Enzymes Lab 5. Enzymes Reaction characteristics – Enzymes are catalysts: substances that speed up...

Enzymes

Lab 5

Enzymes

• Reaction characteristics– Enzymes are catalysts: substances that speed up

or facilitate a chemical reaction by LOWERING the activation energy

– Energy of Activation: Amount of energy needed to start a reaction

Activation Energy

Endergonic Reaction Exergonic ReactionRequires energy Releases energy

Ways to Lower the Energy of Activation

• Enzymes– Protein catalysts that lower the amount of energy

needed to get the chemical reaction going– They maintain their original chemical composition while

causing a change in the substrate (reactant)– The specific shape of the enzyme allows it to catalyze

only one reaction– Active site = place on the enzyme that binds substrate– Since the enzyme does NOT change its shape, it is

REUSABLE

Altering the Rate of an Enzymatic Reaction

1. Temperature2. pH

Altering Temperature• Gradual ↑ in temperature will INCREASE the rate of the

reaction – How? By an increase in the speed at which the molecules are

moving– This results in increased collisions of the enzyme and substrate

• Extremely low temperatures will SLOW DOWN or STOP the reaction– Why? The enzyme and substrate are moving too slow to collide

• Extremely high temperatures will STOP the reaction– Why? Because the enzyme will be denatured!

Altering pH

• Alterations in pH will STOP the reaction because the enzyme will be denatured!

• Remember, a small pH change does NOT correlate with a small change in the pH of the environment!!– Why? pH scale is logarithmic

Enzyme Questions• The presence of an enzyme _____ the required

energy of activation of a chemical reaction.• Generally, as the amount of substrate is increased,

the rate of the reaction _____.• Raising the temperature to over 50C ___ the rate of

an enzymatic reaction.• Lowering the pH for an enzyme that works best in a

highly acidic environment ___ the rate for the reaction.