Biology: Enzymes Overview

Enzyme Definition

• Enzymes are biological catalysts.
• A catalyst is a substance that increases the rate of a chemical reaction without being changed in the process.

Enzymes as Biological Catalysts

• Enzymes are proteins that speed up chemical reactions by lowering the activation energy.
• They catalyze most chemical reactions in the body's cells.
• Enzyme shapes are specific to their reactants (substrates).

Properties of Enzymes

• Catalytic efficiency: Enzymes are exceptionally efficient, speeding up reactions by factors of 10³ to 10¹⁷ compared to uncatalyzed reactions.
• Specificity: Enzymes are highly specific, interacting with only certain substrates and catalyzing only one type of reaction.
• Mild reaction conditions: Enzymes function under typical biological conditions (37°C, physiological pH, and ambient pressure).

Chemical Composition of Enzymes

• Simple proteins: Composed solely of amino acids.
• Conjugated proteins: Composed of a protein portion (apoenzyme) and a non-protein portion (cofactor).
  • Coenzyme: A loosely bound cofactor that acts as a temporary carrier of atoms or functional groups.
  • Prosthetic group: A tightly bound cofactor, often covalently bound to the apoenzyme.
  • Holoenzyme: The complete, catalytically active enzyme (apoenzyme + cofactor).

Roles of Cofactors in Enzyme Function

• Cofactors modify the shape of the active site to facilitate interaction with substrates.
• Cofactors participate in temporary bonding between the active site and substrate.

Classification of Enzymes

• By composition: Monomeric, oligomeric, or multienzyme complex (e.g., fatty acid synthase).

Nomenclature of Enzymes

• Recommended name: Typically uses the substrate name plus the suffix "-ase" (e.g., lactase).
• Systematic name: Based on the chemical reactions they catalyze (international classification using six classes).

How Enzymes Work

• Enzymes lower the activation energy required for a reaction to occur.
• All chemical reactions require an activation energy (energy barrier) between reactants and products.
• Enzymes facilitate the reaction by stabilizing the transition state, thus reducing the needed activation energy.

Enzymes and Proteins

• All enzymes are proteins, but not all proteins are enzymes.
• Some RNA molecules (ribozymes) also act as enzymes.

The Active Site of Enzymes

• The active site is a specific region of an enzyme where substrates bind and reactions occur.
• It stabilizes the transition state of the reaction.
• The substrate binds to the active site, forming an enzyme-substrate complex.

Enzymatic Reaction Steps

• Substrate approaches the active site.
• Enzyme-substrate complex forms.
• Substrate is transformed into products.
• Products are released.
• Enzyme is recycled.

Enzyme Activity

• Enzyme activity is measured by the amount of substrate converted to product per unit time.
• Enzyme activity is never expressed in terms of concentration; instead, it measures the reaction rate.

Factors Affecting Enzyme Activity

• Substrate concentration.
• Enzyme concentration.
• Temperature.
• pH.
• Activators
• Inhibitors

Enzymes in Clinical Diagnosis

• Enzyme tests (blood or urine) measure the levels of specific enzymes to assess body system function and tissue damage.

Common Enzymes in Clinical Diagnosis

• Alanine aminotransferase (ALT)
• Glutamate pyruvate transaminase (GPT)
• Alkaline phosphatase
• Amylase
• Aspartate aminotransferase
• Creatine kinase
• Lactate dehydrogenase

This quiz covers the essential concepts of enzymes, including their definitions, roles as biological catalysts, and properties such as catalytic efficiency and specificity. Understanding these topics is crucial for studying biochemical reactions in living organisms.