Involve chemical reactions Releases more energy than is absorbed Absorb more energy than is released Involve chemical reactions Excess energy released as heat or light Endothermic reactions Energy is absorbed and released Exothermic reactions Products have more bond energy than the reactants Products have lower bond energy than the reactants Involve changes in energy

KEY CONCEPT Enzymes are catalysts for chemical reactions in living things.

Enzymes are catalysts in living things. Enzymes are needed for almost all processes. Breaking down food and building proteins Most enzymes are proteins.

Who would win this race? Finish Line Team #1 Team #2

Catalysts are substances that speed up chemical reactions. decreases or lower activation energy increases reaction rate

Without a catalyst Activation energy

With a catalyst the reaction starts faster!!!!!! Activation energy

Disruptions in homeostasis can prevent enzymes from functioning. Changes in temperature and pH can break hydrogen bonds An enzyme’s function depends on its structure

Substrates- specific reactants that enzymes act on active site An enzyme’s structure allows only certain reactants to bind to the enzyme. Substrates- specific reactants that enzymes act on active site substrates (reactants) enzyme Substrates bind to an enzyme at certain places called active sites.

The lock-and-key model helps illustrate how enzymes function. substrates brought together bonds in substrates weakened Substrates bind to an enzyme at certain places called active sites. The enzyme brings substrates together and weakens their bonds. The catalyzed reaction forms a product that is released from the enzyme.

How does a catalyst affect the activation energy of a chemical reaction?

Answer Decreases the activation energy needed to start a chemical reaction AND also increases the rate of the chemical reaction.