Question

How fatty acids move in two dimensial fluid of cell? What allow and what limit their movement?

Answer 1

Fatty acids (phospholipid) are made up of a group of different molecules that are distributed across the membrane. If one look at a cell membrane via a microscope, they would see a pattern of different types of molecules put together, also known as a mosaic, that’s why it is known as the mosaic model. These fat molecules are constantly moving in two dimensions, in a fluid fashion.

There are 3 main factors that influence cell membrane movement (fluidity):

1. Temperature: The temperature affect how the phospholipids move and how close together they are found. When the temperature is low, they are found closer together and when temperature is high they move farther apart.
2. Cholesterol: The cholesterol molecules are randomly scattered across the phospholipid bilayer, it helps the bilayer to stay fluid in different environmental conditions. The cholesterol holds the phospholipids together so that they don’t separate and stretch too far away and break, don’t let unwanted substances get in, or compact too tightly so it could restrict movement across the membrane. Without cholesterol, the phospholipids will start to separate from each other, leaving large gaps and break or in cold, it will get too close hindering the normal working of the layer, breaking the 2-d movement and structure integrity.
3. Saturated and unsaturated fatty acids: Fatty acids make up the phospholipid tails. Saturated fatty acids are chains of carbon atoms with single bonds between them. This makes them straight and easy to pack tightly. Unsaturated fats are chains of carbon atoms that have double bonds between them. Double bonds create kinks between the chains, making them hard to pack tightly. There are two possible kinks that can take place:

• Cis-unsaturated fats - both sides of the chain remain on the same side.
• Trans-unsaturated fats - the sides of the chain are opposite from each other

These play role in membrane fluidity, since the kinks increase the space in between the phospholipids, it make them harder to freeze at lower temperatures. Also, some molecules, like CO₂ and O₂ require small spaces between the phospholipid chains, so they can cross the membrane quickly and easily.