Question

Which of the following would produce the most fluid lipid bilayer? O phospholipids with tails of 26 carbon atoms and two double bonds O phospholipids with fully saturated tails of 20 carbon atoms O large amounts of cholesterol O phospholipids with tails of 20 carbon atoms and two double bonds o phospholipids with fully saturated tails of 24 carbon atoms

Answer 1

1) phospholipid with fully saturated tails of 20 carbon atoms is the correct statement because

explanation;

Fluidity of lipid bilayer depends upon the chain length, degree of unsaturation ,cholesterol

As the short chains have the less surface area with whom to form van der waals interactions with each other, so a shorter chain length reduces tendency of hydrocarbon tails to interact with each other.

The longer the phospholipid tails, the more interactions between the tails are possible and the less fluid the membrane will be (because the intermolecular interactions between the phospholipid tails add rigidity to the membrane).

At low temperatures, phospholipids tend to cluster together, but cholesterol in the phospholipid bilayer fill in between the phospholipids, disrupting their intermolecular interactions and increasing fluidity.

At high temperatures, the phospholipids are further apart. In this case, cholesterol in the membrane has the opposite effect and pulls phospholipids together, increasing intermolecular forces and decreasing fluidity.

Saturated tails have no double bonds and as a result have straight, unkinked tails. Unsaturated tails have double bonds and, as a result, have crooked, kinked tails.

2) all the factors are equally important .

Factors which influence the rate at which a molecule will move across the lipid bilayer

- Size of the molecule (if size is large the molecule cant cross the lipid bilayer as they stuck in b/w the lipids so a need of small molecule is appropriate )

- Concentration gradient of the molecule ( since the lipid bilayer allows only the small, uncharged substances such as oxygen and carbon dioxide, and hydrophobic molecules such as lipids, to pass through the cell membrane, down their concentration gradient, by simple diffusion )it is necessary to maintain the conc.   Gradient for crossing the lipid bilayer

-Temperature and cholesterol ( can affect upon the presence of the cholesterol as mentioned in above question’s explanation-At low temperatures, phospholipids tend to cluster together, but cholesterol in the phospholipid bilayer fill in between the phospholipids, disrupting their intermolecular interactions and increasing fluidity. At high temperatures, the phospholipids are further apart. In this case, cholesterol in the membrane has the opposite effect and pulls phospholipids together, increasing intermolecular forces and decreasing fluidity) the fluidity influences the rate at which the molecule move across the lipid bilayer .

-amount of carrier protein capable of transporting the molecule (if the amount of molecule is high but the no. of carrier protein is low the chances of the molecule crossing the memb. goes down so appropriate nos. of carrier protein availability is necessary)