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KEY CONCEPT Life depends on chemical reactions.

Understand how chemical reactions drive life processes and how enzymes catalyze reactions in living organisms. Explore bond energies, activation energy, equilibrium, and the role of enzymes in maintaining homeostasis. Learn how enzymes function, the lock-and-key model, and factors affecting enzyme activity.

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KEY CONCEPT Life depends on chemical reactions.

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  1. KEY CONCEPT Life depends on chemical reactions.

  2. Bonds break and form during chemical reactions. • Chemical reactions change substances into different ones by breaking and forming chemical bonds. • Reactants are changed during a chemical reaction. • Products are made by a chemical reaction.

  3. Bond energy is the amount of energy that breaks a bond. • Energy is added to break bonds. • Energy is released when bonds form. • A reaction is at equilibrium when reactants and products form at the same rate. CO2 + H2O H2CO3

  4. Chemical reactions release or absorb energy. • Activation energy is the amount of energy that needs to be absorbed to start a chemical reaction.

  5. Exothermic reactions release more energy than they absorb. • Reactants have higher bond energies than products. • Excess energy is released by the reaction.

  6. Endothermic reactions absorb more energy than they release. • Reactants have lower bond energies than products. • Energy is absorbed by the reaction to make up the difference.

  7. KEY CONCEPTEnzymes are catalysts for chemical reactions in living things.

  8. A catalyst lowers activation energy. • Catalysts are substances that speed up chemical reactions. • decrease activation energy • increase reaction rate

  9. Enzymes allow chemical reactions to occur under tightly controlled conditions. • Enzymes are catalysts in living things. • Enzymes are needed for almost all processes. • Most enzymes are proteins.

  10. Disruptions in homeostasis can prevent enzymes from functioning. • Enzymes function best in a small range of conditions. • Changes in temperature and pH can break hydrogen bonds. • An enzyme’s function depends on its structure.

  11. substrates (reactants) enzyme Substrates bind to anenzyme at certain places called active sites. • An enzyme’s structure allows only certain reactants to bind to the enzyme. • substrates • active site

  12. Substrates bind to anenzyme at certain places called active sites. The enzyme bringssubstrates together and weakens their bonds. The catalyzed reaction formsa product that is releasedfrom the enzyme. • The lock-and-key model helps illustrate how enzymes function. • substrates brought together • bonds in substrates weakened

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