Intercellular junctions such as tight junctions, desmosomes, and gap junctions connect cells and control what passes between them. The nucleus is the control center of the cell and contains DNA. Cytoplasmic organelles such as the endoplasmic reticulum, Golgi apparatus, mitochondria, lysosomes, and peroxisomes carry out specialized functions like transport, modification and packaging of proteins, energy production, waste digestion, and breakdown of molecules. Cell division occurs through mitosis and meiosis and leads to the reproduction and genetic variation of cells.