Here, we show that a cell consists of a skeleton and membranes, both of which help hold the parts of a cell together. The skeleton also guides cell division by helping chromosomes to migrate to their respective new cells. The membranes around the cell function in interacting with the outside world. Membranes are made mostly of lipid, but they have imbedded proteins that help regulate what goes in and out of a cell (see unit 2). The key interior structures (nucleus, endoplasmic reticulum, mitochondria, and Golgi apparatus) are also surrounded by membranes.
The nucleus houses the chromosomes and their genetic material. Endoplasmic reticulum is where proteins are made, and the final touches in protein production occur in the Golgi apparatus. Mitochondria are the energy production "factories" of the cell.