CHAPTER 5

ENZYMES

ENZYMESENZYMES All organisms require energy to perform life All organisms require energy to perform life

functions. functions. Growth, development, reproduction, etc.Growth, development, reproduction, etc.

Energy needed for living things is derived from Energy needed for living things is derived from nutrientsnutrients. .

Broken down in biochemical reactionsBroken down in biochemical reactions To break down nutrients, an initial amount of To break down nutrients, an initial amount of

energy must be supplied to start the reactions.energy must be supplied to start the reactions. This energy is known as This energy is known as activation energyactivation energy..

To sustain life, biochemical reactions must occur To sustain life, biochemical reactions must occur at very rapid rates.at very rapid rates.

Reactions rates can be accelerated with increased Reactions rates can be accelerated with increased temperature, pressure, or the use of a catalyst.temperature, pressure, or the use of a catalyst.

ENZYMESENZYMES A catalyst is a molecule that speeds up A catalyst is a molecule that speeds up

a reaction.a reaction. Lowers the activation energyLowers the activation energy

Living things cannot have too much Living things cannot have too much increase in temperature or pressure to increase in temperature or pressure to accelerate a reaction, so a catalyst accelerate a reaction, so a catalyst must be used.must be used.

EnzymesEnzymes are biological catalysts that are biological catalysts that accelerate chemical reactions in living accelerate chemical reactions in living cells at normal body temperature.cells at normal body temperature.

ENZYMESENZYMES

ENZYMESENZYMES As with any catalyst, enzymes speed As with any catalyst, enzymes speed

up a reaction but are not used up in up a reaction but are not used up in the reaction.the reaction.

The instructions for producing The instructions for producing enzymes are found on the DNA of the enzymes are found on the DNA of the organism.organism.

Each organism produces thousands of Each organism produces thousands of specific enzymes that the cell needs.specific enzymes that the cell needs.

Each enzyme is very specific on the Each enzyme is very specific on the reaction that it catalyzes.reaction that it catalyzes.

ENZYMESENZYMES

Each enzyme has a specific 3-D shape.Each enzyme has a specific 3-D shape. This shape allows the enzyme to This shape allows the enzyme to

attach specifically to a substrate that attach specifically to a substrate that matches.matches.

Like a puzzle or lock and keyLike a puzzle or lock and key The The substratesubstrate (or reactant) is the (or reactant) is the

molecule to which the enzyme binds.molecule to which the enzyme binds. When attached, an When attached, an enzyme-substrate enzyme-substrate

complexcomplex is formed and the reaction is formed and the reaction proceeds.proceeds.

ENZYMESENZYMES

ENZYMESENZYMES

Enzymes have an Enzymes have an activeactive sitesite, which is the , which is the area where the enzyme binds to the area where the enzyme binds to the substrate.substrate.

Because enzymes are specific, they are Because enzymes are specific, they are named based on the name of the named based on the name of the substrate.substrate.

The first part is the name of the molecule The first part is the name of the molecule to which it can become attached. to which it can become attached.

The second part may indicate the type of The second part may indicate the type of reaction it facilitates.reaction it facilitates.

ENZYMESENZYMES

The third part of the enzyme is “–ase,” The third part of the enzyme is “–ase,” the ending that tells you it is an the ending that tells you it is an enzyme.enzyme.

Lactase (enzyme) acts on lactose Lactase (enzyme) acts on lactose (carbohydrate) (carbohydrate)

Alcohol dehydrogenase acts on alcohol, Alcohol dehydrogenase acts on alcohol, removing a hydrogen ionremoving a hydrogen ion

DNA DNA polymerasepolymerase attaches to a DNA attaches to a DNA molecule and is responsible in increasing molecule and is responsible in increasing its length through polymerization reactionits length through polymerization reaction

Some enzymes have kept their old Some enzymes have kept their old names, e.g., pepsin and trypsin.names, e.g., pepsin and trypsin.

ENZYMESENZYMES Some enzymes need other molecules to Some enzymes need other molecules to

function well.function well. Called Called cofactorscofactors

Cofactors temporarily attach to enzymes Cofactors temporarily attach to enzymes and speed up the reaction.and speed up the reaction.

If the cofactor is not a protein but another If the cofactor is not a protein but another organic molecule, it is called a organic molecule, it is called a coenzymecoenzyme..

Many coenzymes are made from minerals Many coenzymes are made from minerals (zinc, magnesium, or iron) vitamins, and (zinc, magnesium, or iron) vitamins, and nucleotides. nucleotides.

Can be used for many different enzymes.Can be used for many different enzymes.

ENZYMESENZYMES Enzymes are very specific and extremely efficient.Enzymes are very specific and extremely efficient. A single enzyme can accelerate a reaction 10 A single enzyme can accelerate a reaction 10

thousand trillion (1016) times faster per minute thousand trillion (1016) times faster per minute than the reaction would occur without the enzyme. than the reaction would occur without the enzyme.

Temperature has two effects on enzyme action:Temperature has two effects on enzyme action: Can cause the molecules to move fasterCan cause the molecules to move faster Can change the shape of an enzymeCan change the shape of an enzyme

Enzymes can be denatured by high temperatures.Enzymes can be denatured by high temperatures. Enzymes work best at their optimum temperature.Enzymes work best at their optimum temperature.

Usually around normal body temperature Usually around normal body temperature

OPTIMUM TEMPERATUREOPTIMUM TEMPERATURE

ENZYMESENZYMES An enzyme that is denatured has lost its ability to An enzyme that is denatured has lost its ability to

function properly.function properly. Like cooking an eggLike cooking an egg

pH changes can also denature an enzyme and pH changes can also denature an enzyme and impair its function.impair its function.

Each enzyme has an optimum pH at which it Each enzyme has an optimum pH at which it works best, but most enzymes work best around works best, but most enzymes work best around pH 7.pH 7.

There are There are control processescontrol processes in each cell to in each cell to make sure all metabolic reactions occur in make sure all metabolic reactions occur in the proper sequence. the proper sequence.

OPTIMUM pHOPTIMUM pH

REGULATIONREGULATION The number and kind of enzymes produced The number and kind of enzymes produced

are regulated by the cell’s genes.are regulated by the cell’s genes. Enzymes are regulated by Enzymes are regulated by negative-feedback negative-feedback

inhibitioninhibition, which works by inhibiting the , which works by inhibiting the enzyme from performing at its best.enzyme from performing at its best.

InhibitorsInhibitors can also influence the activity of an can also influence the activity of an enzyme by attaching themselves to an enzyme by attaching themselves to an enzyme and interfering with the formation of enzyme and interfering with the formation of enzyme-substrate complex. enzyme-substrate complex.

Competitive inhibitorsCompetitive inhibitors are molecules that are molecules that bind bind to the active site of an enzyme and make it to the active site of an enzyme and make it unavailable to bind to the substrate. unavailable to bind to the substrate.

Is used to control bacterial growthIs used to control bacterial growth

CHAPTER 5

ENZYMES