Fibroblasts are cells located in the upper edge of the dermis bordering the epidermis and are specialised in producing the skin’s collagen and elastin. Collagen proteins found in the skin, as well as in cartilage and bone, form a mesh like framework in the dermis to give the skin strength and elasticity. Moisture binding molecules called glycoproteins enable collagen fibres rich in glycine, to retain water and give moisture to the epidermis. Another coil like connective tissue protein, elastin, which has a high percentage of both glycine and alanine, is found in the dermis giving the skin its ability to return to the original shape, or its elasticity.
Keratins, which have larger amounts of the sulphur-containing amino acid cysteine, assemble into bundles to form intermediate keratin proteins capable of annealing end-to-end into long filaments. These are tough and form unmineralised tissues. Derived from the Greek root kerato meaning “horn like”, filaments called keratin abound in keratinocytes in the cornified layer of the epidermis and are present in epithelial cells in general. These are cells which have undergone keratinisation. For example, thymic epithelial cells are known to react with antibodies for keratin in the thymus.
Combined into “hard” or “soft” cytokeratins, proteins are understood to occur as either neutral basic or acidic keratin in the skin’s stratum corneum of the stratified epithelial layers, cornea of the eye, squamous epithelia and ducts as well as the simple epithelium. More flexible and elastic keratins of the hair are harder and consist of coiled single protein strands which are then twisted helically into ropes that may be further coiled.