module 2.3 chemical reactions so by definition a chemical reaction has occurred every single time that a chemical bond is either formed broken or rearranged or when electrons are transferred between two or more atoms chemical notation is something that you will get more familiar with as you go through your chemistry courses i'm just going to introduce you to the very basics here so chemical notation is a series of symbols and abbreviations used to demonstrate what occurs in a chemical reaction the chemical equation has two parts you have the reactants which go on the left side these are the starting ingredients that will undergo the reaction and the products will be shown on the right hand side of the equation and they are the results of the chemical reaction chemical reactions can either be reversible where they can go either to the right or to the left in both directions or they could be irreversible where they only go in one direction the chemical reaction which you see here has arrows going in both directions indicating that it is reversible in other words the reactants carbon dioxide and water can combine to become carbonic acid which can then disassociate into a hydrogen ion and a bicarbonate ion the products at the same time if we get too much hydrogen and bicarbonate it can recombine to create carbonic acid which can then disassociate into a carbon dioxide molecule and water so this particular chemical reaction goes both ways and you can tell that by arrows in both directions if the arrows only indicated one way that means that the chemical reaction only goes in that direction okay we have three forms of energy in the human body we have chemical energy which is the energy contained in the chemical bonds then we have electrical energy generated by the movement of charged particles and mechanical energy energy directly transferred from one object to another so to make this a little more understandable something that you can relate to we have all these energy forms in the human body and we're constantly converting energy from one form to the other where we typically start is with chemical energy energy that's in our food in the carbohydrates and in the lipids that we eat that's a form of chemical energy in the bonds of the food we're going to break that food down and convert that energy in the bonds of the food into the energy of atp we can then use that atp to generate electrical impulses in our nervous system or we can use that atp to power our muscles in the form of mechanical energy a third way we could use that atp to make more chemicals in our body so we could use that atp to build some proteins or to make enzymes so we're constantly changing the forms of energy in the human body there are three basic chemical reactions which occur in the human body to help us maintain homeostasis those three reactions are catabolic reactions so catabolic are going to break large molecules down to smaller molecules we have exchange reactions occurring where parts of one molecule exchange with parts of a second and we have anabolic reactions notice i have starred these two the catabolic and anabolic so what we're going to do is our focus is going to be on these two we won't talk as much about exchange reactions let's start with catabolic reactions so by definition catabolic reactions occur when a large substance is broken down into smaller substances the mechanism by which this occurs is called a hydrolysis reaction so you can think of it this way catabolic is the big picture view whenever you take a large molecule and break it down into smaller molecules in the human body it's a type of catabolic reaction what is the specific process that the human body uses the type of chemical reaction is called a hydrolysis reaction and it tells you right here how it works hydro water lysis breaking so in our catabolic reactions we're going to use a molecule of water to break the bond which links the two molecules together the general chemical notation for this reaction is a connected with b so this represents our large molecule with the bond between them when we break it down in a catabolic reaction we're now going to have the separate molecule a plus the separate molecule b so we have broken the bond using a hydrolysis reaction usually we release energy because chemical bonds are broken okay where is the energy stored in any molecule the energy is stored in the bond so whenever we break the bond we release the energy if we have to create a bond it's going to require energy to be input into that chemical reaction examples in the human body of catabolic reactions include breaking down food in our gastrointestinal tract so for instance we break proteins down into amino acids we break carbohydrates down into simple sugars we also use catabolic reactions when we recycle damaged cells so we don't throw ourselves into the garbage in our body we actually recycle them so we break them down and recycle the parts that were used to put them together another example of catabolic reaction in our liver our skeletal muscles we have stored excess glucose in the form of glycogen a large carbohydrate when we need that glucose then we break that glycogen back down to the simple sugars which make it up glucose the other type of reaction is called an anabolic reaction and by definition anabolic reactions occur when small subunits are united by chemical bonds to make a larger substance the specific type of chemical reaction or the mechanism which is used to accomplish this is called dehydration synthesis in other words we're going to dehydrate the two molecules we're going to remove a molecule of water to synthesize them or to create the new larger molecule the general chemical notation for this reaction is separate molecule a plus the separate molecule b can be combined into a single molecule a b with the dash representing the chemical bond which unites the two so we've gone from smaller units to a larger molecule these reactions typically require energy why because where is the energy at in any molecule it's in the bonds so whenever we create bonds we have to put energy into that process examples of where this occurs in the human body when we take amino acids in our muscles and put them together to create proteins or when we link amino acids together to create enzymes which are a type of protein when we have excess glucose in our bloodstream such as right after a meal that excess glucose will go to the liver where the glucose is linked together into a larger storage molecule called glycogen now for a reaction to occur atoms must collide with enough energy to overcome the repulsion of their electrons remember electrons circle around the outside of an atom in orbitals and they have negative charges so negative repels negative so we've got to have enough energy to first bring those atoms together the energy that's required for all chemical reactions to get started is called the energy of activation enzymes lower the energy of activation so i wanted to briefly introduce you to the concept of what is an enzyme here in anatomy we're going to use this more when we get to physiology but it's nice to have heard this twice so i'm introducing you to the concept what is an enzyme an enzyme is a type of protein which is designed to lower the energy of activation and that will then speed up the rate at which chemical reactions can occur in all honesty human life would not be possible without the assistance of enzymes in our body so the result speeds up the rate of chemical reactions to the point that our bodies can sustain life here's how it works here on the left are reactants here on the right are our stable products and they're at a lower energy level so we want these reactants want to become products because it's a more stable union of the participants but in order to get this chemical reaction going we've got to put some energy into it so this line this dashed line represents the amount of energy required without the assistance of an enzyme that's an exorbitant amount of energy if we had to put that much energy every time into a chemical reaction it would slow down the rate at which chemical reactions would occur this right here represents the amount of energy then that we have to put into the chemical reaction with the assistance of an enzyme so an enzyme greatly reduces the energy of activation by reducing the energy of activation this enzyme will make it more conducive for more reactants to become products so enzymes lower the energy of activation and therefore speed up the rate of chemical reactions all right so properties of enzymes enzymes are biological catalysts that speed up the rate of chemical reactions most all enzymes end in that suffix ase and most are proteins made from proteins and amino acids with the following properties number one they speed up the reactions by lowering the activation energy number two they're highly specific for individual substrates in other words enzymes are able to accomplish their task because they have a specific shape so if they have a specific shape that means that they can only facilitate a chemical reaction with reactants that have a specific shape also so for instance lactase is an enzyme which can catalyze the breakdown of the carbohydrate lactose chymotrypsin and trypsinogen are enzymes secreted from the pancreas that can only break down proteins lipase is also secreted from the pancreas and it can only break down lipids so that's what they mean by highly specific they do not alter the reactants or products so when we utilize an enzyme to catalyze the chemical reaction it does not in any way change the reactants or change the products all it does is speed up the rate of the chemical reaction and last of all they're reusable not only do they facilitate a chemical reaction without changing the reactants or products but we can use them again and again and again so here's a little schematic from the textbook company just to show you the general idea of what an enzyme does so notice here on the enzyme a specific shape here and a specific shape here so the substrates or the reactants are going to bind to the active site and the active site has a specific shape that will fit each of the reactants now the reactants have docked they're in place and this is going to the enzyme will help hold the substrate in this specific position which will help or facilitate to create a chemical bond between the two substrates now we've created the chemical bond so they're no longer substrates now we have product and what's the enzyme going to do we're going to go ahead and release the product what will this enzyme do now wait for two more substrates to dock so that it can facilitate another chemical reaction let's do some review questions for module 2.3 just to cover the big picture number one what type of chemical reaction is used to break down food in the gastrointestinal tract these chemical reactions are called catabolic reactions because they take a large molecule and break it into smaller molecules and the specific mechanism or chemical reaction which is used is called a hydrolysis reaction hydro water lysis breaking we will use a molecule of water to break the chemical bonds number two what type of chemical reaction is used to build proteins from amino acids this type of chemical reaction is called an anabolic chemical reaction whenever we take smaller molecules and build them into larger molecules the specific mechanism or chemical reaction which is used to accomplish this is called dehydration synthesis we will remove a molecule of water from the substrates to help create the new chemical bond number three what is the name of the biological catalyst that speeds up a chemical reaction by lowering the energy of activation that biological catalyst is called an enzyme and number four will the enzyme lipase break down a carbohydrate made from lactose well the enzyme lipase facilitates chemical reactions involving lipids lactose is a carb type of carbohydrate so will an enzyme that breaks down lipids break down a carbohydrate and that answer is no because enzymes are highly specific their function is based upon shape and a lipid is going to have a very different shape from a carbohydrate