Summary: Essential Cell Biology (Alberts et al) - Second part

This summary is based on the 3rd edition of Essential Cell Biology from Alberts et al. The first 10 chapters are open access and can be found here: First part of the summary

11. Membrane structure

Cell membranes enable a cell to create barriers that confine particular molecules to specific compartments. The simplest bacteria have only a single membrane, the plasma membrane. Eucaryotic cells, however, contain in addition a profusion of internal membranes that enclose intracellular compartments. All cell membranes are composed of lipids and proteins and share a common general structure. The lipid component consists of many millions of lipid molecules forming a lipid bilayer. This lipid bilayer gives the membrane its basic structure and serves as a permeability barrier.

The lipid bilayer

The lipids in cell membranes combine two very different properties in a single molecule: each lipid has a hydrophilic (‘water-loving’) has and one or two hydrophobic (‘water-hating’) hydrocarbon tails. There are three major classes of membrane lipid molecules:

  1. Phospholipids
  2. Sterols
  3. Glycolipids

The most abundant lipids in cell membranes are phospholipids, and the most common type of phosphoslipid in most cell membranes is phosphatidylcholine. Molecules with both hydrophilic and hydrophobic properties are termed amphipathic. This chemical property plays a crucial part in driving these lipid molecules to assemble into bilayers. They assemble spontaneously into bilayers when placed in water, forming closed compartments that reseals of torn.

Amphipathic molecules re subject to two conflicting forces: the hydrophilic head is attracted to water, while the hydrophobic tail shuns water and seeks to aggregate with other hydrophobic molecules. This conflict is resolved by the formation of a lipid bilayer, because the hydrophilic heads face the water at each of the two surfaces of the sheet of molecules and the hydrophobic tails are all shielded from the water and lie

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