Phospholipids are amphipathic molecules that compose the cell bilayer membrane. Among the options, D is correct. Hydrophobic fatty acid regions face each other within the interior of the cell membrane.
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Two lipidic layers compose the cell membrane. There are also proteins and glucans incrusted in between.
The complex lipids that compose the membrane are amphipathic molecules. A phospholipid is composed of
- two fatty acid chains ⇒ hydrophobic tails,
- glycerol and a phosphate group ⇒ hydrophilic heads negatively charged
Phospholipids are arranged as a bilayer. Their hydrophilic polar heads face the exterior and the interior of the cells, while their hydrophobic tails are hidden against each other, constituting the internal part of the membrane.
According to this framework, we can choose the best answer among the options,
A) Hydrophilic phosphate regions face each other within the interior of the cell membrane ⇒ Incorrect ⇒ Heads are not facing each other. They are in contact with the cell exterior and interior.
B) Hydrophilic phosphate regions are positioned toward nonpolar environments ⇒ Incorrect ⇒ Phosphate regions are in contact with water.
C) Hydrophobic fatty acid regions are positioned toward polar environments ⇒ Incorrect ⇒ tails can not be in contact with water.
D) Hydrophobic fatty acid regions face each other within the interior of the cell membrane ⇒ CORRECT.
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