Enzymes are biological catalysts that speed up chemical reactions in the body without being consumed in the process.

Properties of Enzymes

• Specificity: Enzymes are specific to substrates and catalyze particular reactions due to their unique active site shape.

• Efficiency: They can accelerate reactions significantly, often up to millions of times faster than reactions would occur without them.

• Reusability: Enzymes are not consumed in the reaction, allowing them to be used repeatedly.

• Sensitivity to Conditions: Enzyme activity can be affected by changes in temperature, pH, and concentration levels of substrates and products.

• Regulation: Enzyme activity can be regulated by inhibitors and activators, which can modify the enzyme's ability to catalyze reactions.

Activation Energy

Activation energy is the minimum amount of energy required for a chemical reaction to occur. It is the energy barrier that must be overcome for reactants to be transformed into products during a reaction.

Mechanism of Enzyme Action

1. Lock and Key Model: This model suggests that the enzyme's active site (the 'lock') is specifically shaped to fit a particular substrate (the 'key'). When the substrate binds to the active site, it forms an enzyme-substrate complex, allowing the reaction to occur. This model emphasizes the specificity of enzymes for their substrates.

2. Induced Fit Model: According to this model, the active site of the enzyme is flexible and can change shape to accommodate the substrate. This change in shape enhances the binding affinity and helps properly position the substrate for the reaction. The induced fit model explains how enzymes can catalyze reactions for different substrates with slight variations in structure.Kai is thinking...

Factors Affecting Rate of Enzyme Activity

• Temperature: Enzymes have an optimum temperature range. High temperatures can denature enzymes, reducing their activity, while low temperatures slow down molecular movement, leading to lower reaction rates.

• pH: Each enzyme has an optimum pH level. Deviations from this pH can lead to reduced activity or denaturation of the enzyme.

• Substrate Concentration: Increasing substrate concentration usually increases enzyme activity to a point (saturation point), after which the rate of reaction levels off as all active sites of the enzyme molecules are occupied.

• Enzyme Concentration: More enzymes generally lead to more active sites available for substrate binding, increasing the reaction rate, provided there is an adequate amount of substrate.

• Inhibitors: Molecules that decrease enzyme activity. They can be competitive (competing for the active site) or non-competitive (binding elsewhere and changing the enzyme's shape).

• Activators: Molecules that increase enzyme activity by enhancing the binding between enzyme and substrate or altering the enzyme’s shape favorably.Kai is thinking...

Classification of Enzymes

Enzymes can be classified based on various criteria. Some common classifications include:

• By Type of Reaction Catalyzed:

  • Oxidoreductases: Catalyze oxidation-reduction reactions.

  • Transferases: Transfer functional groups from one molecule to another.

  • Hydrolases: Catalyze hydrolysis reactions, breaking bonds with the addition of water.

  • Lyases: Catalyze the breaking of bonds by means other than hydrolysis or oxidation.

  • Isomerases: Catalyze the rearrangement of atoms within a molecule.

  • Ligases: Catalyze the joining of two molecules with the expenditure of energy from ATP.

• By Source:

  • Animal Enzymes: Enzymes derived from animal tissues.

  • Plant Enzymes: Enzymes derived from plant tissues.

  • Microbial Enzymes: Enzymes derived from microorganisms.

• By Cofactor Requirement:

  • Apoenzymes: Enzymes that require additional non-protein molecules (cofactors) to be active.

  • Holoenzymes: Active enzymes that are bound to their cofactors.

• By Active Site Characteristics:

  • Endoenzymes: Enzymes that act within cells.

  • Exoenzymes: Enzymes that are secreted and act outside the cell.

• Isoenzymes: Enzymes that catalyze the same reaction but differ in structure and kinetic properties.

Cofactors

Cofactors are non-protein molecules that assist enzymes in catalyzing reactions. They can be classified into two main types:

• Coenzymes: Organic molecules that serve as cofactors and often act as carriers for chemical groups or electrons during enzymatic reactions. Examples include vitamins like NADH and FADH2.

• Metal Ions: Inorganic molecules that assist enzyme function. Common metal cofactors include zinc, magnesium, iron, and copper, which can help stabilize enzyme structure.Kai is thinking...

Enzyme Inhibitors

Enzyme inhibitors are molecules that decrease enzyme activity. They can be classified into two main types:

• Competitive Inhibitors: These inhibitors compete with the substrate for the active site of the enzyme. When a competitive inhibitor binds to the active site, it prevents the substrate from binding, thus reducing the rate of reaction. The inhibition can be overcome by increasing the concentration of the substrate.

• Non-competitive Inhibitors: These inhibitors bind to a site other than the active site (allosteric site) and change the enzyme's shape, which decreases its ability to catalyze reactions. This type of inhibition cannot be overcome by increasing substrate concentration since the inhibitor affects the enzyme regardless of whether the substrate is present or not.

• Uncompetitive Inhibitors: These inhibitors bind only to the enzyme-substrate complex, preventing the complex from releasing products. This type of inhibition decreases both the rate of reaction and the apparent affinity of the enzyme for the substrate, as it effectively locks the substrate in place.

• Allosteric Inhibitor is an inhibitor which binds to the allosteric site and modifies the activity by causing a reversible change in the active site of enzyme.

Negative Feedback

Negative feedback is a regulatory mechanism in biological systems that helps maintain homeostasis. In this process, a change in a physiological variable triggers a response that counteracts the initial change, returning the system to its set point. For example, in temperature regulation, if the body's temperature rises, mechanisms such as sweating are activated to cool the body down, effectively reducing the temperature back to normal levels. This feedback system is crucial for regulating various body processes, including hormonal levels, metabolism, and other physiological functions.