One of the qualities that distinguishes living things from non-living things is that living things have the ability to carry out chemical reactions that are crucial for survival. Even single-celled organisms are able to perform hundreds of chemical reactions within their cell wall. Imagine the countless number of reactions that take place in a large organism such as a human! None of these reactions are possible without enzymes. Enzymes are biological catalysts or reaction assistants. Enzymes are made up of various types of proteins that work together to drive a chemical reaction. Enzymes can get a reaction underway or can speed it up. For example, in the presence of certain enzymes, substrates (the chemical reactants) can be transformed into usable products at the rate of millions of times per second! In the absence of the enzymes, however, the reactants could take years to be converted into usable products, if at all. The work of enzymes is crucial to the existence of life on Earth. Enzymes are globular proteins: they have a specific 3D shape that is determined by the electrostatic charges of their constituents attracting and repelling one another. The 3D shape of a protein is critical to its function. Enzyme activity is described by a lock and key model, also known as the induced fit model. Enzymes have active sites where they come into contact with specific substrates. Once a substrate has come into contact with the active site of an enzyme, it is manipulated by the enzyme into the final product. When the process is complete, the enzyme releases the product and is ready to begin the process with new substrates. Enzymes are reusable and therefore always recycled.
The environment of an enzyme also has an effect on its 3D shape. For example, pH affects the shape of the enzyme's active site. In the presence of excess H+ or OH- ions, the active site on the enzyme becomes progressively distorted; this decreases the enzyme's activity until it can no longer function as a catalyst. This process is called denaturation of the enzyme. Temperature also affects the activity of enzymes. Chemical reactions accelerate as temperature increases, so, in general, catalysis will increase at higher temperatures. However, each enzyme has an optimum temperature point beyond which the enzyme's functional 3D shape is lost and catalysis decreases. Boiling temperatures will denature most enzymes by stretching the molecular bonds present in the enzyme beyond repair. Many enzymes that are present in our bodies help us break down our food. Digestive enzymes are secreted all along the digestive track including the mouth (saliva), stomach, small intestine, and large intestine. Each stop along the digestive track has its own physiological environment and the enzymes in each environment must be able to perform certain functions. The enzyme, amylase, breaks down starches into simpler sugars. Another enzyme, lipase, breaks down fats into simpler molecules. Proteases break down proteins into simpler molecules called peptides. Enzymes make use of the chemical process of hydrolysis, in which a larger molecule is cleaved into two parts by the addition of a molecule of water. Thus, if a compound is represented by the formula AB in which A and B are atoms or molecules, and water is represented by the formula HOH, the hydrolysis reaction may be represented by the reversible chemical equation: AB + HOH ﾠ ↔ﾠﾠﾠﾠﾠﾠ AH + BOH
As mentioned above, amylase breaks down starches into simpler sugars. Amylase catalyzes the breakdown of starch by cutting off the disaccharide maltose (two glucose molecules linked together). As the reaction progresses, the starch disappears and the sugar content (maltose) increases. Experiments
In the experiments that follow, you will perform some tests to learn about enzyme activity. These experiments examine the effects that environmental pH and temperature have on the rate of amylase digestion of starch. This will be...
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