Enzymes

Enzymes and What They Do for You

Most introductory biology courses begin with a basicA solution with a pH above 7, having a lower concentration of H⁺ ions. lesson in chemistry.  Why? All life depends on chemical reactions.  In all living organisms, small moleculesGroups of atoms bonded together. are anabolized to form large molecules and large molecules are catabolized into smaller ones.  Even within a living organismA living individual made up of cells. comprised of a single cell, there are millions of chemical reactions taking place.  The balance of catabolic (breakdown) and anabolic (build-up) reactions is known as metabolismThe sum of all chemical reactions in the body..  How is this balance maintained effectively?  With what speed and what kind of precision do these reactions take place?  The answer, in part, is through the use of enzymesProteins that speed up chemical reactions in the body.. 

Cupid is a Catalyst

Catalyzing a reaction can be accomplished by reducing the energyThe capacity to do work or cause change. required to perform the reaction otherwise known as activation energyThe minimum amount of energy required to start a chemical reaction..  Using a match to light a fire as opposed to using two sticks can illustrate the concept of an enzyme.  Rubbing together two sticks to start a fire requires a good amount of physical energy whereas a match reduces the physical energy needed, making the fire (reaction) start quicker.   Enzymes not only reduce barriers to reactions but they also increase the overall rate of the reaction.  The digestive enzymes in the human stomach are an excellent example of how enzymes can reduce the time it takes a reaction to come to completion.  Digestive enzymes break down food enabling the complex human form to harvest energy from food at a rate that supports all of life’s activities.

Enzyme Working Conditions

Enzymes are biological catalysts that affect both the rate and direction of metabolic reactions (whether mostly anabolic or mostly catabolic).   The rate of chemical reactions can also be influence by temperature.  Thermal energy, defined by the motion of molecules at specific temperatures, can increase the likelihood of a reaction.  Enzymes are more likely to encounter their substrate molecule and proceed with their reaction at higher temperatures.

Lock and Key: The Perfect Fit

The substrate has a specific shape compatible with the enzyme’s active siteThe specific region of an enzyme where a substrate binds and a reaction occurs. in a lock and key fashion.  This induced fit specifically pairs the enzyme and its substrate.  Enzymes are not multi-taskers, and have specific shapes matching only one or very few molecules.  Once the substrate has fit into the active site, the enzyme chemically acts upon the substrate converting it into the product(s) of the reaction.  When the products are released from the enzyme, the enzyme is free to seek out another substrate molecule and repeat this process, as the enzyme itself is not consumed or converted during the reaction.

The physical shape of active sites can be altered by denaturing an enzyme.  Denaturing an enzyme involves changing the enzyme shape using an agent such as heat or acids.  Cooking and marinating meat for consumption at dinner are common ways to denatureThe process in which a protein loses its shape and function due to heat or pH changes. protein molecules, breaking down the protein structure and making them more suitable for the human digestive system.  Enzyme inhibitors can also disable an active site, preventing the substrate from connecting with the enzyme. 

The Ever-Lasting Enzyme

Enzymes, as catalysts, regulate chemical reactions without being consumed themselves.  For this reason, a small quantity of enzyme can cause large scale chemical changes.  Anyone who has ever endeavored to make yogurt or cheese at home has encountered the high price of the rennin or other enzymes needed to culture these dairy products.  A crucial question to ensure affordability is: What’s the smallest amount of enzyme needed to make this reaction happen?  The urease baseline experiment assess different concentrations of urease in an effort to determine the smallest urease concentration needed to produce measurable results.  Students will be designing their own experiment in the future, and the optimal urease concentration will be needed to design that experiment.

Dairy Don’ts

When some people eat dairy products (milk, ice cream, and cheese), they experience digestive discomforts such as flatulence (gas), bloating, cramping, and even diarrhea. These individuals do not produce enough of an enzyme called lactase, the enzyme that digests lactoseA disaccharide sugar found in milk., a carbohydrateOrganic molecules composed of carbon, hydrogen, and oxygen, primarily used for energy. found in milk. When undigested lactose accumulates in the intestine of a person with lactose intolerance, bacteria in the intestine feed on the lactose and produce waste gases that cause flatulence and bloating. Large amounts of undigested lactose may also cause waterThe universal solvent essential for life. to diffuse from the blood into the intestine resulting in diarrhea.

Lactase is a protein enzyme that digests (breaks down) lactose (milk sugar) into glucoseA simple sugar that is the main source of energy for cells. and galactose (smaller sugars). The chemical equation below illustrates what happens when the enzyme lactase digests lactose (milk sugar).

Lactose       +      Lactase      =      Lactase/Lactose Complex      =      Glucose      +      Galactose      +      Lactose
Substrate            Enzyme          Substrate/Enzyme Complex               Product                Product                    Enzyme

There is a dietary supplement called LACTAID that contains the enzyme lactase. The makers of LACTAID promise that the lactase in this product will allow people with lactose intolerance to enjoy eating dairy products. Read the product information below from the box of LACTAID pills.