Objectives

• Students will explore the importance of chemical reactions in biology

• Students will discuss the role of enzymes as catalysts in biological reactions.

• Students will analyze graphs showing how catalysts lower reaction thresholds.

• Students will write and draw biological vocabulary on a variety of words.

Today you need: textbook, notebook, pen or pencil.

• Vocabulary: 1. Reactant 2. Product 3. Activation energy 4. Catalyst 5. substrate 6. Chemical reaction • Keep your textbooks when you are done

Chemical Reactions and Enzymes

As we have seen living things are made of chemical compounds, but more importantly chemistry isn’t just what life is made of, chemistry is also what life does.

Chemical Reactions

• Chemical reaction – is a process that changes one set of chemicals into another set of chemicals.

• The elements or compounds that enter into a chemical reaction are the reactants.

• The elements or compounds produced by a chemical reaction are known as products.

Chemical Reactions

• Ex) photosynthesis

• Chemical reactions always involve the breaking of bonds in reactants and the formation of new bonds in products.

Energy

• Chemical reaction are either:

• 1. Endothermic (need/absorb energy)

• - need an energy source

–(activation energy)

• 2. Exothermic (give off energy)

–- usually spontaneous

Energy in Reactions

• Energy is neither created nor destroyed, therefore energy is released or absorbed whenever chemical bonds form or are broken.

• Chemical reactions that release energy often occur spontaneously. Chemical reactions that absorb energy will not without a source of energy.

Ex) 2H2 + O2 yields 2H20

The reverse reaction takes an electrical current through water to decompose water into hydrogen and oxygen gas.

Activation Energy • What significance do these

energy changes have to do with living things?

In order to stay alive, organisms need to carry out reactions that require energy.

Activation Energy

• Do all reactions occur spontaneously?

• If this were true what would happen to your textbooks?

• It will burn only if you light it with a match.

• Chemists call the energy that is needed to get a reaction started the activation energy

• Fig 2 – 19 shows, activation energy is a factor in whether the overall chemical reaction releases energy or absorbs energy.

Enzymes • Some chemical reactions that make life possible

are too slow or have activation energies that are too high to make them practical for life.

• These reactions require catalysts or substances that speed up the rate of a chemical reaction.

• Catalysts work by lowering a reaction’s activation energy (making it easier to trigger)

Enzymes

• Enzymes – are proteins that act as biological catalysts.

• Enzymes speed up chemical reactions that take place in cells.

• Enzymes are very specific, generally catalyzing only one chemical reaction.

Enzymes

• For a chemical reaction to occur, the reactants must collide with enough energy so that existing bonds will be broken and new bonds will be formed.

• Enzymes provide a place where reactants can be brought together to react.

• The reactants of enzyme – catalyzed reactions are known as substrates.

The Enzyme – Substrate Complex

• During one of these reaction, a phosphate group is transferred from ATP to the glucose molecule. This is how the human body gets energy from stored food.

• Each protein (enzyme) has a specific shape, the substrate binds to the active site on the protein to help speed up the reaction.

• AKA “lock and key”

Copy this picture:

To rephrase….

• Enzymes provide a place for the substrates

(2 reactants) to meet.

• The chemical reaction takes place and the parts split.

• The result is a new chemical (the product)

Another version

One more…..

Regulation of Enzyme Activity

• Because they are catalysts for reactions, enzymes can be affected by any variable that influences a chemical reaction.

•

What affects enzymes

1. Temperature

2. PH

3. Concentration of chemicals

4. IONs