When placed in water, hydrophobic molecules tend to form a ball or cluster. The hydrophilic regions of the phospholipids tend to form hydrogen bonds with water and other polar molecules on both the exterior and interior of the cell.
Thus, the membrane surfaces that face the interior and exterior of the cell are hydrophilic. In contrast, the interior of the cell membrane is hydrophobic and will not interact with water.
Therefore, phospholipids form an excellent two-layer cell membrane that separates fluid within the cell from the fluid outside of the cell. A phospholipid molecule Figure 2 consists of a three-carbon glycerol backbone with two fatty acid molecules attached to carbons 1 and 2, and a phosphate-containing group attached to the third carbon.
This arrangement gives the overall molecule an area described as its head the phosphate-containing group , which has a polar character or negative charge, and an area called the tail the fatty acids , which has no charge.
The head can form hydrogen bonds, but the tail cannot. Micelles are lipid molecules that arrange themselves in a spherical form in aqueous solution.
The formation of a micelle is a response to the amphipathic nature of fatty acids, meaning that they contain both hydrophilic and hydrophobic regions. Boundless vets and curates high-quality, openly licensed content from around the Internet. This particular resource used the following sources:. Skip to main content. Search for:. Learning Objective Describe phospholipids and their role in cells. Key Points Phospholipids consist of a glycerol molecule, two fatty acids, and a phosphate group that is modified by an alcohol.
The phosphate group is the negatively-charged polar head, which is hydrophilic. Enzymes 6. Cell Respiration 9.
Photosynthesis 3: Genetics 1. Genes 2. Chromosomes 3. Meiosis 4. Inheritance 5. Genetic Modification 4: Ecology 1. Energy Flow 3. Carbon Cycling 4. Climate Change 5: Evolution 1. Evolution Evidence 2. Transmembrane proteins can have a variety of functions. Peripheral proteins.
These are found only on one side of the membrane. They can be found on either the cytoplasmic side or the outside of the membrane. These consist of a protein in the plasma membrane with chains of carbohydrates projecting out of the cell. These are chains of carbohydrates attached directly to a lipid in the membrane. Both glycoproteins and glycolipids act as labels to identify the cell.
Filaments of cytoskeleton are found along the cytoplasmic side of the membrane and provide a scaffolding for the membrane. Additional Functions of the Plasma Membrane The plasma membrane may have extensions, such as whip-like flagella or brush-like cilia , that give it other functions.
Feature: My Human Body If you smoke and need another reason to quit, here's a good one. Review What are the general functions of the plasma membrane? Describe the phospholipid bilayer of the plasma membrane. Identify other molecules in the plasma membrane, and state their functions. Why do some cells have plasma membrane extensions such as flagella and cilia? Explain why hydrophilic molecules cannot easily pass through the cell membrane. What type of molecule in the cell membrane might help hydrophilic molecules pass through it?
Which part of a phospholipid molecule in the plasma membrane is made of fatty acid chains?
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