Illustration of the structure of a typical animal cell. The cell nucleus is at centre left. It holds the cell's genetic material in the form of DNA (deoxyribonucleic acid). Surrounding the nucleus is the endoplasmic reticulum (ER). Some parts of the ER are studded with ribosomes (white dots), sites of active protein synthesis. Vesicles (spheres) leave the rough ER, releasing their protein cargo into the Golgi apparatus (pink at bottom and top left) where the proteins are stored before being re-packaged for transport. Mitochondria (white and red ovals) are the sites of energy synthesis within the cell.