Hemoglobin and Iron Metabolism Practice Questions

Q: Which of the following is a synthetic oxygen carrier?

Perfluorocarbon. **Perfluorocarbon** - **Perfluorocarbons** (PFCs) are synthetic organic compounds that are chemically inert and can dissolve large amounts of gases, including oxygen. - Due to their ability to carry oxygen, PFCs have been investigated as **blood substitutes** and in drug delivery systems. *2,4-dinitrophenol* - **2,4-dinitrophenol** (DNP) is an **uncoupler of oxidative phosphorylation**, meaning it prevents ATP synthesis while electron transport continues, generating heat instead. - It is a metabolic poison and has been used as a weight-loss drug but is not an oxygen carrier. *Chlorofluorocarbon* - **Chlorofluorocarbons** (CFCs) are organic compounds containing carbon, chlorine, and fluorine, primarily known for their role as **refrigerants** and in **aerosol propellants**. - CFCs are environmentally harmful due to their impact on the ozone layer and do not function as oxygen carriers. *1-fluoro-2,4-dinitrophenol* - **1-fluoro-2,4-dinitrophenol** is a derivative of dinitrophenol and would likely share similar properties as an **uncoupler of oxidative phosphorylation**. - It is not recognized for its ability to carry oxygen.

Q: Heme is synthesized from ?

Glycine + succinyl CoA. ***Glycine + succinyl CoA*** - Heme biosynthesis begins with the condensation of **glycine** and **succinyl CoA** to form **δ-aminolevulinic acid (ALA)**, catalyzed by **ALA synthase (ALAS)**. - This initial reaction is the **rate-limiting step** in heme synthesis and determines the overall production of heme. - This reaction occurs in the **mitochondria** and requires **pyridoxal phosphate (vitamin B6)** as a cofactor. *Lysine + succinyl CoA* - While succinyl CoA is a precursor, **lysine** is an essential amino acid involved in protein synthesis and other metabolic pathways, but not directly in heme synthesis. - The primary amino acid precursor for heme is **glycine**, not lysine. *Arginine + Malonyl CoA* - **Arginine** is involved in the urea cycle and nitric oxide synthesis, not heme synthesis. - **Malonyl CoA** is a key intermediate in **fatty acid synthesis**, not heme synthesis. *Glycine + Malonyl CoA* - **Glycine** is indeed a precursor for heme synthesis. - However, **malonyl CoA** is not involved in heme synthesis; rather, **succinyl CoA** is the correct coenzyme A derivative that condenses with glycine.

Q: Which of the following factors in diet increases iron absorption?

Vitamin C. ***Vitamin C*** - **Vitamin C** (ascorbic acid) enhances **non-heme iron absorption** by reducing ferric iron (Fe3+) to ferrous iron (Fe2+), which is more soluble and readily absorbed in the gut. - It also counteracts the inhibitory effects of certain dietary components like **phytates and tannins** on iron absorption. *Iron-fortified foods* - While iron-fortified foods *provide* iron, they don't inherently increase the *efficiency* of absorption of all forms of iron present in the meal. - The absorption of iron from these foods still depends on the **form of iron used** for fortification and the presence of **absorption enhancers** or inhibitors. *Vitamin A* - **Vitamin A** plays a role in iron metabolism by influencing red blood cell development and mobilization of iron from stores, but it does **not directly enhance iron absorption** from the gut. - Deficiency in Vitamin A can *exacerbate* iron deficiency anemia, but its supplementation doesn't primarily serve to increase absorption. *Fibre diet* - A **high-fibre diet** can *decrease* iron absorption because certain components of fibre, particularly **phytates** (found in whole grains and legumes), bind to iron and hinder its uptake. - While fibre is important for digestive health, it is generally considered an **inhibitor** of iron absorption, especially of non-heme iron.

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

The fall in 2,3-DPG is less.. ***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.

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 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: Pruritus [Itching] associated with Congenital Erythropoietic Porphyria is caused by deficiency of -

Uroporphyrinogen - III synthase. ***Uroporphyrinogen - III synthase*** - Congenital Erythropoietic Porphyria (CEP) is caused by a **deficiency of uroporphyrinogen III synthase**, leading to the accumulation of uroporphyrinogen I and coproporphyrinogen I. - These accumulated **Type I porphyrinogens** are non-functional in heme synthesis and are highly **photoreactive**, causing the characteristic photosensitivity and skin symptoms, including intense pruritus. *5-ALA dehydratase* - Deficiency of **5-ALA dehydratase** (also known as porphobilinogen synthase) is associated with **ALA dehydratase deficiency porphyria (ADP)**, a very rare acute hepatic porphyria. - Symptoms primarily involve **neurovisceral attacks** and do not typically include pruritus or photosensitivity. *Uroporphyrinogen - I synthase* - **Uroporphyrinogen I synthase** is an outdated and incorrect term; the correct enzyme in the heme synthesis pathway is **hydroxymethylbilane synthase (HMB synthase)** or **porphobilinogen deaminase (PBG deaminase)**, which synthesizes HMB. - Deficiency in HMB synthase leads to **acute intermittent porphyria (AIP)**, characterized by acute neurological attacks, not severe pruritus. *HMB synthase* - **HMB synthase** (hydroxymethylbilane synthase), also known as **porphobilinogen deaminase (PBG deaminase)**, is deficient in **acute intermittent porphyria (AIP)**. - AIP is marked by intermittent neurological dysfunction and abdominal pain, with **no significant photosensitivity or pruritus**.

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.

Question 1

Which of the following is a synthetic oxygen carrier?

Accepted Answer

Perfluorocarbon

Answer

Chlorofluorocarbon

Answer

1-fluoro-2,4-dinitrophenol

Answer

2,4-dinitrophenol

Question 2

Heme is synthesized from ?

Accepted Answer

Glycine + succinyl CoA

Answer

Lysine + succinyl CoA

Answer

Arginine + Malonyl CoA

Answer

Glycine + Malonyl CoA

Question 3

Which of the following factors in diet increases iron absorption?

Accepted Answer

Vitamin C

Answer

Iron-fortified foods

Answer

Vitamin A

Answer

Fibre diet

Question 4

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 5

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

Accepted Answer

The fall in 2,3-DPG is less.

Answer

It has a higher pH level than acidic-citrate-dextrose.

Answer

It is more effective in oxygen delivery.

Answer

It has a longer shelf life than acidic-citrate-dextrose.

Question 6

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 7

Which protein is responsible for conserving iron in the body?

Accepted Answer

Ferritin

Answer

Hepcidin

Answer

Hemopexin

Answer

Transferrin

Question 8

Pruritus [Itching] associated with Congenital Erythropoietic Porphyria is caused by deficiency of -

Accepted Answer

Uroporphyrinogen - III synthase

Answer

Uroporphyrinogen - I synthase

Answer

5-ALA dehydratase

Answer

HMB synthase

Question 9

Which is an inhibitor of ferrochelatase ?

Accepted Answer

Lead

Answer

Mercury

Answer

Iron

Answer

Arsenic

Question 10

Aminolevulinic acid is a metabolic product in the synthesis of -

Accepted Answer

Heme

Answer

Tryptophan

Answer

Collagen

Answer

Glycosaminoglycans

Hemoglobin and Iron Metabolism — MCQs

Hemoglobin and Iron Metabolism — MCQs

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