Answer to Question #167675 in Human Anatomy and Physiology for Jasmine Elfaqir

Question

. It is known that granules of pigment - melanin can be found in two types of cells of the skin epidermis: melanocytes and keratinocytes. Explain the mechanisms of the appearance of melanin granules in these types of cells. Which cell is involved in its synthesis?

Answer 1

Melanin granules are synthetized in melanocytes. The first step of the biosynthetic pathway for both eumelanins and pheomelanins is catalysed by tyrosinase.

Tyrosine → DOPA → dopaquinone

Dopaquinone can combine with cysteine by two pathways to benzothiazines and pheomelanins:

Dopaquinone + cysteine → 5-S-cysteinyldopa → benzothiazine intermediate → pheomelanin

Dopaquinone + cysteine → 2-S-cysteinyldopa → benzothiazine intermediate → pheomelanin

Also, dopaquinone can be converted to leucodopachrome and follow two more pathways to the eumelanins:

Dopaquinone → leucodopachrome → dopachrome → 5,6-dihydroxyindole-2-carboxylic acid → quinone → eumelanin

Dopaquinone → leucodopachrome → dopachrome → 5,6-dihydroxyindole → quinone → eumelanin

Keratinocytes don't syntetyze melanin, they get it from melanocytes. Each melanocyte in the epidermis has several dendrites that stretch out to connect it with many keratinocytes. The melanin is then stored within keratinocytes and melanocytes in the perinuclear area as supranuclear “caps”, where it protects the DNA from UVR-induced damage.