Made up of amphipathic molecules (have both polar and non-polar regions).
Polar Heads: Hydrophilic, face the water.
Non-polar Tails: Hydrophobic, face away from water.
Naturally forms a spherical shape due to its amphipathic nature.
Membrane Proteins
Embedded within the phospholipid bilayer.
Serve various functions such as:
Transport: Assists in the movement of chemicals and materials.
Signaling: Involves in cell signaling mechanisms.
Carbohydrates
Present on the outer surface of the cell membrane.
Function: Used for cell-to-cell recognition, helping in identifying the identity, type, and origin of cells.
Cholesterol
Embedded within the phospholipid bilayer.
Function: Provides fluidity and stability to the cell membrane.
Analogous to adding salt to water to change boiling/freezing points.
Selective Permeability of the Phospholipid Bilayer
Small, non-polar, electrically neutral molecules can pass through the bilayer.
Example: Steroids
Proteins: Generally too large to pass through.
Lipids: Can pass through due to being non-polar.
Ions: Electrically charged, repelled by the non-polar bilayer.
Water: Does not easily pass due to its polar nature.
Carbohydrates: Polar and large, do not pass easily.
Conclusion
The phospholipid bilayer's selective permeability allows only certain molecules to pass through, influencing cellular operations.
Other forms of transport will be covered in the next videos, including diffusion and additional methods that allow water and carbohydrates to pass through the membrane.