Which of the following groups of amino acid residues (see Ch. 3, Figure 3.2) would likely be found in the portion that crosses the lipid bilayer? a. acidic b. basic c. polar uncharged d. nonpolar

Video transcript

Hello everyone here's our next question which of the following cannot readily cross or diffuse through the cell membrane. As we recall from our content videos. The key characteristic of the cell membrane is that it's selectively permeable. Most things cannot go in or out through the cell membrane on their own, therefore allowing the cell to control um what comes in and out. However, there are a few types of molecules that can diffuse by passive diffusion. I mean they can just pass in and out by dissolving through the cell membrane and so they diffuse in and out just following the concentration gradient. They diffuse in if the concentration is lower inside the cell, diffuse out if it's higher and these kind of molecules are gasses small polar but uncharged molecules and hydrophobic molecules and anything that's charged so charged particles no matter how small or large polar molecules cannot diffuse through the membrane unaided. They need transport proteins to help them get through. So with this in mind let's look at our answer choices to find which of them cannot readily cross. So, choice A. Here is 02 oxygen gas. So that's a gas. So yes, oxygen can diffuse through and therefore is not our answer. But it can Joyce B is C. 02 carbon dioxide also a gas. So it can diffuse through and therefore is not our answer. I'll put gas for each of these to help us remember. Choice C. is H 20. Water. This is a small polar molecule so it can diffuse through so small polar but uncharged so that also can diffuse through and therefore Choice C. Is not our answer. So we're left with Choice D, which is glucose and glucose is polar and two large to diffuse through a needed as we recall. It's a six carbon ring that's too big to allow it to do what won't dissolve in that hydrophobic interior of the cell membrane. So glucose choice D. Is our answer, as it cannot readily cross through the cell membrane. See you in the next video.