A basic cell is bounded by a cell membrane. Within the cell is a nucleus containing chromatin, often condensed at the periphery, along with larger clumps called chromocenters, and in some cells a nucleolus into which RNA is concentrated. The cytoplasm contains the cytosol and a variety of organelles, including mitochondria that power the cell via production of ATP, endoplasmic reticulum and ribosomes that synthesize new materials, a Golgi apparatus, and lysosomes.