1. Enzymes Definition Classification Chemistry Properties
Mechanism of enzyme action
Factors affecting enzyme activity

2. Definition
Enzymes are biocatalyst that speeds up digestion and metabolism.
They are located in the cells, cytoplasm, mitochondria, tissues and body fluids.
Endoenzymes
Enzymes that function within the cells. Most of the enzymes are these types. Eg. metabolic enzymes (cytochrome oxidase)
Exoenzymes
Enzymes that are liberated by cells and catalyse reactions outside the cell. Eg. digestive enzymes (amylase, lipase, protease)

3. Classification
Enzymes are named based on the substrate, reaction, synthesis, chemical nature
Based on the substrate:
Enzymes are named by adding suffix-ase to the name of substrate
Carbohydrates carbohydrases
Protein proteinase
Lipids lipases
Nucleic acids nucleases
Maltose maltase
Lactose lactase
Sucrose sucrase
Urea urease

4. Based on Enzyme Commission of the International Union of Biochemistry, enzymes are classified into six major classes.
Class Reactions catalyzed
Oxidoreductoases Oxidation-reduction
Transferase Transfer group of atoms
Hydrolases Hydrolysis
Lyases Add/remove atoms to/from a
double bond
Isomerases Rearrange atoms
Ligases Combine molecules using
ATP

5. Chemistry of enzymes
Enzymes are specialized large protein molecules made of one or more polypeptide chains.
Enzymes may be composed of only protein or combination of protein and non protein part.
Simple enzymes composed of only protein.
Holoenzymes/conjugated comprise of protein and non protein part.
Protein component - apoenzyme
Non protein part - co-factor
Prosthetic group - co-factor firmly attached to
enzyme
Co-enzyme – co-factor loosely attached to enzyme

6. Properties of Enzymes Proteineous
Accelerate chemical reaction without itself undergoing change
Specific in action
Required in small quantity
Undergoes denaturation
Reversibility of enzyme action

7. Mechanism of enzyme action
Michaelis and Menton proposed a hypothesis for enzyme action.
According to their hypothesis, the following steps occurs:
1. combination of enzyme with substrate
-substrate attaches on the active site of enzyme to form enzyme-substrate complex.
2. Breakdown of substrate
-active site loosens the chemical bonds in the substrate breaking down the substrate into products.

8. 3. Dissociation of enzyme -enzyme finally dissociates from end products and is free to combine another molecule of substrate.

9. Formation of enzyme-substrate complex
Two hypothesis
1. Lock and key hypothesis
2. induced fit hypothesis

10. Lock and Key hypothesis
Proposed by Emil Fisher (1914)
According to this hypothesis, the active sites of enzyme are rigid with proper conformation.
The substrate simply fits into the active site to form a reaction intermediate.

11. Induced fit hypothesis
Proposed by Khosland (1963)
According to this hypothesis, the active sites are flexible.
The enzyme molecule changes shape as the substrate molecules gets close
The substrate changes the conformation of the active site of enzyme closely fitting on it.

12. Induced fit hypothesis

13. Factors affecting enzyme activity
The activity of enzyme is affected by a number of factors.
Temperature
Enzymatic activity increases with increase in temp upto 40⁰C.
Most of the enzyme the optimum temp