hi it's kim and today i am talking to you about energy this topic involves a lot of terminology and on the surface might seem a little boring i'll be the first to admit that but it's very important to understand these concepts as we move toward talking about cellular respiration and photosynthesis to incredibly important metabolic pathways that take place in living organisms and to understand those you need to know some basic concepts about energy we're going to be you know really leading up to talking about cells needing energy how cells produce energy and so it's important right from the beginning to understand really why or when does a cell need energy and there are several reasons when and why the first one obviously that we think about is movement we're talking about movement of materials within the cell so if you think about the lecture on cells materials don't just free float in the cell they move along microtubules with the help of what are called motor proteins and that requires energy so movement of materials in the cell that's going to require energy and also movement of entire cells so if you're a a protist and you need to move your entire cell you're going to require energy to do that cell division taking an existing cell and dividing it into two new cells is going to require energy we're going to talk about the details of cell division in a future lecture molecular transport this doesn't always require energy if you recall our lecture on transport across the cell membrane there's what's called passive transport that doesn't require energy and that was going from area of high concentration to area of lower concentration in molecular transport though if you're going against a concentration gradient remember that requires energy and that was called active transport so this is moving molecules or even ions against a concentration gradient and that is going to require energy okay and then certain chemical reactions require energy to take place not all chemical reactions require energy input they all require a little bit of energy to get started but some require a lot of energy and you'll see when we start talking about these chemical reactions that some chemical reactions actually require a lot of energy input while some chemical reactions actually release energy and we're going to be talking about that in this lecture today important to realize when we talk about energy there are two major categories of energy the first of those is what is called potential energy and potential energy is what we commonly called or called sorry stored energy this is an energy source waiting to be used it's being stored we have already talked about two major sources of potential energy in this class so going back to chemical bonds what type of chemical bonds did we say have a lot of potential energy stored in them it was covalent bonds so covalent bonds of molecules are an excellent source of stored energy another source of energy that we have already talked about in the transport across cell membranes is we talked about concentration gradients being a source of energy and i'm just going to quickly remind you about that because this is going to be a very important part of the story in both cellular respiration and photosynthesis so covalent bonds are going to be important and also concentration gradients so just a reminder of that if i have a membrane and i'm just going to draw it horizontally and let's say that on one side of this membrane i have a lot of hydrogen ions and they are charged and remember this this membrane is mostly a phospholipid bilayer and what do you recall about charged ions or molecules being able to cross the phospholipid bilayer that's right charged ions and molecules cannot cross the phospholipid bilayer they have to have a protein to come across a very specific protein specific to that ion or molecule so in this case these hydrogen ions are all outside the membrane this is a concentration gradient they can't just come back across and when they do come across they're going to come back through a very specific protein and they're going to generate energy as they come across think of water behind a dam so if we happened to have an enzyme embedded in this membrane that would allow these hydrogens to come back across the membrane as they come back across they are going to be a source of energy they're going to create energy so two sources of potential energy this concentration gradient is a good example and then the energy contained in covalent bonds especially the covalent bonds of our food molecules the other category of energy so the first one was potential energy the other category is what is called kinetic energy and really kinetic energy used to just be called the energy of motion i don't really like that because not all energy is something moving so this is really energy being used and there are several sources of this energy there is motion light and heat when we start talking about cellular respiration and also photosynthesis you're going to see light energy and heat involved in both of those stories so potential energy and kinetic energy i'm going to go back to covalent bonds for a moment because we talked about two different types of covalent bonds when we had this lecture earlier in the semester and remember in one type of covalent bonds the atoms are sharing electrons more equally whereas in the other category they're sharing unequally and this is going to be significant when we start talking about potential energy so remember two categories nonpolar covalent bonds and remember this happened when the two atoms had the same or similar electronegativities they shared more equally and then we also had polar covalent bonds and in a polar covalent bond the two atoms sharing electrons have a relatively large difference in electronegativity and they do not share electrons equally so this is unequal sharing of electrons and remember water was our big example of that in the category of nonpolar covalent bonds we showed several examples but one of the classic examples of that is when carbon and hydrogen share with each other and remember that is the basis for all of those macromolecules the macromolecules are these chains of carbon and hydrogen or rings of carbon and hydrogen so carbon and hydrogen bonded to each other that's a really good example of a nonpolar covalent bond when we're talking about potential energy these nonpolar covalent bonds contain a lot more potential energy than the polar covalent bonds so non-polar covalent bonds more potential energy that means our food molecules contain a lot more energy than water and you probably already know that if you eat glucose you're going to get a lot more energy out of that than if you drink a glass of water right that water is not really going to provide you with energy it's going to provide you with a lot of other important things you need water for other reasons but as far as extracting energy from the bonds of those molecules you want to do that mostly from a non-polar covalent bond and that is all the macromolecules okay primarily the lipids and the carbohydrates that's where we mostly get our energy a little bit from protein also so that's really important to to realize so if you'll recall when you look at those four categories of macromolecules really the nucleic acids are not really participating in this story because we don't really use nucleic acids for energy when we break down a nucleic acid we're using those nucleotides to build more dna rna atp adp we're not using that for an energy source so three of them equal what we call energy sources and the more non-polar bonds contained in a molecule the more energy it has and if you think about which one of those had just pure carbon and hydrogen a hydrocarbon chain which one was that that had the hydrocarbon chain remember carbohydrates had carbon and hydrogen but they also had those hydroxyl groups attached the one that was just carbon and hydrogen a hydrocarbon chain those were the lipids okay which included the fatty acids this is why lipids contain more energy per gram than carbohydrates and proteins and we already gave these numbers when we talked about those molecules but i'll remind you that carbohydrates and proteins contain four kilocalories of energy per gram while what we call fats fatty acids contain nine kilocalories of energy per gram and the reason for that is those molecules contain more non-polar covalent bonds they're a really rich energy source so i mentioned before that certain chemical reactions require energy while others are going to actually release energy and the reason for that is based on how much energy is contained in the reactants versus how much energy is contained in the products so remember if we have a chemical reaction just really you know i'm just going to do this for a really generalized chemical reaction remember everything on the left side of the arrow these are the reactants and on the right side of the arrow these are the products and sometimes we have reversible arrows and in that case you know whichever direction the reaction is is going we're always going from reactants to products we start with reactants we end with products how much energy is contained in each of those is very significant so let's start with the first example i'm going to draw a diagram here this is very generalized so this is going to be energy in kilocalories and i'm going to show you how much energy is in the reactants and i'm going to represent that with an r and then we're going to have p equal the products so if my reactants have that much energy contained in the bonds and then my products have this much energy which one of those has more energy the reactants or the products it's very obviously the products right so if you start with this much energy in the reactants and you end up with that much energy in the in in the products do you think you had to put energy in or do you think energy was released a good way to think about this is think about your bank balance okay so if you started with this much money in the bank and you ended with this much money in the bank did you have to put money in or did you take money out you had to put money in and the same thing goes for energy this required energy input to get to products that have more energy than reactants you had to put energy into the system that energy is now stored in the covalent bonds of that product so reactants that have less energy than the products this for this reaction to proceed it requires energy input from an energy standpoint a reaction that requires energy input to get to the products is called an endergonic reaction in an endergonic reaction the reactants have less energy than the products and therefore energy input is required let's look at the opposite of that okay again we have energy on the side here in kilocalories and i'll just make this a little taller and in this case i have reactants with this much energy and i have products with only this much energy so in this case what has more energy the reactants or the products okay it's the reactants right when you have reactants that have more energy than their products again let's think about bank balance we started with this much money in the bank we ended with this much money in the bank did we put money in or did we take money out we took money out okay same thing goes for energy in this case energy is released so these products have a lot less energy than we started with to get to those products energy was released and that is called an exergonic reaction i like to think of energy is exiting the system versus in the ender energy is being put into the system in the cell there is a process called reaction coupling and there's one reaction in particular that is coupled to drive chemical reactions in the cell if you can take an exergonic reaction that is releasing energy and use that to drive an endergonic reaction that requires energy you can make it happen okay so we can break covalent bonds or we can use concentration gradients to generate an energy source that can then be used to drive an energy requiring reaction so an exergonic and endergonic reactions can be coupled they can be put together so that an exergonic reaction that releases energy can be used to drive an endergonic reaction that requires energy also associated with this are two other terms that are important to know and that is catabolic reactions and anabolic reactions so let's first start with this term metabolism okay metabolism is a very misunderstood term in energy it doesn't mean how fast you break down your food or how fast you burn calories metabolism really is the sum of all chemical reactions in an organism so your metabolism is all of your chemical reactions that are taking place and as part of your metabolism we have some pretty significant metabolic pathways metabolic pathways are multi-step reactions where the product of one step becomes the reactant of the next step and enzymes are required some metabolic reactions that are multi-step are called metabolic pathways they're sometimes called biochemical pathways as well they're multi-step and the re the product of one step then becomes the reactant of the next step okay so if i had a plus b becoming c okay now c is going to become the reactant in the next step becomes d which becomes e which could become our final product and at each step in this process sorry i didn't mean to do that and each step in this proc at each step in this process there's going to be an enzyme required the reason i'm telling you this it's very important to realize that sometimes we have just a summary reaction that we write so for example for cell respiration and photosynthesis there's this general equation but that arrow actually represents multiple steps and cell respiration and photosynthesis are both metabolic pathways they take multiple steps to get to that final product and enzymes are required at each step and the product of one step then becomes the reactant of the next step so we have c as our product here but then now c becomes the reactant to become d d is the product that it becomes the reactant to become e and so on so photosynthesis and cellular respiration are both examples of this so let's go ahead and write the general equations for both of those reactions because we're going to be talking about these a lot so let's start with photosynthesis the most important chemical reaction on earth photosynthesis general equation is carbon dioxide in water i'm going to start by with water so water carbon dioxide multiple steps to get to these products and there's going to be light energy from the sun that's going to come in and drive this and we're going to end up with a sugar we don't directly get glucose as you'll see and oxygen sorry i'm getting really close to the edge there that arrow represents multiple steps to get to those products you don't just get the carbohydrate in the oxygen all in one step okay cellular respiration is really kind of the reverse general equation this is taking the sugar and oxygen in multiple multiple steps to get to carbon dioxide and water as the products i'm going to be using these two general equations throughout a lot of the rest of the lecture today as examples of these concepts we're talking about okay let's look at photosynthesis from the standpoint of endergonic versus exergonic water and carbon dioxide could you eat water and carbon dioxide and get energy out of that okay probably not and the reason for that is polar covalent bonds okay both of these molecules have polar covalent bonds versus we know that glucose is the sugar we know that when two oxygens share they must be sharing equally because they're the same atoms so equal sharing of electrons these are nonpolar covalent bonds okay so even if you didn't know that there wasn't energy in water when you drink it you know that that's a polar covalent bond and we just said earlier that nonpolar covalent bonds contain more energy so from an energy standpoint if we look at photosynthesis and you look at how much energy is in the reactants versus the products reactants water and carbon dioxide low energy products glucose high energy so when so when photosynthesis be [Music] endergonic or exergonic reactants have less energy than the products would that be endergonic or exergonic endergonic energy input required in the case of photosynthesis where does that energy come from it's the light energy from the sun primarily you're going to see that it's also a concentration gradient that is going to exist when we strip hydrogens away from the water and set up a concentration gradient we don't really do that but we're going to see that that happens in photosynthetic organisms we don't carry out photosynthesis okay so in photosynthesis less energy in the reactants than the products energy input required let's look at cellular respiration from an energy standpoint okay in cellular respiration we start with glucose and oxygen so non-polar covalent bonds and we end up with carbon dioxide and water polar covalent bonds so we know that nonpolar covalent bonds have more energy we also know that we eat glucose and it has a lot of energy right so in that case we're starting off with reactants that have a lot of energy and ending up with products that have very little energy so would cell respiration be endergonic or exergonic it would be exergonic in other words energy is released it's released when we break the covalent bonds of those glucose molecules or the other nonpolar covalently bonded macromolecules that enter cellular respiration another thing that you can consider here is in photosynthesis we're really putting a molecule together so we're breaking the bonds of water and carbon dioxide and remember in a chemical reaction matter is not created or destroyed all we're doing is we're breaking those bonds and eventually rearranging those molecules to i'm sorry rearranging those same atoms we're rearranging those same exact atoms to build new molecules so we're taking all of these hydrogens carbons and oxygens and rearranging them and remember if we count how many are on each side they're going to be equal we're just breaking the bonds and rearranging but there's also an energy component so we're having to either put energy in or energy is being released to get to those products what's significant about that is if we're putting something together from a metabolic pathway standpoint it's what we call anabolic and if we're breaking something apart it's what we call catabolic so in terms of metabolic pathways we have two possibilities catabolic reactions and anabolic reactions okay anabolic reactions this is molecules being assembled and catabolic is molecules breaking apart now first of all i realize that in all chemical reactions bonds are being broken and things are being rearranged but in catabolic we're going from complex to simple in an anabolic we're going from simple parts to complex they're the opposite of each other so an anabolic we're building something and in catabolic we're breaking something apart i like to think of ikea furniture okay when you assemble ikea furniture you're putting furniture together from simpler parts you're building something more complex that's called anabolic if you take anabolic steroids you're building muscle you're putting muscle tissue together catabolic catastrophes break things apart catabolic reactions break more complex molecules down into simpler parts so you're going from complex to simple one of these requires energy input and one releases energy so if we look at those two from an energy standpoint breaking bonds is going to release energy creating new bonds is going to require energy so anabolic reactions typically require energy input so energy input required and is that endergonic or exergonic when in when energy input is required so that's endergonic so from an energy standpoint putting things together is endergonic we call it anabolic from a metabolic pathway standpoint so if you're putting more complex molecules together from simpler parts it's called anabolic and from an energy standpoint is endergonic so those go together catabolic energy is released when you're breaking those bonds so that is exergonic so catabolic reactions are exergonic going back to our photosynthesis and cell respiration and now trying to categorize those is either catabolic or anabolic in cell respiration we're blake breaking glucose apart we're releasing that energy so it's exergonic but when you're breaking a more complex molecule down into simpler molecules that is a catabolic reaction in photosynthesis we are making a carbohydrate well we aren't but photosynthetic organisms are they are making this more complex sugar from simpler parts so this is going to be anabolic reaction and remember energy input is required to build those more complex molecules versus energy is released when we break those bonds okay so those are really important terms in the energy story i have a couple of other terms to give you i keep looking at my paper because i really want to make sure i know this is a bunch of disjunct terms but they're all going to come together in the stories of cellular respiration and photosynthesis so they're really important terms to know okay some laws of thermodynamics come into play here i know you normally think of laws of thermodynamics being in a physics class or a chemistry class but they are a part of the story we need to tell in energy and the first law of thermodynamics tells us that energy is never created or destroyed it just changes form by the way that's all one word i just accidentally had a little space there so energy is never created or destroyed it just changes form so as we carry out a chemical reaction some of that energy when we break the covalent bonds some of that energy is going to get released as heat that heat is still in the universe and never gets destroyed it's just changing form so in that covalent bond we have this nice neat package of energy but as those bonds are broken a lot of that energy is lost as heat as we go through cell respiration in particular you're going to see that not all of the energy contained in the covalent bonds of our food molecules gets directly transferred into the atp molecule a lot of that energy is lost as heat just as when your engine is breaking down the bonds of the fuel that you put into your car a lot of that energy is released as heat and that's why your engine is hot so energy is never created or destroyed it's just going to change form the second law of thermodynamics tells us that as energy is being used it's going from an orderly state to a disorderly state okay so that covalent bond that we're breaking that's a nice little orderly package of energy but when it's released as heat heat is very disorderly and you can't now repackage that heat back into a covalent bond so let's say you take a log and you put it in the fireplace okay that log is a nice neat little package of energy all these covalent bonds in the cellulose of that plant material and now you're going to light it you're going to com bust that log and you need to have oxygen present and you're going to start you're going to start causing that cellulose to break down and those covalent bonds are going to start releasing energy that energy is going to get released into the room as heat very disorderly form of energy you can't now take that heat and repackage it back into a log again right there's no way to do that so as energy is used it changes from an orderly state to a disorderly state and that disorderly state is called entropy in other words we could say that entropy increases disorder increases as energy is used so entropy in chemistry and physics is disorder so the entropy of heat energy is much higher than the energy contained in that covalent bond okay two more big concepts in energy a lot of terms here okay redox reactions okay redox is a term that stands for oxidation and reduction and these two always go together and i guess someone decided that ox red didn't sound so great so they call it redox reduction and oxidation they always go together you have actually already seen an example of this let me just give you the definition of these two terms and then i'm going to give you some significant examples one of which you've already seen so oxidation is loss of electrons and reduction is gain of electrons a good way to remember this is it sounds really silly but believe me it helps leo the lion says ger gur loss of electrons is oxidation gain of electrons is reduction leoker it will help you i know there are some other little mnemonic devices that people use for this but that's the one that i use so i'm not going to give you multiple mnemonic devices i'm just giving you the one that i like okay what does this mean well first the reason they go together is when when electrons are lost they're not just lost to the universe they're actually transferred to another molecule or atom okay so as electrons are lost by something they're gained by something else and whoever's gaining those electrons isn't just gaining them from the universe they're gaining them from someone who lost them so they always go together you have seen an example of this when we talked about ions remember sodium atomic number 11 that means it has 11 protons and 11 electrons in its atomic state but remember when it comes in contact with chlorine atomic number 17 so 17 protons and 17 electrons it tends to lose its electron to chlorine and the reason for that if you recall that electron configuration sodium atomic number 11 remember the first shell can hold two the next shell can hold eight remember when i told you we never learned anything in this class and just put it in a drawer and never visit it again well here you go i bet you never thought you'd be drawing electron configuration diagrams again did you and here is one right now so that means sodium just has this one electron out there all by itself that means sodium has seven spots it has to fill to become stable the other thing it can do though is it can give that electron away it can lose it and who does it tend to lose it to it tends to lose it to someone who needs it so chlorine needs that electron to complete its outer shell because it's atomic number 17 which means 2 plus 8 is 10. so that means chlorine has seven electrons in its outer electron shell the valence shell it just needs one more to complete its valence shell so if sodium gives that electron away chlorine gains one electron okay and sodium loses one electron and now they each have a full outer shell so they're both stable they become ions but this is oxidation and reduction so when that happens when sodium loses an electron loss of electron is oxidation so this is called oxidation chlorine gained an electron gain of electron is reduction so we call this reduction you can also use the verb okay so oxidation and reduction are nouns you can also use the verb we can say that sodium is oxidized that's the verb okay and we can say that chlorine is reduced how does this relate to cellular respiration and photosynthesis well those are both redox reactions too and you're going to see that there is going to be a lot of oxidation and reduction going on in those processes so it's important to realize what's happening sometimes loss of electron oxidation so loss of electron loss of electrons can also be loss of hydrogen remember that hydrogen has one electron gain of electrons which is reduction can also be a gain of hydrogen because hydrogen has one electron so let's look at the chemical formula for photosynthesis just the general reaction so remember water and carbon dioxide and we typically write glucose as our sugar but again you're going to see we don't directly make glucose our plants and other photosynthetic organisms don't for carbon dioxide to become glucose and water to become oxygen oxidation and reduction had to occur so let's start by looking at carbon dioxide becoming glucose okay co2 okay c o so we've got carbon and oxygen we've got carbon and oxygen for carbon dioxide to become glucose did it gain hydrogen or did it lose hydrogen hydrogen has now appeared and it wasn't there to start with okay so that's a gain of hydrogen gain of hydrogen equals gain of electrons okay and that is ger that is reduction we could use the verb we can say that co2 is reduced to form glucose reduction for water to become oxygen did it gain hydrogen or lose hydrogen there's no hydrogen in oxygen right so it lost hydrogen loss of hydrogen equals loss of electrons leo so that is oxidation so water becoming oxygen is oxidation so we say that water is oxidized to form oxygen cell respiration is going to be a similar story oxidation and reduction are going to happen you're going to see we have electron carriers that are oxidized and reduced also in both of these stories so those terms are very important oxidation and reduction loss of electrons and gain of electrons sometimes it's loss of hydrogen or gain of hydrogen one more term this is it phosphorylation transfer of a phosphate group from one molecule to another that equals energy transfer and i'm going to show you how okay reminder of what a phosphate group is remember a phosphate group is a functional group oxygen phosphorus oxygen oxygen oxygen that's a phosphate group do you remember what type of macromolecule has a phosphate group just a reminder it had a pinto sugar and then it had a phosphate group and then it had a nitrogenous base over here and remember that was a nucleotide so nucleic acids have phosphate groups rna dna adp atp this story we're telling is energy which of these nucleotides these nucleic acids has energy associated with it both of these okay these were part of the energy story these are part of the genetics story so adp and atp are going to be what we're talking about okay so atp and adp are both nucleotides but they're pretty crazy because they have more than one phosphate group attached remember a nucleotide is a ribose or deoxyribose sugar depending on which nucleotide we're talking about rna atp and adp i'll have ribosis the sugar adenine as the base and then in the case of atp atp stands for adenosine triphosphate atp for short and adp is adenosine diphosphate it has two phosphate groups why do we care about this the reason we care about this is because this is the energy currency of the cell atp is the energy currency of the cell how does atp drive chemical reactions in the cell how does atp cause a chemical reaction to happen it does it through phosphorylation transfer of a phosphate group from one molecule to another if we break this bond of atp and release this phosphate group if this phosphate group gets transferred to another molecule it equals energy okay so energy is released when that happens this is catabolic and it's exergonic so breaking that bond and releasing that energy that's exergonic it releases energy that energy then can get coupled that energy release can get coupled with an endergonic reaction and through reaction coupling we can drive that reaction with the energy that's released so transfer this phosphate group cutting this breaking this bond this high energy bond and releasing that phosphate group that represents a lot of energy transfer it's exergonic but now what are we left with we're left with just two phosphate groups because that one was transferred okay that is phosphorylation transferring that phosphate group and it's exergonic it releases energy but now we're left with adp we need to now stick another phosphate group on there to regenerate atp so when we quote make atp in cellular respiration all we're doing is adding a phosphate group to adp to regenerate atp we're re-phosphorylating we're transferring a phosphate group from somewhere else back to adp to make atp so you can see that happening here you can see this phosphate group is going to get added back to adp and we're going to regenerate atp that is endergonic it requires energy input where does the energy come from to do that it comes from two places it comes from the energy in our food in the covalent bonds of our food it's going to come from a concentration gradient that we're going to set up in the cell and in the case of photosynthesis it also comes from the sun so we're going to have multiple energy sources at play when we make atp we're going to make atp again i say we but i'm what i mean is we're going to show the process of making atp in photosynthetic organisms we don't do that and you're going to see that in photosynthesis these organisms make atp that atp then becomes the energy source for making carbohydrates from water and co2 so even the energy from the sun has to get converted to atp for that process to take place so atp is going to be the energy source in both cellular respiration and in photosynthesis and the way we derive that endergonic reaction is by the potential energy in covalent bonds okay in the concentration gradient that's going to get set up i'm just abbreviating kant's gradient okay and in the case of photosynthesis we're talking about the sun the light energy from the sun these are all going to be a part of the stories of photosynthesis and cell respiration important to realize breaking this bond and releasing a phosphate group that is exergonic adding that phosphate group back on that's endergonic that's going to require energy input and when we say we're making atp we're never making it from scratch okay we're not assembling atp from scratch what's happening is that third phosphate group is getting added back on to adp adenosine diphosphate to make adenosine triphosphate okay i know that was a lot if you have questions please don't hesitate to ask these are all important terms that are going to be used in the next two lectures to explain cellular respiration and photosynthesis two incredibly important chemical reactions