3.3 Enzymes

Enzymes Enzymes are their own class of proteins. Living things could not survive without enzymes. Without enzymes, chemical reactions of life would occur to slowly to survive. We call these substances a catalyst

Enzymes and Substrates Substrate is the term used to describe the molecules that an enzyme acts upon. For example, amylase is an enzyme (a type of carbohydrase) that breaks down polysaccharides into monosaccharides. The amylase attaches to the starch, which is the substrate, and helps to break it down into individual glucose molecules.

Lock and Key/Puzzle Enzymes and substrates follow the “Lock and Key” model. Each enzyme only reacts with a particular substrate. For example: if you are eating a cheeseburger for dinner, amylase will only react with the starch found in the bun. It will not break down the other types of food molecules. Only one substrate (lock) per enzyme (key)! The active site of an enzyme is the specific area of the enzyme where it bonds with the substrate.

Enzyme Substrate Complex Once the substrate bonds with the enzyme, it temporarily forms an “enzyme substrate complex” until the reaction occurs. Once the products are formed, they are released, and the enzyme is free to react again (enzymes release the products and move on to the next substrate). Example: the products of amylase and starch would be smaller glucose molecules broken apart. Enzymes can also join smaller molecules together, resulting in one large product.

How do Enzymes Work? Enzymes work by weakening the bonds between monomers. This lowers the activation energy. Activation energy is the energy needed for a chemical reaction to occur.

What Affects Enzyme Activity? Three main factors: 1. Environmental Conditions 2. Cofactors and Coenzymes 3. Enzyme Inhibitors

1. Environmental Conditions 1. Extreme temperatures are the most dangerous - High temps may denature (unfold) the enzyme 2. pH -most prefer a pH 6 – 8, near neutral 3. Ion concentration-salt ions

2. Cofactors and Coenzymes Inorganic substances (zinc, iron) and vitamins (respectively) are sometimes needed for proper enzymatic activity. Example: Iron must be present in the hemoglobin (protein) structure in order for it to pick up oxygen.

3. Enzyme Inhibitors Competitive inhibitors: Are chemicals that resemble an enzyme’s normal substrate and competes with it for the active site. Noncompetitive inhibitors: Inhibitors that do not enter the active site, but bind to another part of the enzyme causing the enzyme to change its shape, which in turn alters the active site.