Amin W., Zara A., Melissa L., Mesret , Urwa, Carolina B.IB Biology: Topic 3.6 EnzymesIntroduction to Enzymes Enzymes are a biological catalyst or protein that catalyses chemical reactions in living organisms.During enzyme activity, substrates are the reactant in the biochemical reaction, enzymes act as thecatalyst for the reaction, and the active site is the entire region where the enzyme and substrate bind,which catalyses the reaction. During the reaction, the substrate locks into the active site, is catalyzed,then the products of the biochemical reaction are released and the enzyme is then reused.Enzyme Activity DiagramTypes of models on Enzyme Activity There are different ideas on models of the cause of enzyme activity. One theory states howenzymes and substrates are only able to react with one another if they are chemically and structurallycompatible; this is known as The Lock-and-Key Hypothesis. But this model is not a viable theory. If thismodel were to be true, only one enzyme could catalyze one reaction when in reality an enzyme cancatalyze multiple reactions.
Amin W., Zara A., Melissa L., Mesret , Urwa, Carolina B.The Lock-and-Key Model The induced-fit model is known to be a better theory of enzyme activity as it states that when asubstrate approaches an enzyme, it induces a sort of change in the active site, then changing shape inorder to fit the substrate. The activation energy is reduced because of the stressing of the substrate inthis reaction.Induced-Fit ModelFactors that affect enzyme based reactionsEffect of temperature Both enzymes and substrate motion is dependent on temperature of the fluid. Fluids with highertemperature have faster moving molecules. The faster the molecules move the more they collide withgreat energy. The reaction rate increase with the increase in temperature. The temperature increase canaffect the shape of the enzyme which can lead to its denaturation.
Amin W., Zara A., Melissa L., Mesret , Urwa, Carolina B.Effects of pH The pH of the solution is dependent on the relative number of hydrogen ions (H+) compared tohydroxide ions (OH-) in the same solution. Substrate giving off hydrogen ions is an acid with pH below 7.Substrate giving off hydroxide ions is a base with pH more than 7. Water is neutral with equal number ofboth ions. Amino acids are charged positive and negative, the opposite charge must match the whensubstrate is in active site for a catalytic action. With too much acid or too little the charge does not bondcorrectly and can lead to reaction being inefficient or inactive.Effects of substrate concentration With increase of substrate concentration there is an increase of molecular collisions leading tothe rate of reaction increase. The more molecules there are, the more they collide but enzymes have amaximum rate in which they work. Increase in substrate solution when the enzymes are working as fastas possible will not increase the reaction rate.