Chapter 5 Section 5 Enzymes Mrs. Kerstetter Biology

Objectives Explain how enzymes affect activation energy. Describe how an enzyme’s shape is important to its function. Describe how a substrate interacts with an enzyme.

Enzymes =specialized proteins that coordinate a cell’s activities In order for a chemical reaction to begin, bonds need to be weakened in the REACTANTS. -reactants are the starting substances in a reaction -PRODUCTS are the ending substances in a reaction This activation process requires that the molecules ABSORB energy

Activation Energy =the start-up energy that activates the reactants and triggers a chemical reaction Some ways to activate reactants: Heat-destroy a cell Mix-not easy to do in a cell Enzymes-”cell-friendly”

Enzymes Cells rely on CATALYSTS to speed up a reaction (rxn) Main catalyst of chemical reactions in organisms are specialized proteins called enzymes

Enzymes -enzymes provide a way for rxns to occur at the cell’s normal temperature *Doesn’t supply activation energy to the reacting molecules, but instead LOWERS the energy requirements Each enzyme catalyzes a specific kind of reaction

How Enzymes Work Why do enzymes catalyze only one type of reaction? the shape of each enzyme only fits the shape of its reactant molecules *the specific reactant acted upon by an enzyme is called its SUBSTRATE *the region on the enzyme into which the substrate fits is called its ACTIVE SITE

How Enzymes Work -the fit between substrate and active site is not rigid like a lock and a key -more like a hand in a glove -this positions the FUNCTIONAL GROUPS of the active site in an area where it can catalyze a rxn

How Enzymes Work -most enzymes end in –ase What type of reaction occurs as the water molecule comes in and the substrate is converted to products? HYDROLYSIS Product  glucose and fructose -the products are released, and the enzyme can now catalyze another sucrose molecule

How Enzymes Work Another way that enzymes can lower activation energy is by accepting TWO reactant molecules into adjacent sites Enzyme's structure and shape are essential to its functions *pH and temperature affects how well or if an enzyme works at all