Enzymes - Biological Catalysts
Understanding how enzymes speed up chemical reactions in living organisms
Life's Speed Controllers
Enzymes make reactions happen millions of times faster
Enzymes are proteins that act as biological catalysts. A catalyst is a substance that speeds up a chemical reaction without being used up itself. Without enzymes, many reactions in your body would happen too slowly to keep you alive. Enzymes can speed up reactions by millions of times.
Key Features:
- Reusable: After helping one reaction, an enzyme can be used again and again
- Specific: Each enzyme only works with one type of substrate (the molecule it acts on)
- Sensitive: Enzymes are affected by temperature, pH, and concentration
Every enzyme has an active site - a special region where the substrate binds. The shape of the active site is perfectly matched to the substrate, like a lock and key. When the substrate enters the active site, it forms an enzyme-substrate complex. The enzyme then converts the substrate into products and releases them.
Substrate Approaches
The substrate molecule moves toward the enzyme
Binding
Substrate fits perfectly into the active site
Reaction
Enzyme converts substrate into products
Release
Products leave, enzyme is ready again
Induced Fit Model (Advanced):
A more accurate model shows that the active site isn't rigid. When the substrate binds, the enzyme changes shape slightly to fit even better around the substrate. This is called induced fit. Think of it like a glove molding to fit your hand.
Why Are Enzymes Specific?
Each enzyme has a unique 3D shape determined by its amino acid sequence. The active site shape only matches one substrate (or a group of very similar substrates). This is why amylase breaks down starch but not protein, and why protease breaks down protein but not starch.
Temperature
As temperature increases, enzyme activity increases because molecules move faster and collide more often. Most human enzymes work best at around 37°C (body temperature) - this is the optimum temperature.
Above 40-45°C, enzymes denature - the high temperature breaks the bonds holding the enzyme's shape, permanently changing the active site. The substrate no longer fits, and the enzyme stops working. Denaturation is irreversible.
pH (Acidity/Alkalinity)
Each enzyme has an optimum pH where it works best. Most enzymes prefer neutral pH (~7), but there are exceptions:
- Pepsin (stomach enzyme) works best at pH 2 (very acidic)
- Amylase (saliva/pancreas) works best at pH 7-8 (neutral/slightly alkaline)
- Trypsin (small intestine) works best at pH 8 (alkaline)
Enzyme Concentration
More enzymes = more active sites available = faster reaction rate. As you add more enzyme, the rate of reaction increases proportionally - but only if there's enough substrate available.
Substrate Concentration
More substrate = more collisions with enzymes = faster reaction. However, at high substrate concentrations, all the enzyme active sites become occupied.
Amylase
Breaks down: Starch → Maltose (sugar)
Found in: Saliva, pancreas, small intestine
Protease
Breaks down: Proteins → Amino acids
Found in: Stomach (pepsin), pancreas, small intestine
Catalase
Breaks down: Hydrogen peroxide → Water + Oxygen
Found in: Nearly all living cells
Free Enzyme
Substrate Approaching
Enzyme-Substrate Complex
Product Release
Enzyme (with active site)
Stage 1: Free Enzyme
Enzyme with empty active site waiting for substrate
Current Activity: 100%
Optimum range: Maximum enzyme activity!
Enzyme
Question:
A student investigates the effect of temperature on the enzyme catalase. They measure the rate of reaction at 10°C, 25°C, 37°C, 50°C, and 70°C. Predict and explain the results.
Answer:
10°C - Low activity:
Molecules move slowly at low temperatures. Few successful collisions between enzyme and substrate. Reaction rate is slow.
37°C - Highest activity (optimum):
This is around human body temperature and the optimum for catalase. Maximum number of successful collisions per second. Reaction rate is at its peak.
70°C - No activity:
Enzyme is completely denatured. Active site is permanently damaged. Substrate can no longer bind. No reaction occurs.
What is the optimum temperature for most human enzymes?