The following information is a summation of the material we have discussed in class. Feel free to utilize the discussion button above to add notes about information you would like further clarification of...

Biological Catalysts:

Whenever we encounter a person who is reknown for driving situations and causing important things to happen, we may refer to that person as a catalyst. Enzymes can be thought of in that same fashion. They are extremely important protein molecules that drive metabolic and digestive reactions by lowering the energy needed to start the reactions (energy of activation- energy needed to "activate" a reaction). By lowering the activation energy the reaction can occur more quickly- always a beneficial situation for a living system that must produce its own energy all day, everyday.

Formation of an Enzyme:

Enzymes are proteins; therefore, they form the same way all proteins do- through primary, secondary, tertiary, and quaternary stages. Unlike other proteins, enzymes have an a unique portion of their molecule called an active site. Enzymes carry out catabolic and annabolic reactions (these are not terms you need to know for the quiz). This means they either break down other molecules or build them up. Think about breaking down the food you eat and using the resulting monomers to build up the molecules your body actually needs to survive. In order to build up or break down molecules the molecules must have to spot to which to bind so the reaction can occur. This spot on the enzyme is called the active site.
Animation: Enzymes in Action l
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How Enzymes Work

Hydrolysis of Sucrose

How Enzymes Function:

The substrate molecules are molecules that bind to the active site. There may be one molecule that binds to be broken down or more than one molecule that bind to be put together. The fit between a substrate and enzyme are sometimes referred to as being similar to a lock and key in that an enzyme will only drive a certain kind of reaction, for example, proteases that break down proteins will not also break down lipids. Enzymes are very specific for their substrate(s). When a substrate binds to the active site it slightly changes the shape of the enzyme which causes the substrate to be put under stress so bonds will either break or be forced to form.

How Enzymatic Reactions are Controlled:

Reactions driven by enzymes can be controlled by several mechanisms. Two of these mechanisms are competitive and noncompetitive inhibition. Noncompetitive inhibition is the same as allosteric inhibition. Competitive inhibition occurs when a molecule other than the substrate bonds to the active site and keeps the original substrate from binding. An example of this would be the power of antibiotics. When you have a bacterial infection and have to take antibiotics, the antibiotics bind to the bacterial enzymes, so the bacteria cannot make the substances necessary for their survival, such as their cell wall which protects them. Allosteric inhibition occurs when a molecule binds to the enzyme but not at the active site. Most metabolic pathways are controlled in this fashion. In fact, most products of metabolic pathways also serve to inhibit the reaction. The product, obviously a different shaped molecule than the substrate, will bind somewhere on the enzyme, cause the enzyme to change shape, and distort the active site so no substrate can bind.
How important are our enzymes? Heavy metals such as lead and mercury can bond to an enzyme and cause its shape to change, so it no longer functions. Arsenic, a metalloid, can do this as well. Allosteric inhibition gone bad! Arsenic poisoning