Animal cell structure. Illustration of the internal structure of an animal cell. Inside the cell, the cellular structures (organelles) include the Golgi apparatus, the rough endoplasmic reticulum (folded), mitochondria (oval), the cell nucleus (upper right), various cytoskeleton elements (cylinders and strands), and internal transport vesicles (green spheres). The cell nucleus has been dissected to reveal its interior where the genetic material DNA (deoxyribonucleic acid) is stored, shown here as chromosomes (red). Also shown are chemicals (small spheres) entering the cell at bottom through membrane pores.