Hello All,
As I mentioned I will take your questions here and address them so all can find the answers to them. There was not very many questions today, so either I did a fabulous job explaining the material (which I highly doubt) or maybe you have not yet gotten to this material, or maybe it really is review, or maybe you are nervous to contact me. With that in mind, please remember three things: 1. Don't let yourself get behind on material, there will be a lot of material covered and your time is VERY VALUABLE in medical school; 2. This may feel like review, but it is at a different level than you have probably covered it in the past. Therefore, work through some practice problems even if you feel like you know this stuff to know if you can answer questions similar on this material on the exam; and 3. I promise I am approachable and available to answer your questions and NO QUESTION is stupid (chances are if you wondered it at least ONE other of you also wondered it so be brave and ask)!!!
Okay, so here ARE the questions that I received: There was an initial question regarding logistics and then there are a few following questions about Membrane Transport. Hopefully this posting is helpful. If, however, it produces additional questions please do not hesitate to contact me either by posting a comment on the blog or by sending an email.
1. This is regarding accessing
your G-Drive Questions you mentioned today in lecture. Would you email detailed
instructions on where to find them?
There are questions posted on the G-drive and you need to be accessing the network G-drive from on campus (not via a web-source). In any folder for my lectures there will be additional folders titled 'study quiz' or 'thought questions'. When on the network G-drive, copy the entire folder of either to your computer and then you can access the questions from that folder by pulling the 'quiz' into an open web-browser.
Alternatively, these same questions are available within the 'notes' section of the last two slides of every one of my lectures.
2. Are pores selective to what molecules can pass
through? How do they regulate if they are selective? If not then why are
there different types of pores like aquaporins and connexin etc?
Pores are SOMEWHAT selective, as in aquaporins are small enough that only water (and other molecules smaller than water) can move through them. Connexin, or gap junctions, on the other hand are not very selective. They allow for charged ions (virtually all charged ions) to move from one cell into another. Pores, however, are not as selective to what they allow to move as channels and transporters where a signal needs to create them to open and for a transporter the actual molecule causes the transporter to transport the molecules.
3. I had a question on
slide 17 of todays lecture. It says that the opening and closing of ion
channels can be regulated by "Mechanical Forces".
What are these
mechanical forces?
Great question. Mechanical forces are physically (mechanically) pushing on the membrane causing an actual physical change in the membrane that causes the channel to open/close. For example, your touch receptors on your fingers are mechanically gated and pressure on your skin causes them to open creating a change that ultimately results in your 'feeling' what you are touching.
4. I had a question
regarding secondary active transport. More specifically in slide 31.
I know that secondary active transport requires the energy one of
substance in order to move another substance, in the example given Na is moving
down the gradient which drives the transport of another molecule against its
gradient. My question is, is the Na moving down the gradient enough of a
driving force to move the other molecule against its gradient without ATP/GTP?
I got a little confused because in the notes of slide 26 it says that it needs
ATP to establish a gradient with one of the substances.
Remember that the gradient that is being used (Na+ gradient for example) was created and is being maintained by a primary active transporter and the energy from ATP/GTP (typically Na/K ATPase for example). Therefore, indirectly the secondary active transporter is utilizing the energy source and without it, the secondary active transporter could not continue to function.
Thank you for doing this! You are awesome! :)
ReplyDeleteI was wondering if pores and channels were considered to be facilitated diffusion or simple diffusion. I think a slide described them as simple, but because they are using a protein to move across the membrane, shouldn't they be facilitated diffusion?
ReplyDeleteThanks for the clarification.
I see your confusion. Indeed they ARE using a protein, but the determination between facilitated diffusion and passive diffusion involves the kinetics of the movement of molecules through the plasma membrane. Under this definition, the movement of molecules through the membrane by facilitated diffusion reaches a maximal flux, while the movement of molecules by passive diffusion (through pores and channels) does not reach a maximal flux. THerefore, for physiological definition, the movement of molecules through pores and channels is passive diffusion not facilitated diffusion.
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