Enzymes as Biological Catalysts
Enzymes act as biological catalysts, speeding up the rate of reactions without being used up in the process. They can affect the structures and functions of organisms both intracellularly and extracellularly.
Enzyme Structure
Enzymes are globular proteins with an active site where the substrate molecule binds. The specific shape of the active site is determined by the 3⁰ structure. Enzymes are highly specific and only bind to certain substrates, forming an enzyme-substrate complex.
How Enzymes Speed Up Reactions
Enzymes reduce the amount of activation energy required for chemical reactions. They can hold substrates close together, reducing repulsion and facilitating bonding. Enzymes can also strain the bonds in the substrate, making it break up more easily.
Models of Enzyme Action
There are two models of enzyme action: the lock and key model and the induced fit model. While the lock and key model emphasizes the exact fit between enzyme and substrate, the induced fit model explains why enzymes are so specific and how they change shape accordingly.
Factors Affecting Enzyme Activity
Temperature
The rate of reaction increases with temperature, as molecules move faster and collide more energetically. However, enzymes have an optimum temperature, and when the temperature exceeds this, the enzyme is denatured, leading to a loss of complimentary shape between the active site and the substrate.
pH
Enzymes also have an optimum pH, and deviations from this pH can break the ionic and hydrogen bonds in the enzyme's 3° structure, causing denaturation.
Enzyme Concentration
Increasing enzyme concentration increases the rate of reaction, but only up to a certain point where the available substrates are limited.
Substrate Concentration
Higher substrate concentration increases the likelihood of enzyme-substrate complexes and the rate of reaction. However, at the saturation point, adding more substrate will have no further effect.
Cofactors and Enzyme Inhibition
Cofactors are non-protein substances that some enzymes require in order to function. Inorganic cofactors help enzyme and substrate bind together, while organic cofactors participate in the reaction and are changed by it.
In conclusion, enzyme-controlled reactions are crucial in biological systems, and their activity is influenced by various factors such as temperature, pH, enzyme and substrate concentration, as well as cofactors. Understanding these factors is essential in practical applications and in the study of enzyme kinetics.
