Chapter Two The Chemistry of Life

Section 2-4Chemical Reactions and Enzymes

Chemical Reactions

Chemical reaction – a process that changes (or transforms) one set of chemicals into another.

examples • A + B î C + D• A + B î C• A î E + F Chemical

Reactions• Energy in

Reactions• Enzymes• Enzyme

Action

Chemical Reactions

• Parts of a reaction–Reactants are the elements or

compounds that enter into (begin) a chemical reaction.

–Products are the elements or compounds that are produced by (result from) a chemical reaction.

Reactants Products

Chemical Reactions

• Energy in Reactions

• Enzymes• Enzyme

Action

Chemical Reactions

Chemical reactions always involve changes in the chemical bonds that join atoms in compounds.

Chemical Reactions

• Energy in Reactions

• Enzymes• Enzyme

Action

Energy in Reactions

Depending on the number and types of chemical bonds broken and formed, energy may be either released or absorbed by chemical reactions. • Chemical

Reactions Energy in

Reactions• Enzymes• Enzyme

Action

Energy in Reactions

Recall (from 2 minutes ago) that–Reactants are the elements or

compounds that enter into (begin) a chemical reaction.

–Products are the elements or compounds that are produced by (result from) a chemical reaction.• Chemical

Reactions Energy in

Reactions• Enzymes• Enzyme

Action

Energy in Reactions

If the reactants (the starting conditions) have more energy than the products (the ending conditions), then energy is released (also known as an exothermic reaction). • Chemical

Reactions Energy in

Reactions• Enzymes• Enzyme

Action

Energy in Reactions

If the reactants (the starting conditions) have less energy than the products (the ending conditions), then energy is absorbed (also known as an endothermic reaction). • Chemical

Reactions Energy in

Reactions• Enzymes• Enzyme

Action

Endo- and Exothermic Reactions

Energy-Absorbing Reaction Energy-Releasing Reaction

Products

Products

Activation energy

Activation energy

Reactants

Reactants

Endothermic Reaction Exothermic Reaction

• Chemical Reactions

Energy in Reactions

• Enzymes• Enzyme

Action

Energy in Reactions

• Activation energy is the energy needed to get a chemical reaction started.

• Example– Paper (cellulose) burns in the presence

of oxygen and releases heat and light.– Why then aren’t your books all on fire?– You need a spark to get the reaction

started.• Chemical

Reactions Energy in

Reactions• Enzymes• Enzyme

Action

Energy in Reactions - facts

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

• Chemical Reactions

Energy in Reactions

• Enzymes• Enzyme

Action

Energy in Reactions

In reversible reactions, one direction will produce energy, A + B î C + D + energy and the other direction will require energy, C + D + energy î A + B

• Chemical Reactions

Energy in Reactions

• Enzymes• Enzyme

Action

Enzymes

• A catalyst is a substance that speeds up the rate of a chemical reaction.

• A catalyst does this by lowering a reaction’s activation energy.

• Chemical Reactions

• Energy in Reactions

Enzymes• Enzyme

Action

Enzymes

• Enzymes are proteins that act as biological catalysts.

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

• Like other catalysts, enzymes do this by lowering the activation energy of a reaction.

• Chemical Reactions

• Energy in Reactions

Enzymes• Enzyme

Action

Energy diagram of a chemical reaction

• In terms of energy, what an enzyme (or any catalyst) does to a reaction is to lower the activation energy.

Reaction pathwaywithout enzyme Activation energy

without enzyme

Activationenergywith enzymeReaction pathway

with enzyme

Reactants

Products

Enzymes

• Without enzymes, the thousands of chemical reactions necessary to sustain life would simply be

t o o s l o w.• Chemical

Reactions• Energy in

Reactions Enzymes• Enzyme

Action

Enzyme Action

• Enzymes work by creating an ideal environment for the reaction to take place.– Proximity– Orientation

• This reduces the energy needed for the reaction to take place. • Chemical

Reactions• Energy in

Reactions• Enzymes Enzymes

Action

Enzyme Action

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

• Substrates bind to a specific location on the enzyme known as the active site.

• Chemical Reactions

• Energy in Reactions

• Enzymes Enzymes

Action

Enzyme Action

• This association is called the enzyme-substrate complex.

• The fit between substrate and active site is so precise that it is frequently compared to a “lock and key”.

• Chemical Reactions

• Energy in Reactions

• Enzymes Enzymes

Action

Enzyme Action

• It is the shape of these large enzyme molecules that allows them to function.

• Changes in pH or temperature can cause changes in an enzyme’s shape that can reduce (or destroy) its effectiveness as a catalyst (read “Analyzing Data” on pg. 51 in your text). (Denaturing the enzyme)

• Chemical Reactions

• Energy in Reactions

• Enzymes Enzymes

Action

Enzyme animation

The end of Chapter Two The Chemistry of Life

• http://www.stolaf.edu/people/giannini/flashanimat/enzymes/biochem.path.swf

• http://www.dannynicholson.co.uk/enzymetale.swf

• http://www.stolaf.edu/people/giannini/flashanimat/enzymes/prox-orien.swf

• http://www.northland.cc.mn.us/biology/Biology1111/animations/enzyme.swf• http://www.stolaf.edu/people/giannini/flashanimat/enzymes/prox-orien.swf• http://www.tvdsb.on.ca/westmin/science/sbi3a1/digest/enzymes.htm• http://www.hillstrath.on.ca/moffatt/bio3a/digestive/enzanim.htm• http://www.stolaf.edu/people/giannini/flashanimat/enzymes/enzyme.swf• http://www.biotopics.co.uk/other/anenz.html• http://www.dannynicholson.co.uk/enzymetale.swf

• http://www.stolaf.edu/people/giannini/flashanimat/enzymes/biochem.path.swf• http://www.sigmaaldrich.com/Area_of_Interest/Life_Science/Metabolomics/K

ey_Resources/Metabolic_Pathways/Glycolytic_Pathway.html• http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/fre

e/0072437316/120070/bio09.swf::A%20Biochemical%20Pathway

Chemical Reactions and Enzymes (2-4)

Chemical Reactions (today)Energy in Reactions (today)Enzymes (10/9)Enzyme Action (10/9)