Properties of Enzymes Study Notes

Properties of Enzymes

Introduction

• Every cell in the body is genetically programmed for specific functions and must carry out various internal processes to maintain itself.

  • Internal processes include:

  • Taking materials into or exporting them out of the cell

  • Generating chemical energy (ATP)

  • Making biomolecules: proteins, hormones, enzymes, etc.

• Processes rely on the activity of enzymes.

• Enzymes

  • Most are proteins; act as catalysts (increase reaction rates without being consumed).

  • Function: Speed up chemical reactions by lowering activation energy.

Activation Energy

• Enzymes lower the activation energy required for reactions (Figure 1).

Enzyme Specificity

• Enzymes are highly specific to the reactions they catalyze.

• Grouped by specific functions:

  • Examples include: peroxidase, carboxylase, phosphatase, protease.

  • Clues about enzyme action come from these classifications.

Reactions and Substrates

• Enzymes catalyze a myriad of reactions, including:

  • Breaking down metabolic by-products (e.g., hydrogen peroxide)

  • Cleaving side-groups (e.g., phosphate)

  • Splitting disaccharides into monosaccharides.

• Cells require a variety of enzymes, but they are not consumed in reactions and are rapidly turned over.

• Each enzyme has a unique active site that binds to a specific substrate forming an enzyme-substrate complex, leading to product formation and enzyme recycling (Figure 2).

Factors Affecting Enzyme Function

• Various biotic (biological) and abiotic (environmental) factors can affect enzyme functionality:

  • Abiotic factors include:

  • Temperature

  • Radiation (irradiance)

  • Humidity

  • Pressure

  • pH

  • These factors can:

  • Influence the activation energy needed for reactions.

  • Affect enzyme's structural integrity, leading to conformation changes and potential denaturation.

  • Affect substrate binding via inhibition or competitive exclusion.

Focus: Peroxidase Enzyme

• We will examine peroxidase (from horseradish), which is common in various organisms and breaks down hydrogen peroxide ($H<em>2O</em>2$) into water and oxygen.

• Its activity can be tracked with a colorimetric assay using guaiacol, which changes from colorless (reduced state) to brown (oxidized state/tetraguaiacol) with enzymatic activity (Figure 3).

Monitoring Enzyme Activity

• The reaction's progress can be monitored with a spectrophotometer to quantify peroxidase activity.

  • Data can be plotted, showing absorbance change over time, determining enzyme activity from the slope of the line.

• Key factors influencing enzyme function investigated include:

  • Temperature

  • pH

  • Substrate concentration

  • Salt concentration

Procedure for Experiment

1. Preparation of “Blank”

   • Setup: Spectrophotometer warm-up to 500 nm readout, use only fresh tips to avoid contamination.

   • Cuvette 1 (Blank):

     • Contains dH2O, guaiacol, and H2O2 but no enzyme.

     • Total Volume components: 3.2 mL dH2O, 0.1 mL guaiacol, 0.2 mL H2O2, 0 mL peroxidase.

2. Basic Reaction Setup

   • Cuvette 2 includes:

     • 3.0 mL dH2O, 0.1 mL guaiacol, 0.2 mL H2O2, 0.2 mL peroxidase.

   • Reaction occurs quickly; initial readings at 30 seconds, taken at 30-second intervals for 3 minutes.

   • Data to be recorded in Table 3.

Results Compilation

• Record absorbance at 500 nm for trials across time in Table 3, computing the mean value for three trials.

Investigating Enzyme Activity

• Consider additional factors that may influence enzyme activity:

  • pH Variation (testing buffers of pH 3, 5, 6, 7, 9)

  • Replace distilled water with buffers accordingly.

  • Temperature Variation (testing at 0°C, room temp (22°C), 45°C, 60°C, 100°C)

  • Specific setups required for each temperature (Table 6).

Investigations on the Effect of pH

• Setup for pH includes preparing cuvettes with respective buffer pH as outlined in Table 4.

• Cuvette setups will include:

  • Buffer pH 3 through 9, maintaining constant volumes for guaiacol, H2O2, and peroxidase.

Results for Effect of pH

• Measurement data will show absorbance at specified times in Table 5 to determine optimal pH for horseradish peroxidase activity.

Investigations on the Effect of Temperature

• Setups for temperature as shown in Table 6; critical to only test one sample at a time.

• Record data similarly in Table 7 to analyze temperature effects on enzyme activity.

Conclusion and Discussion Points

• Identify the optimal pH and temperature based on absorbance readings.

• Discuss how temperature might affect enzyme activity and summarize conclusions drawn from experimental data.

1. Start With the BIG IDEA (15–20 min)
   Before memorizing details, understand what enzymes do. Make sure you can explain out loud:

   • Enzymes = proteins that speed up chemical reactions

   • They lower activation energy

   • They are not used up

   • Substrate → enzyme → product
     👉 If you can explain that without notes, you’re already halfway there.

2. Study Each Bullet Point Separately (Use This Order)
   A. Background & Terms (MOST IMPORTANT)

   • Make a mini cheat sheet: Know these definitions: enzyme, substrate, active site, product, activation energy, denaturation, optimal conditions, pH & Temperature

   • Memorize these rules:

     • Low temp → reaction slows

     • Optimal temp → fastest reaction

     • High temp → enzyme denatures

     • Wrong pH → active site changes shape
       👉 Draw a simple bell-shaped graph for temperature/pH vs reaction rate.

   B. Equipment & Reagents (10 min)

   • Ask yourself: What enzyme was used? What substrate? How was reaction measured? (color change? bubbles? absorbance?) Any buffers or indicators?

   • Tip: Picture the lab setup in your head like a movie scene.

   C. Experimental Procedure (VERY COMMON TEST QUESTIONS)

   • Understand these words clearly:

     • Control = normal setup for comparison

     • Experimental group = condition being tested

     • Blank = contains everything EXCEPT enzyme or substrate (used for calibration)

   • Practice answering:

     • 👉 Why do we use a control?

     • 👉 What does a blank measure?

   D. The Chemical Reaction

   • Know: What molecule was broken down or formed

   • Reactants → Products

   • Usually written like: Substrate + Enzyme → Enzyme-Substrate Complex → Products + Enzyme

   • You don’t always need exact formulas — understand the process.

   E. Optimal Conditions

   • Be able to answer:

     • How do we find optimal temperature? → test multiple temperatures & compare reaction rates

     • How do we find optimal pH? → same idea, different pH levels

   • Key idea: 👉 Highest reaction rate = optimal condition.

3. Active Study Method (THIS IS THE PART PEOPLE SKIP)

   • Do this instead of rereading notes:

   • Step 1 — Cover & Recall (20 min)

     • Cover notes and answer: What happens if temperature is too high? What is a blank? Why enzymes stop working at extreme pH? If you hesitate → review only that part.

   • Step 2 — Teach an Imaginary Student (10 min)

     • Explain the entire enzyme experiment out loud like you’re teaching someone. If you get stuck → that’s what you study again.

   • Step 3 — Draw Everything (10 min)

     • Draw: enzyme + substrate diagram, temperature graph, pH graph, experimental setup

     • Drawing = fastest memorization for bio.

4. Night-Before Quick Review (15 min)

   • Only review: definitions, graphs, controls vs blanks, optimal conditions

   • DO NOT reread entire chapters.

⭐ What Teachers Usually Ask (High Probability)
Expect questions like:

• What happens when enzymes denature?

• Why use a control or blank?

• Effect of temperature/pH on enzymes

• Identify optimal condition from a graph

• Label enzyme diagram

If you want, I can also make you a super short “memorize-this” enzyme cheat sheet that fits on one page — most students use that right before quizzes.

⏱ 45–60 Minute Enzyme Lab Study Plan

✅ 0–10 min — Understand the Experiment (MOST IMPORTANT)

Be able to explain this in simple words:

What enzyme was used?
👉 Peroxidase (from horseradish)

Lab 4 - Enzymes_F25(1) (1)

What does it do?
👉 Breaks down hydrogen peroxide (H₂O₂) into water + oxygen.

How did we measure activity?
👉 Using guaiacol:

• colorless → turns brown (tetraguaiacol)

• more brown = more enzyme activity

• measured using a spectrophotometer at 500 nm

  Lab 4 - Enzymes_F25(1) (1)

⭐ MEMORIZE THIS SENTENCE:

If you know this, you understand the whole lab.

✅ 10–20 min — Chemical Reaction (Guaranteed Question)

Know the reaction conceptually:

Peroxidase + H₂O₂ + Guaiacol → Oxidized guaiacol (brown product)

Key ideas:

• enzyme NOT used up

• enzyme + substrate → enzyme-substrate complex → products

• color change shows reaction rate

They may ask:

• What indicates enzyme activity?
  
  ✅ Increase in absorbance (brown color).

✅ 20–30 min — Controls, Blank, Procedure (VERY TESTABLE)

🧪 What is the BLANK?

From your lab:

Blank contained:

• water

• guaiacol

• H₂O₂

• NO enzyme

  Lab 4 - Enzymes_F25(1) (1)

Purpose:

👉 sets spectrophotometer to zero

👉 shows background absorbance

Quiz answer:

🧪 Why add enzyme LAST?

Because:

👉 reaction starts immediately.

🧪 Why record absorbance over time?

To calculate:

👉 reaction rate (slope of graph)

Lab 4 - Enzymes_F25(1) (1)

✅ 30–45 min — pH & Temperature Experiments (BIG SECTION)

You tested environmental effects.

🌡 Temperature Effects

Temperatures tested:

• 0°C

• Room temp (~22°C)

• 45°C

• 60°C

• 100°C (boiled enzyme)

  Lab 4 - Enzymes_F25(1) (1)

Know the pattern:

KEY WORD:

👉 Denaturation = enzyme shape changes

🧪 pH Effects

Buffers tested:

pH 3, 5, 6, 7, 9

Lab 4 - Enzymes_F25(1) (1)

Concept:

• enzyme has optimal pH

• too acidic/basic → active site changes → slower reaction

Expected optimal:

👉 usually near neutral (~pH 6–7).

How do we determine optimal conditions?

SUPER IMPORTANT:

✅ 45–55 min — Memorize These High-Probability Answers

You should instantly know:

1. What is an enzyme?

Protein catalyst that lowers activation energy.

2. What is the substrate here?

Hydrogen peroxide (and guaiacol indicator).

3. What shows enzyme activity?

Increase in brown color / absorbance.

4. What is a blank?

Everything except enzyme.

5. Why extreme temperature stops reactions?

Denaturation.

6. Optimal condition definition

Condition producing fastest reaction rate.

✅ LAST 5 MIN — Rapid Self-Test (Do This)

Answer OUT LOUD:

• Why was guaiacol used?

• What does the spectrophotometer measure?

• Why add enzyme last?

• What happens at 100°C?

• How do you know optimal pH?

If you can answer without notes → you’re ready.

⭐ Ultra-Short Memory Cheat Sheet (Read Before Quiz)

Enzyme: peroxidase

Substrate: H₂O₂

Indicator: guaiacol → brown

Measurement: absorbance @ 500 nm

Blank: no enzyme

Rate: slope of absorbance vs time

Optimal condition: highest reaction rate

High temp: denaturation

Wrong pH: active site changes