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Questions and Answers
What is the primary function of enzymes in biochemical reactions?
Which of the following enzymes is classified as a hydrolase?
What type of reaction do ligases specifically catalyze?
What type of reaction do oxidoreductases typically catalyze?
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Which enzymes are specifically involved in the fermentation of sugar into ethanol?
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Which enzyme class is responsible for transferring a chemical group from one compound to another?
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What do isomerases primarily catalyze?
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In enzyme nomenclature, which suffix is typically added to the name of a substrate to denote an enzyme?
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Which part of the Enzyme Commission number indicates the functional group upon which the enzyme acts?
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What type of reaction does phosphoglucoisomerase catalyze?
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Study Notes
Enzymes Overview
- Enzymes are biological catalysts primarily composed of proteins.
- They accelerate biochemical reactions without being consumed in the process.
- Enzymes are classified into six main categories: Hydrolases, Oxidoreductases, Lyases, Isomerases, Ligases, and Transferases.
Hydrolases
- Catalyze hydrolysis reactions by adding water to cleave bonds.
- Subdivided into three classes:
- Carbohydrases (e.g., Sucrase, Diastase)
- Proteases (e.g., Pepsin, Trypsin)
- Esterases (e.g., Lipase, Chlorophyllase)
Oxidoreductases
- Catalyze oxidation/reduction reactions by transferring H, O atoms, or electrons.
- Subdivided into four classes:
- Oxidases
- Peroxidases
- Dehydrogenases
- Catalases (e.g., converts hydrogen peroxide into water and oxygen)
Lyases
- Catalyze the breaking of bonds by removal of groups, without adding water.
- Example: Zymase converts sugar into ethanol and carbon dioxide.
- Aldolase is involved in glycolysis and splits fructose-1,6-diphosphate.
Isomerases
- Catalyze geometric or structural changes within a single molecule.
- Example: Phosphoglucoisomerase converts glucose-6-phosphate to fructose-6-phosphate.
Ligases
- Join two molecules by synthesizing new covalent bonds with the breakdown of ATP.
- Examples include Asparagine synthetase and RNA Ligase.
Transferases
- Catalyze the transfer of chemical groups from one compound to another.
- Examples include transaminases (transfer amino groups) and hexokinases (transfer phosphate groups).
Enzyme Nomenclature
- Trivial names (e.g., Pepsin, Trypsin) or suffix "-ase" added to substrates (e.g., Sucrase).
- Reaction type nomenclature also uses "-ase" (e.g., Carboxylase).
- Enzyme Commission (EC) numbering system categorizes enzymes based on class and substrate involved.
Structure of Enzymes
- Two types of protein enzymes:
- Simple Protein Enzymes (consist of protein only).
- Complex (Conjugated) Protein Enzymes (contain protein and non-protein components).
- Apoenzyme (protein part) and Cofactor/Coenzyme (non-protein part).
- Holoenzyme is the complete enzyme.
Cofactors
- Types of cofactors include:
- Prosthetic groups (tightly bound, e.g., FAD).
- Coenzymes (detach from the enzyme post-catalysis, e.g., NAD+).
- Activators (usually metal ions, e.g., Zn²⁺, Ca²⁺).
Enzyme Functionality
- Substrates are reactants that bind to enzymes to form enzyme-substrate complexes.
- The active site is where the substrate binds and catalysis occurs.
- Enzymes remain unchanged post-reaction.
Characteristics of Enzymes
- Needed in small amounts to catalyze larger reactant quantities.
- Sensitive to temperature and pH levels.
- Highly specific for particular reactions.
- Exhibit colloidal nature.
Mechanism of Enzyme Action
- Substrate binds to enzyme's active site forming the enzyme-substrate complex.
- This complex transforms into products, regenerating the original enzyme.
Factors Affecting Enzyme Activity
- Enzyme activity is influenced by:
- Substrate concentration
- Enzyme concentration
- Temperature
- pH levels
- Inhibitors
Temperature and pH Effects
- Rate of reaction increases with temperature until a maximum is reached, after which it declines.
- Each enzyme has an optimal pH for maximum activity; deviations can lower activity or inactivate the enzyme.
Concentration Effects
- Increasing substrate concentration typically increases reaction rate until enzymes are saturated.
- Higher enzyme concentrations yield faster reactions until the substrate becomes limiting.
Inhibitors
- Competitive inhibitors block the active site.
- Non-competitive inhibitors bind elsewhere on the enzyme, reducing its efficiency.
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