Vitamins and Coenzymes Practice Questions

Q: A patient whose diet mainly consists of pulses and rice presents with bowed legs. Which of the following vitamins could have prevented this condition?

Vitamin D. ***Vitamin D*** - This vitamin is essential for the absorption of **calcium** and **phosphate**, minerals necessary for bone mineralization. - A deficiency results in **Rickets** (softening and weakening of bones in children), leading to classic deformities like **bowed legs (genu varum)**. *Vitamin A* - Vitamin A deficiency primarily affects vision, causing **night blindness** and **xerophthalmia**. - It is crucial for cell differentiation and immune function, but its deficiency does not cause **rickets** or bowed legs. *Vitamin B₁₂* - Deficiency leads to **megaloblastic anemia** and often **peripheral neuropathy** (subacute combined degeneration). - While essential for cell division and nerve function, it is not directly involved in the calcium homeostasis required to prevent bone deformities. *Vitamin C* - Vitamin C deficiency causes **scurvy**, characterized by impaired **collagen synthesis**, leading to bleeding gums and poor wound healing. - It is not the primary factor preventing defective bone mineralization (rickets) that causes **bowed legs**.

Q: Which vitamin deficiency can lead to lactic acidosis?

Thiamine. ***Thiamine*** - **Thiamine (Vitamin B1)** is a crucial cofactor for the enzyme **pyruvate dehydrogenase (PDH)**, which converts **pyruvate** to **acetyl-CoA** to enter the Krebs cycle. - When thiamine is deficient, pyruvate cannot be processed efficiently, leading to its accumulation and subsequent shunting into **lactate** via **lactate dehydrogenase**, thus causing **lactic acidosis**, characteristic of **beriberi**. *Riboflavin* - Riboflavin (Vitamin B2) is a precursor for the coenzymes **FAD** and **FMN**, essential for redox reactions, but its deficiency symptoms mainly involve the oral cavity and skin. - Deficiency leads to **angular cheilitis**, **glossitis**, and **corneal vascularization**, and is not the direct cause of severe lactic acidosis. *Niacin* - Niacin (Vitamin B3) is a precursor for **NAD+** and **NADP+**, vital for many metabolic reactions. - Deficiency causes **pellagra**, characterized by the 3 D's: **Dermatitis**, **Diarrhea**, and **Dementia**, not primarily lactic acidosis. *Biotin* - Biotin (Vitamin B7) acts as a coenzyme for **carboxylase enzymes** (e.g., pyruvate carboxylase, acetyl-CoA carboxylase), which are necessary for gluconeogenesis and fatty acid synthesis. - While **pyruvate carboxylase** uses biotin, thiamine deficiency specifically impairs the key step of converting pyruvate to acetyl-CoA (via PDH complex), making it the primary cause of vitamin-deficiency-related lactic acidosis.

Q: Which of the following enzymes is dependent on Vitamin C for its activity?

Prolyl hydroxylase. ***Prolyl hydroxylase***- **Prolyl hydroxylase** requires **Vitamin C** (ascorbic acid) to reduce the ferric iron (Fe3+) in its active site back to **ferrous iron (Fe2+),** thereby maintaining its catalytic function.- This enzyme hydroxylates **proline** residues, a critical post-translational modification necessary for the stabilization and proper triple-helical winding of **collagen**; deficiency results in **scurvy**. *Lysyl dehydrogenase*- This enzyme is involved in **lysine catabolism** via deamination and is generally not associated with the direct role of Vitamin C in collagen synthesis.- It is distinct from **lysyl hydroxylase**, which *is* a Vitamin C-dependent enzyme modifying lysine in collagen. *Lysyl oxidase*- **Lysyl oxidase** is responsible for forming covalent **cross-links** between collagen and elastin molecules, stabilizing the extracellular matrix structure.- This enzyme requires **copper** (Cu2+) as a cofactor for its activity and is not directly dependent on Vitamin C. *Hydroxyprolyl kinase*- This is not a standard physiological enzyme involved in the key metabolic pathways of **collagen synthesis** or degradation.- Kinase activity concerns **phosphorylation**, which is unrelated to the **hydroxylation** mechanism essential for Vitamin C dependence in connective tissue metabolism.

Q: A patient presents with gum bleeding, petechiae, poor wound healing, and other related symptoms. Which of the following vitamin deficiencies is most likely responsible for this presentation?

Vitamin C. ***Vitamin C*** - Vitamin C (ascorbic acid) is essential for the hydroxylation of **proline** and **lysine** residues during collagen synthesis, crucial for maintaining the integrity of blood vessels and skin. - Deficiency results in **scurvy**, characterized by defective collagen, leading to fragile capillaries (manifesting as **gum bleeding** and **petechiae**) and impaired **wound healing**. *Vitamin A* - Deficiency is primarily associated with visual disturbances, most notably **night blindness** (**nyctalopia**), and **xerophthalmia** (dry eyes). - Its main roles involve vision, epithelial differentiation, and immune function, not the stability of subendothelial collagen required to prevent bleeding tendencies described here. *Vitamin B6* - Pyridoxine deficiency symptoms include **seborrheic dermatitis**, **stomatitis**, **cheilosis**, and neurological issues like **peripheral neuropathy** and seizures in infants. - While involved in numerous metabolic pathways, its deficiency is not responsible for the characteristic symptoms of capillary fragility (petechiae and bleeding). *Vitamin B3* - Niacin deficiency causes **pellagra**, classically identified by the "3 D's": **Dermatitis** (photosensitive rash), **Diarrhea**, and **Dementia**. - Although pellagra involves epithelial changes (dermatitis), it does not typically present with the severe vascular fragility, gum manifestations, and poor generalized wound healing seen in scurvy.

Q: Vitamin A deficiency leads to?

Xerophthalmia. ***Xerophthalmia***- **Vitamin A** (retinol) is essential for the formation of **rhodopsin**, the photopigment necessary for low-light vision, making deficiency a primary cause of **night blindness** (nyctalopia).- Deficiency leads to **keratinization** of the *corneal and conjunctival epithelium*, resulting in dryness of the eye (*xerosis*), progressing to corneal ulcers and potentially blindness (*keratomalacia*).*Beriberi*- Caused by a deficiency of **Vitamin B1** (**thiamine**), which is crucial for carbohydrate metabolism.- Symptoms include **peripheral neuropathy** (dry beriberi) or high-output cardiac failure (wet beriberi).*Pellagra*- Caused by a deficiency of **Vitamin B3** (**niacin**), or its precursor **tryptophan**.- Classically presents with the '3 Ds': **dermatitis**, **diarrhea**, and **dementia** (and eventually death).*Neuropathy*- While severe Vitamin A deficiency can cause secondary issues, primary **neuropathy** is mainly associated with deficiencies of B-vitamins like **B1** (thiamine), **B6** (pyridoxine), or **B12** (cobalamin).- *Neuropathy* is a symptom and not the specific disease term commonly linked directly and primarily to Vitamin A deficiency, which is **xerophthalmia**.

Q: A 34-year-old male whose staple diet primarily consisted of only maize presents with diarrhea, dementia, and photosensitive dermatitis in sun-exposed areas. Which vitamin is most likely deficient in this patient?

Niacin. **Correct: Niacin** - The constellation of **dementia**, **diarrhea**, and **photosensitive dermatitis** (the 3 Ds) is the hallmark presentation of **Pellagra**. - A diet reliant on **maize** (corn) is a classic cause of Pellagra because maize is deficient in **tryptophan**, a vital precursor to Niacin (Vitamin B3). - Pellagra can progress to a fourth D (**Death**) if untreated. *Incorrect: Vitamin B6* - Deficiency typically manifests as **peripheral neuropathy**, **seborrheic dermatitis** (non-photosensitive), and microcytic anemia (**sideroblastic anemia**). - It is not associated with the severe chronic diarrhea or the characteristic sun-exposed rash seen in Pellagra. *Incorrect: Ascorbic acid* - Deficiency causes **Scurvy**, characterized by **bleeding gums**, **perifollicular hemorrhages** (petechiae), and **impaired wound healing**. - Neurological symptoms typical of dementia and pronounced gastrointestinal symptoms are not primary features of Scurvy. *Incorrect: Biotin* - Biotin (Vitamin B7) deficiency is rare, usually presenting with **alopecia**, non-specific dermatitis, and sometimes hypotonia or developmental delay. - It is differentiated by the absence of characteristic photosensitive rash and the severe central nervous system symptoms (dementia) that define this case.

Q: Which vitamin deficiency causes xerophthalmia, a condition which causes dry eyes?

Vitamin A. **Vitamin A** - It is critical for the differentiation and maintenance of epithelial tissues, including the **conjunctival** and **corneal** epithelium. - Deficiency impairs the eye's ability to produce necessary mucous and results in **xerophthalmia** (pathological dryness of the conjunctiva and cornea) and **night blindness**. *Vitamin B* - Deficiencies in B vitamins (e.g., B1, B2, B3, B12) primarily affect cellular metabolism, causing conditions like **Beriberi** (B1) or **Pellagra** (B3). - While ocular issues like angular blepharitis can occur with deficiencies like Riboflavin (B2), the primary cause of severe **xerophthalmia** is not Vitamin B deficiency. *Vitamin C* - Vitamin C is essential for **collagen synthesis** and acts as a powerful antioxidant. - Its deficiency leads to **scurvy**, characterized by fragile blood vessels, **gingivitis**, and impaired wound healing, unrelated to primary eye dryness or **xerophthalmia**. *Vitamin D* - This vitamin is primarily involved in maintaining **calcium and phosphate homeostasis** for bone health. - Deficiency causes **rickets** in children and **osteomalacia** in adults, systemic conditions that do not cause **xerophthalmia**.

Q: Which of the following vitamins functions as a coenzyme in transamination reactions?

Vitamin B6 (Pyridoxine). ***Vitamin B6 (Pyridoxine)*** - **Pyridoxal phosphate (PLP)**, the active coenzyme form of Vitamin B6, is absolutely essential for **transamination reactions** (transfer of amino groups from an amino acid to a keto acid), making it critical in amino acid metabolism. - PLP is also involved in other enzymatic reactions, including decarboxylation and racemization of amino acids, and is crucial for **heme synthesis** and **neurotransmitter synthesis**. *Vitamin B1 (Thiamine)* - Functions primarily as **thiamine pyrophosphate (TPP)**, which is a coenzyme for enzymes involved in the transfer of **aldehyde groups**, such as **pyruvate dehydrogenase** and alpha-ketoglutarate dehydrogenase (oxidative decarboxylation). - Deficiency leads to Beriberi (wet, dry, and infantile) and **Wernicke-Korsakoff syndrome**. *Vitamin B12 (Cobalamin)* - Serves as a coenzyme in **methylation reactions** (methionine synthase) and **isomerization reactions** (methylmalonyl-CoA mutase). - Essential for **DNA synthesis**, **red blood cell formation**, and **neurological function**. - Deficiency leads to **megaloblastic anemia** and **subacute combined degeneration** of the spinal cord. *Vitamin B2 (Riboflavin)* - Serves as a precursor for the coenzymes **flavin mononucleotide (FMN)** and **flavin adenine dinucleotide (FAD)**. - These coenzymes are crucial for various **oxidation-reduction reactions** (electron transfer) in intermediary metabolism, such as those catalyzed by succinate dehydrogenase.

Q: A patient presents with anemia, positive Romberg sign, and other neurological findings suggestive of vitamin B12 deficiency. Laboratory findings show elevated homocysteine levels. Which amino acid is likely to be deficient in this patient?

Methionine. ***Methionine*** - Vitamin B12 is an essential cofactor for the enzyme **methionine synthase**, which converts **homocysteine** into methionine. - A deficiency in B12 blocks this essential metabolic step, leading to the accumulation of homocysteine and a resultant deficiency of **methionine**. *Cysteine* - **Cysteine** is derived from methionine via **homocysteine** and requires **Vitamin B6** (pyridoxal phosphate) for its synthesis, not Vitamin B12 directly. - While B12 deficiency results in increased homocysteine which is an intermediate, the direct deficiency relates to the product of the B12-dependent step, **methionine**. *Tyrosine* - **Tyrosine** is synthesized from **phenylalanine** by the enzyme phenylalanine hydroxylase, a pathway entirely separate from **Vitamin B12** and homocysteine metabolism. - It is generally considered a non-essential amino acid whose metabolism is disturbed primarily in conditions like **Phenylketonuria (PKU)**. *Glutamate* - **Glutamate** is a crucial excitatory neurotransmitter whose synthesis and metabolism are not directly linked to the **methionine synthase** reaction or **Vitamin B12** deficiency. - Neurological symptoms associated with B12 deficiency (like Romberg sign) are due to impaired **myelin synthesis** caused by reduced SAM (derived from methionine) and methylmalonyl-CoA accumulation.

Q: A child presents with a history of fractures, multiple petechiae, perifollicular hemorrhages, and gum bleeding. Which of the following enzyme defects is involved?

Prolyl hydroxylase. ***Prolyl hydroxylase*** - **Vitamin C (Ascorbic acid)** is a necessary cofactor for Prolyl hydroxylase and Lysyl hydroxylase, which are essential for the hydroxylation of proline and lysine residues in procollagen. - Deficiency of Vitamin C leads to inactivation of this enzyme, resulting in unstable and defective **collagen** that causes vascular fragility (leading to petechiae and gum bleeding) and impaired bone matrix (resulting in fractures). *Lysyl oxidase* - **Lysyl oxidase** is required for the crucial cross-linking of collagen and elastin fibers, a process that relies on **copper**, not Vitamin C, as a main cofactor. - A defect in this enzyme primarily causes syndromes like certain types of **Ehlers-Danlos Syndrome** (Type V) or features associated with **Menkes disease**. *Tyrosinase* - **Tyrosinase** is the key enzyme in the biosynthesis of **melanin** from tyrosine. - A defect in Tyrosinase causes various forms of **Albinism**, characterized by lack of pigmentation in the skin, hair, and eyes, which is unrelated to the described hemorrhagic and skeletal findings. *Alkaline phosphatase* - **Alkaline phosphatase (ALP)** plays a vital role in bone mineralization by hydrolyzing pyrophosphate, preventing its inhibitory effect on calcification. - While important for bone health, ALP deficiency causes **Hypophosphatasia**, and it is not directly involved in the pathogenesis of structural collagen defects seen in **Scurvy**.

Question 1

A patient whose diet mainly consists of pulses and rice presents with bowed legs. Which of the following vitamins could have prevented this condition?

Accepted Answer

Vitamin D

Answer

Vitamin A

Answer

Vitamin B₁₂

Answer

Vitamin C

Question 2

Which vitamin deficiency can lead to lactic acidosis?

Accepted Answer

Thiamine

Answer

Riboflavin

Answer

Niacin

Answer

Biotin

Question 3

Which of the following enzymes is dependent on Vitamin C for its activity?

Accepted Answer

Prolyl hydroxylase

Answer

Lysyl oxidase

Answer

Lysyl dehydrogenase

Answer

Hydroxyprolyl kinase

Question 4

A patient presents with gum bleeding, petechiae, poor wound healing, and other related symptoms. Which of the following vitamin deficiencies is most likely responsible for this presentation?

Accepted Answer

Vitamin C

Answer

Vitamin B3

Answer

Vitamin B6

Answer

Vitamin A

Question 5

Vitamin A deficiency leads to?

Accepted Answer

Xerophthalmia

Answer

Beriberi

Answer

Neuropathy

Answer

Pellagra

Question 6

A 34-year-old male whose staple diet primarily consisted of only maize presents with diarrhea, dementia, and photosensitive dermatitis in sun-exposed areas. Which vitamin is most likely deficient in this patient?

Accepted Answer

Niacin

Answer

Vitamin B6

Answer

Ascorbic acid

Answer

Biotin

Question 7

Which vitamin deficiency causes xerophthalmia, a condition which causes dry eyes?

Accepted Answer

Vitamin A

Answer

Vitamin C

Answer

Vitamin D

Answer

Vitamin B

Question 8

Which of the following vitamins functions as a coenzyme in transamination reactions?

Accepted Answer

Vitamin B6 (Pyridoxine)

Answer

Vitamin B1 (Thiamine)

Answer

Vitamin B12 (Cobalamin)

Answer

Vitamin B2 (Riboflavin)

Question 9

A patient presents with anemia, positive Romberg sign, and other neurological findings suggestive of vitamin B12 deficiency. Laboratory findings show elevated homocysteine levels. Which amino acid is likely to be deficient in this patient?

Accepted Answer

Methionine

Answer

Tyrosine

Answer

Cysteine

Answer

Glutamate

Question 10

A child presents with a history of fractures, multiple petechiae, perifollicular hemorrhages, and gum bleeding. Which of the following enzyme defects is involved?

Accepted Answer

Prolyl hydroxylase

Answer

Tyrosinase

Answer

Alkaline phosphatase

Answer

Lysyl oxidase

Vitamins and Coenzymes — MCQs

Vitamins and Coenzymes — MCQs

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