Adrian Fraser
AP Biology period 5
Due date: 10-5-07
How substrate concentration affects enzyme reaction rates
Introduction:
Our bodies are constantly at work, each individual cell that makes up our body is constantly producing certain molecules from other molecules, either combining multiple particles into one big one, or breaking apart one big one into multiple smaller particles. The thing that helps cells do this so efficiently is a type of protein called an enzyme. Enzymes are incredibly complex molecules, which act as organic catalysts (something that speeds up a reaction) inside a cell. There are many different types of enzymes, but each enzyme can only catalyze one type of reaction; for example, catalase, usually found in the liver, can only act as a catalyst in the following reaction:2H2O2 -> 2H2O + O2. The way that an enzyme manages to be so specific to one reaction has to do with how it works. In order for an enzyme to catalyze a reaction for its substrate, that substrate first needs to enter the enzyme's activation site, this is a part of the enzyme which is specifically shaped for the substrate. Once the substrate enters the activation site, the enzyme reshapes itself around the substrate, and begins to catalyze the reaction. Once the reaction is finished, the enzyme returns to its original form, and the product exits the activation site. The reason why only one specific substrate can enter the enzyme is similar to a lock and key mechanism: only one key works for each lock. The reason why enzymes are so efficient is because they are catalysts, not reactants. The difference between a catalyst and a reactant is that a catalyst speeds up a reaction, without getting consumed, whereas a reactant starts a reaction, but also gets consumed. This means that an enzyme can, theoretically, catalyze an infinite number of reactions, without getting consumed, assuming that there's enough substrate to be catalyzed. If a graph were to be made based on substrate consumption over time, it would start out as a straight line going diagonally up and to the right, and then slowly curve to a horizontal line. This is because, at first, there'd be enough substrate to keep the reactions going at a constant rate, but after a while, there wouldn't be enough substrates for the enzymes to keep working, so the rate of the substrate consumption would slowly reach zero, at which point there's not any substrate left to be consumed. This leads to the purpose of this lab. The purpose of this lab was to determine how extreme this effect really is, whether the rate stays constant for just a short time longer, or whether it really prolongs the time until the reaction rate slows down, or if it even has any effect whatsoever; another thing would be how quickly the reaction slows down, or, the speed at which the graph goes from a straight, diagonal line to a horizontal line. My hypothesis was that by increasing the substrate concentration, it would be possible to keep a constant reaction going for a much longer time, but that the speed at which the reaction slows down would only be decreased by a slight amount.