Activation Energy …• is the amount of

energy needed to start reaction

• In order to speed up reaction, catalysts are used

• Enzymes are catalysts in cells.

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protein

active site

non-protein

part

holo enzyme (active enzyme)

apoenzyme

Cofactor

- inorganic

- ex: zinc, iron, potassium, copper

Coenzyme

- organic

- ex: vitamins, NAD, FAD, NADP+

Non-protein part can be a cofactor or a coenzyme. It is the part which makes an enzyme active.

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Enzymes…

• Are made up of proteins• Simple Enzymes: only made

up of proteins.• Complex Enzymes: are made

up of proteins + non protein part

Structure of Enzymes…Two major parts:Protein part: Apoenzyme : made up of protein. not catalyze the reaction by itself has to interact with non protein part Non- protein part : Coenzyme: made up of organic molecules

(vitamins) Cofactor: made up of inorganic molecules (K, Ca )+ +

Structure of Enzymes…• Substrate:The

molecule which enzyme acts on

• Active site: Specific region on the enzyme that substrate binds

• Lock and key

• Enzyme –Substrate Complex

• Enzymes are not changed or used up• The same enzyme works for the forward and

reverse of the reactions Lipid +H2O 3 Fatty Acids +Glycerol

• One apoenzyme works with only one coenzyme or cofactor

Lipase

Properties of Enzymes

Specificity: • Enzymes work with only

one type of substrate• Final molecule of the

reaction is product• Not used up, destroyed

at the end of reaction• Can be used over and

over until destroyed by other factors (heat)

Properties of Enzymes…

Reversibility

• Catalyze reactions for forward and reverse directions

• Not determine direction

• Ratio of equilibrium• Only digestive

enzymes catalyze reaction in one way

Naming

• According to molecules they act :

-aseExp: Lipase, Amylase or Pepsin, Tripsin• According to type of

reaction catalizing.

Properties of Enzymes…

The exact point of effect

• Surface of area Wider surface

Greater rate of reaction

Speed

• Speed up reaction• Without enzyme

breaking down takes more time

Properties of Enzymes…

Work in Teams• the product of one

reaction catalyzed

• The substrate for another enzyme

Place of synthesis

• Apoenzyme part is protein, so synthesized in ribosomes just like proteins

• Gene destroyed

• Enzyme not synthesized

• Cell dies

Starch

Amylase Maltase

MaltoseMolecules

Glucose Molecules

There are two models that provide explanation to enzyme action:

1.Lock and Key Model: The substrate(s) fits exactly into the active site of the enzyme.

E + S

E – S E + P

Enzyme

Substrate

Enzyme-substrate complex

(temporary)

Enzyme

Product

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In this model, the enzyme has no rigid shape. Instead the enzyme changes shape slightly as the substrate enters the active site. Once it has changed shape, the enzyme fits tightly around the substrate. As the enzyme embraces the substrate it can weaken the chemical bonds in the substrate, which helps the reaction to proceed.

The enzyme changes shape slightly to grasp the substrate at the active site.

2. Induced Fit Model: @

Characteristics of Enzyme Action:

1. Small amounts of an enzyme can cause the reaction of large quantities of substrate.

- The time needed for an enzyme-substrate complex to form and a reaction to occur is very short.

- A simple enzyme molecule can catalyze thousands of substrate reactions in a second.

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2. Enzymes enable cell reactions to take place at normal temperatures.

0 10 20 30 40 50 60

Optimum temperature for many enzymes (about 36oC)

temperature (oC)

enzyme activity

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At OoC, enzymes do not function although their structure is not changed (they are not denaturated). The temperature at which an enzyme is most effective is called the optimum temperature of an enzyme. At their optimum temperature values enzymes work best.

At higher temperatures (like 55oC) enzymes are denaturated and they lose their properties. So they cannot catalyse a reaction.

3. Each enzyme works best at a certain pH.

0 2 4 6 8 10 12 14

enzyme activity

pH

Optimum pH for pepsin Optimum pH for many

enzymesOptimum pH for trypsin

The effectiveness of an enzyme depends on the pH of medium.

Each enzyme works at different pH values.

5. Some enzymes need substances called activators in order to function. Activators are coenzymes or cofactors.

6. Some enzymes function inside the cell, others act outside of the cell. Ex: pepsin

7. Inhibitors stop or slow down the activity of enzymes.

Inhibitors Antibiotics, pesticides, herbicides, heavy metal ions (Pb+2, Hg+2, Ag+2

), CO, snake and scorpion poisons, CN, Cu

They slow down or stop the activity of enzymes

Inhibitors

Non - Competitive

CompetitiveThose inhibitors compete with the normal substrate in attachment to the active site

They have an influence on the protein part of the enzyme apart from the active site

Enzyme activity

Concentration of inhibitor or activator

enzyme + activator

enzyme

enzyme + inhibitor

8. Amount of water affects the enzyme activity.

If a medium contains less than 15% water, then the enzyme activity stops.

9. Substrate surfacerate of reaction

surface area

• Enzyme action begins from the substrate surface.

• Therefore, increasing surface area of substrate increases the rate of recation until a maximum rate is reached.