In eukaryotic cells, the largest portion of the cell cycle is interphase, which is divided into three stages, G1, S, and G2. In G1, the first gap phase, a newly generated daughter cell grows in size and prepares for DNA duplication in the next phase. Now, in S, the synthesis phase, cells duplicate their nuclear DNA, which remains packaged as chromatin. Cells also duplicate the centrosomes, the microtubule organizing structure which forms the mitotic spindle apparatus. Finally, in G2, the second gap phase, cells continue to grow, multiply organelles and proteins that are required for mitosis and replenish their energy stores. The cell is now ready to enter the first stage of mitosis.