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In this article, we will discuss the mechanism of action of enzymes and their denaturation. But before proceeding to discuss the action and denaturation of enzymes, first, let us recall what are enzymes and what role they play in our digestion.
What are Enzymes?
Enzymes are defined as:
The proteins that act as a biological catalyst (speed up the reactions) are referred to as enzymes
It should be kept in mind that while speeding up the reactions, enzymes do not become a part of those reactions or change their nature. It means that throughout the reaction, their nature remains unchanged.
Some of the key points related to enzymes are summarized below:
- Enzymes are proteins that play the role of the biological catalyst and speed up the chemical reactions. They do not change or get used up in the reaction
- They are composed of living cells, therefore we call them biological
- Enzymes play a vital role in all living organisms because they help in carrying out the metabolic reactions in the bodies of living organisms at a rate that is critical for sustaining life. For instance, due to digestive enzymes in our body, we can digest our food within hours. In the absence of these enzymes, our body may take weeks to digest the food.
Enzymes and Food
We already know that biological molecules such as carbohydrates, lipids, and proteins are required by our body for growth, repair, and metabolism. These molecules are made up of chemicals that are essential for our growth. Our food is the source of these biological molecules. Initially, these molecules are quite large and cannot pass from the intestine to our blood. Our digestive system breaks down these molecules into simpler ones. In the next sections, we will discuss which enzymes in our bodies are responsible for breaking down carbohydrates, lipids, and proteins in our body.
Carbohydrates
Examples of carbohydrates include starch, sucrose, glycogen, and glucose. The primary building block of a carbohydrate molecule is a monosaccharide. A monosaccharide is a simple sugar that includes fructose and glucose. Disaccharides (two monosaccharides) and polysaccharides (long chains of monosaccharides) are created by joining monosaccharides together through enzymes.
The parts of our body where these enzymes are produced include our mouth (in saliva), small intestine, and pancreas.
Proteins
Proteins refer to the large molecules that are composed of long-chain amino acids. Enzymes, collagen, haemoglobin, and keratin in our body are all made up of proteins. Each protein is composed of hundreds or even thousands of amino acids joined together in a distinctive sequence and folded into a specific shape. Due to this, every protein has unique properties which set it apart from other proteins.
Enzymes that break down proteins
The enzymes that break down proteins in our food into amino acids are known as proteases. Different enzymes also join the amino acids together to create new proteins that are required by our body. The parts of our body where protease enzymes are produced include our stomach, small intestine, and pancreas.
Lipids
Lipids include fats and oils. They are large molecules that are composed of smaller units of glycerol and fatty acids.
Enzymes that break down lipids
Digestive enzymes known as lipase break down lipids in our food into glycerol and fatty acids. The parts of our body where these enzymes are produced include the pancreas and small intestine.
We know that enzymes are proteins that act as biological catalysts. They are neither being used up in the reaction nor changing their state. They only speed up the reaction in our bodies. They work on the substrate to form product(s). Enzymes are folded in complex 3D shapes that enable smaller molecules to fit into them. The active site of the enzyme and the substrate have a complementary shape. Active site refers to the place where the smaller molecules fit. The enzymes are specific to the substrate, i.e., that it will only act upon a single substrate. Enzyme-substrate complexes are created when enzymes and substrates collide with each other.
Lock and Key Hypothesis
Enzymes break down the substrate, but in a few cases, they also build them. When the reaction happens the products are released and enzymes get free afterward to act again. This theory is referred to as a lock and key model. It tells us why each enzyme acts upon one substrate only. In other words, we can say that according to the lock and key hypothesis, each kind of enzyme can catalyze one type of reaction only. There may be an exception where an enzyme can catalyze some types of reactions.
Example
For instance, the amylase in its active site is only complementary to the starch. Hence, it will break down starch only, rather than protein or fat.
What are Inhibitors?
Inhibitors refer to the molecules that partially fit into an enzyme's active site, however, they are not broken down. Unlike enzymes that speed up the reaction, inhibitors inhibit the reaction. When they are in the active site, the substrate cannot enter to be broken down. Hence, in this way, they slow down the rate of reaction.
In the next section of the article, we will discuss the mechanisms of enzyme action and their denaturation.
The Mechanism of Enzyme Action
The mechanism of enzyme action is explained below:
- Enzymes are specific to a single substrate. This is because the active site of the enzyme where the substrate is attached is of a complementary shape to the substrate.
- As the substrate moves into the enzyme's active site, an enzyme-substrate complex is produced
- When the reaction is completed, the products leave the enzyme's active site and the enzyme becomes free to be taken up by another substrate
Summary of the Steps
The steps involved in the enzyme-catalyzed reaction are summarized below:
Step 1: Enzymes along with the substrates move randomly in a solution
Step 2: An enzyme-substrate complex is produced and the reaction occurs when an enzyme and its complementary substrate collide with each other
Step 3: A product(s) is created and released from the active site. The enzyme remains unchanged and is used to catalyze the next reactions.
In the next section, we will discuss the denaturation of enzymes.
Denaturation of Enzymes
The following points explain the denaturation of enzymes:
- Enzymes refer to proteins that are of a specific shape. They are held in place by bonds.
- Bonds are very important around the active site because the specific shape of this region of enzyme basically ensures that the substrate will fit into the active site and allow the reaction to go further.
- If the bonds that are holding these enzymes together are broken or disrupted, then the active site of the enzyme will lose its shape. This is referred to as the denaturation of the enzyme.
What Happens When Denaturation of Enzymes Occur?
When enzymes are denatured, then the substrate cannot fit into them because of the loss of their active site. Remember that the denaturation of enzymes is irreversible. It means that once they are denatured, they cannot regain their original shape. As a result, the reaction they are speeding up will stop. Certain factors such as extremes of pH and high temperatures and cause denaturation of enzymes.
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