Animal cell structure. Computer artwork of a section through an animal cell. At the centre is the nucleus (red), which contains the cell's genetic information in the form of DNA (deoxyribonucleic acid, blue). Surrounding the nucleus is endoplasmic reticulum (ER, bright blue), a membrane bound organelle that is the site of lipid synthesis and the production of membrane- bound proteins. ER may be either rough (RER), that is with ribosomes (blue dots), or smooth (SER), without ribosomes. Also present are mitochondria (blue ovals), which produce the cell's energy, and golgi bodies (dark green), a membrane-bound organelle that modifies and packages proteins. The bright green spheres are storage vesicles. The cell membrane (dark blue) is a phospholipid bilayer that contains proteins that act as channels and receptors.