Nucleus, Mitochondria, Chloroplasts

As you learned in our last lesson, most cells are eukaryotic cells.

Cells are composed of three major regions:

1. The membrane, the barrier between the cell and its surroundings. The membrane is called a semi-permeable barrier, because it lets some chemicals in and out, but prevents some chemicals from leaving the cell and others from entering.
2. The nucleus, (the center or "brain" of the cell), the region of the cell where the genetic information – the DNA is stored and from where messages are sent to the rest of the cell. These messages are instructions for the formation of proteins. The nucleus has its own double semi-permeable membrane.
3. The cytoplasm (which contains everything between the membrane and the nucleus, including organelles: tiny organs that perform the cell's functions)