1. Enzymes

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Enzymes

Introduction to Enzymes

Enzymes are biological catalysts that accelerate chemical reactions in living organisms. They are essential for processes such as metabolism, DNA replication, and cellular signaling. Enzymes are typically proteins, although some RNA molecules (ribozymes) also possess catalytic activity.

Definition: Enzymes are macromolecules that increase the rate of biochemical reactions without being consumed in the process.
Function: They lower the activation energy required for reactions, making them proceed faster under physiological conditions.
Example: Alcoholic fermentation is catalyzed by enzymes, converting sugar into alcohol.

Catalysis

Role of Enzymes in Catalysis

Enzymes facilitate chemical reactions by providing an alternative reaction pathway with a lower activation energy. This process is known as catalysis.

Activation Energy: The energy barrier that must be overcome for a reaction to proceed. Enzymes lower this barrier.
Reaction Rate: Enzymes can increase reaction rates by factors of up to 1012 compared to uncatalyzed reactions.
Equilibrium: Enzymes do not change the equilibrium position of a reaction; they only accelerate the rate at which equilibrium is reached.
Equation: The relationship between free energy and equilibrium constant is given by:

Catalytic Groups

Functional Groups Involved in Enzyme Catalysis

Enzymes use specific amino acid side chains and cofactors to facilitate catalysis. These are known as catalytic groups.

Amino Acid Side Chains: Common catalytic residues include Serine, Histidine, Aspartate, and Glutamate.
Cofactors: Non-protein molecules required for enzyme activity, such as metal ions (e.g., Zn2+, Mg2+) and organic molecules (coenzymes).
Mechanism: Catalytic groups may act as nucleophiles, electrophiles, or acid/base catalysts during the reaction.
Example: Alcohol dehydrogenase uses a zinc ion as a cofactor to facilitate the conversion of alcohols to aldehydes.

Binding & Specificity

Enzyme-Substrate Recognition

Enzymes exhibit high specificity for their substrates, ensuring that only the correct molecules are transformed into products. This specificity is determined by the unique three-dimensional structure of the enzyme's active site.

Lock-and-Key Model: The substrate fits precisely into the enzyme's active site, like a key into a lock.
Induced Fit Model: The enzyme undergoes a conformational change upon substrate binding, optimizing the interaction.
Product Yield: Enzymes typically produce products in very high yields, with minimal side reactions.
Example: Hexokinase specifically phosphorylates glucose, not other sugars, due to its active site structure.

Historical Context: Alcoholic Fermentation

Discovery of Enzyme Catalysis

The process of alcoholic fermentation, where sugar is converted to alcohol, was historically studied by scientists such as Louis Pasteur and Justus von Liebig. Their work helped establish the role of enzymes in biological reactions.

Louis Pasteur: Demonstrated that fermentation is catalyzed by living cells (yeast), leading to the concept of enzymes as biological catalysts.
Justus von Liebig: Proposed that chemical processes in cells are responsible for fermentation, contributing to the understanding of enzyme function.
Reaction: Sugar → Alcohol (catalyzed by enzymes such as zymase in yeast)