Transcript for:
कोशिका की संरचना और कार्य

class and welcome to chapter five which will be where we're talking about the working cell we're going over to some of the functions of the cell um including how the cells work using their membranes which is kind of the exterior coating of the cell how they create energy and what enzymes do in the cell this is a really cool look at the cell membrane and again this is kind of the border between the cell on the inside and what lies on the exterior of the cell so this is what the cell's membrane looks like and some big ideas again for this chapters we're going to be looking at the cell membrane structure and function how cells will create energy and then how enzymes will work in the cell we'll first look at membrane structure and function biologists use what we call the fluid mosaic model to describe a membrane structure this includes a diver diverse protein molecule suspended in a fluid phospholipid bilayer the plasma membrane exhibits what we call selective permeability and that just means that it only allows certain things to get through while other things are unable to pass through and the proteins within that cell membrane perform various functions as we will see some of smaller particles can easily diffuse across the membrane like oxygen and carbon dioxide and then we have different proteins which are seen here and these different proteins just help other certain ions or particles pass through the cell so here's a look at the diffusion of small nonpolar molecules freely passing through the cellular membrane if anything small enough like oxygen or carbon dioxide and nonpolar meaning it doesn't have a charge to it meaning it's not positive or negative it can easily pass through the membrane because it's small this is a look at transport proteins and they allow specific ions or molecules to enter or exit the cell and they're really important whether it's a hormone or an enzyme to enter or exit the cell these are enzymes and enzymes some membrane proteins are enzymes and enzymes could be grouped to carry out a sequential reaction where there's kind of a series of reactions that need to take place and they're a part of that series attachment proteins attached to the extracellular matrix which is anything outside of the cell and the cytoskeleton which are like the bones of the of the skull of the cell these proteins help support the membrane and they can coordinate external and internal changes receptor proteins are signaling molecules when they bind to receptor proteins the receptor proteins will relay the messenger by activating other molecules inside of the cell so again we're looking at different proteins that are within the cell membrane of the cell junction proteins form intercellular junctions that just help to attach adjacent adjacent cells together glycoproteins serve as id tags so this means that they may be recognized by membrane proteins of other cells to help these cells to recognize which cell they're close to and this is just a summary of all of the proteins within the plasma membrane and the different structures and functions they can have here's a great animation of the overview of cell signaling and another animation of the signal transduction pathway what this animation just shows about what happens when a signal molecule binds to a receptor protein in the membrane and the different reactions that can take place then with in within inside the cell uh phospholipids spontaneously self-assemble into simple membranes and that's because their um hydrophobic regions of their tails always point to each other and their hydrophilic tails point to the exterior and heads point to the exterior and interior of the cell so that's a little bit of the connection of the phospholipids here's a look at a water-filled bubble made of phospholipids just showing showing how they spontaneously form membrane bounded sacs diffusion is the tendency of a particle to spread out evenly in a available space and diffusion often occurs across the cell membrane it never requires energy and so it's called passive transport and diffusion across the membrane is called passive transport because it doesn't require any energy so here's just a look at diffusion of one type of molecule across the membrane and it's just showing how the molecules of a dye will eventually spread out until equilibrium is reached meaning each molecule the dye is spread out exactly equal in comparison to the rest and they will travel through the membrane in order to reach equilibrium so the net diffusion as you can see here this is diffusion of two types of molecules across a membrane and you can see here in which direction net diffusion occurs and again diffusion just means they spread out from an area of high concentration to low concentration until equilibrium is established another way great way to describe diffusion is if when you have a cup of black coffee and you put a little creamer in it the creamer eventually diffuses into all parts of the coffee until equilibrium is reached or that nice kind of cream color that i like in my coffee and that's like just an example of diffusion here's a great animation of diffusion again to watch these animations you just have to download the powerpoints from canvas and then you're able to watch all of those another great animation about membrane selectivity which just shows which things are able to pass through the membranes and which are not the diffusion of water across a selectively permeable membrane is what we call osmosis and if a membrane permeable to water but not to a solute separates two solutions with different concentrations of solute water will cross the membrane moving down its own concentration gradient until the solute concentration on both sides is equal so predicting the net water movement between two solutions which has a less concentrated 0.5 sucrose solution and a 2 sucrose solution separated by a permeable membrane not permeable to sucrose sucrose which is just sugar what will happen here is water will travel into the two percent sucrose solution because water will add always travel into an area that's morally highly concentrated by the solute to try to reach equilibrium and this is shown kind of by this diagram so here's the solute molecule on the left and the right you can see there's a higher concentration of solute and when we say solute we just mean sugar or salt or something that's trying to dissolve there's a semi-permea or selectively permeable membrane which means that only water can pass through it and not solute particles so in order for equilibrium to be established meaning equal concentrations of solute on both sides water will have to move through that membrane because on the left side of this kind of u-shaped beaker there's less solute molecules and on the right side there's more so for equilibrium to be reached water will always travel into an area of higher concentration of solute and when water does that will kind of sway the scales and there will be more water than on the right side then on the left side and now you can see that there's an equal concentration on each side of that selectively permeable membrane in relationship to the number of solute particles to the volume of water and this is just showing kind of zooming in on the selectively permeable membrane showing how water is able to pass through but the solute molecules are unable to pass through because they're too large and this is a great animation of osmosis describing what we just talked about as well water balance between cells and their surroundings is very crucial to organisms tonicity is a term that describes the ability of a surrounding solution to cause a cell to gain or lose water cells will shrink in a hypertonic solution and that's because water will leave the cell to travel into a more concentrated hypertonic solution so the cells will shrink and cells will swell in a hypotonic solution and that means cells are placed into a hypotonic solution which is less concentrated because of that water will travel into the cell causing them to swell in isotonic solutions animal cells are normal but plant cells are what we call flaccid so here's a look explain the function of the contractile vacuoles in the freshwater parmasium in terms of what you've just learned about the water balance in cells in these vacuoles will just help the cells from becoming flaccid if water enters the plant cell here's a look um again at what happens in an animal in a plant cell when the cell is placed into a hypotonic solution which means that surrounding the cell is a lower concentration into an isotonic solution where the um surrounding the cell is equal concentration and into a hypertonic solution where surrounding the cell is a much highly concentrated solution so an animal and plant cell when placed into a hypotonic solution water will flow into the cell because water always flows into an area of higher concentration and this when this happens it just causes the cell to swell and it could eventually lyse or split open in a plant cell it just remains normal in the isotonic solution it could cause the plant cell to become flaccid or kind of thinner in a normal cell in an isotonic solution nothing happens there's no net movement of water and in the hypertonic solution um water will leave the cell and it can become shriveled up and this is what happens if you were to drink salt water you're bathing your cells into a hypertonic solution which means that your cells water will osmose and leave the cells just dehydrating them and this is just a look at the animal cell and what happens when a cell is placed into a hypotonic isotonic or hypertonic solution and then in the plant cell and this is a great video about the chlamydomona which is a great animation to see and then the plasmolysis which happens in plant cells the target elodea these are all great animations transport across the transport proteins can also help facilitate diffusion across membranes hydrophobic substances can easily diffuse across the cell membrane however polar or charged substances do not easily cross the cell membranes and instead these polar or charged substances move across membranes with the help of specific transport proteins called facilitated diffusion facilitated diffusion does not require energy and relies on a concentration gradient which means things will always flow from an area of high concentration to low concentration transport proteins help specific substances diffuse across the membrane and down their concentration gradients and thus requires no input of energy and the very rapid diffusion of water into and out of certain cells is made possible by a protein channel called an aquaporin and how do transport proteins contribute to a membrane selective permeability they will just help certain substances get into or out of the cell so here's a look at a transport protein providing a channel for the diffusion of a specific solute across a membrane if we look at an example of a scientist dr peter auger received the 2003 nobel prize in chemistry for his discovery of aquaporins and his research on rh protein used in blood typing led to the discovery and here's a look um as the at the osmotic swelling of aquaporins rna injected and control injected oocytes following a transfer to a hobotonix hypotonic solution just showing the relative volume of representative eggs within these injected eggs and the control eggs doing um kind of using the dr agar experiment so you guys can kind of skip over that for now but i want you to focus we've talked about passive transport and now we're going to talk about active transport which is when a cell must expend energy to move a solute against its concentration gradient the energy molecule atp supplies the energy for most active transport and the following figures will show the four main stages of active transport cells will actively transport calcium out of the cell so do you think calcium will be more concentrated inside or out of the cell and why well for something to move passively down its concentration gradient it always moves from an area of high to low concentration and if cells are actively transporting calcium out of the cell they're most likely moving calcium into an area of more highly concentrated calcium which will be out of the cell so here's a look at active transport of a solute across the membrane step one is the solute binds to the transport protein step two is atp will provide energy for the change in the protein shape and step three then after the substance gets transported the solute whatever gets transported across the membrane the protein will return to its original shape so more solute combined and here's a great animation on active transport a cell uses two other mechanisms to move large molecules across membranes these are exocytosis and endocytosis exocytosis is used to export bulky molecules such as proteins or polysaccharides which are just many sugars and endocytosis is used to take in large molecules and in both cases the material to be transported is packaged into what we call a vesicle that fuses with the membrane there are two kinds of endocytosis so bringing something into the cell phagocytosis is the engulfment of a particle or solid by the cell wrapping the cell membrane around it forming a vacuole and receptor-mediated endocytosis using membrane receptors for specific solutes in either case material to be transported is packaged within a vesicle that fuses with the membrane so here's just pictures we'll look at endocytosis whether it's phagocytosis or receptor mediated endocytosis the phagocytosis the cell membrane engulfs the food particles and the receptor-mediated endocytosis um the specific molecule bind to receptors and then those receptors will form a vacuole around the coated vesicle so here's phagocytosis endocytosis bringing something into the cell and then receptor mediated endocytosis as well lots of animations here which will be really great for you to look through then we'll talk about energy in the cell which um energy in the cell is the capacity to cause change so all cells need energy to function kinetic energy is the energy of motion and potential energy is energy stored in the location or structure of matter and it includes chemical energy according to the laws of thermodynamics energy can change form but can never be created or destroyed and also that energy will transform transfer or transform transformations will increase disorder or entropy with some energy always being lost as heat so if we look here we're looking at the two laws of thermodynamics transformation of energy and the increase in entropy so this is just a look at how fuel is taken into a car and through combustion um it's transferred to kinetic energy to allow movement and some of that energy is lost as heat and we always get a waste product from a car carbon dioxide and water well that same type of idea is happening in your cells your cells take in glucose and oxygen oxygen from when you're breathing glucose from the breakdown of what you're eating and within the cell your cell takes glucose and oxygen and creates atp which is the energy currency needed for cellular work heat energy is always given off during this process of cellular respiration as well as waste products carbon dioxide and water how does your cell and body get rid of waste products well that happens when you exhale you're exhaling the waste products of cellular respiration carbon dioxide and water vapor energy concepts this is a great video about potential and kinetic energy exergonic reactions release energy and endergonic reactions require energy and will always yield products rich in potential energy metabolism encompasses all of the cell's chemical reactions and here's a look at the exergonic reaction how energy will always be released if we look at turning a reactant into some sort of product energy will always be released and the amount of energy released is the difference of the reactants and the product potential energy here's exergonic reaction energy is also kind of put into the reaction and the difference of the amount of energy required is just the difference in the potential energy between the reactants and products atp is the energy currency of the cell it drives cellular work by coupling exergonic and endergonic reactions atp powers nearly all forms of cellular work and the transfer of a phosphate group from atp is involved in chemical transport and mechanical work and we'll talk about how atp transfers energy from exergonic to endergonic processes in the cell basically that happens when a phosphate group is transferred so here's a look at the hydrolysis of atp so if we would were to break these three phosphate groups apart whenever we break or take away a phosphate group that creates energy so when we add in a water we break away a phosphate group to create energy and we turn adenosine triphosphate three phosphate groups into adenosine triphosphate with two phosphate groups and an extra phosphate and energy when we've broken that bond that connects those two phosphate groups together here's a look at how atp power cellular work basically what atp does is it uses its extra phosphate group to help form a product whether that's transporting a protein transporting a solute helping with the motor protein in the motor filament in muscle contraction so atp is used when it's extra phosphate group is broken or taken away to help do some sort of process within the cell the atp cycle so energy from cellular respiration creates atp and atp synthesis always requires energy so we create atp but we need a little bit of at to create itself then atp hydrolysis or the breaking apart of atp releases energy and this gives us energy for cellular work and we come back to kind of an extra phosphate group in adp which will then continue entering this energy cycle to create more atp and then we'll talk about the last thing in this chapter about how enzymes function an enzyme is what we call a catalyst that decreases the activation energy needed for a reaction to begin without being consumed by the reaction so if we look here at the effect of an enzyme and lowering the activation energy what enzymes will do is they just make it easier for reactants to become products because they lower the activation energy barrier for the reactants to become a product so here's again just to look at the activation energy barrier and with an enzyme present it just makes it easier from those reactants to get to the products because there's less of an activation barrier present so here's the activation energy barrier you can see there with that gray bar graph without an enzyme and with an enzyme it's a lot lower meaning that there's not as much energy needed for the reactants to become the product here's the effect of an enzyme and lowering the activation energy again you can see in red is showing the work of an enzyme and a versus b is showing the difference in activation energy required for the reactants to become the products you can see here that in red the enzyme gets the reactants to the products a lot more quickly because it doesn't have to go over this big energy barrier bump here's a great animation on how enzymes work talking about the difference in activation energies an enzyme substrate fits specifically in a region on the enzyme called the active site and the following figure will illustrate this so here's a look at an enzyme it's available with an empty active site so here's the enzyme and it's ready to bind to a substrate the substrate will enter the active site which enfolds the substrate with an induced or perfect fit and the substrate is then converted into products using the help of the enzyme the products are then released and the enzyme can go on and do its work again explain how an enzyme speeds up a specific reaction it helps to lower the activation energy barrier required for reactants to become products enzyme inhibition can regulate enzyme activity in a cell as well a competitive inhibitor reduces an enzyme's productivity by blocking the substrate molecules from entering the active site a non-competitive inhibitor does not enter the active site instead it binds to a site elsewhere on the enzyme and its binding changes the enzyme shape so that the active site no longer fits the substrate and feedback inhibition will always help regulate metabolism so here's a look at how inhibitors interfere with substrate binding you have a substrate in active site a competitive inhibitor will bind instead of the substrate or a non-competitive inhibitor will bind but change the shape of the active site here's a look at feedback inhibition of the metabolic pathway in which product d acts as an inhibitor of enzyme number one so you can see that here product d will bind to the enzyme to change the shape just so that the substrate cannot bind as well explain an advantage of feedback inhibition to a cell but whenever we have more kind of control processes or kind of checkpoints in the cell it always just adds for more precise control of the cell to make sure that it's doing its job at the time it should be many beneficial drugs also act as enzyme inhibitors like ibuprofen enzyme inhibitors have also been developed as pesticides deadly poisons for warfare what determines whether an enzyme inhibition is reversible or irreversible and that'll depend on the shape of the enzyme inhib inhibitor and what it actually does to the specific enzyme so from this chapter use these last couple slides to make through you kind of got through the basic ideas of the chapter shoot me a question shoot me a message if you have any questions please download the animations from the chapter because i think they're all really good at helping explain further what we've talked about and as usual at the end of the chapter there's some really great slides that you can fill in on your own as some practice who knows maybe you'll see one of these practice slides in a test some time filling in these blanks might show up on a test sometime we'll see thanks for listening guys i hope you're all doing well