In intestinal epithelial cells the different plasma membrane

In intestinal epithelial cells, the different plasma membrane domains are separated from each other by special barriers. Indicate true (T) and false (F) statements below regarding this separation. Your answer would be a four-letter string composed of letters T and F only, e.g. FFFF. There are no spaces between the letters. These barriers are set up by nanoscale lipid raft domains. Proteins normally cannot pass through these barriers, whereas any membrane lipid can do so freely. The asymmetric distribution of membrane proteins resulting from these barriers is functionally important. These barriers are a result of proteins of the apical surface forming a large aggregate together that excludes proteins of the other domains.

Solution

1.

Lipid rafts are membrane sub domains. The hundreds of lipids and proteins in the plasma membrane domain are not uniformly mixed but form a sub domain or micro domains. Lipid raft is one such micro domain. It consists of closely packed glycosphingolipids that occur in outer leaflet of plasma membrane and cholesterol. The given statement is false.

2.

Some proteins associate with rafts including GPI- linked proteins and some of these participate in transmembrane signaling processes. Cholesterol alone cannot form bilayer due to its small head group. Therefore, the Glycosphingolipids in lipid rafts associate laterally through weak interactions between the carbohydrate head groups and spaces between tails is filled by Cholesterol. The gicen statement is true.

3.

Biological membranes are asymmetrical because, they vary in the protein, lipid proportions in them. The proteins and lipids are not occurring in equal proportions on both sides of the biological membranes. The Glycoproteins and Glycolipids are oriented differently with their carbohydrate residues facing exterior to the cell. Action of phospholipases on inner and outer membrane lipids established the fact of asymmetric distribution of membrane lipids.The given statement is true.

4.

Phospholipases cannot penetrate into the membranes and thus, interact with the surface proteincomponents that form aggregates and are susceptible to hydrolysis by phospholipases. By the enzymatic studies proving the asymmetric distribution of membrane lipids suggest that the biological membranes are asymmetrical. The given statement is true.

The order of statements is FTTT.