Respuesta :
Answer: A. The drug is a small nonpolar molecule.
Explanation:
The plasma membrane is a lipid bilayer that delimits the entire cell. It is a semi-permeable membrane, also called selectively permeable membrane that will allow certain molecules or ions to pass through it by diffusion, and occasionally specializes in "facilitated diffusion". The rate of passage depends on the osmotic pressure, concentration, electrochemical gradient, and temperature of the molecules or solutes on either side, as well as the permeability of the membrane for each solute. Depending on the membrane and solute, permeability may depend on the size of the solute, solubility characteristics, or chemistry.
Simple diffusion is the process by which molecules flow through a permeable membrane without any external input of molecular energy. This process, which is ultimately due to a difference in molecular concentration between the two media separated by the membrane, does not require an input of energy because its main driving force is the increase in the total entropy of the system.
The plasma membrane consists of hydrophobic and hydrophillic characteristics. Towards the outsides, they are hydrophillic, so they can create bonds with water. The insides are hydrophobic, allowing no water inside and keeping them tight together due to the polar forces.
In the case of living cells, the simple diffusion process is established across the cell membrane. Since the velocity-limiting process is diffusion through the separating medium, a model can be simplified where the particle flow depends on the concentration difference between the two sides of the separating medium and the type of interactions that the molecule that is going to cross the membrane with that medium has.
The molecules that can easily pass through the cell membranes due to this phenomenon are gases, hydrophobic molecules and small nonpolar molecules. On the other hand, large polar molecules such as glucose, amino acids and charged molecules or ions interact too strongly with the aqueous environment outside the lipid bilayer, and it is therefore very unfavourable from an energy point of view to break these interactions to cross the central hydrophobic region. As a consequence, biological membranes are practically impermeable to this type of molecules, so they require other transport mechanisms.
So, a non-polar particle (if small), can pass through this membrane because it does not interfere with the hydrophobic/hydrophillic (polar) nature of the plasma membrane. However, polar particles would not have the opportunity to move in, because the insides (hydrophobic) are literally afraid of water, or charges, don't allow polar substances to pass through. So only hydrophobic (nonpolar), gases, and small particles (nonpolar) can pass through.
The statement best supports the alternative hypothesis that the new drug will exhibit simple diffusion across plasma membranes is "the drug is a small non-polar molecule".
SIMPLE DIFFUSION:
- Simple diffusion is a kind of transport in which molecules move down a concentration gradient i.e. from region of high concentration to region of low concentration.
- Simple diffusion across a membrane is applicable to only small and non-polar molecules like oxygen, carbon dioxide etc. as the plasma membrane is permeable to them.
- According to this question, two scientists hypothesizes concerning a particular drug. The first biologist hypothesizes that the drug requires membrane proteins to enter the cell while the second biologist alternatively hypothesizes that the drug can enter the cell via simple diffusion.
- This means that for the hypothesis of the second biologist to be true, the drug must be a small non-polar molecule in order to diffuse into the cell.
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