abdominal pain, nausea, vomiting, and constipation. She has experienced similar, though less severe, episodes previously. During examination, she appears agitated and confused, making an accurate history difficult. An emergency laparotomy reveals no pathology. An older surgeon suggests the possibility of porphyria. The porphyrias are biochemical abnormalities in which of the following pathways?

Accepted Answer

Heme synthesis

Answer

Glycogen degradation

Answer

Lipoprotein degradation

Answer

Nucleotide degradation

Question 3

A 20-year-old woman complains of intermittent, colicky abdominal pain, fine tremors of her hands, excess sweating, and a general feeling of restlessness. Laboratory studies reveal an inherited defect in the biosynthesis of heme. This patient's genetic disease is most likely caused by deficiency of which of the following liver enzymes?

Accepted Answer

Porphobilinogen deaminase

Answer

Alanine aminotransferase

Answer

Alkaline phosphatase

Answer

Uridine diphosphate glucuronyl transferase

Question 4

In intermittent porphyria, what is present in the urine?

Accepted Answer

Porphobilinogens

Answer

Biliverdin

Answer

Uroporphyrin

Answer

Bilirubin

Question 5

Which of the following is an allosteric protein?

Accepted Answer

Haemoglobin

Answer

Transferrin

Answer

Ceruloplasmin

Answer

Phosphofructokinase

Question 6

The Watson-Swartz test is primarily used to diagnose which of the following conditions?

Accepted Answer

Acute intermittent porphyria

Answer

Hemochromatosis

Answer

Wilson's disease

Answer

All of the above

Question 7

Oral contraceptive pill intake can cause psychiatric symptoms and abdominal pain. What is the diagnosis?

Accepted Answer

Acute intermittent porphyria

Answer

Systemic lupus erythematosus

Answer

Thrombosis

Answer

Anemia

Question 8

The conversion of Fe+2 to Fe+3 is called which reaction?

Accepted Answer

Fenton's reaction

Answer

Haber-Weiss reaction

Answer

Nernst reaction

Answer

Donnan reaction

Question 9

What is the most common enzyme deficiency leading to porphyria in humans?

Accepted Answer

Uroporphyrinogen decarboxylase

Answer

PBG deaminase

Answer

Ferrochelatase

Answer

Coproporphyrinogen oxidase

Question 10

Which substance is typically excreted in lead poisoning?

Accepted Answer

Coproporphyrin

Answer

Urobilinogen

Answer

Bilirubin

Answer

Bile salts

Hemoglobin and Iron Metabolism — MCQs

Hemoglobin and Iron Metabolism — MCQs

On this page

Practice by Chapter

Want unlimited practice?