Cell structure. Confocal light micrograph of cultured endothelial cells. A fluorescent dye has been used to show the cell structure. Nuclei (blue) contain the cell's genetic information, DNA (deoxyribonucleic acid) packaged in chromosomes. Actin filaments, which form part of the cell cytoskeleton are green. The cytoskeleton is responsible for the structure and motility of the cell. Actin is the most abundant cellular protein. The golgi apparatus, or body (red), is a membrane-bound organelle that modifies and packages proteins. It consists of long flattened vesicles arranged in stacks. Endothelial cells are flat and line all of the body's blood vessels.