In the diagram provided, a section is labeled with a question mark. This is where the substrate will bind. What is the scientific term given to this part of the enzyme? Show
This question asks us to identify a specific portion of the enzyme–substrate complex. Let’s briefly review what an enzyme and substrate are in order to answer our question correctly. You might remember that an enzyme is also called a biological catalyst. This is because enzymes accelerate chemical reactions. A chemical reaction is the process in which a substance or multiple substances are changed into a new substance or new substances. The initial substance is called a reactant, and the final substance of the reaction is called a product. Enzymes only speed up this process. This means they are not used up during the course of the reaction. The reactants in an enzyme-catalyzed reaction are called substrates. Note that every enzyme has a specific substrate to which it binds. As you can see in these diagrams, the substrate must have a complementary structure to a specific site on its matching enzyme. Only when this complementarity is given can the substrate and enzyme correctly bind to each other. The area on the enzyme where this occurs is called the active site. Now that we have reviewed the basics of enzyme-catalyzed reactions and the enzyme–substrate complex, we know the correct answer to our question. The area in which the substrate binds to the enzyme is the active site. The active site of an enzyme is the region that binds substrate molecules. This is crucial for the enzyme’s catalytic activity. Enzymes are proteins that drastically increase the speed of chemical reactions by lowering their activation energy. They do this by interacting with chemical reactants – the substrates – in ways that make them more likely to undergo their chemical reaction. This interaction is carried out at the active site, where the enzyme binds the substrates to increase their chances of reacting. The role of enzymesEnzymes catalyze countless chemical reactions. For example, stringing together nucleotides and amino acids to make DNA and proteins, breaking down sugar and fat into energy, and breaking down toxins in the liver. Thus, enzymes are some of the most important molecules in biology. Without enzymes, life as we know it could not exist. Bacteria dehydrogenase enzyme with active site shownFeatures that Determine Active Site SpecificityBecause enzymes – like all proteins – are made of amino acids, there are a wide variety of potential sequences. Therefore, their active sites also have diverse sequences, structures, and physical properties. This is an important feature that allows enzymes to bind specifically to different substrates. Some of the properties that affect substrate binding include:
Active Site Binding TheoriesThere are two theories about how exactly an enzyme active site binds to substrates. These are the lock and key model and the induced fit model. The Lock and Key ModelThe lock and key model of active site binding postulates that active sites possess the perfect shape to bind their substrates. When they make contact, the substrate can “pop” into place at the active site, similar to a lock and key. The Induced Fit ModelThe induced fit model competes with the lock and key model. It states that the active site and the substrate are not necessarily an ideal fit for each other in their resting states. Instead, as the substrate draws near to the enzyme, one or both undergo shape changes as a result of interacting with each other. In this model, it is the continuing interaction of the binding site and the substrate that drives the substrate into its new formation. After the reaction is complete and new products form, the product and enzyme are no longer compatible and they separate. The induced fit model is more in line with current scientific evidence and is more widely accepted. Induced fit model for enzyme functionExamples of EnzymesSome examples of chemical reactions catalyzed by enzymes include the breakdown of starch by maltase, the breakdown of proteins by pepsin, and the synthesis of DNA by DNA polymerase. For each of these reactions, the characteristics of the active site are crucial. Maltase and StarchMaltase is an enzyme found in saliva. It breaks down starches – long chains of sugar molecules that don’t taste sweet – into simpler, sweeter tasting sugars. The reaction catalyzed by maltase is shown below: Starch + Water → Sugars You can see maltase in action if you chew on a saltine cracker for a few minutes. While the cracker did not initially taste sweet, after a few minutes, you will be able to taste the sugars that the maltase is creating from the starch! Pepsin and ProteinAnother enzyme that is important for digestion is pepsin. The cells of the stomach release pepsin, allowing it to catalyze the reaction of proteins with stomach acid. Therefore, pepsin allows your body to break down protein from food into amino acids. Your body can use these amino acids to build new proteins. The reaction occurs as follows: Protein + Acid → Amino acids DNA PolymeraseAnother essential enzyme is DNA polymerase. It’s DNA polymerase that allows your cells to multiply, by making copies of their DNA to pass on to daughter cells. DNA polymerase does this by stringing together nucleic acids in the correct sequence. This synthesis reaction is the opposite of the breakdown reactions of maltase and pepsin. The reaction catalyzed by DNA polymerase is as follows: DNA triphosphate molecule + DNA strand → Longer DNA strand + diphosphate molecule Quiz1. Without enzymes, our cells would not be able to digest food, break down toxins, or create new DNA. A.True B.False 2. Enzymes and substrates are perfectly shaped to fit together, like a lock and key. A.True B.False 3. Enzymes need to be constantly replenished because they are used up in their reactions with substrates. A.True B.False Enter your email to receive results: Loading...
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