Skin cells. Coloured transmission electron micrograph (TEM) of a section through keratinocyte skin cells, which are found in the epidermis layer of the skin. The cells have a large nucleus (yellow), which contains their genetic information. The cells' cytoplasm is rich in filaments of the protein cytokeratin (dark brown). The filaments extend into junctions between the cells known as desmosomes, which help the cells to withstand mechanical stress.