Illustration of the structure of an animal cell. The cell nucleus is the large sectioned sphere. It holds the cells genetic material in the form of DNA (deoxyribonucleic acid). At its centre is a nucleolus, which is responsible for producing components of ribosomes, the cells protein-manufacturing organelles. Surrounding the nucleus is the endoplasmic reticulum (ER). Some parts of the ER are studded with ribosomes (dots). Also featured is the Golgi body (in front of ER), associated with the storage and subsequent transport of proteins produced by the ER and several rod-shaped mitochondria, the sites of energy synthesis within the cell.