Hemoglobin and Iron Metabolism — MCQs

Hemoglobin and Iron Metabolism Indian Medical PG Practice Questions and MCQs

Question 221: Why is blood stored in citrate-phosphate-dextrose considered more beneficial for hypoxic patients compared to blood stored in acidic-citrate-dextrose?

A. The fall in 2,3-DPG is less. (Correct Answer)
B. It has a higher pH level than acidic-citrate-dextrose.
C. It is more effective in oxygen delivery.
D. It has a longer shelf life than acidic-citrate-dextrose.

Explanation: ***The fall in 2,3-DPG is less.*** * **Citrate-phosphate-dextrose (CPD)** better preserves levels of **2,3-bisphosphoglycerate (2,3-DPG)** in stored red blood cells. * Higher 2,3-DPG levels are crucial for **oxygen unloading** from hemoglobin in tissues, which is particularly beneficial for hypoxic patients who need efficient oxygen delivery. *It has a higher pH level than acidic-citrate-dextrose.* * While CPD does maintain a **less acidic pH** than acid-citrate-dextrose (ACD), which is generally favorable for red blood cell viability, the most direct benefit for hypoxic patients relates to 2,3-DPG. * The slightly higher pH indirectly contributes to better 2,3-DPG preservation but isn't the primary reason for improved oxygen delivery. *It is more effective in oxygen delivery.* * While the *consequence* of using CPD is **more effective oxygen delivery** due to better 2,3-DPG preservation, this option describes the outcome rather than the underlying mechanism compared to the more specific answer regarding 2,3-DPG. * The increased efficacy in oxygen delivery is directly attributable to the preserved 2,3-DPG levels. *It has a longer shelf life than acidic-citrate-dextrose.* * The storage solutions primarily impact red blood cell viability and function, but the **shelf life** (typically 21-35 days depending on the anticoagulant/preservative) is generally determined by other factors, including the additive solutions used with the anticoagulant. * While CPD improves red blood cell quality, the primary advantage for hypoxic patients specifically lies in oxygen affinity rather than overall storage duration.

Question 222: In which type of hemoglobin are zeta 2 and gamma 2 chains present?

A. Gower I
B. Gower II
C. Portland (Correct Answer)
D. Fetal hemoglobin

Explanation: ***Portland*** - **Portland hemoglobin** is a primitive embryonic hemoglobin composed of **zeta (ζ) 2 and gamma (γ) 2 chains** (ζ2γ2). - It plays a role in early fetal oxygen transport, particularly in the yolk sac stage. *Gower I* - **Gower I hemoglobin** is another embryonic hemoglobin, but it consists of **zeta (ζ) 2 and epsilon (ε) 2 chains** (ζ2ε2). - This composition is crucial for oxygen delivery during the very initial stages of embryonic development. *Gower II* - **Gower II hemoglobin** is an embryonic hemoglobin made up of **alpha (α) 2 and epsilon (ε) 2 chains** (α2ε2). - It represents a transitional form as the embryo develops and starts producing alpha globin chains. *Fetal hemoglobin* - **Fetal hemoglobin (HbF)** consists of **alpha (α) 2 and gamma (γ) 2 chains** (α2γ2). - It is the predominant hemoglobin during the second and third trimesters of pregnancy and has a higher affinity for oxygen than adult hemoglobin.

Question 223: Which protein is responsible for conserving iron in the body?

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

Explanation: ***Ferritin*** - **Ferritin** is the primary intracellular protein that **conserves iron** in the body by storing it in a safe, non-toxic, and bioavailable form - It is found mainly in the liver, spleen, and bone marrow, serving as the body's **iron reserve** - When iron is abundant, ferritin stores it; when iron is needed, ferritin releases it, thus **conserving iron for future use** - Serum ferritin levels directly reflect total body iron stores *Hepcidin* - **Hepcidin** is a regulatory peptide hormone that controls iron homeostasis by inhibiting **ferroportin**, the iron export channel - It reduces iron absorption from the intestine and iron release from macrophages during inflammation or iron overload - While it regulates iron distribution, it is a hormone, not a storage protein, and does not directly conserve iron within cells *Hemopexin* - **Hemopexin** binds free **heme** in plasma, preventing oxidative damage and delivering it to the liver for catabolism - It helps recover iron from heme but does not store or conserve iron in the body *Transferrin* - **Transferrin** is a plasma protein that **transports iron** from absorption sites (intestine) and storage sites (liver, spleen) to tissues that need it - Its role is iron delivery, not conservation or storage

Question 224: Aminolevulinic acid is a metabolic product in the synthesis of -

A. Tryptophan
B. Collagen
C. Glycosaminoglycans
D. Heme (Correct Answer)

Explanation: ***Heme*** - **Aminolevulinic acid (ALA)** is the first committed precursor in the **heme biosynthesis pathway**. - Its formation from succinyl CoA and glycine is catalyzed by **ALA synthase**, which is the rate-limiting enzyme. *Tryptophan* - **Tryptophan** is an essential amino acid and a precursor for molecules like **serotonin**, **melatonin**, and **niacin**. - Its synthesis does not involve aminolevulinic acid. *Collagen* - **Collagen** is a structural protein primarily composed of amino acids such as **glycine, proline, and hydroxyproline**. - Its synthesis pathway is distinct and does not utilize aminolevulinic acid. *Glycosaminoglycans* - **Glycosaminoglycans (GAGs)** are long, unbranched polysaccharides consisting of repeating disaccharide units, significant components of the **extracellular matrix**. - Their synthesis involves various sugars and enzymes, but not aminolevulinic acid.

Question 225: Which is an inhibitor of ferrochelatase ?

A. Lead (Correct Answer)
B. Mercury
C. Iron
D. Arsenic

Explanation: ***Lead*** - **Lead** is a potent environmental toxin that directly inhibits the enzyme **ferrochelatase**, preventing the insertion of **iron** into **protoporphyrin IX** to form heme. - This inhibition leads to the accumulation of **protoporphyrin IX** and can cause **anemia** due to impaired **heme synthesis**. *Mercury* - While **mercury** is a heavy metal and neurotoxin, its primary mechanism of toxicity does not involve direct inhibition of **ferrochelatase**. - Its effects are more commonly associated with protein denaturation and enzyme inactivation through binding with **sulfhydryl groups**. *Iron* - **Iron** is a substrate for **ferrochelatase**, not an inhibitor. **Ferrochelatase** catalyzes the insertion of **iron** into **protoporphyrin IX** to complete the synthesis of **heme**. - Deficiencies or excesses of **iron** can affect **heme synthesis**, but **iron** itself does not inhibit the enzyme in a toxic manner. *Arsenic* - **Arsenic** is a metalloid that is toxic through various mechanisms, including interference with cellular respiration and DNA repair. - However, **arsenic** is not known to be a direct inhibitor of **ferrochelatase** in the same way **lead** is.

Question 226: What is the iron requirement for a normal menstruating adult female?

A. 30 mg/day
B. 35 mg/day
C. 20 mg/day
D. 15 mg/day (Correct Answer)

Explanation: ***15 mg/day*** - The recommended daily iron intake for a normal menstruating adult female was **15 mg/day** according to guidelines at the time of this examination (NEET-2013). - This higher requirement compared to males and post-menopausal women is due to **iron loss in menstrual blood**, averaging approximately **0.5-1 mg/day** additional iron loss. - **Note:** Current guidelines recommend **18 mg/day** (US RDA) or **21 mg/day** (ICMR, India), but this question reflects the 2013 standard. *20 mg/day* - This amount is **higher than the typical recommendation** for healthy menstruating women without significant pathology. - While some women with heavier menstrual bleeding might require this, it's not the baseline requirement for normal menstruation. *30 mg/day* - This intake level is typically recommended for **pregnant women** in the second and third trimesters or individuals with **diagnosed iron deficiency anemia** requiring therapeutic supplementation. - It is significantly more than the daily requirement for a healthy menstruating female. *35 mg/day* - This is an **excessively high** daily iron intake for a healthy menstruating female. - Such high doses are usually prescribed for **severe iron deficiency anemia** or specific medical conditions under supervision. - Chronic intake at this level without medical indication could potentially lead to adverse effects.

Question 227: Which porphyrin forms the organic component of heme?

A. Uroporphyrin
B. Coproporphyrin
C. Deuteroporphyrin
D. Protoporphyrin IX (Correct Answer)

Explanation: ***Protoporphyrin IX*** - **Heme** is formed by the insertion of an **iron atom (Fe2+)** into the center of **protoporphyrin IX**. - **Protoporphyrin IX** is the immediate precursor to heme in the **heme synthesis pathway**. *Uroporphyrin* - **Uroporphyrin** is an earlier precursor in the **heme synthesis pathway** and is much more hydrophilic than protoporphyrin. - It accumulates in diseases like **congenital erythropoietic porphyria (CEP)**, leading to photosensitivity. *Coproporphyrin* - **Coproporphyrin** is an intermediate in the **heme synthesis pathway**, formed after uroporphyrinogen. - It is also more water-soluble than protoporphyrin and its accumulation can be seen in various porphyrias. *Deuteroporphyrin* - **Deuteroporphyrin** is a synthetic porphyrin or a less common natural porphyrin that is not directly involved as the organic component of heme in mammals. - While it is structurally similar to protoporphyrin, it does not serve as the direct precursor for heme formation in the human body.

Question 228: Which of the following statements about hemoglobin is true?

A. Each hemoglobin molecule can bind up to six O2 molecules.
B. Each hemoglobin subunit contains two heme groups, which bind oxygen.
C. Hemoglobin consists of two alpha and two beta subunits, each capable of binding one O2 molecule. (Correct Answer)
D. Each hemoglobin molecule is made of 6 polypeptide chains.

Explanation: ***Hemoglobin consists of two alpha and two beta subunits, each capable of binding one O2 molecule.*** - A **hemoglobin molecule is a tetramer**, meaning it is composed of four protein subunits: two alpha (α) chains and two beta (β) chains. - Each of these four subunits contains one **heme group**, which is an iron-containing porphyrin complex that can reversibly bind one molecule of **oxygen (O2)**. *Each hemoglobin molecule can bind up to six O2 molecules.* - A single hemoglobin molecule, with its **four heme groups**, can bind a maximum of **four O2 molecules**, not six. - The capacity for oxygen binding is directly proportional to the number of heme groups present in the hemoglobin molecule. *Each hemoglobin subunit contains two heme groups, which bind oxygen.* - Each individual **hemoglobin subunit (alpha or beta)** contains **only one heme group**, not two. - Therefore, a complete hemoglobin molecule (with four subunits) contains a total of four heme groups. *Each hemoglobin molecule is made of 6 polypeptides, one for each subunit.* - A hemoglobin molecule is composed of **four polypeptide chains** (two alpha and two beta), not six. - This tetrameric structure is crucial for its function and **cooperative oxygen binding**.

Question 229: Which isoform of LDH is raised in Anemia ?

A. LDH 5
B. LDH 4
C. LDH 1
D. LDH 2 (Correct Answer)

Explanation: ***Correct: LDH 2*** - **LDH 2 (H3M1)** is highly abundant in **red blood cells (RBCs)**, second only to LDH 1. - In **hemolytic anemia**, there is increased destruction of red blood cells, leading to the release of intracellular LDH isoforms into the bloodstream. - Both **LDH 1 and LDH 2 are significantly elevated** in hemolytic anemia, as RBCs contain predominantly these two isoforms. - The elevation of LDH 2 is particularly notable and diagnostically useful in anemia, especially hemolytic conditions. *Incorrect: LDH 1* - **LDH 1 (H4)** is the most abundant isoform in **heart muscle** and is also present in **red blood cells**. - While LDH 1 is indeed elevated in hemolytic anemia, this option is not the best answer in this context. - LDH 1 elevation is classically associated with **myocardial infarction**. *Incorrect: LDH 4* - **LDH 4 (HM3)** is present in various tissues, including **liver, skeletal muscle, and kidneys**, but in lower concentrations. - Not the primary isoform associated with anemia. *Incorrect: LDH 5* - **LDH 5 (M4)** is predominantly found in the **liver and skeletal muscles**. - Elevation of LDH 5 typically indicates **liver damage, muscle injury, or malignancies**, not primarily anemia.

Question 230: What is the rate-limiting enzyme in heme synthesis?

A. ALA synthase (Correct Answer)
B. HMG CoA reductase
C. ALA dehydratase
D. Uroporphyrinogen 1 synthase

Explanation: ***ALA synthase*** - **Aminolevulinate synthase** (ALA synthase) is the first and **rate-limiting enzyme** in the heme synthesis pathway. - Its activity is tightly regulated, and its overexpression or deficiency can lead to disorders like **acute intermittent porphyria**. *Hmg coa reductase* - **HMG-CoA reductase** is the **rate-limiting enzyme** in the **cholesterol biosynthesis pathway**, not heme synthesis. - It is the target enzyme for statin medications, which lower cholesterol levels. *ALA dehydratase* - **ALA dehydratase** (also known as porphobilinogen synthase) is the second enzyme in the heme synthesis pathway, responsible for converting two molecules of **ALA to porphobilinogen**. - While critical, it is not the rate-limiting step; inhibition of this enzyme can lead to **lead poisoning**. *Uroporphyrinogen 1 synthase* - **Uroporphyrinogen I synthase** (also called hydroxymethylbilane synthase or porphobilinogen deaminase) catalyzes the formation of **hydroxymethylbilane** from four molecules of **porphobilinogen**. - A deficiency in this enzyme is associated with **acute intermittent porphyria**, but it is not the rate-limiting enzyme of the overall pathway.

Practice by Chapter

Hemoglobin Structure and Function

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Oxygen Transport and Oxygen-Hemoglobin Dissociation Curve

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Hemoglobin Variants and Hemoglobinopathies

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Thalassemias

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Methemoglobin and Abnormal Hemoglobins

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Hemoglobin Synthesis

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Heme Synthesis and Porphyrias

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Iron Absorption and Transport

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Iron Storage and Recycling

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Disorders of Iron Metabolism

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Anemia: Biochemical Aspects

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Biochemistry of Hemostasis

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