Enzymes are globular proteins that act as catalysts

• Enzymes are globular proteins that act as catalysts and help complex reactions occur. Cytochrome P 450 Liver Enzyme

• Enzymes catalyze reactions by lowering the activation energy necessary for a reaction to occur.

• The molecule that an enzyme acts on is called the substrate. • In an enzyme-mediated reaction, substrate molecules are changed, and product is formed. • The enzyme molecule is unchanged after the reaction, and it can continue to catalyze the same type of reaction over and over.

• Each enzyme is specific for the reaction it will catalyze. • Even when different substrate molecules are present, only those that have the specific shape complementary to the active site are able to bind with the enzyme's active site.

• When an enzyme binds to the appropriate substrate, subtle changes in the active site occur. • This alteration of the active site is known as an induced fit. • Induced fit enhances catalysis, as the enzyme converts substrate to product.

• When an enzyme's shape is significantly altered because of p. H or temperature variation, the enzyme may no longer catalyze reactions. • An enzyme is said to be denatured when it loses its functional shape.

• Competitive inhibition refers to a competition for the active site of the enzyme by an interfering agent (poison) called a nonsubstrate. • The nonsubstrate’s shape resembles the proper substrate’s shape, but when the nonsubstrate and the enzyme join no reaction occurs.

• Cyanide, a component of cigarette smoke, is a competitive inhibitor of an enzyme in the mitochondria. When it attaches to the enzyme it stops the use of oxygen by the cell, causing the cell to suffocate.

• The name of an enzyme usually ends in “ase” and includes the name of the substance that it acts upon. • Examples: peptidase breaks peptide bonds sucrase breaks down sucrose lactase breaks down lactose catalase breaks down hydrogen peroxide

• Coenzymes are substances that co-operate with an enzyme to help it and its substrate fit together better. Vitamins and minerals often act as coenzymes.

• Catabolic reactions occur when a molecule is broken down by an enzyme. • These reactions are exothermic and provide body heat to the organism.

• Anabolic reactions occur when smaller molecules are bound together, by an enzyme, to form one larger molecule. • These reactions are endothermic and occur in warm blooded animals during sleep or after they have eaten.

• Metabolism is the sum of all your body’s catabolic and anabolic reactions; your metabolic rate.