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Title: Which molecule will cross a lipid bilayer quicker? Post by: smmrwds on Feb 15, 2013 Here is the question:"Assume that equilibrium in the bicarbonate equation relies on the movement of the constituents across the plasma membrane. Which of the following constituents will cross the membrane fastest?"
a.)H2O b.)HCO3- c.)O2 d.)H2CO3 The answer is A, but I do not understand why the answer is not C? Can someone please make this clear to me? Title: Which molecule will cross a lipid bilayer quicker? Post by: tos4lovy on Feb 15, 2013 Speed of transport across a lipid bilayer is based on two main things:
1. The size: the smaller a molecule is, the faster and more readily it will cross (B and D are bigger) 2. The charge: lipid bilayers are nonpolar, so any charged particles will have a tough time crossing the barrier, and polar molecules will have a difficult time as well. (B is charged, water is polar, but we know it moves readily through membranes) With this in mind, it would be difficult to determine the answer between A and C However, in the case of this question, there is one more thing to consider, which is the equation. Since for every turn of the reaction, 2 H2O is produced for every O2 molecule, at equilibrium, it is twice as abundant, which means that most likely it is moved out of the cell more quickly to maintain homeostasis. |