8. Describe the structure of the lipid bilayer that makes up the cell membrane. What role does the cell membrane play?
8. Describe the structure of the lipid bilayer that makes up the cell membrane. What role does the cell membrane play?
answers:
Lipid Bilayer Structure
The lipid bilayer is a universal component of all cell membranes. Its role is critical because its structural components provide the barrier that marks the boundaries of a cell. The structure is called a "lipid bilayer" because it is composed of two layers of fat cells organized in two sheets. The lipid bilayer is typically about five nanometers thick and surrounds all cells providing the cell membrane structure.
Lipids and Phospholipids
The structure of the lipid bilayer explains its function as a barrier. Lipids are fats, like oil, that are insoluble in water. There are two important regions of a lipid that provide the structure of the lipid bilayer. Each lipid molecule contains a hydrophilic region, also called a polar head region, and a hydrophobic, or nonpolar tail region.
The hydrophilic region is attracted to aqueous water conditions while the hydrophobic region is repelled from such conditions. Since a lipid molecule contains regions that are both polar and nonpolar, they are called amphipathic molecules.
The most abundant class of lipid molecule found in cell membranes is the phospholipid. The phospholipid molecule's polar head group contains a phosphate group. It also sports two nonpolar fatty acid chain groups as its tail.
The fatty acid tail is composed of a string of carbons and hydrogens. It has a kink in one of the chains because of its double-bond structure.
The Bilayer
The phospholipids organize themselves in a bilayer to hide their hydrophobic tail regions and expose the hydrophilic regions to water. This organization is spontaneous, meaning it is a natural process and does not require energy. This structure forms the layer that is the wall between the inside and outside of the cell.
Properties of the Lipid Bilayer
As we have already mentioned, the most important property of the lipid bilayer is that it is a highly impermeable structure. Impermeable simply means that it does not allow molecules to freely pass across it. Only water and gases can easily pass through the bilayer. This property means that large molecules and small polar molecules cannot cross the bilayer, and thus the cell membrane, without the assistance of other structures.
The functions provided by the cell membrane helps the cell to maintain homeostasis. They are-
1)They provide protection to the cell- and prohibits the entry of toxic or unwanted substances.
2)The semi-permeable nature of the membrane allows only the specific ions and molecules to enter the cell.
3)The fluidity of the membrane helps in the regulation of temperature inside the cell.
4)The membrane prevents the exit of important or useful substances.
5)The cell membrane helps in the maintenance of the ratio of water- outside and inside the cell. Excess water is removed through the process of diffusion.
6)Waste substances are excreted outside the membrane through the process of diffusion or osmosis.
7)It maintains the chemical levels inside the cell by regulating the movement of ions across it. It is selectively permeable to- small, non-polar substances. It restricts the movement of- large, highly charged molecules across it.
8)It maintains the ratio of minerals inside the cells.
9)It also stops the osmotic pressure changes across the membrane.
10)It maintains a perfect balance of macromolecules like- lipids, proteins, carbohydrates, etc.
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