Question

Keeping in view the structure of the cell membrane, which one of the following statements is correct with respect to the movements of lipid and proteins from one lipid monolayer to the other (flip flop movement) (a) While proteins can flip flop, liquids can’t
(b) Neither lipids or proteins can flip flop
(c) Both lipids and proteins can flip flop
(d) While lipids can rarely flip flop, proteins cannot

Answer 1

The movement of a molecule is called transverse diffusion or flip-flopping, from one side of the membrane to the other. Overcoming a high energy barrier involves transverse diffusion. This is because the molecule's polar region must find its way through the membrane's hydrophobic center. There are smaller polar regions of phospholipids, while the protein has a wide polar field.

Complete Step by Step Answer: One of the tenets of the Fluid-Mosaic membrane model is that the bilayer components are free to pass. The first form of movement of phospholipids is rotational. Here, the phospholipids rotate on its axis to interact with its immediate neighbors. The second form of movement is lateral, where the phospholipids travel in a single leaflet. Finally, the phospholipids can pass between the two leaflets of the bilayer in transverse motion, in a "flip-flop" fashion. They can undergo rotational and lateral movement in the case of membrane proteins. However, between the leaflets, there is no transverse movement of proteins.

So, the answer is, “While lipids can rarely flip flop, proteins cannot.”

Additional Information: Transverse motion is what allows for the maintenance of asymmetry. Uncatalyzed phospholipid movement between the bilayers is possible, but this is sluggish and cannot be depended on to preserve the balance of asymmetry. Instead, phospholipid movement between the bilayers is catalyzed by lipid translocator proteins.
Phospholipids form the outer leaflet to the inner leaflet are transferred by flippases. Flippases primarily transport phosphatidylserine and, to a smaller degree, phosphatidylethanolamine to preserve the charge gradient across the membrane. In the opposite direction, floppases transfer phospholipids, especially phosphatidylcholine and sphingomyelin, phospholipids derived from choline. Floppases also mediate the transport of cholesterol to the extracellular monolayer from the intracellular monolayer. Typically, these catalyzed motions are based on ATP hydrolysis. Scramblases, which exchange phospholipids between the two leaflets in an ATP-independent process triggered by calcium, is the third class of protein.

Note: - While phospholipids and lots of proteins can tour notably without problems and quickly withinside the lateral path of the molecular membrane, they locate it a great deal more difficult to tour withinside the vertical path. -Lateral movement is what offers a fluid form to the membrane.
- Phospholipids stay for a quick time in a single place earlier than leaping to every other location. The interplay among the actin cytoskeleton and the membrane created with the aid of using the areas among which the phospholipids hop appears to be because of this compartmentalization of the lateral movement.
- Intrinsic membrane proteins are intently embedded withinside the hydrophobic core, even as extrinsic membrane proteins are related to their required leaflets. For transferring any form of membrane protein throughout the bilayer, the power necessities could be excessive.