Do not confuse the pigment Carotene with the protein Keratin
Carotene is a pigment found in plants, as an accessory to chlorophyll in the absorption of light for photosynthesis. It gives colour to carrots, hence the name, but it is found in other vegetables and fruits. It is widely used as a food colouring additive (E number: E160a).
There are actually a number of molecules called carotene, and associated compounds called carotenoids, but this one, β (beta) -carotene, is the main one.
It effectively consists of two molecules of vitamin A, so it may be considered as a storage form: a 'provitamin'. Its molecular structure, with cyclohexene rings at each end and a connecting unsaturated hydrocarbon chain and methyl groups, makes it hydrophobic so it is highly soluble in fats, and it absorbs light most strongly between 400-500 nm (the green/blue part of the spectrum) so it appears orange.
Its IUPAC name is:
It is broken down (splitting in the middle of the 18-carbon chain with the addition of oxygen) in the epithelium of the human small intestine by the enzyme
β-carotene 15,15'-monooxygenase, resulting in two molecules of retinal.