Let’s take some daily life examples to understand the concept of enzyme in biology.
- Have you ever wonder how stains on your T-shirt are disappeared when washed with detergent?
- At lunchtime you feel hungry, what happened to the food you ate in the morning?
- In the warm season, why food left on the kitchen slab is spoiled?
The answer to all these questions is enzymes
What is enzyme in biology?
Enzymes are the biological catalyst that speeds up the reaction without being themselves consumed. They are very important for the survival of living organisms.
Now, what does biological catalyst means? Biological meaning that enzymes are related to a living organism or in other words, they are present in living organisms only.
While catalyst is a substance that accelerates a chemical reaction and in the end, it is not changed or reduced.
For example, conversion of A into B required 3 hours, if you add catalyst C into the reaction then conversion of A into B might be done in less than 1 minute. Similarly, in living organisms, enzymes speed up the conversions of substrates into products in a minute amount of time.
Structure of enzymes
They are protein in nature. Hundreds of amino acids join together by peptide bonds to form a polypeptide. Several polypeptides then combine and coil upon themselves to make the globular structure of the enzyme.
Active site, substrate, and products
There is a specific site specialized for catalytic activity on the globular structure of the enzyme known as the active site. The substances or molecules that need to be broken attach themselves to the active site of the enzyme. These substances are called the substrate, while the substances after breakage are called products. For example, amylase is an enzyme that converts starch molecules into simple glucose. In this example, starch is the substrate, while glucose is the product.
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| Structure of enzyme. Image created in BioRender.com |
Cofactor
Some enzymes require non-protein parts or metal to perform their catalytic function. This non-protein part or metal is known as a cofactor. The cofactor is vital for the proper functioning of the enzyme.
It is required for correct attachment of the substrate to the active site of enzyme as well as help in chemical reactions. The cofactor is also known as an activator because it switches on the enzyme or increases its activity.
Coenzyme
The coenzyme is a cofactor that is loosely attached to the enzyme and play important role in enzyme-mediated chemical reactions. Vitamins B12 is a famous coenzyme in living organisms. Other examples of coenzyme included nicotinamide adenine dinucleotide (NAD), nicotinamide adenine dinucleotide phosphate (NADP), and coenzyme A.
Coenzymes can be used again and again and are not consumed during the chemical reactions just like enzymes. This is a reason why you need small quantities of vitamins.
Prosthetic group
The non-protein part covalently bonded to the enzyme is known as the prosthetic group. It might be inorganic (metal) or organic (lipid, carbohydrate, or vitamin).
Apoenzyme
Enzyme becomes inactive if the cofactor is not attached to it. Such an inactive enzyme is called apoenzyme.
Holoenzyme
Holoenzyme is a whole enzyme with its cofactor or coenzyme. It is an active enzyme that is ready to perform catalysis function.
Video Lesson
Location of enzymes
Enzymes are located in the cell according to their function. They can be found freely in cytoplasm, attached to the cell membrane, or inside lysosomes, chloroplast or mitochondria.
Inside lysosomes, digestive enzymes can be found, while chloroplast and mitochondria contain enzymes related to photosynthesis and respiration, respectively. Some enzymes can also be found in ribosomes which are concerned with the synthesis of proteins.
Functions of enzyme
The main function of enzymes is to speed up the chemical reactions. They are involved in digestion, growth, reproduction, healing as well as in defense of cells. Some general enzymes according to their function are:
- Amylase breaks down starch into glucose.
- Protease breaks down protein into amino acids.
- Lipase breaks down lipids into fatty acids and glycerol.
Some questions and answers
1. Define enzyme
A. Enzymes are the biocatalyst that speeds up or regulates the chemical reaction without being consumed. Examples of enzymes include protease (breaking protein into amino acids) and lipase (breaking lipid or fat into glycerol and fatty acids).
2. Are all enzymes protein in nature?
A. Most of the enzymes are protein in nature. However, recent studies have shown that some RNA molecules also act as enzymes and are called ribozymes.
3. List three enzymes that work in the digestive system.
A. Protease, lipase, amylase are three enzymes that help in the digestion of protein, fat, and starch, respectively.
4. Differentiate between cofactor and coenzyme.
A. Cofactor is a non-protein part or metal which is required by the enzyme to perform their catalytic function. It is also known as an activator because it switches on the enzyme or increases its activity. On the other hand, the coenzyme is an organic non-protein molecule that is loosely attached to the enzyme and play important role in enzyme-mediated chemical reactions.
5. How first discovered the enzyme?
A. Wilhelm Kuhne was the first person to discover the enzyme in 1978. He called that molecule enzyme.
6. State three functions performed by enzymes.
A. Enzymes are involved in digestion, growth, reproduction, healing as well as in defense of cells.
7. Where does substrate attaches to the enzyme surface?
A. There is a specific site specialized for catalytic activity on the globular structure of the enzyme known as the active site. Substrates attach themselves at the active site of the enzyme and are converted into products.
8. Does holoenzyme has cofactor?
A. Holoenzyme is a whole enzyme with its cofactor or coenzyme. It is an active enzyme that is ready to perform catalysis function.
9. Where do enzymes are located in a cell?
A. Enzymes can be found freely in cytoplasm, attached to the cell membrane, or inside lysosomes, chloroplast or mitochondria.
10. Vitamin B12 is coenzyme or cofactor?
A. Vitamins B12 is a famous coenzyme present in living organisms.
References
- Abeles, R. H., & Dolphin, D. (1976). The vitamin B12 coenzyme. Accounts of Chemical Research, 9(3), 114-120.
- Vandamme, E. J. (1992). Production of vitamins, coenzymes and related biochemicals by biotechnological processes. Journal of Chemical Technology & Biotechnology, 53(4), 313-327.
- Ferrer, J. L., Austin, M. B., Stewart Jr, C., & Noel, J. P. (2008). Structure and function of enzymes involved in the biosynthesis of phenylpropanoids. Plant Physiology and Biochemistry, 46(3), 356-370.
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