okay well are going to cover our last part of our chemistry review part 6 and that is on chemical reactions and enzymes so we've talked a bit about chemical reactions already we talked about the dehydration synthesis is a chemical reaction the definition of a chemical reaction is the conversion of one substance into another through the creation or breaking of chemical bonds and so we really see chemical reactions going in one of two directions either in building larger substances out of smaller substances or breaking apart larger substances into those smaller substances the first kind of reaction that we've talked about to this point is called the synthesis reaction synthesis means to put together we also call this an anabolic reaction and the definition of a synthesis synthesis reaction is when two or more smaller substances are joined by chemical bonds to make a larger substance and examples of synthesis reactions that we've seen already we saw dehydration synthesis in the creation of proteins in protein synthesis and the combination of amino acids to create a larger protein we also see a synthesis reaction in the creation of the ATP molecule from the ADP molecule and that's the addition of a phosphate group that's a adenosine diphosphate two phosphate groups where we end up with adenosine triphosphate ATP has three phosphate group now in contrast to that we have decomposition reactions they're called catabolic reactions and that's where a larger substance is broken down into its parts by breaking those chemical bonds that hold it together and an example of that would be the various sugar molecules that we've looked at sugar is broken down for energy into the substances carbon dioxide and water and just like we saw the synthesis reaction where we built ATP from adp we can see a decomp position reaction where we can remove a phosphate group from ATP and it will then become ADP again it's breaking down many reactions in the body are very reversible in fact that's one of the ways that we maintain homeostasis the direction that a reaction flows in is very often influenced by the concentration of the substances as we continue moving on and talking about substances moving in and out of cells that concentration of substances will become important okay so to facilitate chemical reactions because we have all these chemical reactions occurring within the body we need particular molecules that assist these various chemical reactions and those molecules are called enzymes enzymes are molecules that influence chemical reactions enzymes are three-dimensional proteins they're synthesized from our DNA code so enzymes are proteins that have gone through the primary the secondary and the tertiary folding so that they have their final structure and that gives them functionality enzymes catalyze which means to speed up a reaction and lower the amount of energy required for a reaction so we get two benefits we get a reaction occurring faster than it normally would because of enzymes and we get a lower amount of energy required for that chemical reaction because of enzymes enzymes then increase the rate of reaction what's interesting is enzymes are not consumed or changed in a chemical reaction so they facilitate they assist in the reaction and on the slide after the next I'll show you a picture that kind of represents that but the enzyme itself is not consumed or changed and in fact they get reused over and over again enzymes induce the catalysis through a change in conformation so enzymes allow for a change in shape and that change in shape gives the enzyme its function that allows for an increased rate of reaction all enzymes have what's called an active binding site on them that will attract and bind to a specific substance that fit into that site so enzymes are very specific to the substances that they're going to work with to either put together or break apart the substances that enzymes interact with that either are put together or are broken apart are called substrates now enzymes need to be able to recognize what substrates that they are going to bind to because enzymes need to be specific so we see this idea of enzyme specificity which allows us to determine which substrates will bind to that enzyme and we have different enzymes for different molecules different enzymes for breaking down lipids for breaking out amino acids and so on we also have the idea of what's called enzyme affinity and enzyme affinity describes the strength of attraction between the enzyme and the substrate in other words sometimes the enzyme has a stronger attraction to its substrate than other enzymes and that can change based on cellular conditions so if your cell conditions aren't in a good homeostatic condition then your cell may not be able to maintain its enzyme affinity and be able to attract the substances it needs lastly our structures called cofactors or coenzymes and cofactors or coenzymes are very important because they serve the function of either turning on or off an enzyme so a cofactor or coenzyme allows for an enzyme to either interact with its substrate by turning it on or by turning it off it will prevent the enzyme for interacting with its substrate one of the effects is that when we see an enzyme in presence of the substrates that it requires less energy so here we have two diagrams one representing a chemical reaction without an enzyme and one representing a chemical reaction with an enzyme and what we see here is that as the reactants are trying to be synthesized put together you can see without the enzyme how much energy is required for that activation for that chemical reaction to occur and you can see by this large spike here that a large amount of energy is required to get these two reactants to actually form into a product now if we look over here in the presence of an enzyme we see the same two reactants but look how much less energy is required to get these two reactants to actually form into a product and so the presence of the enzyme we requires a much much less energy for a chemical reaction to occur enzymes decrease the activation energy required for a given chemical reaction to occur without an enzyme the energy input needed for reaction to begin is very high but with the help of an enzyme less energy is needed for a reaction to begin okay so here is our last slide and what this really shows us is how an enzyme functions so here we have our enzyme remember this is a protein and we can see the active sites the places that are going to allow the substrates to bind and notice the shape of this substrate kind of looks like a lock and a key and that key right here at the end of the substrate is gonna fit right here into the enzyme same thing with the other substrate the other part that's going to be combined we can see this triangular key here is going to fit right into that active site if those are not the correct shapes on these substrates then this enzyme cannot interact with them and the enzyme doesn't you do anything to help these two substrates bind together but in this case those are the correct substrates and so look substrate 1 and substrate to bind into these active sites of the enzyme the enzyme then is facilitating the bonding between substance 1 or substrate 1 and substrate 2 when that bonding occurs now we get what's called the product with so now we have substrate 1 bound to substrate two a new substance and that enzyme now is done and it simply releases the product so the product is now detached and this product of this chemical reaction can go off and serve whatever function it needs to what's interesting is that the enzyme is not destroyed so this enzyme can recycle itself right back here to step a and find two new substrates and continue facilitating that chemical reaction steps in an enzymatic reaction then substrates approach the active binding sites substrates bind to the active sites producing an enzyme substrate complex and that's B changes in the internal to the enzyme substrate complex facilitate interaction of the substrates in other words that's bonding now and then the products are released and the enzyme returns to its original form ready to facilitate another enzymatic reaction this video for YouTube here at the bottom is a great opportunity to watch and learn a little bit about enzymes and how they function this wraps up our chemistry review and wraps up our first introduction series of lectures our next series of lectures we'll cover cell review