Is there a 10-point search item? No, I'm passing back the exams, so the ones that are left over are the ones that were here. Sorry?
I already put it into Blackboard but I'm going to be passing the exams back. You guys should be able to see the grades with the curve. Here I didn't include the curve but it's on Blackboard. You look really nice. Thank you.
Finally getting over what I had. with the group. I don't know if I can get it. I'm not sure too.
I'm not a man. I'm not a man. I'm not a man. Yeah. Alright, happy Friday everyone.
So first thing I'm going to do is pass back the exams. I've already included the curve on blackboard, so the curve one. An additional two points to everybody's exam.
So that's a 4% increase in your grade. Now the average was pretty close to a 70, so that's actually a really good average, and that's where the professors kind of use those. cut off to not curve. And so, yeah, a lot of professors are like, oh, that's a great first exam average.
You don't need to curve it. But I promised, so I did end up adding the two points. And then what was the other thing?
thing. So yeah so at the very end of the semester when all the grades are in I'll make an Excel spreadsheet and then I will go in and I will decide what's the cutoff for an A or a B or a C or D. So I can say for instance just a hypothetical example that everybody that got in the class overall an 85 and up would be an A and 84 to like a 7 would be a B and like so on so keep that in mind that this isn't gonna necessarily be the letter grade that you're seeing in the future for the entire semester I know that you know these exams aren't gonna be too easy but I'm hoping to prepare you guys well for them and I'm not trying to fail anybody I want everybody to do well but just make sure you just keep doing what you're doing showing up to class asking questions coming to office hours and improving so that you guys can take this knowledge and it will make it a lot easier for you in your future biology classes like the upper level bio classes I've also confirmed that I'm going to be teaching microbiome here next semester for anybody who is interested all right so I'm gonna call your name up and if you don't mind if you guys are sitting in the middle or back coming up to me so I don't have to run around to everybody and and so I'll give you this back after this class I will post the exam key on blackboard so you guys can go through and look at what you got wrong and it's up to you guys in the first 24 hours to go through and look through it and make sure you know what you got wrong and why you got it wrong you can talk to each other you can use the lectures you can use whatever you want but don't contact me the first 24 hours because I know you can figure it out on your own and then After the 24 hours, if you still feel like there's something that doesn't make sense, you're welcome to talk to me about it. And most importantly, if you notice that your Scantron was misread for some reason, if the machine didn't pick up something that you got right and marked it wrong, obviously tell me because I want to give you those points back. All right?
The exam key isn't posted yet. everything away. Just a reminder, your first quiz is going to be on, or sorry, your third quiz is going to be on Monday. Your first quiz for this unit. So quiz three will be on Monday.
So it's going to be just on chapter five materials, so what we did Wednesday and today. Alright? Okay.
So last week, or sorry, on Wednesday, we stopped here. We were talking about osmotic concentration in the video that I left you off with, introduced these terms about different osmotic concentrations and solutions. So if a solution is a solution, it's a solution that's going to be used to has a higher solute concentration that is going to be called hypertonic so hyper as in you know something is moving and there's a lot of it and so that's where that comes from and the solution that hypotonic means that it has a lower solution concentration so hypo kind of means like the absence of something so that would be a lower solute and we're talking just about solute concentration here so although osmosis is the diffusion of water molecules across a membrane that's dependent on the solute concentration.
So in this case, the solute is the urea molecule. And so when two solutions have the same osmotic concentration, we call that an isotonic solution. And in osmosis, the specialized channels that are used are called aquaporins, so aqua meaning water, and quorns, so it's a protein that has pores in it to allow things to go in and out and in this case it's water to facilitate osmosis.
Okay, quick concept check for you guys. So we talked about the fluid mosaic model and four things that it consists of. So can anybody tell me what these four things are? You can tell me one. You have to tell me all four.
The tubules? So the cytoskeleton, yeah, that's one of them. Those are the filaments, so that makes up the cytoskeleton.
The microtubules, the actin filaments. and yeah that's the cytoskeleton what else yeah phospholipid bilayer yep every membrane has one what else yeah so the proteins we're calling them the transmembrane proteins because they're within the membrane and outside of the membrane. And then there's one more. Sugar.
Yeah, the cell surface markers. Yeah, good job. So those markers usually are that sugar that's attached to a protein.
So those are the cell surface markers. Good job. And then we talked about cell membranes mediating transport.
There's three different types of transport. And the first one we talked about was passive transport. In passive transport, do things move?
move up or down the concentration gradient. So is it from low to high concentration or high to low? Some people are saying hi to low, Raymond.
Hi to low. Yeah, so remember passive transport. Think of the air freshener analogy that I gave.
If you spray it in one corner, you have a high concentration of it at first, but naturally it wants... to pass and diffuse through the entire room. So that's going from a high concentration to a lower concentration in that space because those solutes are essentially filling up the entire enclosed system. And so in the case that of a membrane it would be in the membrane I guess and so that we call up or down the concentration gradient down yeah think of like a slide if you want to go down a slide you don't need to put energy and you just kind of go down whereas if you try to move up a slide you're gonna have to put in the extra energy it's going to be harder so when something is moving passively from high to low concentration it's going to be moving down its concentration gradient And the three types of passive transport that we talked about were simple diffusion, which is just simple.
You, like the air freshener model, are putting a little bit of ink into a water beaker. And in the case of membranes, it would be nonpolar molecules being able to pass through the membrane because it can pass through that hydrophobic interior. Osmosis is the movement of water. And then there's facilitated diffusion for those other polar molecules.
ions that need facilitation through a protein, either a channel or a carrier. Alright, any questions on this? So today we're going to finish off, we're going to talk about this, the active transport and bulk transport. So these two require energy, energy is usually in the form of ATP.
So defining active transport, it's the movement of molecules through the membrane in which energy is required in the form of ATP, and the molecules move against a concentration gradient or up a concentration gradient. We use those synonymously. And usually it's going from a lower concentration gradient to a lower concentration gradient. to a higher concentration. And when we need that energy, we need those proteins to be very, very selective.
So it requires the use of highly selective carriers. I'll give you some examples of that. Alright, so carrier proteins that are used in active transport can be called uniporters, which means that they move one molecule at a time, or they could be simporters and antiporters, which both move two molecules at a time.
but simporters move them in the same direction, antiporters move them in the opposite direction. So these terms are also they're not specific for active transport but we tend to use these terms because an active transport like I said, they are highly selective proteins and so usually a protein will selectively only move like the sodium potassium pump, which I'm going to show you next, it's just selective for those two things and so that's why we use these terms more. And yeah, so symporter, S for same, antiporter, anti, opposite, you should remember that, but they both move two molecules and uniporter moves one.
Easy? that make sense? So the sodium potassium pump is a protein carrier system that transports sodium and potassium across the plasma membrane and for every three sodium ions that are transported out of the cell there are two potassium ions transported into it.
The movement is against the concentration gradient because it's active transport so it's going from a low to high concentration and this one uses an anti-porter to move so it's moving both sodium and potassium but they're moving in opposite directions. Sodium is transported out, potassium is transported in. Energy here is provided by the direct use of ATP and the ATP is used to change the conformation of the protein and so the really important thing to remember here is that you know Everything I hold obviously is going to be really important for you to remember, but in this particular one, it's directly using ATP.
Some other active transporters use ATP but not directly, and we'll talk about that in a few slides, but I just want to make sure I emphasize that point there. And so none of that makes sense to me in words unless I see it in a picture format. So let's go through this.
Here, this is number one in the middle here. So we have this protein carrier and this and In the square is the sodium and in the circle we see potassium. So the sodium is able to bind in the protein on this side because that's the conformation that fits in it and usually they are very, remember they're highly selected.
they're highly specific so not just anything can bind here it has to be sodium ions so when those three sodium ions bind to this protein then there's ATP that's bound and that ATP comes off and it leaves one phosphate group so it phosphorylates the pump so ATP comes in puts a phosphate group and that phosphorylation essentially causes the conformational change in this protein so So it changes its shape and that causes it to not have a high affinity for sodium anymore so it releases it out there. But then when the sodium is diffused out, this conformation now has a high affinity for potassium so those come in here and then this, when this potassium ions bind, then that will remove this phosphate group and the removal of this phosphate group is called called dephosphorylation. And when that happens, the protein then releases these ions into the cell, these potassium ions, and it goes back to its original shape. And then that cycle can start again where ATP binds, and you phosphorylate it, and get the Na in there. And so it's a cycle.
It keeps on going. Does that make sense? Okay, well if that did it, I have a video for you. The sodium-potassium pump is an active transport mechanism. Three sodium ions bind to the protein channel, and an ATP provides the energy to change the shape of the channel, that in turn drives the ions through the channel.
One phosphate group from the ATP remains bound with the channel. The sodium ions are released on the other side of the membrane outside of the cell, and the new shape of the channel has a high affinity for potassium ions and two of them. of these ions now bind to the channel. This binding again causes a change in the shape of the protein channel, and this conformational change releases the phosphate group on the cytoplasm side. This release allows the channel to revert to its original shape, and as a result, the potassium ions are released inside the cell.
In its original shape, the channel has a high affinity for sodium ions, and when these ions bind again, they initiate another cycle. cycle. The important characteristic of this pump is that both sodium and potassium ions are moving from areas of low concentration to areas of high concentration. That is to say each ion is moving against its concentration gradient. This type of movement can only be achieved by the constant expenditure of ATP energy.
Okay, any questions on the sodium potassium pump? How frequent is this process happening? How frequent?
It's happening all the time in our cells. It's really important to have it regulated. Because if you think about it, this is all happening in cells.
So cells need to regulate the sodium and potassium going in and out. Alright, any other questions? Okay, so another type of active transport is called coupled transport and this one uses ATP indirectly. So basically it uses the energy stored in a gradient from a different... molecule.
Another way to say that is ATP is released when a molecule moves through its pump and that happens in order to supply energy for the active transport of a different molecule. This can be a symporter or an antiporter so the sodium potassium pump was an antiporter they're going in opposite directions but you can have coupled transport that does things in the same direction and the one example I'm going to give you of a coupled transport system is this glucose sodium symporter and it basically captures the energy from sodium diffusion in that sodium potassium pump to move glucose against its concentration gradient so it's still active transport of glucose because it's going against this concentration gradient but the ATP isn't directly doing anything that energy is usually used from the sodium the sodium being moved so here I'm showing you there's they're coupled right so there's one protein here this is the sodium potassium pump and then this is a couple transport protein. So this is the one, so basically when we have the sodium ions, so these squares, they usually come out of the cell.
Well, in order for this to keep occurring, this cycle, we need sodium to come back in the cell for it to be pushed out. So in this case, we have sodium ions that have this energy because of the ATP here, and this energy gradient is used to basically put sodium back in the cell. and then glucose ends up coming through the cell as well into the cell so our cells all need glucose glucose is the preferred method of having having energy for ourselves to you know maintain everything about them so the gradient driving the sodium entry allows those sugar glucose molecules to be then transported against their concentration gradient so you see here one glucose here there are four so from low high concentration.
So in this example both molecules are moving in the same direction therefore this is a symporter. Yeah so this one is an antiporter, this one's a symporter. They're both types of active transport. This one uses ATP directly this one uses it indirectly so similarities and differences there questions all right well another video this chapter just had a lot of videos and I was loving it so here you go When substances need to be driven against their concentration gradient from low to high concentrations, active transport is required. This process uses energy to move a substance across the membrane using selective protein carriers.
The sodium-potassium pump is a specialized membrane protein carrier, common in most animal cells, that moves sodium and potassium ions across the plasma membrane. ATP fuels the pump in the... movement of these ions from low to high concentrations, moving sodium ions outside of the cell where they become concentrated, and bringing potassium ions into the cell where their concentration is higher relative to the outside. In other instances of active transport, the concentration gradient created from the action of one pump can be used as the input of energy to drive a different pump, a process known as coupled transport.
The large concentration gradient of sodium ions is used to bring glucose into the cell against its concentration gradient. Okay, any questions on that? All right, so the last type of transport that we're going to talk about is bulk transport, and that includes endocytosis and exocytosis. So endocytosis is the movement of substances into the cell.
And usually that happens when the plasma membrane envelops things, whether it's a bacteria or a food particle. And this requires energy, so it's a type of active transport. And the two examples are phagocytosis.
which means that the cell will just take in that matter and then receptor mediated endocytosis where basically the cell takes in that matter but those molecules are specific because they have to bind to a receptor on the surface of the cell. There's one more example in your book of endocytosis it's called pinocytosis and that just refers to basically a cell taking in fluid not particulate matter. I don't have it on here so You don't have to know it, but it is in the video I'm going to show you soon. Exocytosis, so think exit, the discharge of materials and substances outside of the cell. And this usually happens in the form of a vesicle at the cell surface that will just fuse with the cell membrane and push everything out.
So this requires energy too. Thank you. So in phagocytosis, usually it can be different things that the cell is taking in. It can be, you know, a macrophage, so an immune cell that is supposed to, you know, protect against infection.
So if we have a bacterial infection, our... immune system has these phagocytes, so that's the type of cell that we call it, that will engulf the bacteria and take it in and destroy it and then kill it and release it so that it doesn't continue to replicate. Now in this example, we have a cell here.
This is a mouse epithelial cell. And this is a bacteria that's being engulfed by the cell. But in this case, this bacteria, this is Rickettsia, you don't have to remember the names or anything. But this one has developed a mechanism where it can use this method of being phagocytosed into a cell in order for it to hide out in the cell and replicate.
Okay. And so some bacteria have evolved mechanisms to do that. And so this is just an example of it.
So it enters the host cell by phagocytosis and replicates in the cytoplasm. But, you know, this could also be food particles and things. It doesn't have to be bacteria, but it's usually like matter. It's not liquid when it's phagocytosis. And so here we have the membrane, and usually the membrane...
will enclose and fold over on that particulate matter bacteria in this case and then once it folds over on itself it ends up detaching as a vesicle and so the key here is that this bacteria is not free floating in the cytoplasm it's actually contained in this vesicle that's been pinched off of the cell membrane You'll learn a lot more about this in my microbiology class in the context of bacterial diseases and infections. Now the receptor-mediated endocytosis is basically similar but the molecules have the target molecule here is specific and it has to bind to these specific receptors in the plasma membrane. So these receptors have everything that is a receptor and here at the target molecule We call a substrate because it binds to the receptor Everything has to have a specific confirmation so it can fit snugly into that receptor So different cell types have different receptors for different molecules so it's very specific and when enough of these bind over here there's this coating here called a coating pit so when these are full eventually this coating pit will the receptors will close over and they'll form this internal vesicle over here and so the cell will react when all of these are filled initiating endocytosis but it's receptor mediated so so yeah so phagocytosis and receptor mediated endocytosis are both types of endocytosis because they're taking things into the cell Any questions? Yeah. What kind of stuff are they breaking?
In this case, so it can be anything that has something like a target molecule on its receptor. So for example, there are bacteria. that instead of the bacteria being taken up there's actually little proteins or something on the bacteria that triggers the cell to be like oh that's something that is like bad for the cell or it's harmful and so it will bind those specific things. And there's other immune cells that are involved in breaking down the bacteria and taking just that protein and then bringing it to this cell membrane so that that specific protein can bind to the receptor. That's a really good question.
But yeah, so they usually are some sort of marker for something that is, you know, the cell is going to know, like, oh, okay, this is a foreign particle, so I'm going to engulf it. and take it in and kind of, it's a protective mechanism. Yeah, good question.
Any other questions? Okay. How would you guys feel if Adrian College had an immunology class?
Would you guys take it? Basically just learning about how our immune system works? Maybe?
Okay for those of you that want to maybe do med school that would probably be useful. Just a thought. Now on the other hand we have exocytosis where the materials are being discharged out of the cell.
And so here we're seeing inside of the cytoplasm. There's a vesicle. Remember these things are always in a vesicle when they come in or if they're about to go out they're not just floating around they're contained and this vesicle is a secretory vesicle because it's going to fuse with the plasma membrane and secrete those products out so it's the same thing but in reverse And so this usually is used in plants to export cell wall material if the cell wall is being broken down by something or even it's used in animals to secrete things like hormones, neurotransmitters, digestive enzymes, just a bunch of things.
But what you have to know is that it's the movement of these particles outside of the cell through the secretory vesicle fusing with the plasma membrane. Okay. So easy enough. Here's a video to reiterate all of that. The substances used as fuel by single-cell organisms include other smaller cells, particles of organic material, and large molecules that cannot pass through the plasma membrane.
Many single-cell eukaryotes use a mechanism that can be used to control the plasma membrane. called endocytosis to ingest such food particles. In this process, the plasma membrane surrounds and engulfs the food particle. Cells use three basic types of endocytosis, depending on the size and nature of the material.
to be ingested, phagocytosis, pinocytosis, and receptor-mediated endocytosis. If the material the cell takes in is particulate, such as a bacterial cell or an organic fragment, the process is called phagocytosis. If the material is a liquid, it is called pinocytosis. Some types of molecules, such as low-density lipoproteins, LDLs, are transported across the plasma membrane by receptor-mediated endocytosis.
These molecules first bind to specific receptors embedded in the plasma membrane. The receptor molecules are concentrated in an indented pit coated by the protein clathrin. When sufficient target molecules accumulate in the coated pit, the pit deepens, seals, and is incorporated into the plasma membrane.
into the cell as a coated vesicle. Axocytosis is the reverse of endocytosis. This process results in the discharge of materials from membrane-bound packages that migrate to the inner surface of the plasma membrane, fumes with the membrane, and then release their contents to the outside of the cell.
Alright, so you don't have to remember the clathrin, the coded protein pit, the name of it, but you do need to know that there is a coded pit there, but you don't have to remember that specific name, just an FYI. Alright, so in your... book chapter 5 table 2 there's a really good summary of all of this so there's the passive transport processes the direct ones the direct simple diffusion where basically nonpolar molecules are able to move from a high to low concentration. There's facilitated diffusion which requires the facilitation of these proteins either in the form of a channel or a carrier and then osmosis is basically the movement of water molecules across something but these are all going from a high to low concentration of the solute. And then there's the active transport that we talked about.
and then the endocytosis and exocytosis as well. So a couple of concept check questions for you guys. You may or may not see these on the quiz on Monday.
So first one is the movement of water across a membrane is dependent on what? Yeah. B. Solute concentration.
Who else thinks it's B? Yeah. For those that didn't raise their hand, what do you think?
Everybody thinks it's B? Well then everybody's right, because it is B. So, yes, and so a lot of people might think that it might be the solvent, which is the water, because it's the water that's moving across the membrane. But if you go back to the slide, remember, everything I ask can be inferred from my slides.
Basically, osmosis is, yes, the diffusion of water across the membrane, but it's moving towards a higher solute concentration, so it's going down its concentration gradient. Because if the solute concentration is higher than the... the water concentration is going to be lower. So that's how it's always dependent on the solute concentration.
So it's B. Does that make sense? Okay.
Second one, how are active transport and coupled transport related? Take a second to read them. You can talk to your neighbor. Alright, you can raise your hand if you think you have it. Yeah.
A. Everybody think A. Anyone else think something else? Yeah. D. Anyone else have a different answer?
Yeah. C. Okay, so let's go through this. How are they related? They both use ATP directly to move molecules. Remember, active transport uses ATP directly, but coupled transport uses ATP indirectly.
So the active one is the sodium-potassium pump example, coupled transport is the glucose going in. So A is not correct. B says active transport establishes a concentration gradient, but coupled transport doesn't. Not true because everything that's being transported, whether it's passive or active, it's going to depend on a concentration gradient. C is the correct answer.
Coupled transport uses the concentration gradient established by active transport. And D isn't describing active or coupled transport. D is just describing what a uniporter is versus a symporter or antiporter. So the D would be correct if it said a uniporter moves one molecule, but symporter or antiporter transports two, moves two molecules. So make sure you guys know those terms.
Those are just more general terms to describe the number of molecules and the direction they're moving in. But so this is, so the answer to this is C. All right.
Does that make sense? Okay. Well. Well, have a good weekend.
I'll see you guys on Monday.