Topic 3.6: Enzymes

Assessment statements:

• 3.6.1: Define enzyme and active site• 3.6.2: Explain enzyme-substrate specificity• 3.6.3: Explain the effects of temperature, pH,

and substrate concentration on enzyme activity

• 3.6.4: Define denaturation• 3.6.5: Explain the use of lactase in the

production of lactose-free milk.

Enzymes are organic molecules which act as catalysts

• Enzymes are long chains of amino acids that have a very specific three-dimensional shape– Globular shape

• Shape is complex but very specific– Somewhere in the three-

dimensional shape of the enzyme is an area that is designed to match a specific molecule known as that enzymes substrate (active site)

Enzymes are organic molecules which act as catalysts

• Two Analogies– Glove fits over a hand• Glove represents the active site and hand represents

the substrate

– Lock and Key• Lock represents the enzyme’s active site and the key

represents the substrate

Enzymes are organic molecules which act as catalysts

• As catalysts, enzymes influence the rate of reactions– Reactants in the presence of an enzyme will form

products at a faster rate than without the enzyme• Lowers the energy level needed to start the reaction

(referred to Activation Energy)• Catalysts (enzymes) can be reused over and over again

Factors affecting enzyme-catalyzed reactions

• The reaction rate are affected by temperature, pH, and substrate concentration

Factors affecting enzyme-catalyzed reactions

• Temperature:– Both the enzyme and substrate

are in motion and the rate of that motion is dependent on the temperature of the fluids.• Fluids with higher temperature will

have faster-moving molecules.• Reactions are dependent on

molecular collisions and the faster the molecules are moving the more often they collide.

Factors affecting enzyme-catalyzed reactions

• Temperature:– Reactions which use enzymes do

have an upper limit• Limit is based on the temperature

at which the enzyme begins to lose its three-dimensional shape • When the enzyme loses its shape,

including the shape of the active site, it is said to be denatured– Denaturation is sometimes permanent

and sometimes only temporary until the molecule re-forms its normal shape.

Factors affecting enzyme-catalyzed reactions

• pH – The pH of a solution is dependent on the relative

number of hydrogen ions (H+) compared to hydroxide ions (OH-) in the same solution• Any solution that gives off hydroxide ions is a base and

results in a solution with a pH higher than 7• Any solution that give off hydrogen ions is an acid and

results in a solution with a pH lower than 7• Any solution that results in an equal number of

hydrogen ions and hydroxide ions

Factors affecting enzyme-catalyzed reactions

• The negative and positive areas of a substrate must match the opposite charge when the substrate is in the active site of an enzyme in order for enzyme to have catalytic action– When the solution is too acidic, the

relatively large number of hydrogen ions can bond with the negative charges of the enzyme or substrate and not allow proper charge matching between the two (same thing with base)

Factors affecting enzyme-catalyzed reactions

• Most enzymes in the human body are active at or near neutral.– Pepsin is an exception to this rule. Pepsin is an

enzyme that is active in the stomach. The environment of the stomach is highly acidic and pepsin is most active in an acidic pH

Factors affecting enzyme-catalyzed reactions

• Substrate concentration– If there is a constant amount of

enzyme, as the concentration of a substrate increases, the rate of reaction will increase as well.• If there is more reactant molecules,

there are more to collide• There is a limit to this however. The limit

is due to the fact that enzymes have maximum rate at which they can work– If every enzyme molecule is working as fast

as possible, adding more substrate to the solution will not further increase the reaction rate

Use of lactase in the production of lactose-free milk

• Lactose is a disaccharide (glucose + Galactose) milk sugar – Around 90% of all humans show some kind of

lactose intolerance. • People who are lactose intolerant can drink

milk if it is lactose free.• Lactase is an enzyme extracted from yeast

that can digest the milk sugar to glucose and galactose.