enzymes: molecules that speed up reactions. what are enzymes enzymes are proteins that speed up the...

Enzymes: Molecules That Speed Up

Reactions

What are Enzymes

• Enzymes are proteins that speed up the rate of all reactions. Also know as Biological Catalysts.

• Enzymes lower the Activation Energy, which is the energy required to break down existing bonds between atoms

• Enzymes speed up two types of reactions:1. Exergonic Reactions

2. Endergonic Reactions

Enzyme 3D Molecular Model

Activesite

(a) (b)

How Enzymes Work• Every cell carries out many thousands of

metabolic reactions per second. Each reaction starts with Reactants (molecules undergoing the reaction) and ends up with a Product or Products.

• Reactants (also known as Substrates) bind to the Active Site of the enzyme and form an Enzyme-Substrate Complex. At this time reactants undergo chemical changes that involve the “making or breaking” bonds

• Then reactants are transformed into products

Enzymes at Work

Enzymes at Work

Enzyme Reactions

• Enzymes speed up two types of reactions:

1. Exergonic Reactions: Bond Breaking

2. Endergonic Reactions: Bond Making

Exergonic Reactions

• Reactions that break bonds (bond breaking)

• Release energy stored within the bonds

Energy is Released

Endergonic Reactions

• Reactions that build bonds (bond making)

• Require the input of energy to make bonds

Energy is Required

Factors Affecting Enzymes1. Enzyme Concentration

• The total amount of enzyme present at the time of the reaction

2. Temperature• Enzymes work best at an optimum temperature• Most enzymes in humans work best at 37ºC

3. pH• Most enzymes are effective only in a narrow pH

range • Enzymes work best at on optimum pH

Factors Affecting Enzymes4. Cofactors: Substances that bind to enzymes and

help enzymes work best

• Organic Cofactors: Vitamins and other compounds made from vitamins. Organic cofactors are alos known as coenzymesEx: Vitamins A, B, D, E, K, etc.

• Inorganic Cofactors: Metal atoms such as Copper, Zink, Magnesium, Iron, etc.

5. Inhibitors: Substances that interfere with enzymes, reducing or even destroying the enzyme activityEx: Cyanide, poisons, pesticides, painkillers, etc

Figure 6-12Page 132

Mosthuman

enzymes

Pepsin

Trypsin

Enzymes ofheal-tolerant

bacteria

pH

Rat

e o

f re

acti

on

Rat

e o

f re

acti

on

Temperature (˚C)

(a)

(b)

Rat

e o

f re

acti

on

Rat

e o

f re

acti

on

Enzyme concentration Substrate concentration

(a) (b)