Introduction
Enzymes are proteinaceous molecules that help in catalysing the biochemical reactions in our body. Due to this property, they are also known as biocatalysts. As they are proteinaceous in nature, they also possess secondary and tertiary structures. When the enzymes are present in their tertiary structure, their protein chains get folded upon themselves, and due to this, many crevices are formed that are termed as active. These active sites are mainly responsible for the mechanism of enzyme action and also the mechanism of enzyme catalysis.
The human body is made up of many cells, tissues, and organs, and all of them work accordingly. The body releases certain types of chemicals known as enzymes. These enzymes control biological processes like respiration, reproduction, excretion, digestion, and excretion, and try to act as per the body clock. They are important not only to human survival, but also to look after the same biological activities in animals. Mostly, they are made up of proteins which act as a catalyst in a biological process.
The initial stage of biological activity is triggered by the enzyme which interacts with the molecule in the human body, called a “substrate”. They are further processed to form “products”. Mostly, the enzymes have proteins, except those related to the RNA. We can find enzymes in most of the organs and cells of human and animal bodies. Intracellular enzymes are the enzymes that help in metabolic activity. Enzymes are generally made up of chains of amino acids and are three dimensional in structure. Enzymes are temperature and pH sensitive, they lose their function when the pH or temperature increases or decreases. They vary in size based on the amino acid molecules.
Enzymes are divided into oxidoreductases, transferases, hydrolases, lyases, isomerases, and ligases; this division is based on the functional use of the enzymes. Oxidoreductases are enzymes that transfer electrons from one place to another place and control oxidation activity. Transferases are the enzymes that help in transporting from the donors to the receptors in the human body. Hydrolases help in catalysing hydrolysis activity in the human body. Lyases are the enzymes that add ammonia, water, and carbon dioxide to the bonds.
Enzyme Type and Functions
Enzyme Action
To understand the enzyme mechanism and enzyme action, two hypotheses were proposed. They were:
1. Lock and Key Hypothesis:
This hypothesis was proposed by Emil Fischer in 1894. This hypothesis helps us understand the mechanism of action of enzymes. According to this hypothesis, the enzyme and substrate molecules exhibit various geometrical shapes and these shapes are very specific. Just as the lock and key model, this hypothesis states that the active sites of enzymes act as a lock that has specific molecules, such as -COOH and -SH. These enzyme molecules can only be opened with the help of specific substrate complexes. This hypothesis explains the specificity of enzymes and also the mode of action of enzymes. The substrate comes in contact with the active site of the enzyme complex and then forms an enzyme-substrate complex. When this complex is formed, it undergoes chemical changes, and then, eventually, a product is formed. When this product is formed, it no longer fits into the active site and escapes out into the surrounding area. In this way, the active site is available again for fresh substrates. By this hypothesis, it can be concluded that a very small amount of enzyme can act upon large substrate molecules. It also explains how the enzymes are not used in the reaction and can be used again and again. Moreover, it helps us to understand the mechanism of competitive inhibition.
2. Induced Fit Hypothesis:
Koshland proposed this hypothesis in the year 1960. This hypothesis is actually quite different from the previous hypothesis. It states that the active site of the enzyme is flexible in shape and can change its shape according to the nature of the substrate, which means that it can form its active site complementary to the substrate. It is easy to understand how a hand induces a change in the glove, that is, the same way an active site induces a change in the chemical substrate. The substrate gets into the active site of the enzyme. According to this, the structure of the active site of an enzyme is flexible. There are two types of groups that are present in the active site of the enzyme. One is a buttressing group and the other is a catalytic group. The buttressing group helps in supporting the substrate, whereas the catalytic group helps to explain the mechanism of enzyme catalyses. When the buttressing group comes in contact with the substrate, changes take place in the active site and these changes help to bring the catalytic group opposite to the substrate bonds that are needed to be broken. The above two models help us deeply understand and describe the mechanism of enzyme action.
Mechanism of Enzyme Catalysis
Enzymes are responsible for bringing out the high rate of chemical conversions. The substrates are converted into products. The substrates get bound to the active site of the enzyme, and then, there are changes in the enzyme complex, which bring about changes in the enzyme-substrate complex, and thus, a product is formed from the substrate. This enzyme-substrate complex is formed for a very short time and is thus known as a transient phenomenon. The transient state structure is formed when the substrate gets bound to the active site of the enzyme. Then, some making/breaking of bonds takes place and a final product is formed. Activation energy is the energy that is required to start the reaction. Enzymes work by lowering these high activation energies of the reactions.
Nature of Enzyme Action
There is a presence of an active site on each enzyme molecule. Substrate comes in contact with the enzyme and then an enzyme-substrate complex is formed. After a while, the enzyme-substrate complex changes to enzyme-product complex, and then the product gets separated from it. This way, the enzyme is not used up in the reaction. The catalytic cycle helps to explain the mechanism of enzyme action through the following points:
The substrate gets bound to the active site.
This induces an alteration in the shape of the enzyme.
The enzyme-product complex is formed by making and breaking bonds.
Enzyme releases away from the product and it is available again for a fresh batch of substrates.
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Factors Affecting Mechanism of Enzyme Catalysis
Three factors are responsible for affecting the mechanism of enzyme catalysis:
Temperature: Enzyme catalysis works in a narrow range of temperature. Optimum temperature is the temperature at which the enzymes show the highest catalytic activity. Anything above and below the optimum temperature declines the enzyme activity. Low temperature makes the enzymes inactive, whereas high temperature denatures the structure of enzymes.
Hydrogen Ion Concentration: As there is an optimum temperature required for the enzyme to function, there is also an optimum pH concentration. Any fall or rise in pH reduces the activity of enzymes. Some enzymes show good catalytic activity in acidic medium, whereas some show good activity in alkaline medium. Every enzyme has an optimum pH, where their activity is maximum.
Substrate Concentration: Substrates act on enzymes and are then changed to products. An increase in the concentration of substrate results in increasing the velocity of enzymes.
Mechanism of Enzyme Action in Biochemistry
There are two types of changes observed in chemical compounds, that are, physical change and chemical change. Physical changes take place by only changing the shape of the compound. No bonds are broken in physical changes. Whereas, in chemical changes, new bonds are formed and broken during the transformation process. When the ice melts into water, it is termed a physical change as there is a change of state. Hydrolysis of starch into glucose is a type of chemical change. The rate of both these physical and chemical processes is the amount of product formed per unit of time. When a direction is specified to rate, it is called velocity. Temperature influences the rate of chemical and physical processes. Various types of enzymes are present and each has a unique catalytic activity or a unique chemical or metabolic reaction. A metabolic pathway is a pathway when one enzyme catalyses the reaction at different steps. When there are one or two additional reactions in the metabolic pathway, it gives rise to a variety of end products. So, this helps us to understand the mechanism of enzyme action in biochemistry.
Conclusion
From the above discussion, we can conclude that enzymes are proteinaceous in nature and are involved in catalysing various biological and biochemical processes. Different models are proposed to understand the mechanism of enzyme action, such as the Lock and Key hypothesis and Induced Fit model. A basic understanding is that enzymes have an active site on them and the substrates get bound to it, and then change into the product. In this way, the enzyme can be used again and again as it is not used in the reaction. Temperature, pH, and substrate concentration are the factors that can affect the rate of enzyme action.
FAQs on Mechanism of Enzyme Action
1. What is the fundamental mechanism of enzyme action?
The fundamental mechanism of enzyme action involves an enzyme binding with a specific substrate to form a temporary, unstable enzyme-substrate complex. This complex lowers the activation energy required for the reaction to proceed. The enzyme's active site facilitates the chemical conversion of the substrate into a product, forming an enzyme-product complex. Finally, the enzyme releases the product, returning to its original state, ready to catalyse another reaction.
2. What are the key steps in the catalytic cycle of an enzyme?
The catalytic cycle of an enzyme, as per the CBSE Class 11 curriculum, can be summarised in four key steps:
- Substrate Binding: The substrate binds to the specific active site on the enzyme.
- Enzyme-Substrate Complex Formation: This binding induces a change in the enzyme's shape, leading to a tighter fit and the formation of the enzyme-substrate complex.
- Catalysis: The active site performs the catalytic action, breaking or forming chemical bonds to convert the substrate into the product.
- Product Release: The product, having a different shape from the substrate, detaches from the active site, leaving the enzyme free to bind with another substrate molecule.
3. How does the Induced Fit model differ from the Lock and Key hypothesis?
The two models explain the enzyme-substrate interaction differently. The Lock and Key hypothesis proposed that the enzyme's active site has a rigid, fixed shape, perfectly complementary to its specific substrate, like a key fitting into a lock. In contrast, the Induced Fit model suggests that the active site is flexible. The initial binding of the substrate induces a conformational change in the enzyme, optimising the fit for catalysis. This model is more widely accepted as it better explains the dynamic nature of enzyme function.
4. What are the primary factors that affect the rate of enzyme activity?
The rate of enzyme activity is primarily influenced by three main factors:
- Temperature: Each enzyme has an optimum temperature at which it functions most effectively. Activity decreases at lower temperatures and at higher temperatures, the enzyme can become denatured.
- pH: Similar to temperature, every enzyme has an optimum pH. Extreme changes in pH can alter the ionisation of amino acids in the active site, disrupting the enzyme's structure and function.
- Substrate Concentration: As substrate concentration increases, the rate of reaction increases until the enzyme active sites become saturated with substrate. At this point, the reaction rate reaches its maximum velocity (Vmax) and plateaus.
5. Why does enzyme activity decline at temperatures above the optimum?
Enzyme activity declines sharply at temperatures above the optimum because high thermal energy disrupts the weak hydrogen bonds that maintain the enzyme's specific three-dimensional tertiary structure. This process, known as denaturation, alters the shape of the active site, making it unable to bind effectively with its substrate. The loss of structure leads to a rapid loss of catalytic function. This change is often irreversible.
6. Are all enzymes made of protein? Explain with an example.
While the vast majority of enzymes are proteinaceous in nature, there are exceptions. Not all enzymes are proteins. A notable example is ribozymes, which are RNA molecules that possess catalytic activity. For instance, ribozymes play a crucial role in the ribosome, where they help catalyse the formation of peptide bonds during protein synthesis. This discovery challenged the long-held belief that only proteins could function as biological catalysts.
7. How do enzymes (biocatalysts) differ from inorganic catalysts?
Enzymes, or biocatalysts, differ significantly from inorganic catalysts in several ways:
- Specificity: Enzymes are highly specific, typically catalysing only one or a very small number of reactions. Inorganic catalysts are often less specific.
- Efficiency: Enzymes are far more efficient, speeding up reactions by millions of times under mild conditions.
- Operating Conditions: Enzymes function optimally under specific, mild physiological conditions of temperature and pH. Inorganic catalysts often require high temperatures and pressures.
- Structure: Enzymes are complex, large protein (or RNA) molecules, whereas inorganic catalysts are usually simple, small molecules or metal ions.
8. What is the importance of enzyme action in everyday industrial applications?
The mechanism of enzyme action is crucial for many industrial processes. For example:
- In the food industry, proteases are used to tenderise meat, and amylases are used in baking and brewing to break down starch into sugars.
- In detergents, enzymes like lipases and proteases are added to break down fat and protein stains, allowing them to work effectively at lower washing temperatures.
- In the pharmaceutical industry, enzymes are used in the synthesis of antibiotics and other drugs.
