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Six types of enzymes

Video transcript

so today we're going to talk about enzymes and all the different kinds of reactions that enzymes can catalyze but before we do that let's review the idea that enzymes make biochemical reactions go faster and if you look at a reaction coordinate diagram you'd notice that enzymes speed up reactions by lowering their activation energy now enzymes are generally named for their reactions which is convenient because it makes it a lot easier to remember what an enzyme does if someone gives you its name and a great example of this is that one of the enzymes involved in DNA replication is called DNA polymerase which is named as such because it acts on DNA and specifically makes polymers of DNA now the suffix ace is usually just one that you find at the end of most enzyme names now another great example is that the enzyme that catalyzes the first step of glycolysis which you may remember is the reaction between glucose and ATP to form glucose 6-phosphate and ADP it's called hexokinase and hexo refers to the number six which is a reference to glucose being a sixth carbon sugar and kinase is a term referring to enzymes that add phosphate functional groups to different substrates so overall hexokinase adds phosphates to six carbon sugars like glucose now generally every enzyme has a very specific name that gives insight into the specific reaction that that enzyme can catalyze so we can actually divide most enzymes into six different categories based off the kinds of reactions that they catalyze now our first group is the transfer ace group and the basic reaction that transferases catalyze are ones where you move some functional group X from molecule B to molecule a and a great example of one of these reactions occurs during protein translation where amino acids bound to tRNA molecules are transferred over to the growing polypeptide chain so in this case a refers to our amino acid chain B refers to our tRNA and X refers to this lysine residue which is being transferred from B to a and this reaction particular is catalyzed by an enzyme called peptidyl transferase which is an appropriate name since it is a transfer ace involved in making peptides next we have the ligase group which catalyzes reactions between two molecules a and B that are combining to form a complex between the two or a B and an example of a reaction using a ligase that you might be familiar with occurs during DNA replication where two strands of DNA are being joined together so in this reaction a and B represent the two separated DNA polymers which are being joined to form a single strand and this reaction particular is catalyzed by an enzyme called DNA ligase which is named since the ligase that works on DNA strands now our third group is the oxido reductase group which is a little different from the other since it actually includes two different types of reactions and these reactions involve transferring electrons from either molecule B to molecule a or from molecule to molecule B now we say that an oxidase is directly involved in oxidizing or taking electrons away from a molecule while a reductase is involved in reducing or giving electrons to a molecule and we call these enzymes oxido reductase --is together because they can usually catalyze both the forward and reverse reactions which is why I've used equilibrium arrows here instead of just a normal single headed arrow now a great example of an oxidation reduction reaction occurs during lactic acid fermentation where electrons are either passed from NADH to pyruvate or from lactic acid to nad now this reaction is catalyzed by an enzyme called lactate dehydrogenase remember that the word dehydrogenase refers to the removal of a hydride functional group and that's the same as saying the removal of electrons since hydrides are basically just hydrogen atoms with two electrons on them instead of just one now this enzyme is given its name since it's able to remove a hydride or remove electrons from a molecule of lactic acid next we have the isomerase group and enzymes in this group are typically involved in reactions where a molecule like molecule a is being converted to one of its isomers and an example of this type of a reaction is the conversion of glucose 6-phosphate to fructose 6-phosphate which is one of the steps of glycolysis that you may remember now this reaction is catalyzed by an enzyme called phospho glucose isomerase which is appropriately named since it creates isomers of glucose molecules that are phosphorylated now our next category is the hydrolase category and hydrolases use water to cleave a molecule like molecule a into two other molecules b and c and a great example of one of these reactions is the hydrolysis reaction that can occur to peptide bonds and if we have this lysine alanine dipeptide here it could be reacted with water to form two individual amino acids that are no longer bound and this particular hydrolysis reaction can be catalyzed by a class of enzymes that we call serine hydrolases which some people call serine proteases and they are named this way because they are hydrolases that use a serine residue as the key catalytic amino acid that is responsible for breaking the peptide bond now our last category is a little more complicated than the others and it's the lai ace group now Lices catalyze the dissociation of a molecule like molecule a into molecule B and C without using water like hydrolases would and without using oxidation or reduction like an oxido reductase would and one example of a reaction catalyzed by elias is the cleavage of arginine o succinate into arginine and succinate and this reaction takes place during the urea cycle which you also might be familiar with now this specific reaction is catalyzed by an enzyme called argininosuccinate lyase which is appropriately named because it does a lie ace that catalyzes the breakdown of an arginine o sucks in a molecule now it's important to recognize that since lyases don't use water or oxidation to break a bond they need to generate either a double bond between two atoms or a ring structure in a molecule in order to work so what did we learn well first we learn that enzymes are sometimes name for their reactions and next we learned about the six different types of enzymes we have transferases which transfer functional groups from one molecule to another ligases which ligate or join two molecules together oxido reductase is which move electrons between molecules isomerases which convert a molecule from one isomer to another hydrolases which break bonds using water and lyases which break bonds without using water and without using oxidation