BIO 110-003 CH.5 Notes Part 1
BIO 110-003 CH.5 Notes Part 1 BIOL 110
University of Louisiana at Lafayette
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This 9 page Class Notes was uploaded by Kaylen Harrison on Sunday September 11, 2016. The Class Notes belongs to BIOL 110 at University of Louisiana at Lafayette taught by Patricia L. Mire-Watson in Fall 2016. Since its upload, it has received 10 views.
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Date Created: 09/11/16
CH. 5 Notes Kaylen Harrison Phospholipid=major component of cell membranes o Hydrophilic (polar)=head o Hydrophobic(nonpolar)=fatty acid tail § So an amphipathic molecule o Benefit????--an amphipathic molecule has an area that likes to hang out with water and that doesn’t Biological membranes o Fig 5.1--phospholipid bilayer o B/c have water on both sides have to have… o If just a single layer of phospholipids wouldn’t work b/ c then the tails would be hanging around the water and that doesn’t work o Cholesterol • Have to have it b/c we are animals o Most of plasma membrane is taken up by the tails ---the fatty acid tails in the middle o So majority of the membrane is hydrophobic Fluid-mosaic model o Fluid portion comes from the fact that molecules have the ability to move o Lipids and proteins can move around relative to each other o Mosaic part comes from it is made up of a bunch of different things put together such as phospholipids, proteins and carbohydrates Proteins bound to membranes • Protein portion of the membranes are composed of proteins that are attached or associate with the membrane in two potential ways o 2 groups of proteins • Are classified by how they are att ached in the membrane 1. Integral membrane proteins i. Integral=inside ii. Integrate=to put it inside something else i. Proteins that are inside the membrane i. Transmembrane proteins • Membranes that pass all the way through the hydrophobic region of the bilayer (two layers of phospholipids) • On one side of the membrane there's one part of it that sticks out of the membrane and out on the other and goes all the way through b. lipid anchor proteins i. Proteins that are covalently attached to a lipid ii. Lipid itself is part of the membrane iii. These are covalently attached iv. Covalent (strong bond) v. The reason it’s still integral b/c its protein is covalently attached to the lipid so together they make up one whole molecule C. peripheral i. They hang out on the outside of the lipid bilayer and not covalently attached to anything ii. Non covalent bonds make them hold on to the surface regions of integral membrane proteins, or to the polar head groups of phospholipids • Ex. Of non-covalent interaction: • Hydrogen bonds • Van der Waal • Ionic • Hydrophobic interactions • Types of interactions that peripheral membrane proteins are going to _____ • Fig. 5.2--transmembrane protein o Go all the way through the phospholipid bilayer o The parts that are sticking out of the membrane are hydrophilic b/c the cytosol is watery o Middle part that goes through the fatty acid tail region=hydrophobic § So this is amphipathic o If you have another protein hanging out with the transmembrane protein and there's non covalent interaction that’s allowing the attachment to occur then the green protein is the peripheral protein and it can be on either sides, but this one happened to by in the cytosol o Lipid linked --you can see the protein is covalently a ttached to a lipid o Even though it looks like a peripheral protein, its covalently attached to the lipids and is stuck there Factors affecting fluidity • Not all membranes are the same with respect to how fluid they are and even portions of membranes can be more fluid than other portions of the membrane • The things that can affect the fluidity of a membrane are: o length of fatty acid • The fatty acids tails are all hydrophobic • hydrophobic interaction: where things that are hydrophobic like to hang out with each other • The longer the tails are, the more hydrophobic interactions there can be, so this makes the membrane more solid/ less fluid. • Shorter tails =fewer hydrophobic inter actions o Presence of double bond in the tail • A fatty acid with a double bond is unsaturated • Single bond=saturated • If we're saturated, we're all straight, so we can get really close together • But if we have a kink in our tail then we have a covalent bond . That bond is what causes the kink • The kinks represent bends in the tails, causing them to move farther apart, making the membrane more fluid • The saturated makes it more solid, b/c all of the saturated ones have straight tails and are compacted real clo se together and that makes it more solid. Less fluid. More solid=less fluid • So where you have unsaturated fatty acids in the phospholipids, you're going to have more fluid membranes there o Presence of cholesterol • Is complex • Effects depend on temperature but it also tends to stabilize the membrane. Makes it less fluid • Stabilize=making less fluid § Single bond =saturated • Animal cell membranes have cholesterol. Plant cell membranes don’t. SO why do animal cell membranes need cholesterol to stabilize them , but plant cells don’t??? o Plant cells have a cell wall around them o That cell wall is rigid and it helps to prevent the cell membrane from dissolving or breaking apart or being too fluid o The animal cells don’t have cell walls that add rigidity so the cholesterol adds rigidity to it Glycosylation--gently attaching a carbohydrate to a protein or lipid • On membranes of many kinds, especially of animals, there's a sprinkling of sugar on the membrane=A sugar coat. • Sugar coat =glycocalyx o A shield • If the sugars are attached to a lipid then it’s called a glycolipid, I o sugar is attached to a lipid= glycolipid o sugar attached to a protein= glycoprotein • These are important in cell to cell recogn ition • So when one cell meets up with another cell, one of the ways that they recognize each other is by noticing the sugar coats • That is important for knowing that the cells in your body belong in your body and important for recognizing cells that come into your body that are foreign and don’t belong in your body • Also helps cells to recognize what kinds of cells they are to each other • The sugar coat plays a role in cell migration • The sugar can absorb water • Water sticks to the sugar b/c sugars are polar and water is polar • Makes the cell have a slippery, slimy coat and allows cells to squeeze around and move around in your body o Ex. White blood cells • There are particular types of white blood cells that leave your blood vessels when you have an affection of some kind • In the blood cells without the infection and when the infection happens the cells start to crawl along the wall of your blood vessel • And when they get to a space between the cells making up the wall of the blood vessel, they squeeze in betwee n the space • And they go out into the tissue and they'll find the bacteria that is causing the infection and gobble it up • So b/c of their glycocalyx they can do that which is sugar coat • Cell membranes are selectively permeable o Things can go in and out that are selected o This allows to be sure that essential molecules can come into the cell, waste products and other things can get out of the cell, but the things that need to stay in the cell, like the metabolic intermediate that needs to be used for things, remain inside the cell Phospholipid bilayer is a barrier • The phospholipid portion of the membranes create a barrier for hydrophilic substances • The whole interior of the phospholipid bilayer of the plasma membrane is hydrophobic b/c you have those two layers of tails that are facing each other so almost anything hydrophilic is not going to be able to pass through the phospholipids' • Even if they would want to move b/c of diffusion • Diffusion is the movement of anything o A substance from an area where there is more of it to an area where there is less of it o The reason things to diffuse like that has to do with the fact that they are always going to be in motion (kinetic energy) o The tendency of the universe is to make things disordere d so you have a collection of molecules and they all are in one area so that’s a very ordered space as opposed to be spread out everywhere o There are solutes (substances dissolved in a solvent) that will want to move from where there is a higher concentration to where there is a lower concentration o But if the substance is hydrophilic, it won’t be able to pass through the membrane (lipid bilayer) to diffuse through the phospholipids (to diffuse from one side of the cell to the other) b/c it can’t pass through the hydrophobic interior o There are things that want to diffuse from across the membrane. If they're hydrophilic they're going to need a transport protein to help them move through o The only molecule that can move through the lipid bilayer without the hel p of a protein (just through the phospholipids) are things that are hydrophobic and small o Anything too large and hydrophilic won ’t be able to do it o Gases can do it b/c they're small and in the gaseous state, so they have a lot of kinetic energy that can put it through • There's this barrier that the phospholipid has and so just by the fact that it’s made up of phospholipids, it’s going to stop anything hydrophilic from crossing it • Times when hydrophilic substances need to cross the membrane at any time are: o Glucose sugars needs to get into your cells • Sugars § Polar molecules § Have OH (anything with OH group is pola r) • Can’t get glucose in your cells just by diffusion through the lipid bilay er Cells maintain gradients • Cells use ions as electrical signaling mechanisms • Ions are charged particles so they can't cross the lipid bilayer on their own • Anything polar or ionic has to have a protein of some kind to allow it to cross • Cells take advantage of this. Cells know that they have this lipid bilayer and so they can prevent any hydrophilic from crossing them and so if they have a protein in there that’s going to let certain hydrophilic things pass, they can control what hydrophilic things le ave and come and that lets the cell use concentration gradients as a way to make signals. • The concentration difference across a membrane is when you're looking at solutes ==transmembrane gradient • If looking at ions, ions are electrically charged, so wheth er or not an ion wants to move from one place to another, it not only depends on its concentration difference, but also depends on the charge • When dealing with a movement of an ion, you have to consider the concentration difference but also the charge difference and that’s called electrical chemical gradient • What kind of cells specialize in transporting signals?? o Neurons Passive Transport • There are different types of transports of substances that occur across the membrane o Passive transport =cell doesn’t have to use any of its own energy to move that substance • Substance is going to move by its own kinetic energy § 2 types of passive transport that cells participate in: 1. Passive (simple) diffusion i. When a solute diffuses throu gh the membrane without the help of a transport protein • So what kind of molecules will be able to pass through the membrane without the help of a transport protein??? • Hydrophobic b/c its relatively small • Steroids b/c they're small • Gases • Anything hydrophilic or too large even its going to be passive transport, needs the help of a protein to get it across ==Facilitated diffusion • Cell is still not using its energy to move the molecule. It’s still passive transport. The cell hasn’t expended any energy to move the solute across, but there has to be a protein there to make it safe for that substance to pass o Fig. 5.10 ---a substance moving from the top towards the bottom • Its passing through the lipid bilayer • This is a passive transport and specifically passive diffusion • At the bottom have a substance moving from the top to the bottom and it’s a higher concentration here • Still a passive transport, but now there's a protein that provide s a passageway for it to safely cross ==facilitated diffusion • So the blue molecule is hydrophilic • Only hydrophilic molecules, or molecules that are sometimes too large to go through the lipid bilayer would use facilitated diffusion § There has to be a concentration gradient for facilitated diffusion § So there's nothing forcing the molecules to move here § There moving by diffusion and they are going through the passageway made by the protein Tonicity o Tonic=refers to solute o Isotonic, hypertonic, hypotonic • refers to what the solute concentration is like across the membrane' • They're all used to describe comparing a s olution on one side of the membrane and 2 of the solutions on the other side of the membrane o Isotonic • Iso=the same on both sides • Concentration of the solute is the same on both sides of the membrane • Equal water and equal solute • If solution is made up of a solute in water and the solute conce ntration is equal on both sides, the water concentration also has to be equal o Hypo=means less • Less concentration than the other o Hyper=means more • Higher concentration than the other • What you are can change depending on what's on the other side • Can’t just say the solution is hypertonic. Makes no sense. Hypertonic to what?? The cell. • The cytosol is a solution so have to say to the cytosol § Ex. The isotonic solution is hypertonic to the cytosol • If the solute concentration come across a membrane, it determines whether or not the solutions are iso, hypo, or hypertonic ___ the membranes • Water concentration also matters b/c the solute is dissolved in water • Why do we care about this???? ---Fig. 5.15 Osmosis o Well, we have animal cells and animal cells don’t have cell walls so they have the cholesterol to try to help them maintain their rigidity so if you put your cells into a hypotonic solution and if the solute particles even though the solute particle is going to want to move out of the cell b/c there's a higher concentration of them inside than out but if these are polar ionic substances they won’t be able to go through the lipid bilayer o However, water, even though its polar, can pass through most cell membranes pretty easily and part of it is due to a lot of cells having facilitated diffusion of water, but also water b/c it’s so small it can slip through the phospholipids sometimes without a protein o (still looking at bottom picture) if the solute can't move, there's still a concentration difference across the membrane and water can move so water is going to move into the cell b/c if you have fewer solute [articles on the outside of the cell that also means you have more water. So this is 10% solute which means there will be 90% water whereas on the inside, its 90% solute so only 10% water. So water is going to want to come into t he cells and your little animal cells are going to start taking in water and for a while they will be able to start swelling, but eventually they're going to burst===called cytolysis • If put some cells in a hypertonic solution and the solute can’t move acr oss the membrane but water can, water will move to the outside of the cell and animal cells will shrink and turn into little raisins and cells can’t function if they're raisins. o Both (cells bursting and shrinking) are not good • So the movement of water ac ross the membrane is called osmosis and it has repercussion especially for animal’s cells but it does also affect plant cells, but plant cells have a better way of dealing with it than animal cells do • Water is going to want to diffuse through a membrane f rom where there is more water, to where there is less water • And if solutes can’t move across the membrane, then the water will move across the membrane and movement of water will make cells ______ • All cells have an electronic pressure (refers to how much pressure is there on water to move into the cell) • If animal blood cells, such as red blood cells are in a isotonic solution the concentration of the solute across the cell is equal • The concentration of water across the cell is equal • So there will not be any net movement across the red blood cell • So there's still some water molecules coming and then leaving, there's just the same number doing it • So these cells are not going to be happy cells • Red blood cells are normally shaped like donuts without the hole s in them • So it’s important that the f luid(plasma) surrounding red blood cells concentration be the same as your cytosol concentration in red blood cells • What happens if the plasma becomes hypotonic to your cells? o There's less solute on the outside of the cell which means there's more water o And the solute can’t move, but the water can move into those cells, they swell and turn into little water balloons and they'll pop. This is called cytolysis o And when red blood cells pop, if enough of them pop, then you die • Cytolysis --when cells swell and then pop • So if they come to do an I.V. on you at the hospital you don’t want distilled water (pure water) going into blood b/c its concentration is 100% and the plasma has so lutes in it , so you start diluting the solute concentration of you plasma and are making a hypotonic solution in your blood and cells will pop and then cells can ’t carry oxygen to your tissues and you die o Salt water could cause the pop • Salt causes a higher concentration then your plasma • The salt concentration in the bottom (fig 5.15) is higher in the solution than in the cytosol. So it’s a hypertonic solution. The solutes can ’t move but water can, so higher salt on the outside means lower water. Water will leave the cells and then shrink. This is called crenation. o Crenation--when cells turn into little raisins • Cells don’t burst when put in hypotonic solutions • As water comes into the cell, the water gets stored into this large bubble which is the cen tral vacuole • b/c the water is being put in a special space, it’s not out in the cytosol diluting all of the proteins and stuff in there. Its stored in the vacuole which is helpful. • This will increase its size as more water comes in and it ’s going to start pushing on the cell wall. So once it gets filled enough, it puts a pressure onto the cell wall. The cell wall is rigid so it ’s going to push back and that pressure of the cell wall is called turgor pressure. Turgor pressure forms when plant cells are in hypotonic solution Osmosis o Once filled up enough, puts pressure on cell wall • Turgor pressure • When cells are in a hypotonic solution • When cells are in a hypertonic solution ---cells lose water from its vacuole. • The vacuole gets smaller; the cell membrane might wrinkle b/c its losing water but the cell wall wont shrink • So still have cell wall holding in place where the cell would normally be • You can still kill the cell, if the cell stays this way for too long • So this loss of turgor pressure is called plasmolysis • Crenation=when cells shrink in animal cells • Plasmolysis=when cells shrink in plant cells • So if cells stay like this for too long, they will die, but if they take in water soon enough, they can just re-expand again and get their turgor pressure again • If you forget to water your plant, it will look pretty bad because since you haven't watered it lately the solution in the plant tissue has become hypertonic (=low on water) and so the cell has loss water to the solution _____ and it has _____so it realizes that there is not turgor pressure pushing against the cell walls so they become _____. But when you water it , they take up the water , expand again, and the plant stands up again and gets happy. • If we want to move anything hydrophilic across the membrane its going require proteins to help us do that = transport proteins o There are two kind of transport proteins • Channels--Fig 5.17 § A protein that provides an open safe passageway for solutes to diffuse § Channels participate in facilitated diffusion b/c the molecules still diffuse from where there's more of them to where there is fewer of them § Molecules are still moving on their own by diffusion, but the protein is still providing the safe passageway § Cells don’t have to use their own energy to make the molecules move • Ex. Aquaporin • Channels that are in cell membranes that provide passageway for water • Ex. • Kidney cells • Red blood cells • These have aquaporins (water channels) • Transporters a.k.a carries (not channels)--Fig 5.19 § Difference btw channels and transporters • There's no gating • They don’t go straight th rough an open passageway, they bind to the proteins at a particular place and are unbinding (turning it loose) to get to the other side • Involved in carrying, physically grabbing hold of the solute and moving it • Uptake of organic molecules • Key role in export