Yeast nucleus. Coloured scanning electron micrograph (SEM) of the nucleus (orange, round) of the yeast Saccharomyces cerevisiae. The nucleus contains the cell's genetic information in the form of DNA (deoxyribonucleic acid). The yellow round structures are nuclear pore complexes (NPCs), complexes of proteins that are embedded in the nuclear envelope. All material moving between the nucleus and the cytoplasm passes through these channels. They allow passive transport (diffusion) of ions and small molecules and active transport (energy dependent) of proteins and RNAs (ribonucleic acids). Magnification: x90,000 when printed 10 centimetres wide.