How Do Enzymes Work? Understanding Their Structure and Action
Enzymes are protein catalysts that speed up the rate of biochemical reactions but do not change the structure of the final product. Like a catalyst, without being used up, the enzymes control the speed and specificity of the reaction, but unlike catalysts, only living cells generate enzymes.
The rate of biochemical reaction often influences enzymes like catalysts, so that they can take place at a relatively low temperature. The enzymes are thus known to lower the energy of activation. In certain cases, the biological response is initiated by enzymes.
The term enzyme is derived from the Greek word enzymes, meaning 'in yeast' since the enzyme activity in living organisms was first discovered by the yeast cells. The enzyme term was invented by W. Kuhne in 1878.
Properties of Enzymes can be classified into:
Physical properties
Chemical Properties
General properties
Physical Properties of Enzymes
Physically, enzymes act as colloids or as high-molecular-weight compounds.
At a temperature below the boiling point of the water, enzymes are killed or inactivated.
Most enzymes in the liquid medium are inactivated at 60 degrees Celsius.
Extracting dried enzymes can withstand temperatures of 100 degrees Celsius to 120 degrees Celsius or even higher. Enzymes are, therefore, thermos-labile.
The optimum activity of each enzyme is always at a particular temperature, which typically varies from 25 degrees Celsius to 45 degrees Celsius. At 37 degrees Celsius, enzyme action is strongest and as temperatures rise above 60 degrees Celsius, enzymes become inactive.
Chemical Properties of Enzymes
Catalytic Properties: Biological catalysts are enzymes. The greater amounts of compounds are catalyzed by a small number of enzymes. This means that enzymes are highly capable of turning giant amounts of the substrate into a substance. Enzymes improve the reaction rate and remain unaffected by the reaction they catalyze.
Enzyme Specificity: Enzymes are extremely variable in nature, which means that a specific enzyme can catalyze a specific reaction. For example, only sucrose hydrolysis can be catalyzed by Enzyme sucrase.
General Properties of Enzymes
Enzymes initiate the biochemical reaction rate and accelerate it.
The activity of enzymes depends on the medium acidity of the (pH specific). At a particular pH, each catalyst is most active. PH 2 for pepsin, pH 8.5 for trypsin, for example. At near neutral pH, most intracellular enzymes act.
The reaction in either direction can be accelerated by enzymes.
Both enzymes have active sites involved in biochemical reactions.
Enzymes, often soluble in water, dilute glycerol, NaCl, and dilute alcohol, are very unstable compounds.
At the optimum temperature, enzymes work aggressively.
In nature, all enzymes are proteins, but all proteins may not be enzymes.
Enzymes lower the molecule's activation energy so that the biochemical reaction can take place at the normal temperature of the body, which is 37 degrees Celsius.
Chemical Nature of Enzymes
Proteins are all enzymes, but all proteins are not enzymes. However, there are several conjugated enzymes bound to the protein portion of the enzyme with a non-protein moiety, which is called the Apo enzyme. The portion of the non-protein is known as the cofactor. If the co-factor, like Potassium, calcium, magnesium, manganese, is of an inorganic type, it is known as the prosthetic group. In general, the prosthetic group is closely bound to the protein portion of the enzyme and it is difficult to separate it with a simple technique such as diffusion. The enzyme is called a holoenzyme with the prosthetic group and the Apo enzyme.
If organic molds such as NADP, NAD, FAD, etc. are co-factor attached to an enzyme protein, it is called a coenzyme. In general, a coenzyme is loosely bound to the Apoenzyme and can be isolated easily from the prosthetic group. Often, coenzymes are heat tolerant.
Mechanism of Enzyme Action
The behavior of the enzyme is greatly influenced by the reaction conditions; unique temperature and pH conditions are needed for most enzymes. The lock and key model will better describe the mechanism of enzyme action and its selectivity.
By providing a surface for the substrate, an enzyme brings down the activation energy of the reaction. The mechanism of enzyme action has been a matter of research ever since their identification. The enzyme provides the substrate with a surface for the response to take place. A complex (intermediate) forms the substrate, which then supplies the substance and the enzyme. There is a complex configuration of the substrate that is connected to the enzyme and can only fit into a specific enzyme similar to that of a lock that has a particular key.
The activity of enzymes in the biological system and their selective nature have led to many biological catalysts being produced. Scientists are now working on several artificial enzymes being synthesized. In the coming days, the analysis of bio-reactions and their catalysts will serve as the basis for making wonders.
Difference between ApoEnzyme and Cofactor
Apo enzyme is being referred to as a macromolecule here which represents the protein part of the enzyme. Whereas the cofactor is defined as the micro molecule which is the non-protein part of the enzyme.
When the cofactor is present, then only the Apo enzyme acts whereas the cofactor becomes a metal ion or a complex organic compound which makes the Apo enzyme functional.
The Apo enzyme is said to be thermo-labile and the co-factor is thermostable.
Enzymatic activities are conducted by the Apo enzyme whereas co-factor activities mold the enzyme and coenzyme which carries the groups removed from the substrate.
The enzyme system is specified in the Apo enzyme whereas there are many enzymes for co-factors.
What are the Most Important Properties of an Enzyme?
Catalytic Property: The extraordinary catalytic power is present in the enzymes which are active in very small quantities. A large quantity of substrate can be converted with the help of a small amount of the enzyme. After the reaction the enzyme becomes unchanged. The range of the turnover of the enzymes is from 0.5 to 600000. The number of substrate molecules that are converted from one molecule of enzymes per second at the time of its activeness is saturated with the substrate is called turnover.
Specificity: There is another level of specificity in the enzymes where particular enzymes are acted upon the particular substrates only. The enzymes are affected by specific types of reactions that may not be too strong in some rare instances. There are different types of specificity in enzymes:
Bond Specificity: Also referred to as relative specification. Here the enzymes are directly related to the obligation. Eg; peptidase is a specific bond or peptide, lipase is directly related to the ester bond in lipid.
Group Specificity: Also called structural specifications. Here are group-specific enzymes. Eg; pepsin hydrolyses peptide bonds between groups of amino acids that are part of the fragrant amino acids.
Substrate Specificity: Also called complete specification. Here the enzyme only works on a particular substrate. Eg; arginine only works on arginine; Carbonic anhydrase only works on carbonic acid.
Optical Specificity: Also called stereo-specificity. This is the highest specificity expressed by an enzyme. Here the enzymes are targeted not only at the substrate but also at their optical activation. For E.g. L amino acid oxidase works only for L-amino acids, not for D-amino acids. Similarly, alpha-amylase works only in the alpha-14 glycosidic interaction of starch and glycogen. Unable to hydrolyze the beta-14 glycosidic binding of cellulose.
Cofactor Specificity: This indicates that the enzymes are not only specific to the substrate but also specific to its cofactors.
Geometric Specificity: Here the specification is very small. Other enzymes will work on a small array of similar substrates with the geometry of the same structure. E.g. Alcohol dehydrogenase can convert methanol and n-propanol into aldehydes.
Reversibility: Most of the enzymes in catalyzed reactions are reversed. Reversal of response depends on cell requirements. In some cases, there are different enzymes for reaction and regression. Some enzyme-induced reactions are irreversible.
FAQs on Properties of Enzymes: Comprehensive Guide for Students
1. What are the main properties of enzymes explained for Class 12?
Enzymes are biological catalysts with several distinct properties crucial for biochemical reactions. The main properties include:
- Catalytic Efficiency: Enzymes are highly efficient, accelerating reaction rates by millions of times. A small amount of an enzyme can process a large amount of substrate.
- High Specificity: Enzymes are very specific. A particular enzyme typically catalyses only one type of reaction or acts on a specific substrate. For example, the enzyme urease only acts on urea.
- Sensitivity to Temperature and pH: Each enzyme functions best within a narrow range of temperature and pH, known as the optimum temperature and pH. Extreme changes can cause denaturation, where the enzyme loses its shape and activity.
- Proteinaceous Nature: Almost all known enzymes are proteins (though some RNA molecules, called ribozymes, also act as catalysts). This protein structure is essential for their function.
- Reversibility: Most enzyme-catalysed reactions are reversible, meaning the enzyme can catalyse the reaction in both forward and reverse directions depending on cellular needs.
2. How do enzymes differ from inorganic catalysts?
While both enzymes and inorganic catalysts speed up reactions without being consumed, they differ in several key ways:
- Efficiency: Enzymes are far more efficient than inorganic catalysts under biological conditions.
- Specificity: Enzymes are highly specific to their substrate, whereas inorganic catalysts are often non-specific and can catalyse a wide range of reactions.
- Operating Conditions: Enzymes function under mild conditions of temperature and pH typical of living cells. Inorganic catalysts often require high temperatures and pressures.
- Regulation: Enzyme activity can be precisely regulated by other molecules (inhibitors or activators), allowing cells to control metabolic pathways. The activity of inorganic catalysts is harder to control.
- Structure: Enzymes are complex globular proteins, while inorganic catalysts are simple inorganic molecules or metal ions.
3. Why is enzyme specificity so important for living organisms?
Enzyme specificity is crucial for maintaining order and control within a cell. Because each enzyme catalyses only a specific reaction, it ensures that metabolic pathways proceed correctly without producing unwanted side-products. This high degree of control allows for the precise regulation of thousands of complex biochemical reactions simultaneously, preventing metabolic chaos and ensuring that energy and resources are used efficiently for growth, repair, and maintenance.
4. How does a change in temperature affect the properties of an enzyme?
Temperature has a significant impact on an enzyme's activity. As temperature increases from low levels, the rate of reaction increases because molecules have more kinetic energy. However, each enzyme has an optimum temperature at which it functions most effectively. If the temperature rises too far above this optimum, the enzyme starts to lose its specific three-dimensional shape. This process, called denaturation, deforms the active site and causes a rapid loss of catalytic activity. At very low temperatures, the enzyme becomes inactive but is usually not denatured.
5. What is the importance of an enzyme's active site?
The active site is the most important part of an enzyme. It is a specific region, usually a small pocket or crevice on the enzyme's surface, with a unique shape and chemical composition. Its importance lies in its dual function: it first binds to the specific substrate molecule (the binding site) and then carries out the chemical reaction (the catalytic site). The precise shape and amino acid arrangement of the active site are what determine the enzyme's high specificity, as explained by the lock-and-key or induced-fit models.
6. What is the role of a cofactor in enzyme function?
Many enzymes are not functional on their own and require a non-protein component called a cofactor to become active. Cofactors can be metal ions (like Zn²⁺, Mg²⁺) or complex organic molecules called coenzymes (like vitamins). The cofactor binds to the enzyme and helps in the catalytic process, often by assisting in substrate binding or by participating directly in the chemical reaction. An enzyme without its necessary cofactor is called an apoenzyme, while the complete, active enzyme with its cofactor is called a holoenzyme.
7. Can an enzyme catalyse any type of chemical reaction?
No, an enzyme cannot catalyse any type of chemical reaction. Due to their property of high specificity, enzymes are limited to catalysing only one or a very small group of related reactions. For example, proteolytic enzymes like pepsin break down proteins but have no effect on carbohydrates or fats. This specificity ensures that the correct metabolic pathways are followed within a cell without interference from other reactions.
