in this video we're going to give you sort of an overview of the biochemical reactions that are involved in metabolism so metabolism has two main types of reactions anabolic reactions or sometimes we'll refer to this as a synthesis reaction this is where we build larger molecules from smaller ones so these smaller ones tend to be monomers and then we chain these monomers together via chemical bonds so in essence in an anabolic reaction we are inputting energy into the system and that energy is in the form of a chemical bond in catabolic reactions known as excuse me in catabolic reactions known as sort of uh decomposition reactions basically what happens is we're doing the reverse so we're using water to break down that chemical bond hence why it's called hydraysis so we're breaking chemical bonds down and we're releasing the energy that was stored in that chemical bond so the process of cellular respiration because respiration usually when we think about it we think about oxygen right but cellular respiration is the breakdown of food material to capture the energy in the form of ATP so really all we're doing is in the end we're using oxygen yes that's the respiration part but we're using it to repurpose energy in fact that's all metabolic processes are repurposing energy so we're taking the energy that is found in the chemical bonds of nutrients and going through a sequence of reactions that ultimately invest the energy into the chemical bonds found in ATP now of course we know ATP is the energy currency of the cell the energy that ATP holds is found in those very high energy phosphate bonds so enzymes facilitate this process and they help us to make ATP and we keep this as sort of a common currency because the ATP then in turn can be used as an energy source to do work so enzymes can shift the energy back from those high energy phosphate groups of ATP and reinvest it into chemical bonds of a new molecule that we might be building and those molecules in turn have some important cellular functions so when we look at the stages of metabolism the big picture ingestion of food stuff the digestion right so the catabolic breakdown of the carbohydrates the proteins the lipids that we're consuming the absorption of those monomers or in the case of lipids the components the fatty acids and the glycerol the transportation to the tissues that's all sort of the focus of the previous module in this module we're going to focus on the cellular processing so within the cell how do we synthesize lipids proteins and glycogen how do we break those components down ultimately into manufacturing ATP now when we talk about ATP there are two main ways that we can generate ATP the first is a very inefficient way it's called substrate level phosphorilation so the term phosphorilation just means you're putting a phosphate group onto a molecule so in substrate level phosphorilation basically you have some molecule that already has a phosphate group on it and an enzyme is going to facilitate this process but you have ADP a denisonin diphosphate and basically what's going to happen is you're going to break this chemical bond and you're going to add the phosphate group onto ADP and then now it has three phosphate so it's ATP so basically you're taking away a phosphate group for one molecule and you're adding it to ADP to make ATP so this is a fairly inefficient process the second type of ATP generation that we'll talk about is called oxidative phosphorilation so the main difference here is you have phosphate groups that are floating around in the cytool and you're going to use energy from chemical bonds to basically put this phosphate group onto ADP and subsequently you make ATP so this is a very in a very efficient process that allows you to repurpose the energy from the breakdown of things like glucose and the intermediates that we'll talk about now of course we do generate waste products and the waste products here are going to be carbon dioxide and water so think about that the next time you are exhaling the CO2 that you're exhaling is actually coming from this process so a lot of our discussion is going to revolve around energy so we need to sort of backtrack and uh revisit this topic of energy so remember in our earlier discussions of chemistry when we were talking about electrons electrons based on the distance they are from the nucleus electrons don't have a whole lot of mass but they have energy so we can just think of electrons as energy now what type of energy is this there are two main types there's stored energy or inactive energy that's potential energy then there's the energy of motion and the energy of action that's called kinetic energy well when we talk about electrons and the distance they are from the nucleus we're talking about the potential energy now remember when we form a chemical bond a chemical bond is the sharing of electrons or giving up you know the donation and reception of electrons well if electrons represent energy and chemical bonds are made up of electrons well a chemical bond also is representative of energy so a chemical bond represents stored energy or potential energy that an organism can then repurpose to do work and the three main types of work and we mentioned this in a previous video we can repurpose that energy to do chemical work so we can build molecules so we break some molecules down and use that energy to build other molecules up we can move material across the cell membrane so that's transport work or alternatively we can use that energy to change shape so change the shape of proteins change the shape of cells or tissues that allows for locomotion now this process is not 100% efficient in fact about 60% of the energy is going to be lost as heat now I say lost though technically energy is neither lost or gained in the universe but we consider it lost because the body can't use it to do work okay so even in ATP when we break down those chemical bonds 60% of that energy is lost as heat and only 40% is usable this is the reason why when we look at ATP specifically we talk about how you have a phosphate group and then the last two phosphate groups uh usually in figures you don't see a straight line you see a little squiggly line because this chemical bond and this chemical bond have higher energy than your average coalent bond so when I break this high energy bond in ATP I still lose 60% but the 40% that remains is equal to the energy found in a regular chemical bond this is why sort of ATP is the perfect energy source to use because of that onetoone relationship if I took any regular molecule and broke the chemical bond I would not have enough energy to repurpose that into a another regular chemical bond because I would only have access to 40% so there is something called the first law of thermodynamics where the definition is energy is neither created nor destroyed but I like to use a different definition i like to think of the first law of thermodynamics as energy can be repurposed so you can convert potential energy into kinetic energy kinetic energy back to potential energy to infinity so here we have an example where solar energy through the process of photosynthesis is converted into chemical energy so the sugars that the plant makes we consume the plant and we can repurpose the energy that is found in the chemical bonds of the sugars the proteins the lipids that are found in that plant and we repurpose that energy to make ATP that then in turn allows us to do work so this is a process that occurs in nature and again highlights how energy is going to be interchangeable now the last topic I want to touch on here refers to chemical reactions so if all molecules have chemical bonds all molecules have energy the more chemical bonds you have the more inherent energy you have within the molecule the more potential energy you have so if I look at a traditional chemical reaction let's say A + B as the reactants and they go through a reaction to form two products C and D well A and B have chemical bonds have energy and C and D have energy and we can compare the total energy that is found in A and B and the total energy that is found in C and D now if the total energy in A and B is greater than the total energy in C and D that means we're going to be releasing energy into the system we refer to this as an exorgonic reaction if however the reactants have less energy than the products we have to invest energy so we have to invest outside energy to generate a chemical reaction so these are known as endergonic reactions now doesn't matter if we're talking about an exroonic or endergonic usually there has to be an initial investment in the chemical reaction to get it started this initial investment is known as activation energy and it is what enzymes help to lower to make reactions more likely to occur so what is activation energy well think about A and B when A and B come together they don't undergo a reaction necessarily until they have the right amount of energy the right orientation of the molecules and such so if they're lacking any of those the A and B collision won't necessarily give rise to C and D now what an enzyme does is it puts the molecules in the right orientation so more likely when they come together there's a chemical reaction superficially we think the reaction speeds up but in reality what happens is the probability of the formation of products increases because we're in the right orientation so look at this particular exonic reaction here's our activation energy here that's our initial investment we get that investment back and then some that we can then use this outside energy or this this energy excuse me not outside energy we could use this energy to do work okay now in the reverse reaction the activation energy would be significantly higher so less likely to spontaneously happen and this is the additional amount of energy you have to invest into the system from the outside so what biological systems will do is they will couple the more favorable exroonic reactions with the less favorable endergonic reactions so you have net zero energy so an example would be the breakdown of ATP into ADP and phosphate this is going to release energy it's an exorgonic reaction anytime you break a chemical bond it's going to be an exorgonic reaction and we can couple that with the formation of a peptide bond between two amino acids so we're investing the energy from the ATP hydraysis into the new peptide bond between these two amino acids so we can couple those two reactions