noun, plural: melanosomes
A melanosome is an organelle of a pigment cell, such as a melanocyte. A melanocyte is a pigment cell that produces melanin, a natural pigment responsible for the color of skin, hair, eyes, etc. Melanin is synthesized and stored within the melanosome. Melanogenesis is the process of producing melanin. Producing melanin is important since it is a means of the body to protect the underlying skin layer such as the hypodermis from adverse effects (e.g. DNA photodamage) of UV-B light exposure. The black (or dark brown) pigment allows the absorption of the majority of the UV-B light passing through the skin layer.1 Thus, increased exposure to UV-B radiation leads to heightened melanogenesis.
Melanosomes are elongated organelles and resemble sausage or cigar in shape. They may reach up to 500 nm in length. The organelle is bounded by a bilipid membrane. Some melanosomes are capable of movement within the melanocyte. They do so by forming pseudopodia that aid in their movement within the cell in response to UV light (photoprotective function).
Word origin: Greek melas ("black, dark")
1 Agar, N. & Young, A. R. (2005). "Melanogenesis: a photoprotective response to DNA damage?". Mutation Research. 571 (1–2): 121–32.