Chemistry of skin and pigmentation MCQs With Answer

Chemistry of Skin and Pigmentation MCQs With Answer

This quiz set is tailored for M.Pharm students studying Herbal Cosmetics (MPG 204T) and focuses on the chemical principles underlying skin pigmentation. It covers melanogenesis pathways, pigment chemistry (eumelanin vs pheomelanin), key enzymes and transcriptional regulators, melanosome biology, effects of UV and oxidative stress, and common natural and synthetic depigmenting agents used in herbal formulations. Questions also examine analytical methods for pigmentation assessment and the biochemical basis of pigmentary disorders. Each question is crafted to deepen conceptual understanding and support application in formulation, evaluation, and research of herbal cosmetic actives targeting pigmentation.

Q1. Which pigment is primarily responsible for the long-term brown to black color of human skin?

• Melanin
• Hemoglobin
• Carotene
• Bilirubin

Correct Answer: Melanin

Q2. What are the two major classes of melanin found in human skin?

• Eumelanin and Pheomelanin
• Neuromelanin and Hemomelanin
• Carotenoid-melanin and Lipomelanin
• Porphyrin and Bilirubin

Correct Answer: Eumelanin and Pheomelanin

Q3. Which enzyme is considered the rate-limiting enzyme in the melanogenesis pathway?

• Tyrosinase
• Monoamine oxidase
• Peroxidase
• Lipoxygenase

Correct Answer: Tyrosinase

Q4. Tyrosinase catalyzes the initial conversion in melanin biosynthesis from which substrate to which product?

• L-tyrosine to L-DOPA
• DOPA to dopamine
• DOPA to dopachrome
• Cysteine to cysteinyldopa

Correct Answer: L-tyrosine to L-DOPA

Q5. Which transcription factor is the master regulator of melanocyte differentiation and melanogenic enzyme expression?

• MITF (microphthalmia-associated transcription factor)
• NF-κB
• AP-1
• STAT3

Correct Answer: MITF (microphthalmia-associated transcription factor)

Q6. Activation of the melanocortin 1 receptor (MC1R) primarily increases which intracellular second messenger to stimulate melanogenesis?

• cAMP
• cGMP
• IP3
• Calcium

Correct Answer: cAMP

Q7. Pheomelanin differs chemically from eumelanin mainly by the incorporation of which element?

• Sulfur
• Iron
• Phosphorus
• Chlorine

Correct Answer: Sulfur

Q8. During melanosome maturation, which characteristic marks Stage III melanosomes?

• Development of an organized fibrillar matrix with progressive melanin deposition
• Complete absence of melanin and presence of vesicular membranes
• Extracellular release of melanosomal contents
• Degradation inside lysosomes

Correct Answer: Development of an organized fibrillar matrix with progressive melanin deposition

Q9. What is the predominant mechanism by which melanosomes are transferred from melanocytes to keratinocytes in human epidermis?

• Phagocytosis of melanocyte dendrite tips by keratinocytes
• Direct fusion of melanocyte nucleus with keratinocytes
• Diffusion of melanin monomers through intercellular space
• Endocytosis of free melanin released into dermis

Correct Answer: Phagocytosis of melanocyte dendrite tips by keratinocytes

Q10. Which plant-derived compound is widely used in herbal cosmetics as a tyrosinase inhibitor and skin-lightening agent?

• Arbutin
• Kojic acid
• Hydroquinone
• Azelaic acid

Correct Answer: Arbutin

Q11. Hydroquinone reduces pigmentation primarily by which combined mechanism?

• Acting as a tyrosinase substrate and causing selective melanocyte cytotoxicity
• Increasing melanosome transfer to keratinocytes
• Stimulating melanocyte proliferation
• Enhancing eumelanin polymerization

Correct Answer: Acting as a tyrosinase substrate and causing selective melanocyte cytotoxicity

Q12. The phenolic oxidation of DOPA in melanogenesis produces which reactive intermediate?

• Dopaquinone
• Dopamine
• Melanogenin
• Serotonin

Correct Answer: Dopaquinone

Q13. Eumelanin formation involves oxidative polymerization through which key indolic intermediates?

• DHI (5,6-dihydroxyindole) and DHICA (5,6-dihydroxyindole-2-carboxylic acid)
• Cysteinyldopa and tyrosine
• Serotonin and melatonin
• Porphyrin and heme

Correct Answer: DHI (5,6-dihydroxyindole) and DHICA (5,6-dihydroxyindole-2-carboxylic acid)

Q14. Ultraviolet (UV) radiation increases melanogenesis primarily by upregulating which pathway in keratinocytes that leads to alpha-MSH production?

• p53-mediated POMC (pro-opiomelanocortin) transcription
• Nrf2 antioxidant response activation
• Wnt/β-catenin pathway inhibition
• JAK-STAT cytokine signaling

Correct Answer: p53-mediated POMC (pro-opiomelanocortin) transcription

Q15. The Fitzpatrick skin phototype classification is primarily used to categorize skin by which clinical criterion?

• Response of skin to UV exposure (tendency to tan or burn)
• Baseline melanin chemical composition
• Dermal collagen density
• Trans-epidermal water loss rates

Correct Answer: Response of skin to UV exposure (tendency to tan or burn)

Q16. Besides light absorption, melanin contributes to skin protection by which chemical activities?

• Scavenging reactive oxygen species and chelating transition metal ions
• Stimulating keratinocyte proliferation
• Promoting lipid peroxidation
• Blocking vitamin D synthesis

Correct Answer: Scavenging reactive oxygen species and chelating transition metal ions

Q17. How does pH generally affect mammalian tyrosinase activity relevant to formulation design?

• Activity is higher at neutral to slightly alkaline pH compared with acidic pH
• Activity is maximal only at strongly acidic pH (<3)
• Tyrosinase is completely inactive above pH 5
• pH has no measurable effect on tyrosinase

Correct Answer: Activity is higher at neutral to slightly alkaline pH compared with acidic pH

Q18. Kojic acid reduces melanin synthesis primarily by which chemical mechanism at the tyrosinase active site?

• Chelation of the copper ions required for tyrosinase catalytic activity
• Providing sulfur for pheomelanin synthesis
• Activating melanocyte cAMP signaling
• Alkalinizing melanosomal pH to enhance enzyme activity

Correct Answer: Chelation of the copper ions required for tyrosinase catalytic activity

Q19. Which non-invasive analytical method is commonly used to quantify skin melanin content or pigmentation changes in cosmetic studies?

• Reflectance spectrophotometry (melanin index)
• Western blot of skin biopsy
• Gas chromatography of skin surface lipids
• Complete blood count (CBC)

Correct Answer: Reflectance spectrophotometry (melanin index)

Q20. Which pigment contributes predominantly to the yellow-orange hue observed in some skin types?

• Carotene
• Melanin
• Hemoglobin
• Bilirubin

Correct Answer: Carotene

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