What are Enzymes?
On average, food takes several hours to a few days to be completely digested and absorbed in the body. This is because the presence of enzymes speeds up the rate of the digestion process. Without enzymes, food would take ages to be digested and absorbed. Enzymes serve as catalysts that speed up the rate of creation without affecting the reaction itself. Enzymes function by lowering the activation energy needed for the reaction to take place. Activation energy is the minimum amount of energy required for the reaction to occur. This means that it reduces the energy cost and increases the rate of a chemical reaction. In fact, without enzymes, the human body would not function properly because the chemical processes essential to maintain the body would simply not occur quickly enough. The nature of enzymes is protein-based; all enzymes are proteins but not all proteins are enzymes. Proteins are made up of several amino acids linked together by peptide bonds forming polypeptide chains. The enzyme itself is not affected or consumed during the reaction, however, it remains as it is and is able to catalyze other reactions.
What is pH?
The "p" in pH stands for potenz, which signifies power in German, while the "H" stands for hydrogen. The pH is simply defined as the measurement of the concentration of hydrogen ions. The pH is an indication of the acidity, alkalinity, and neutrality of a liquid or aqueous solution. The range of pH starts from 0 and ends at 14. pH measurements depend on the concentration of hydrogen (H+) and hydroxide ions (OH-). When the hydrogen ion in a solution exceeds the concentration of hydroxide ions, the solution is said to be acidic. When the hydroxide ion in a solution exceeds the concentration of hydrogen ions, the solution is said to be basic.
- When pH measures from 0 to less than 7, it indicates an acidic solution because the concentration of hydrogen ions is larger than that of hydroxide ions. 1 is the strongest acid, while 6.9 is the weakest acid. Hydrochloric acid is an example of a strong acid. Water is an example of a neutral liquid.
- When pH measures 7, it indicates a neutral solution because the concentration of hydrogen ions is equal to the concentration of hydroxide ions.
- When pH measures from more than 7 to 14, it indicates an alkaline or basic solution because the concentration of hydroxide ions is larger than that of hydrogen ions. 7.1 is the weakest alkaline, while 14 is the strongest alkaline. Sodium hydroxide is an example of a strong base.
Effect of pH on Enzyme Activity
Enzyme activity is defined as the rate of the reaction catalyzed by an enzyme and is represented as the conversion of substrate to product per minute. The activity of enzymes is affected by many factors which include pH and temperature. So, enzymes and pH are correlated. So, why does pH affect enzyme activity? pH affects enzyme activity because enzymes are proteins that get their molecular structure via interactions between the charges of the amino acids that form the protein chains. These interactions are in the form of a hydrogen bond which is affected by the pH level. How does pH affect enzyme reaction rate? Each enzyme has an optimal pH value. The optimal pH of an enzyme is the ideal pH value that the enzyme works the best in, or in other words, the value of the pH where the enzymatic activity is the highest. When the pH decreases below the optimal value, the enzyme activity is decreased as well. When the pH value far increases above the optimal value and becomes unsuitable, the enzyme activity is said to be denatured which makes it inactive.
Acidic solutions have more hydrogen ions which means more positive charges. These positive charges affect the charges of the amino acids inside the protein which render the enzyme more or less active depending on the optimal pH of the enzyme. Here are some examples of enzymes with their optimal and denatured pH.
|Enzyme||Optimal pH||Denaturated pH|
How Does pH Affect Enzyme Activity?
Any reaction consists of reactants and products. The enzymes bind with the reactant or the molecules that need to be changed, transformed, or broken down. This molecule is called a substrate. Enzymes have the tertiary structure of the proteins that give them the ability to fold in order to bind with the substrate. The lock and key theory states that an enzyme has the ability to bind with a substrate in a way that resembles the lock and the key. The enzymes bind with the substrate in a location called the active site which acts as a lock and key. This gives the enzyme specific characteristics as it can only bind with certain substrates to fit within them. When the enzyme binds with the substrate, it forms a structure called an enzyme-substrate complex. The binding of the enzyme to the substrate causes conformational change to the substrate. The formed complex reduces the activation energy of the reaction. Consequently, the reactant transforms into an enzyme-product complex. The enzyme is released from the product and ready to catalyze a new reaction.
This equation simplifies the above description of what happens when an enzyme is added to a reaction:
- Reactant + Enzyme --> Substrate-enzyme complex
- Substrate-enzyme complex--> Product-enzyme complex
- Product-enzyme complex--> Enzyme + Product
- Enzyme is ready to catalyze another reaction
Enzymes are proteins that have a 3D structure (tertiary structure). These tertiary structures play a key role in binding the enzyme with the active site of the substrate. How does pH affect enzyme function? When the pH is above the optimal level, the enzyme is denatured. Denaturation means that the shape of the enzyme changes making it unable to bind with the active site of the substrate. When an enzyme loses its ability to bind with a substrate, it is said to be denatured and loses its activity. When the pH of an enzyme is not optimal, the varying amount of hydrogen ions will impact the linkages that have a charge such as a hydrogen bond. As a result, unsuitable and abnormal pHs can cause these connections to break which results in losing the enzymatic activity.
Enzymes work as catalysts, increasing the pace of formation while having no effect on the reaction itself. Enzymes perform their job by decreasing the activation energy required for the reaction to occur. The activation energy is the bare minimum of energy necessary for the reaction to take place. Enzymes are proteins composed of several amino acids joined together by peptide bonds to create polypeptide chains. During the process, the enzyme is not affected or consumed. The pH scale is merely a measurement of the concentration of hydrogen ions. The pH of a liquid or aqueous solution indicates its acidity, alkalinity, and neutrality. The pH scale begins at 0 and finishes at 14. The concentration of hydrogen (H+) and hydroxide ions influence pH readings (OH-). When the concentration of hydrogen ions in a solution exceeds that of hydroxide ions, the solution is said to be acidic. The acidic pH range is from 1 to 6.9. A solution is considered to be basic (alkaline) when the concentration of hydroxide ions in it exceeds the concentration of hydrogen ions. The basic pH ranges from more than 7 to 14. 7 is a neutral pH.
Each enzyme has an optimal pH value. The optimal pH of an enzyme is the ideal pH value at which the enzyme performs best. In other words, the pH value at which the enzymatic activity is greatest. The enzyme binds to the substrate to be altered, converted, or broken down. Enzymes have a tertiary structure that allows them to fold in order to bind with the active site of the substrate as a lock and key to create an enzyme-substrate complex. Unsuitable pH leads to the change in the shape and structure of the enzyme rendering it unable to bind with the active site. This case is called denaturation where enzyme shape is changed and becomes inactive.
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Why does pH affect enzyme activity?
Because enzymes are proteins, their molecular structure is determined by interactions between the charges of the amino acids that compose the protein chains. These interactions take the form of hydrogen bonds, which are altered by pH. These positive charges impact the charges of the amino acids inside the protein, making the enzyme more or less active depending on the enzyme's optimum pH.
What is the effect of pH on enzyme activity?
Each enzyme has an optimal pH value. The optimum pH of an enzyme is the ideal pH value at which the enzymatic activity is greatest. When the pH falls below the ideal level, enzyme activity falls as well. When the pH level rises significantly over the ideal level and becomes inappropriate, the enzyme activity is said to be denatured, rendering it inactive and inert.
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