Hemoglobin and Iron Metabolism Practice Questions

Q: In the context of iron metabolism, what does hepcidin inhibit?

Iron export from enterocytes. ***Iron export from enterocytes*** - **Hepcidin** is a key regulator of systemic iron homeostasis, primarily functioning by **inhibiting iron export** from enterocytes (duodenal mucosal cells). - It does this by binding to and inducing the degradation of **ferroportin**, the sole known iron exporter, thus reducing iron absorption into the bloodstream. *Absorption of cobalamine* - The absorption of **cobalamine (vitamin B12)** is primarily dependent on **intrinsic factor** secreted by gastric parietal cells, not hepcidin. - While iron and B12 deficiencies can coexist, hepcidin does not directly modulate B12 absorption. *Folic acid synthesis* - **Folic acid** (vitamin B9) is an essential nutrient that humans cannot synthesize; it must be obtained from the diet. - Hepcidin has no role in the synthesis or absorption of folic acid. *Respiratory oxidase* - **Respiratory oxidases** are enzymes involved in cellular respiration, particularly within the electron transport chain in mitochondria. - Hepcidin's action on iron metabolism is distinct from the function of these enzymes.

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

Portland. ***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.

Q: Which is an inhibitor of ferrochelatase ?

Lead. ***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.

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

Heme. ***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.

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

Ferritin. ***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

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

15 mg/day. ***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.

Q: Which porphyrin forms the organic component of heme?

Protoporphyrin IX. ***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.

Q: The primary defect which leads to sickle cell anemia is:

Replacement of glutamate by valine in β-chain of HbA. ***Replacement of glutamate by valine in β-chain of HbA*** - The primary defect in sickle cell anemia is a **point mutation** that leads to the replacement of **glutamic acid** with **valine** in the **sixth position** of the β-globin chain [1]. - This mutation causes the hemoglobin (HbS) to polymerize under low oxygen conditions, resulting in the characteristic **sickle-shaped red blood cells** [1]. *A nonsence mutation in the I3-chain of HbA* - A nonsense mutation leads to a **premature stop codon**, which is not the mechanism behind sickle cell anemia. - This mutation does not involve the β-globin chain, which is critical in this specific disorder. *Substitution of valine by glutamate in the a-chain of HbA* - This statement is incorrect as sickle cell anemia specifically involves the **β-chain**, not the **α-chain**. - Substituting valine with glutamate does not cause sickling but rather the opposite of the actual defect observed in this condition. *An abnormality in porphyrin part of hemoglobin* - Sickle cell anemia does not arise from **porphyrin metabolism issues**, which are related to conditions like **porphyrias**. - The primary defect is a change in the amino acid sequence, not in the porphyrin structure of hemoglobin. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Blood And Bone Marrow Disease, pp. 598-599.

Q: Which isoform of LDH is raised in Anemia ?

LDH 2. ***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 1

In the context of iron metabolism, what does hepcidin inhibit?

Accepted Answer

Iron export from enterocytes

Answer

Absorption of cobalamine

Answer

Folic acid synthesis

Answer

Respiratory oxidase

Question 2

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

Accepted Answer

Portland

Answer

Gower I

Answer

Gower II

Answer

Fetal hemoglobin

Question 3

Which is an inhibitor of ferrochelatase ?

Accepted Answer

Lead

Answer

Mercury

Answer

Iron

Answer

Arsenic

Question 4

Aminolevulinic acid is a metabolic product in the synthesis of -

Accepted Answer

Heme

Answer

Tryptophan

Answer

Collagen

Answer

Glycosaminoglycans

Question 5

Which protein is responsible for conserving iron in the body?

Accepted Answer

Ferritin

Answer

Hepcidin

Answer

Hemopexin

Answer

Transferrin

Question 6

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

Accepted Answer

15 mg/day

Answer

30 mg/day

Answer

35 mg/day

Answer

20 mg/day

Question 7

Which of the following statements about hemoglobin is true?

Accepted Answer

Hemoglobin consists of two alpha and two beta subunits, each capable of binding one O2 molecule.

Answer

Each hemoglobin molecule can bind up to six O2 molecules.

Answer

Each hemoglobin subunit contains two heme groups, which bind oxygen.

Answer

Each hemoglobin molecule is made of 6 polypeptide chains.

Question 8

Which porphyrin forms the organic component of heme?

Accepted Answer

Protoporphyrin IX

Answer

Uroporphyrin

Answer

Coproporphyrin

Answer

Deuteroporphyrin

Question 9

The primary defect which leads to sickle cell anemia is:

Accepted Answer

Replacement of glutamate by valine in β-chain of HbA

Answer

An abnormality in porphyrin part of hemoglobin

Answer

A nonsense mutation in the β-chain of HbA

Answer

Substitution of valine by glutamate in the α-chain of HbA

Question 10

Which isoform of LDH is raised in Anemia ?

Accepted Answer

LDH 2

Answer

LDH 5

Answer

LDH 4

Answer

LDH 1

Hemoglobin and Iron Metabolism — MCQs

Hemoglobin and Iron Metabolism — MCQs

On this page

Practice by Chapter

Want unlimited practice?