# Chapter Three: Cell biology

### Cell membrane

| The cell membrane is the thin nearly invisible structure that surrounds the cytoplasm of the cell. In this section we will talk about its structure and its function. In the image at the left you can see that it is a continuous membrane that completely surrounds the cell.

It also connects the the endoplasmic reticulum, and the nuclear membrane. In the image below we have colored the membrane to highlight its composition. The yellow represents the phospholipids. The purple represents the membrane proteins (for more on the structure click next). |

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