Question

3. Many membrane process such as transport or signal transduction depends on the fluidity of lips membrane. How fatty acids and cholesterol effect the fluidity of the membrane.

Answer 1

Fluid mosaic model describes the plasma membrane structure as a mosaic (arrangement) of phospholipids, proteins, and carbohydrates which gives membrane a fluid character. Plasm membrane is made up of phospholipid bilayer in which proteins , cholesterol, carbohydrates are embeded.

Cell membrane is made up of 1) PHOSPHOLIPIDS 2) CHOLESTEROL 3) PROTEINS

1) Phospholipids :

It is made up of two parts a phosphate head and two fatty acids tail , thus known as phospho + lipids.

2) Cholesterol : It is a steroid molecule which helps in entry and exit of molecules through cell membrane.

3) Proteins : Proteins are of two types integral and peripheral proteins. Integral proteins are extended throughout the membrane and helps in transporting large molecules like glucose across the membrane while peripheral proteins are not embeded in the membrane and helps in communication.

The main factors that affect the fluidity of membrane:

• Temperature: Temperature will affect the position of phospholipids in the cell membrane. Lower temperature will bring phospholipids more close while high temperature makes them move apart.
• Cholesterol : Cholesterol is randomly distributed across the membrane. They are important in maintaing fluidity of membrane as they hold phospholipids together so that they can not move apart so far to allow entry of unwanted molecules. They also dont allow phospholipid to come more closer to restrict the transport of essential molecules across the membrane. Without the cholesterol during cold temperature phospholipids will com e closer to each other and thus block the transport of molecules. At normal temperature phospholipids will seperate far apart witout the cholesterol creating large gaps in bilayer.
• Fatty acids (Lipids): Saturated and unsaturated fatty acids plays important role in membrane fluidity. Saturated fatty acids have single bond whike unsaturated fatty acid contains double bond. The double bond between the carbon atoms provides a kink which plays the important role in fluidity. The kink provides space between phospholipids, so thet they can get freeze at cold temperature. This space between the phospholipids allows gases to pass through the membrane.