Hello, welcome to this hall on the topic; types of digestive enzymes, classifications and characteristics of enzymes in biology.
Table Of Contents
- Definition of enzyme
- Types of digestive enzymes
- Classification of enzymes
- Characteristics of enzymes
- Alimentary canal and digestion of food in man.
- Functions of enzymes
- Revision questions
Digestive Enzymes
Definition: An enzyme is an organic catalyst, usually proteinous in nature, which promotes or speed up chemical changes in living cells but are not themselves used up in the process. Enzymes accelerate metabolic reactions without changing their composition in the process.
Types Of Enzymes
There are two major types of enzymes. These are:
- Intracellular enzymes: These enzymes function inside the cells of living organisms. Common examples are the enzymes that catalyse cell respiration inside mitochondria.
- Extracellular enzymes: These are enzymes which carry out their functions outside the cells. Examples of extracellular enzymes are the digestive enzymes.
Characteristics Of Enzymes
- Remain chemically unchained at the end of a reaction.
- Are specific in action/one or a group of enzymes will act on specific substrate.
- Required is small quantities.
- Act best over a specific range of temperature/between 35° to 40°C.
- They are denature/destroyed at high temperature/inactivated at very low temperature.
- Act best at specific pH (either acidic or alkaline).
- Their action is reversible.
- Enzymes action is retarded by poison or inhibitors.
- Some are inactive and require a co-enzyme/agent to activate them.
- They can function outside the body of the organism that produces them.
- Enzymes are protein in nature.
Classification Of Enzymes
The new method of classifying enzymes is based on the nature of chemical changes brought about on a substrate. Such changes may involve oxidation in which case the enzyme will be called an oxidase.
It is it is important to note that the earlier classification based on the substrate an enzyme works on, e.g, amylase for maltose, proteases for protein or lipases for lipids are no longer correct or biochemically acceptable.
As a result of the above information, enzymes are classified as shown below:
Classes Of Enzymes And Action Of Substrate
1. Hydrolases
- Action of substrate: Catalyse the hydrolytic cleavage or breaking up of carbon – oxygen, carbon nitrogen or carbon – bonds.
2. Oxido-reductases
- Action substrate: Catalyse the joining together of two molecules with accompanying hydrolysis of a higher energy bond.
3. Transferases Enzymes
- Action on substrate: Catalyse a reaction of a generation from: A+B+CIA+C+B
4. Isomerase Enzymes
- Action on substrate: Work on isomers and usually change the spatial configuration of a molecule in a living cell.
5. Ligases enzymes
- Action and substrate: Catalyse the joining together of two molecules with accompanying hydrolysis of a higher energy bond.
6. Lyases enzymes
- Action on substrate: Catalyse the breaking up of bond by elimination or addition reactions.
Alimentary Canal And Digestion Of Food In Man
The alimentary canal of Man includes the:
- Mouth
- Oesophagus
- Stomach
- Duodenum
- Small intestine or ileum
- Caecum
- Appendix
- Large intestine or colon
- Rectum
- Anus.
Description, Importance And Uses
The Mouth
- The alimentary canal of Man starts from the mouth. The mouth contains the teeth, salivary gland and tongue.
The Teeth
- The teeth are used to cut, grind or chew food into tiny particles.
- They expose large area of food for the action of enzymes.
The Uses Of Tongue
- The tongue rolls the food into bolus
- It aid movement of food into the mouth.
- It allows mixing of food with saliva or ptyalin.
- It aid swallowing of food into the gullet of oesophagus.
The Salivary Gland
- The salivary gland secrete saliva which contains an enzyme called ptyalin. Ptyalin breaks down starch into maltose which is later swallowed into the gullet in form of bolus.
- It allows easy chewing or movement of food in the mouth for swallowing.
- It also serves as solvent for food.
Oesophagus Or Gullet
- The oesophagus connect the mouth to the stomach. The food swallowed is passed down to the oesophagus by a peristastic movement into the stomach.
The Stomach
- In the stomach, the food is temporary stored for few hours and it is released at a regular interval by opening of the pylotic sphincter. In the stomach, the gastric gland secretes gastric juice which contains two enzymes – renin and pepsin.
Duodenum
- Amylase: This convert starch to maltose.
- Lipase: Lipase convert fats and oils to fatty acid and glycerol.
- Trypsin: It converts protein and peptones to polypeptides.
Small Intestine
- The small intestine or ileum is found between the duodenum and the large intestine. The two major events take place in the small intestine are: (a) digestion and (b) absorption of the digested food.
Caecum And Appendix
- In man, the functions of caecum and appendix are not well-known by the caecum usually contain some bacteria which aid minor digestion of cellulose. Some vitamins such as K and B-complex are partially synthesized in this region.
Large Intestine
- The undigested food passes into the colon or large intestine. Here, water is absorbed. This absorption of water concentrate the waste product and turn them into faeces. This faeces is passed into the rectum and finally out of the body through the anus
Functions Of Digestive Enzymes
Enzymes perform the following functions:
- Enzymes help in breaking down proteins in food into amino acids.
- They also help in breaking down fats and oils into fatty acid and glycerol.
- They help in breaking down of carbohydrates into glucose, fructose and galactose.
- They aid the absorption of digested food through the addition of water to the food.
Revision Questions On This Class
- (a) What is the definition of enzyme? (b) State two types of enzymes
- Outline the classification of enzymes.
- Discuss the 5 classes of enzymes and thier action of substrate.
- State 4 functions of digestive enzymes.
- Briefly explain the alimentary canal and digestion of food in Man.