Читать книгу Introduction to the Human Cell - Danton PhD O'Day - Страница 11

As mentioned above, cholesterol is found at high levels in the cell membrane and to a lesser degree in intracellular membranes. It is a steroid lipid that is also involved in the synthesis of sex hormones but here we’re interested in why it localizes to the cell membrane. As shown in the following figure (Figure 2.5, left side), cholesterol has a flat shape: The planar steroid ring structure allows it to interdigitate between phospholipids (Figure 2.5, right side). It is present in animal and human cell membranes to give stability and rigidity.

Figure 2.5. The structure of cholesterol and its ability to interdigitate between phospholipids in the cell membrane.

The more cholesterol there is the more rigid and inflexible the membrane becomes. As a result, depending on the cell type and its location and function, it will contain different amounts of cholesterol in its cell membrane. There is little cholesterol in cytoplasmic organelle membranes because they need to be flexible and aren’t subjected to events that can disrupt them. Cholesterol is absent from bacteria and most plants where cell walls provide stability and protection.