Section Section 2-4 & 2-52-4 & 2-5

“Chemical “Chemical Reactions & Reactions & EnzymesEnzymes””

Write everything that isWrite everything that is underlinedunderlined

2.4 Chemical Reactions / 2.5 Enzymes

California State StandardsCalifornia State Standards

• The fundamental life processes of plants and The fundamental life processes of plants and animals depend on a variety of chemical animals depend on a variety of chemical reactions that occur in specialized areas of reactions that occur in specialized areas of the organism's cells. As a basis for the organism's cells. As a basis for understanding this concept: understanding this concept: – Students know enzymes are proteins that Students know enzymes are proteins that

catalyze biochemical reactions without catalyze biochemical reactions without altering the reaction equilibrium and the altering the reaction equilibrium and the activities of enzymes depend on the activities of enzymes depend on the temperature, ionic conditions, and the pH temperature, ionic conditions, and the pH of the surroundingsof the surroundings

2.4 Chemical Reactions / 2.5 Enzymes

Section 2-4 KEY CONCEPT: Section 2-4 KEY CONCEPT: Life depends on chemical reactions.Life depends on chemical reactions.

2.4 Chemical Reactions / 2.5 Enzymes

Bonds break and form during Bonds break and form during chemical reactionschemical reactions• Chemical reactions change Chemical reactions change

substances into different ones by substances into different ones by breaking and forming chemical breaking and forming chemical bondsbonds–Reactants are changed during a Reactants are changed during a

chemical reaction chemical reaction (the starting (the starting chemicals)chemicals)–Products are made by a chemical Products are made by a chemical

reactionreaction

2.4 Chemical Reactions / 2.5 Enzymes

Chemical reactions release or absorb energy.Chemical reactions release or absorb energy.

• Activation energy is the amount of Activation energy is the amount of energy needed to start a chemical energy needed to start a chemical reactionreaction

2.4 Chemical Reactions / 2.5 Enzymes

• Exothermic reactions release energyExothermic reactions release energy

2.4 Chemical Reactions / 2.5 Enzymes

• Endothermic reactions absorb Endothermic reactions absorb (use) energy(use) energy

2.4 Chemical Reactions / 2.5 Enzymes

Section 2-5 KEY CONCEPT:Section 2-5 KEY CONCEPT:Enzymes are catalysts for chemical Enzymes are catalysts for chemical reactions in living things.reactions in living things.

2.4 Chemical Reactions / 2.5 Enzymes

I. CatalystsI. Catalysts1. 1. A catalyst lowers activation energyA catalyst lowers activation energy..• CatalystsCatalysts are substances that are substances that speed up speed up

chemical reactionschemical reactions..

– decrease activation energydecrease activation energy

– increase reaction rateincrease reaction rate

2.4 Chemical Reactions / 2.5 Enzymes

II. EnzymesII. Enzymes

A. Enzymes are catalysts in living A. Enzymes are catalysts in living thingsthings..

–Enzymes are needed for almost Enzymes are needed for almost all processesall processes

–Most enzymes are proteinsMost enzymes are proteins..

2.4 Chemical Reactions / 2.5 Enzymes

B. B. Homeostasis disruptions can Homeostasis disruptions can prevent enzymes from prevent enzymes from functioning.functioning.– Definition:Definition:

- Homeostasis: Regulation and maintenance of constant Homeostasis: Regulation and maintenance of constant internal conditions in an organism.internal conditions in an organism.

– Enzymes function best in a small range of Enzymes function best in a small range of conditionsconditions..

– Changes in temperature and pH can break hydrogen Changes in temperature and pH can break hydrogen bonds.bonds.

C. An enzyme’s function depends on its C. An enzyme’s function depends on its structurestructure..

2.4 Chemical Reactions / 2.5 Enzymes

• An enzyme’s structure allows only certain An enzyme’s structure allows only certain reactants to bind to the enzymereactants to bind to the enzyme..

Substrates bind to an enzyme on its Substrates bind to an enzyme on its active sitesactive sites

substrates substrates (reactants)(reactants)

enzymeenzyme

2.4 Chemical Reactions / 2.5 Enzymes

The lock-and-key model helps illustrateThe lock-and-key model helps illustrate

how enzymes functionhow enzymes function– substrates brought togethersubstrates brought together– bonds in substrates weakenedbonds in substrates weakened

Substrates bind to anSubstrates bind to anenzyme at certain enzyme at certain places called active places called active sites.sites.

The enzyme bringssubstrates together and weakens their bonds.

The catalyzed reaction formsa product that is releasedfrom the enzyme.