Nuclear formation, coloured scanning electron micrograph (SEM). The nuclear envelope (red) is forming around the cell's chromatin (green). Chromatin is a complex of deoxyribonucleic acid (DNA) and proteins. This is a nascent (immature) nucleus, as the nuclear pores have yet to form. The nucleus contains the cells genetic information in the form of DNA. Around the nucleus are endoplasmic reticulum (ER, blue) and microtubules (green). ER, a membrane-bound organelle, is the site of lipid synthesis and the production of membrane-bound proteins. This is rough ER (RER), it has ribosomes (yellow dots) on its surface. Microtubules are part of the cell cytoskeleton.