Question

The plasma membrane are composed of specific types of phospholipids that are asymmetrically distributed between the two monolayers of the lipid bilayer. For example, the inner monolayer of the human erythrocyte plasma membrane is primarily composed of phosphatidylethanolamine and phosphatidylserine. On the other hand, the outer monolayer mainly consists of phosphatidylcholine and sphingomyelin. The specific composition and distribution of phospholipids in the two monolayers is continuously maintained.
a.The phospholipids in the plasma membrane can freely diffuse within the bilayer. To maintain the asymmetrical distribution within the bilayer, phospholipases continuously replace the phospholipids in each monolayer
b.Movement of phospholipids in the plasma membrane from one monolayer to the other requires the polar or charged head groupd to enter the hydrophobic interior of the lipid bilayer. This process requires a large positive change in free-energy, thus making this type of movement unlikely without an input of energy.
c.Phospholipids in the plasma membrane are anchored to a specific location in the plasma membrane via strong hydrophobic interactions with neighboring lipids, thus maintaining the asymmetrical distribution of lipids in the bilayer.
d.Specific phospholipids in the plasma membrane covalently attach to certain integral membrane proteins. These covalent interactions anchor the phospholipids to specific locations in the plasma membrane and maintain the asymmetrical distribution of lipids in the bilayer.
e.Membrane lipids are synthesized in the ER, then modified and targeted to specific locations in the inner and outer monolayers of the plasma membrane

Answer 1

Answer:

b.Movement of phospholipids in the plasma membrane from one monolayer to the other requires the polar or charged head groupd to enter the hydrophobic interior of the lipid bilayer. This process requires a large positive change in free-energy, thus making this type of movement unlikely without an input of energy

The plasma membrane serves a protective function for the cell and is a selective membrane for particles entry

Answer 2

Complete Question:

"The plasma membrane is composed of specific types of phospholipids that are asymmetrically distributed between the two monolayers of the lipid bilayer. For example, the inner monolayer of the human erythrocyte plasma membrane is primarily composed of phosphatidylethanolamine and phosphatidylserine. On the other hand, the outer monolayer mainly consists of phosphatidylcholine and sphingomyelin. The specific composition and distribution of phospholipids in the two monolayers is continuously maintained.

Select the statements that describe how the transbilayer asymmetry in the lipid bilayer is achieved and maintained".

A) The phospholipids in the plasma membrane can freely diffuse within the bilayer. To maintain the asymmetrical distribution within the bilayer, phospholipases continuously replace the phospholipids in each monolayer

B) Movement of phospholipids in the plasma membrane from one monolayer to the other requires the polar or charged head groups to enter the hydrophobic interior of the lipid bilayer. This process requires a large positive change in free-energy, thus making this type of movement unlikely without an input of energy.

C) Phospholipids in the plasma membrane are anchored to a specific location in the plasma membrane via strong hydrophobic interactions with neighboring lipids, thus maintaining the asymmetrical distribution of lipids in the bilayer.

D) Specific phospholipids in the plasma membrane covalently attach to certain integral membrane proteins. These covalent interactions anchor the phospholipids to specific locations in the plasma membrane and maintain the asymmetrical distribution of lipids in the bilayer.

E) Membrane lipids are synthesized in the ER, then modified and targeted to specific locations in the inner and outer monolayers of the plasma membrane

Answer:

The correct answer is B: Movement of phospholipids in the plasma membrane from one monolayer to the other requires the polar or charged head groups to enter the hydrophobic interior of the lipid bilayer. This process requires a large positive change in free-energy, thus making this type of movement unlikely without an input of energy.

Explanation:

Biological membranes are formed by two lipidic layers, proteins, and glucans. Membranes are fluid, which means that molecules that form it have the capability to move through it.  

Lipids characterize for being amphipathic molecules, which means that they have a hydrophilic portion and a hydrophobic portion at the same time. These molecules have a lipidic head that corresponds to a negatively charged phosphate group, which is the polar and hydrophilic portion. They also have two lipidic tails that correspond to the hydrocarbon chains -the apolar and hydrophobic portion- of the fatty acids that esterify glycerol.

Membrane lipids are arranged with their hydrophilic polar heads facing the exterior and the interior of the cells, while their hydrophobic tails are against each other, constituting the internal part of the membrane.

Lipids can easily change places with other neighbor lipids by lateral diffusion in the same layer. This is passive diffusion, which means that it does not need energy to happen.

Lipids can also diffuse transversally to the other layer, but this kind of movement is not as easy as lateral diffusion. Jumps between monolayers are infrequent as the lipidic polar heads meet the fatty acid barrier. This movement takes energy to occur, which means that is thermodynamically unfavorable.