Lesson at a Glance | He Tirohanga Whakamua
Ngā Whāinga Ako | Learning Intentions
Students will know
- How temperature affects enzyme rate (low temperature = lower kinetic energy; an optimum gives the highest rate; sufficiently high temperature can disrupt interactions that maintain tertiary structure and alter the active site).
- Why the effects of denaturation depend on the protein and conditions: extensive unfolding and aggregation may be irreversible, while some proteins can refold if the disturbance is mild and conditions are restored.
- The difference between competitive inhibitors (bind active site directly) and non-competitive inhibitors (bind allosteric site, altering active site shape).
- How non-protein helpers support enzyme action: cofactors include inorganic ions, while coenzymes are organic helper molecules.
Students will demonstrate
- By plotting and annotating the supplied substrate-and-inhibitor curves, then explaining the qualitative effects of temperature and pH.
- By completing formative Section 6 in their class exercise book or revision folder.
Curriculum alignment
- NZC (2007) · Science · Level 7 · Living World: “Explore the diverse ways in which animals and plants carry out the life processes.”
Do Now | Tīmatanga Whakaaro (10 min)
Denaturation Prompt:
"When you cook a transparent liquid egg white in a hot pan, it turns opaque white and solid. If you cool the cooked egg back down to 20°C, does it become transparent liquid again?"
Unpack: Cooking causes extensive protein unfolding and aggregation, so cooling does not restore the original egg-white proteins. Heat can disrupt hydrogen bonds, ionic interactions, and hydrophobic interactions that help maintain tertiary structure. This cooked-egg example is effectively irreversible, but denaturation is not automatically irreversible for every protein or every change in conditions.
Factors Controlling Enzyme Reaction Rates (15 min)
🌡️ 1. Temperature Curve
As temperature rises, greater kinetic energy usually increases successful enzyme-substrate collisions up to an optimum. Above the optimum, interactions stabilising the enzyme may be disrupted, changing the active site and reducing the rate. The final rate depends on how much functional enzyme remains; it is not necessarily zero.
🧪 2. pH Optima
Each enzyme has a pH range and optimum. Moving away from that range changes the charges on amino-acid side chains and can alter substrate binding or catalysis; sufficiently extreme pH can disrupt interactions maintaining the active site's shape.
📈 3. Substrate Saturation
Adding substrate increases rate until all active sites are occupied (saturation point). At saturation, adding more substrate has zero effect on rate.
🚫 4. Enzyme Inhibitors
Competitive: Competes with substrate for the active site.
Non-competitive: Binds away from the active site and reduces enzyme activity. Either type may bind reversibly or irreversibly; non-competitive does not mean permanent.
🧩 5. Cofactors & Coenzymes
Some enzymes require a non-protein helper. A cofactor may be an inorganic ion such as Mg²⁺ or Zn²⁺. A coenzyme is an organic helper molecule, often derived from a vitamin, that can carry electrons or chemical groups between reactions; NAD is a coenzyme that carries electrons in cellular respiration. The helper supports catalysis but is not the protein enzyme itself.
Inhibitors & Saturation (15 min)
1. Competitive inhibition
The inhibitor is a similar shape to the substrate and occupies the active site. Add more substrate and it out-competes the inhibitor, so the reaction still reaches its normal maximum rate — it just takes more substrate to get there.
2. Non-competitive inhibition
The inhibitor binds away from the active site and reduces the proportion or activity of functional enzyme. Adding substrate cannot overcome this effect, so the maximum rate drops. Binding may be reversible or irreversible depending on the particular inhibitor.
3. Saturation
Raise substrate concentration and rate climbs, then flattens. At the plateau every active site is occupied — enzyme number, not substrate, is now the limiting factor. That plateau is Vmax.
4. Telling them apart from a graph
Ask one question: does the curve still reach the same Vmax, only later? Competitive. Does it settle at a lower Vmax no matter how much substrate you add? Non-competitive.
Supplied model dataset: reaction rate at increasing substrate concentration
| Substrate concentration (relative units) | No inhibitor | Inhibitor A | Inhibitor B |
|---|---|---|---|
| 0 | 0 | 0 | 0 |
| 2 | 33 | 20 | 17 |
| 4 | 50 | 33 | 25 |
| 8 | 67 | 50 | 33 |
| 16 | 80 | 67 | 40 |
| 32 | 89 | 80 | 44 |
| 64 | 94 | 89 | 47 |
Plotting directions: Put substrate concentration on the x-axis (0–64) and reaction rate on the y-axis (0–100). Use one consistent scale, plot all three series, draw a smooth curve of best fit for each rather than joining points with straight segments, and add a key. Extend each curve cautiously towards its plateau. Identify the inhibitor whose curve approaches the control's maximum rate more slowly, then identify the inhibitor whose curve plateaus near half the control maximum. Justify both classifications using the effect of added substrate and the inferred maximum rate.
📁 Formative Cell Biology Mastery Portfolio — Section 6: Enzyme Kinetic Curves
Complete this formative practice section in your exercise book. This enzyme-kinetics work prepares you for the external standard; it is not a separate NZQA submission. Use the supplied dataset and teaching above, so no external graph sheet or case-study source is required.
Section 6 Requirements:
1. Inhibitor Graph: Plot the three series in the supplied table, label each curve, and classify Inhibitors A and B as competitive or non-competitive.
2. Denaturation Analysis: In one paragraph, explain how high temperature can alter interactions maintaining tertiary structure and active-site shape. State why activity falls and why reversibility depends on the protein and conditions.
3. Helper-Molecule Explanation: Distinguish a cofactor from a coenzyme, give one example of each from the teaching above, and explain how a required helper can affect enzyme activity.
Exit Verification | Ka Mutu Hoki (5 min)
Exit Check:
"My Section 6 graph distinguishes competitive from non-competitive inhibition, and my explanation connects temperature-driven structural change to active-site function."
Teacher Planning & NCEA Alignment
NCEA Level 2 Biology Alignment (4 Credits External):
- Factors Affecting Enzymes: Demonstrate understanding of temperature, pH, substrate concentration, and enzyme inhibitors.
- Denaturation: Explain molecular mechanisms of protein unfolding and loss of active site specificity.
Vocabulary: Optimum temperature, thermal denaturation, optimum pH, saturation point, competitive inhibitor, non-competitive inhibitor, allosteric site, tertiary structure, cofactor, coenzyme.
Paired concept in Guided Media & Evidence: enzyme factors & inhibition →