welcome to unit 4 membrane transport and enzymes part 1 membrane structure and transport functions of the plasma membrane also known as the cell membrane separate cell from the outside environment provide structure which is strengthened shape and protection regulate substances entering and leaving the cell this is known as a gatekeeper is essentially is going to determine what is allowed in and what is allowed out of our cells and each cell is going to be different in what their expectations are we use the fluid mosaic model in order to describe the plasma membrane so it is a mosaic mosaic means a patchwork of separate things that work together to form a whole often this term is used to describe certain types of art so our plasma membrane is a mosaic of protein molecules bobbing in a fluid bilayer of phospholipids even though in this picture everything is stationary and not moving we have to realize that it is not stationary everything's constantly moving for example our phospholipid bilayer our blue heads of our phospholipids as well as our yellow tails they're constantly moving they can move side to side they can even inverse and go to the opposite side we can see our proteins that are moving throughout so that is why we call it fluid because it is constantly moving here's an overall view of all the structures involved in our plasma membrane we will be going through each of these individually this cell in fluid we can magnify to look at its plasma membrane and see the components in it the main structure is the phospholipid bilayer the structure and location of phospholipids this is a double layer of phospholipid molecules with fluid consistency as we saw in the previous slide they're constantly moving they're formed of hydrophilic heads our phosphate group and glycerol outwards and our hydrophobic tails our fatty acid chains sandwiched in the middle if this is seeming a little fuzzy to you please see our unit 2 on our biological molecules the function of the phospholipid bilayer this is to allow water and neutral dissolved substances to diffuse in and out of the cell cholesterol cholesterol is the lipid distributed amongst the phospholipids here you can see the cholesterol shape remember that it is four fused rings that form a cholesterol molecule the function of cholesterol is to re regulate the membrane fluidity by stiffening and strengthening the membrane so without cholesterol in cold conditions our membrane will be rigid it will not be very fluid or flexible and it could break due to this in hot situations without cholesterol we could see that it becomes too fluid too flexible it won't hold shape it'd kind of like be melting so cholesterol is able to maintain our membrane fluidity keeping it just right glycolipids structure and location it's a phospholipid attached with a carbohydrate chain remember that glyco refers to carbohydrate so whenever you see glyco you should instantly think carbohydrate and here we see it is indeed a carbohydrate chain attached on top of a phospholipid lipid is referring to our phospholipids the function of these glycolipids are cell recognitions markers they're saying hey i'm your cell so if you have foreign invaders we can tell that they're foreign invaders because they don't have the right recognitions with the right glycolipids peripheral proteins these are associated with only one half of the lipid bilayer as you can see it's on the inside intracellular or inside of the cytosol side so they are maintained right here as you can see and so you'll never see peripheral membrane proteins on the extras outside extracellular side the function of peripheral proteins are to stabilize and shape the plasma membrane they help anchor the shape next are our integral membrane proteins so we have different types of integral proteins first we'll look at the channel proteins channel proteins are proteins that span the lipid bilayer that means go all the way through both sides they have an opening to allow movement of particular substances across the membrane the function of channel proteins are to allow particular ions or molecules to cross freely the membrane down below we can see different types of channel proteins we can have voltage gated which a change in voltage will open we can have ligand gated extracellular so that means that we have something attaching to it from the extracellular side which is going to create movement and open it and stress activated as well next integral proteins we will look at are the carrier proteins carrier proteins are proteins that span the lipid bilayer just like channel proteins they bind with particular substances to help it cross across pass across the membrane the function of carrier proteins are to selectively interact with specific molecules and ions and allow it to cross a membrane this may sound very similar to channel proteins and indeed they are we will talk a little bit more about carrier and channel proteins when we talk more about transport the next type of integral proteins are receptors receptor proteins are proteins that span the lipid bilayer this is an area for molecules to bind to the function receptors bind with specific molecules and change shape to cause cellular response we will see lots of this especially within our nervous system the next type of integral proteins are enzymatic if you look at this word it looks like enzyme and you'd be right these are enzymes that are integral proteins there are proteins that also span the lipid bilayer and there's an active site found outside or inside of the membrane their function is to carry out or catalyze metabolic reactions directly and next we have our glycoproteins glycogen that means carbohydrates these are going to be attached to a protein so the structure and location these are also proteins that span the lipid bilayer however they have an attached carbohydrate chain notice that the carbohydrate chain is on the extracellular side of the membrane this helps identify the cell so they often work very similar to the glycolipids next we see our cytoskeleton this is affiliated with and often stabilizes our peripheral proteins and internal surfaces above the membrane the function of this is a structural support for our membrane and cell we can see it on the intracellular side of the membrane with inside the cell we will see that our cytoskeleton filaments are made up of our microtubules our microfilaments and our intermediate filaments please see unit 1 during your first assignment if you are unfamiliar with these permeability of the plasma membrane the plasma membrane is incredibly important in the role of maintaining homeostasis in cells and organisms homeostasis maintenance of normal internal conditions via self-regulating mechanisms it does this by regulating the passage of molecules in and out of the cell to maintain the cell's normal compt position this is made possible because the cell membrane is selectively permeable this is a very important term to recognize with plasma membrane it allows certain substances to move across it the passage of molecules can occur without energy or it may require energy so our plasma membrane is going to be permeable to only certain substances and it depends on what kind of cell it is what can or cannot go through the membrane non-charged molecules can go through the membrane water can go move through the membrane macromolecules anything that's really big it's not going to be able to diffuse right across the membrane charged molecules are not able to move past passive transport substance transport not requiring energy so here we're going to see all the ways of moving across the membrane that does not use energy remember when we're talking about energy in cells this means atp which is our currency of energy for ourselves first is diffusion diffusion is the movement of substance down a concentration gradient what is the concentration gradient this is when we go from an area of high concentration to low concentration do you see those square brackets around high and low those are short form for concentration so that is literally saying from an area of high concentration to low concentration the direction high to low requirements the concentration gradient it does need this in order to move the substances that it can move lipid soluble makes sense because this is going to be moving across a phospholipid bilayer water and gases in the diagram below we can see some dye molecules inside of water notice that when you first put the dye molecules they're all together clumped but then they start to move across and eventually they will come to an equilibrium that means that it's going to move around so they're about the same distance away from everything they're going from an area of high concentration they're moving to lower concentrations until everything is about equal this is what diffusion does here's an example with our phospholipid bilayer if these little molecules here are able to move through the membrane they are permeable from the membrane you will see that over time so moving from left to right we will see that it will start to diffuse this is an area of high concentration this is an area of low concentration they're going to move across the membrane until we come to an equilibrium until they are equal then we no longer have an area of high and low concentration therefore they'll be equal movement of molecules there's a special type of diffusion called osmosis learning science is like learning another language unfortunately we have many words for very similar processes this is the exact same thing as diffusion except it's only when water does it so if we hear that water is diffusing we actually say that it's osmosis so what is osmosis movement of water across a membrane down a concentration gradient only water never anything else it goes from an area of high concentration to low concentration it requires the concentration gradient substances only water so in the diagram below we can see that we have a selectively permeable membrane this means that it's not going to allow any of these sugar molecules to move but it will allow water so if over time we're going to see that the water is going to move from an area of low concentration to high of the solutes because if you think about it this area has a high concentration of water molecules compared to solute here it's going to have a low concentration of water molecules to solute it gets a little tricky when you start thinking about it so the area of water is going to want to move from the area of high water molecules to an area of low concentrated water molecules when it does this we'll see the concentration of each solution will be equal the next type of passive transport is facilitated transport this is also known as facilitated diffusion you should be able to recognize and use both terms what is facilitated transport it's the movement of particles down a concentration gradient with the assistance of a channel or carrier protein these are types of integral proteins the direction from high concentration to low concentration requirements a concentration gradient and a channel or carrier protein substances some sugars some amino acids so what we see with passive transport is we have an area of high concentration and an area of low concentration with the help of a channel or a carrier we're going to see that the movement of molecules do not need any energy to go from high to low and however they cannot move through the mammarian itself they would have to move through a channel protein or a carrier protein this is active transport this is not the same so if you see atb here it is not the same even though it looks very similar because it also uses a carrier protein it is not the same there is no atp or energy used for diffusion osmosis or facilitated diffusion through a channel or carrier protein next we're going to talk about tonicity tonicity is defined as a concentration or amount dissolved of a solution a solution is a mixture of solute in a solvent lots of very confusing words here a solute is a substance being dissolved often like coffee or sugar solvent substance doing the dissolving most of the time this is water you can always assume it's water unless it's told you something else wise hypertonic solution the concentration of solutes inside the cell is lower than outside the cell so if water moves out of the cell the change in cell size shrinks so if we're in a hyper tonic solution that means the cell right here is going to have less solutes than it does outside this one doesn't really show it's super great but it means that there's less solutes inside than outside whenever we talk about tonicity it's actually a reference so hypertonic solution means that our cell would be hypotonic a term which we will see soon so the solutes in the solution is greater than the concentration of solutes in the cell hypotonic solution so that's what we were just talking about when we were talking about the cell in the last picture so here we're going to see that the cell has much more solutes in it and the so this is going to be hypertonic to the solution but the solution is hypotonic to the cell pretty tricky make sure you're always referencing what you're talking about is it the solution that's hypotonic or is it the cell that's hypotonic if we have a hypotonic solution we're going to see that water molecules are going to want to come into the cell and very little is coming out so that means that our cell is going to increase it's going to swell so solid concentration of solutes in the solution is less than the concentration of solutes in the cell change in cell size it's going to swell it will get bigger because it's filling up with water isotonic solution iso means the same the concentration of solutes inside the cell is equal to the outside of the cell so water moves in and out of the cell at the same rate there is no change in cell size so solute concentration inside the solution is equal to the solute concentration inside the cell this is what it is trying to always be at it's always wanting to regulate itself so here we can see hypotonic solution we're going to have water moving into the cell okay in these situations the cell can actually burst which means lys another word for it we can have isotonic solutions where the water is moving in and out of the cell at equal rates or a hypertonic solution where water is going to be leaving the cell in order and to come out into the solution and the cell will shrink now we're going to move on to active transport substance transport requiring energy so this is all the types of transport that you need to have atp with active transport that's the name of it it's the transport of molecules across the membrane against the concentration gradient through a protein carrier and input of energy which is atp for example a sodium potassium pump this is a very common example which we will go into more detail about in the nervous system the direction it's opposite to our passive it's low concentration to high concentration this goes against the concentration gradient the requirements a carrier protein and energy in the form of atp substances sugars amino acids ions so here you can see our sodium binding to our sodium potassium pump our atp is going to come over it's going to release one of its phosphate groups creating adp and releasing energy when it does this it's going to change the form of our carrier protein to release the sodium ions cool thing about this is when it's opened out to the extracellular side now potassium can come in we can see the release of that phospho phosphate group which is going to change its shape again in order to release the potassium ions inside the cell exocytosis this is a membrane-assisted type of transport this is when a vesicle created in the cell endo membrane transported to infuses with the cell membrane to release substances so this is when we have a vesicle formed by let's say the golgi apparatus and it's going to go export whatever it is it's going to come up to our plasma membrane it's going to fuse with our plasma membrane and release it to the outside the direction inside the cell to outside the cell it requires a vesicle this is going to use macromolecules so large molecules will exit the cell this way such as proteins here's an example of exocytosis our vesicle is fusing with the membrane as all of the membranes are the same they can actually just be part of the membrane plasma membrane now and you can have different parts of it that will bud off and form vesicles here's another example now we have endocytosis because we can't keep adding to our membrane our membrane would get far too big so this is the same but opposite it's another membrane-assisted transport it is the intake of substances into the cell by pinching of the plasma membrane to form a vesicle it goes from outside the cell to inside the cell it requires a vesicle and again it does macromolecules here's a diagram showing you how it pinches off kind of goes through and eats those substances to bring them inside so we have a two different types of endocytosis first is phagocytosis this is also known as cell eating this is when it draws the item inward while engulfing around it you can see a photo of the side to your right often happens when the cell is trying to destroy or break down something like a virus or food used by the immune system cells so if this was a virus it would be engulfing it in order to break down in this example on the side this is going to be a food particle so it's going to engulf it using phagocytosis in order to form a vacuole which is then going to break down after it stores it goes from outside the cell to inside the cell it requires a vacuole and lysosomes so a vacuole is going to store whatever it is until it's ready to be broken down lysosomes are full of hydrolytic enzymes this is going to break down the molecules if it's food it's going to break it down into its building blocks for example it's going to break down proteins to their amino acid carbohydrates to their monosaccharides it's going to break down nucleic acids to its nucleotides it's going to break down lipids to the glycerol and fatty acids substances macromolecules cells and viruses the next type of endocytosis is pinocytosis which is cell drinking this is when the cell engulfs smaller particles or liquids via endocytosis again from outside the cell to inside the cell it requires vesicles and macromolecules often this is using vesicles is because they're already broken down they're not doing huge ones that are going to need to fuse with a lysosome in order to break it down they're small molecules ready to be used once they are brought into the cell factors affecting cell transport the rate of diffusion is how much solute diffuses into an area in a given amount of time let's predict how would you how would the following affect the rate of diffusion i want you to take the time to think how would increasing the temperature affect this how would increasing the concentration making more of a high concentration on one side and a lower concentration on the other increasing pressure increasing the particle size increasing diffusion distance so how far away or how big the membrane is it has to actually diffuse across or increasing the surface area of the membrane take a moment to pause the video now and take a guess is it going to increase it or decrease the rate of diffusion okay so increasing temperature is going to increase our rate of diffusion increasing concentration gradient is going to increase the rate of diffusion increasing pressure is going to increase diffusion we often sign that if you increase the pressure you're decreasing the volume increasing particle size oops is going to decrease it it's going to take longer because it's a bigger molecule to deal with increasing the diffusion distance it's further to diffuse so it's going to decrease the rate and increasing the surface area of the membrane that's going to increase the rate there's more area to do this too so here's a little example of how big the cell size are so this is what we can normally see with our naked eye okay and this is with a light microscope and electron microscopes atoms are quite small phospholipids are very small and you can see the different sizes so surface area and volume reminders surface area is the total area of all exposed surfaces of an object volume is the amount of space an object occupies that is enclosed in a count and container the cell's surface area is directly proportional to its ability to import or export substances a large cell requires the acquisition of more nutrients and also removal of more wastes so it requires a larger amount of surface area compared to its volume so this is also known as our surface area to volume ratio try this calculate the surface area to volume ratio of each cell in the diagram below please show your work so you're going to reduce surface area to volume please pause the video here and go through each one we're gonna see that in the small cell we have a six to one surface area to volume ratio we took the surface area at six and we did it to one volume the medium cell is going to be 24 to eight when we simplify that that's three to one and when we've calculate our large cell we're going to have a three to one which cell has the greatest surface area to volume ratio the small which cell has a smaller surface area to rate volume ratio is the large what does it mean when you say a cell has a large surface area volume ratio more membrane the surface for its size a more exposed surface for its size what is the relationship between a cell size and its surface area to ratio volume ratio as the cell science increases the surface area to volume decreases i'm not really sure why this is coming up as 1 1 1 2 please ignore that so why are cells so small this is to allow for efficient transport of substances in and out of the cell if they're too big they're they're requiring too much of the nutrients and too many wastes are being produced and there's not quite enough surface area to do this so having a more surface area to volume ratio they're able to actually be much more efficient in what they take in and out of the cell part two enzymes some definitions metabolism the sum of all reactions that occur in a cell we have catabolism breaking big molecules into smaller ones such as hydrolysis reactions anabolism putting small molecules together to make bigger ones synthesis reactions together our catabolism and anabolism will create our metabolism monopolism reactions occur in an organized sequence for substance to end products with the help of enzymes a metabolic pathway a series of linked reactions note substrates are the same as reactants but with enzymes we call them substrates so if you've taken chemistry before you know that whatever we start with is called a reactant and whatever we end in is a product however in biology we call whatever we start with is a substrate for enzymes and what we end up with are products metabolic pathway so here we see a turning to b turning to c turning to d turning to e turning to f turning to g here we have enzyme one this facilitates a turning to b a through f are all substrates b through g are all products all of these e's are enzymes so product b is the substrate for the second reaction whose product is the substrate for the third reaction until the final project is reached g b to f are also known as intermediate products this means that they are products but they're intermediate they're going to be changed into something else this is an example of negative feedback the concentration of the final product gets low again there'll be less inhibition on the enzymes and the metabolic pathway is reactivated so we can see a turns to b this is inhibited by zed so this enzyme that facilitates a to b is going to be stopped by z however if we have no z product made this proc this reactant will happen so this reaction to a to b to c to d to z will occur if there's low amounts of z once said starts creating more then it's going to come over and it's going to inhibit the enzyme that's facilitating this stopping it this is called a negative feedback because then it will stop creating whatever it needs to and only will start making it again in low concentration this helps us not have any waste formed an example amino acid isoleucine is made from an amino acid therian in a five-step pathway see below isoleucine is going to actually inhibit our enzyme number one feedback inhibition prevents cell from wasting chemical resources to synthesize more than necessary which is a great way of making sure we only make enough of what we need activation energy activation energy the energy required to cause molecules to react so here we have our reactants remember this is actually substrates okay so our substrates are going to turn into products unfortunately this they only had one that had a chemistry one for it and if we do not have an enzyme it's gonna take this much energy in order to come down and create our products however with an enzyme it's going to make much less energy to come to our products so the difference between here is going to be how much energy you save so this is the energy of activation from how much our reactants are to how much we need to have in order to come form products versus without an enzyme so it's much easier to do with an enzyme enzymes are proteins which are also known as catalysts enzymes are all enzymes are proteins but not all proteins are enzymes they help speed up chemical reactions by lowering the activation energy of metabolic reactions as we saw in the previous slide a catalyst is a substance that speeds up a reaction without being consumed so all enzymes are catalysts but not all catalysts are enzymes and a little confusing with all the language so if there's no enzyme we might have a substrate that's trying to form a product and it just doesn't have enough energy to make it over that hill see when the cannon ball is trying to go over oh it's not quite enough that means that it's gonna not have this reaction occur our substance straight is not going to turn into a product because there's just not enough energy in order to do so if we add an enzyme it lowers an activation energy so that the substrate has enough energy to become a product this reaction will be able to go through some definitions a substrate is the reactant in the enzyme reactions enzyme subtract complex a very temporary structure where the substrate is combined with the enzyme active site a specific groove or pocket where the substrate attaches enzymes can only bond with one specific substrate so we see within the enzyme the really important part is the active site because that's where the substrate is going to go in in order to be able to get changed into the product cofactors and coenzymes are substances that bind with the enzyme to help make it effective some co-factors are inorganic ions such as copper zinc iron coenzymes are organic molecules and includes many vitamins such as niacin riboflavin enzyme plus substrate is going to turn into an enzyme substrate complex see them bonded together there and it's going to finally make the enzyme and products notice that enzyme is in each step enzymes are never used up in chemical reactions and can go on to help facilitate multiple reactions the only thing that's actually undergoing change is the substrate which is turning into the product or products examples of enzymes you do not need to memorize this for this unit however this is going to be covered in your unit 5 digestive system where you will need to understand and memorize these so starch which is also known as amylose is going to turn into glucose with the help of amylase lipids turn into fatty acids and glycerol with the help of lipase and proteins will turn into amino acids with the help of protease notice that all the enzymes end in a's this is really helpful so you can help kind of pick out what you think are enzymes not all enzymes end in a ase although most do that we will be doing in this course two models of enzymatic action the first is lock and key the enzyme site is specific an exact fit to the substrate just like key is to a lock this is very passive so notice in the picture the substrate looks exactly like the active site to the enzyme it fits perfectly there's not any energy that needs to happen here and the other model for how this works is an induced fit the active site on the enzyme changes slightly to accommodate the substrate this is active we're going to need some energy where the enzyme actually moves a little bit of its active site in order to perfectly fit we actually see that there's a little bit of both there's not one of these models that are accepted more than the other necessarily we do often see induced fit used more when we are talking about enzymatic models factors affecting enzyme activity first is ph remember that enzymes are proteins and the proteins can denature all enzymes have an optimal which means ideal ph if the ph is too high or too low the enzyme will denature this will change shape remember function happens from the structure structure equals function you change the shape you change the function or you stop the function these are examples you do not need to know until unit 5 pepsin is found in the stomach at a ph of 2 it is optimal trypsin is found in the small intestine it works at an optimal ph of eight and amylase in the saliva works on an optimal ph of seven so not all enzymes have their the same optimal ph they'll all have their best notice from this graph that at the top here this is the highest amount of enzyme activity if you drop down on either side of ph you decrease quite dramatically the activity temperature with increased temperature the reaction rate increases to a maximum point which is our optimal temperature the temperature that has the fastest reactions if the temperature gets too high the enzyme will denature so notice the steep cut off here most of our enzymes have an optimal temperature of 37 degrees celsius our body temperature temperature changes affect enzyme shape and hence its activity below 40 degrees celsius change can be reversed above 40 degrees celsius change is permanent there's no ability to regain its function in cold temperatures molecules move so slowly so there's very few collisions that means that there's actually no collisions of having our enzymes with our substrate so reactions cannot happen think about when it's really cold out and you're trying to move your fingers to tie your shoes another point to say is that when it denatures the most important part is the active site the active site is what gets denatured and that is the spot where the subject comes into binds in order to have the reaction rate increased next is substrate concentration the enzyme activity increases as substitute concentration increases but there's only so many enzymes with active sites available so there's a maximum rate so notice here that as you increase the substrate concentration our reaction rate increases but it does until only so much right here it flattens out that means we're not increasing or decreasing our reaction rate that means that we have saturated all of our enzymes all the enzymes are working as fast as they can and there's just no more to use the only way to change the rate at this point is to add more enzymes enzyme concentration determined by the cell's dna because our dna is what creates proteins and enzymes are proteins certain genes are turned on and off to activate or deactive enzyme production only so many enzymes are made for a cell at one time note enzyme and substrate concentration are directly proportional they're related so as you increase your enzyme concentration you increase your rate until you are at maximum all of your enzymes are using the substrate that is available at the time the only way to increase this rate is to add more substrate competitive inhibitors a molecule that is very close to the shape of the true substrate may bind with the enzyme and inhibit the reaction because only binding between the true substrate and enzyme will make the appropriate products for example carbon monoxide and carbon dioxide carbon dioxide is very similar to carbon dioxide and will bind with hemoglobin when this happens hemoglobin is no longer able to bond with carbon dioxide therefore there's not going to be able to move this at all so competitive inhibitors are going to go sit in the enzymes and block the active site with a competitive inhibitor we're going to see that we have a lower rate than without an inhibitor although it's not too impressive because it has to compete some of them are going to still get in there we'll still have substrate out-competing our competitive inhibitor but not all a non-competitive inhibitor non-competitive molecules bind at the non-active which is called the allosteric site and this changes the shape of the enzyme so that the substrate can no longer bind to the active site this includes heavy metals such as lead mercury and cadmium okay so here's an allosteric spot it's going to we're going to find our non-competitive inhibitor is going to bind here which is going to change the site of the active site so the substrate is no longer able to bind so here we saw our competitive inhibitor it's smaller but not as much as are non-competitive our non-competitive inhibitor is going to drastically lower the rate of reactions thank you for listening the notes are also posted underneath this lecture video found in our class online website if you have any questions please contact your teacher thanks for listening