Enzymes

Enzymes are proteins that act as biological catalysts, speeding up chemical reactions in living organisms without being consumed in the process.

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Basic Properties

Enzymes have several key characteristics:

1. Catalytic Function

   • Catalyze metabolic reactions (anabolic or catabolic)
   • Lower activation energy
   • Function intracellularly or extracellularly

2. Specificity

   • Highly specific due to tertiary structure
   • Each enzyme catalyzes one specific reaction
   • Based on active site shape

3. Active Site

   • Specific region where substrate binds
   • Small part of the total enzyme
   • Forms a depression in enzyme surface
   • Shape complementary to substrate

How Enzymes Work

Activation Energy

• Activation energy (Ea) is the minimum energy needed for a reaction
• Enzymes lower the activation energy by:
  • Holding substrates in correct orientation
  • Straining bonds in substrate
  • Creating favorable conditions for reaction

Enzyme-Substrate Complex

When a substrate binds to an enzyme:

1. Forms enzyme-substrate complex
2. Temporary bonds form between enzyme and substrate
3. Lowers activation energy
4. Enables reaction to proceed more easily

The Induced Fit Model

The modern understanding of enzyme action:

1. Active Site Flexibility

   • Active site is flexible
   • Shape changes when substrate approaches
   • Enzyme and substrate modify each other's shape

2. Process

   • Substrate approaches enzyme
   • Active site shape adjusts
   • Perfect fit is induced
   • Reaction occurs
   • Products released

3. Advantages

   • Explains enzyme specificity
   • Accounts for enzyme regulation
   • Better than older 'lock and key' model

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Factors Affecting Enzyme Activity

1. Enzyme Concentration

• Higher enzyme concentration = faster reaction
• Linear relationship until substrate becomes limiting

2. Substrate Concentration

• Increases rate up to maximum velocity
• Follows Michaelis-Menten kinetics
• Plateaus when enzymes saturated

3. Temperature

• Increases rate up to optimum
• Above optimum, enzyme denatures
• Tertiary structure disrupted

4. pH

• Each enzyme has optimum pH
• Changes affect enzyme shape
• Can cause denaturation

5. Inhibitors

Competitive Inhibitors

• Similar shape to substrate
• Compete for active site
• Effects reduced by increasing substrate

Non-competitive Inhibitors

• Bind elsewhere on enzyme
• Change active site shape
• Cannot be overcome by substrate

Enzyme Denaturation

Denaturation occurs when:

• Tertiary structure is disrupted
• Active site shape changes
• Enzyme loses catalytic ability

Causes include:

• Extreme temperature
• Extreme pH
• Some chemicals
• Mutations in primary structure

Learning Objectives

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Key Takeaways

• Enzymes are biological catalysts that lower activation energy
• The induced fit model explains enzyme-substrate interactions
• Multiple factors affect enzyme activity
• Enzyme structure determines its function
• Denaturation disrupts enzyme activity permanently