WorksheetsQUIZ -1 Niacin and Vitamin B9,B12 , Ca & Fe Metabolism Questions
Total questions: 50
Worksheet time: 38mins
A patient with Hartnup disease develops pellagra-like symptoms. The most likely biochemical abnormality is impaired intestinal absorption of which amino acid?
Tyrosine
Methionine
Tryptophan
Lysine
A chronic alcoholic presents with dementia, glossitis, and photosensitive dermatitis. Which coenzyme deficiency primarily contributes to neuronal degeneration in this patient?
FAD
NAD+
TPP
Biotin
Which reaction step differentiates NADP+ from NAD+?
Addition of ribose
Phosphorylation of ribose moiety
Addition of AMP
Addition of methyl group
Which of the following best describes the “fourth D” of pellagra if untreated?
Depression
Delirium
Dysphagia
Death
Which compound acts as an intermediate during tryptophan conversion to NAD+?
Serotonin
Kynurenine
Quinolinate
Xanthurenate
Niacin lowers LDL levels mainly by decreasing hepatic synthesis of:
Apolipoprotein A
Apolipoprotein E
Apolipoprotein B
Apolipoprotein C
A child with pellagra shows mental sluggishness and insomnia. These neurological symptoms are mainly due to impaired:
Neurotransmitter synthesis
ATP production in neurons
Myelin formation
Calcium transport
In niacin deficiency, which of the following tissues is most severely affected?
Skin, intestine, and brain
Liver
Kidney
Bone marrow
Which form of niacin is primarily excreted in urine?
Nicotinic acid
NADH
Nicotinamide
N-methylnicotinamide
Niacin-induced hepatotoxicity is suggested by elevation of:
CK-MB
Serum creatinine
ALT and AST
Alkaline phosphatase only
Vitamin B12 is unique among vitamins because it contains which metal?
Magnesium
Zinc
Cobalt
Iron
Which of the following is the biologically active coenzyme form of vitamin B12 involved in methylation reactions?
Cyanocobalamin
Hydroxocobalamin
Methylcobalamin
Adenosylcobalamin
Adenosylcobalamin acts as a coenzyme for which enzyme?
Methylmalonyl-CoA mutase
Methionine synthase
Homocysteine reductase
Thymidylate synthase
A 52-year-old man presents with progressive unsteady gait, numbness in feet, and memory problems. Blood examination shows macrocytosis. Which biochemical abnormality explains the neurological findings?
Decreased hemoglobin synthesis
Accumulation of methylmalonic acid
Reduced iron absorption
Reduced ATP generation
A patient with Crohn’s disease involving terminal ileum presents with anemia and neuropathy. Which step in vitamin B12 handling is impaired?
Hepatic storage
Absorption of IF–B12 complex
Binding to intrinsic factor
Release from food proteins
A patient with pernicious anemia has adequate dietary intake of vitamin B12. The primary defect lies in:
Hepatic conversion to coenzyme forms
Transcobalamin synthesis
Intrinsic factor secretion
Pancreatic protease deficiency
Why does vitamin B12 deficiency lead to pancytopenia?
Increased hemolysis
Defective DNA synthesis in all rapidly dividing cells
Suppressed erythropoietin
Bone marrow fibrosis
Subacute combined degeneration occurs in vitamin B12 deficiency because of damage to:
Anterior horn cells
Cerebellar cortex
Spinothalamic tract only
Posterior and lateral columns of spinal cord
Loss of vibration sense and positive Romberg sign in vitamin B12 deficiency indicate involvement of:
Corticospinal tract
Spinothalamic tract
Posterior columns
Cerebellum
Impaired activity of methylmalonyl-CoA mutase in vitamin B12 deficiency leads to defective synthesis of:
DNA
Myelin
ATP
Hemoglobin
Which metabolic abnormality best explains hyperhomocysteinemia in vitamin B12 deficiency?
Increased methionine synthase activity
Decreased methionine synthase activity
Enhanced folate polyglutamation
Increased adenosylcobalamin formation
Despite adequate dietary intake, a patient develops vitamin B12 deficiency due to the absence of transcobalamin II. The main defect is in:
Conversion to active forms
Transport to tissues
Storage
Absorption
Why does vitamin B12 deficiency take years to manifest clinically?
Low daily requirement
Efficient renal reabsorption
Large hepatic stores
Endogenous synthesis
In vitamin B12 deficiency, anemia appears earlier than neurological signs because:
Folate compensates initially
Myelin synthesis is delayed
Hematopoietic cells divide rapidly
Neurons regenerate faster
Pernicious anemia is caused by:
Dietary deficiency of vitamin B12
Malabsorption of iron
Failure of intrinsic factor secretion
Increased destruction of RBCs
Which dietary source is the richest in vitamin B12?
Cereals
Green leafy vegetables
Milk
Liver
Dietary folate is poorly absorbed unless first converted to an absorbable form. Which enzyme is responsible for this conversion?
Methionine synthase
Folate conjugase (γ-glutamyl hydrolase)
Thymidylate synthase
Dihydrofolate reductase
Which structural feature of folate explains why dietary forms require digestion before absorption?
Reduced oxidation state
Presence of pteridine ring
Multiple glutamate residues (polyglutamate)
Presence of PABA
Which circulating form of folate predominates in plasma?
THF
Folic acid
N5-methyl THF
Polyglutamate folate
Why does pyridoxine deficiency cause seizures?
Demyelination of the spinal cord
Accumulation of methylmalonic acid
Reduced ATP production in neurons
Impaired inhibitory neurotransmitter synthesis
Why is pyridoxal phosphate required for most amino acid–related reactions?
It donates methyl groups
It stabilizes carbanion intermediates
It provides metabolic energy
It transfers phosphate groups
Why does pyridoxine deficiency cause seizures?
Reduced ATP production in neurons
Impaired inhibitory neurotransmitter synthesis
Accumulation of methylmalonic acid
Demyelination of the spinal cord
Which food provides iron in the most bioavailable form?
Pulses
Spinach
Cereals
Liver
PLP deficiency causes hyperhomocysteinemia because PLP is required for:
Oxidation of homocysteine
Transsulfuration of homocysteine
Renal excretion of homocysteine
Remethylation of homocysteine
Bronze diabetes is classically caused by excessive deposition of iron in which organ leading to diabetes mellitus?
Liver hepatocytes
Pancreatic β-cells
Adrenal cortex
Skeletal muscle
Why are green leafy vegetables less efficient sources of calcium despite high calcium content?
High phosphorus content
Low vitamin D content
Presence of oxalates and phytates
Poor intestinal absorption
The characteristic bronze pigmentation in bronze diabetes is due to:
Iron deposition with increased melanin synthesis
Hemosiderin alone
Increased bilirubin
Advanced glycation end products
The treatment of choice that prevents progression of bronze diabetes is:
Oral hypoglycemic agents
Insulin therapy alone
Regular phlebotomy
Iron supplementation
Active intestinal absorption of calcium is most dependent on:
Gastric acid
Vitamin D–dependent calcium-binding protein
Calcitonin
Parathyroid hormone
Why is ionized calcium considered the biologically active form?
It is protein bound
It reflects total body calcium
It directly interacts with receptors and enzymes
It freely crosses cell membranes
Which conceptual role of calcium best explains its importance in muscle contraction?
Sodium–potassium pump activation
Membrane depolarization
Actin–myosin cross-bridge formation regulation
ATP generation
Which symptom is most specific for hypocalcemia?
Fatigue
Bone pain
Carpopedal spasm
Muscle weakness
Chvostek sign occurs in hypocalcemia because of:
Reduced acetylcholine breakdown
Increased potassium permeability
Increased neuromuscular excitability
Muscle fiber degeneration
Why is milk considered the best dietary source of calcium?
High calcium content only
Absence of absorption inhibitors
Presence of vitamin C
Favorable Ca : P ratio
Calcium acts as a second messenger for epinephrine in liver because it:
Replaces cAMP completely
Activates calmodulin-dependent enzymes
Enters nucleus directly
Activates adenylate cyclase
Why must ferric iron (Fe3+) be reduced before absorption?
Fe3+ is toxic
Only Fe3+ binds transferrin
Fe2+ is more soluble at intestinal pH
Fe3+ is protein bound
Which clinical feature is most specific for iron deficiency anemia?
Jaundice
Neuropathy
Koilonychia
Glossitis
Iron deficiency anemia is characterized by:
Macrocytic anemia
Normocytic anemia
Microcytic hypochromic anemia
Hemolytic anemia
The most biologically active form of calcium in blood is:
A. Protein-bound calcium
B. Citrate-bound calcium
C. Ionized calcium
D. Phosphate-bound calcium
Hemochromatosis is a condition of:
A. Iron deficiency
B. Copper overload
C. Iron overload
D. Zinc toxicity
