Enzymes
What are Enzymes?
- Enzymes are biological catalysts, they speed up metabolic reactions like:
Photosynthesis, Respiration, Digestion, and Protein Synthesis.
An enzyme-catalyzed reaction converts substrate molecules into product molecules.
- Each enzyme is specific to one substrate because each enzyme has a unique shape.
- The active site is the portion of the enzyme that the substrate 'fits into'.
- The active site and its counterpart do not share the same shape.
- The substrate is shaped specific to its complementary substrate.
Lock and Key Hypothesis:
- The enzyme is like a lock, and the substrate is like a key. They must be compatible with each other.
- If the shape of an enzyme changes, it can no longer catalyse its reactions and is useless.
- The active site changes shape, and the substrate doesn't fit.
- The enzyme is denatured. This typically occurs when the pH or temperature is elevated.
- The enzyme isn't dead, but once denatured, it's permanent and irreversible.
Types of enzymes
- Different enzymes can break down different nutrients.
- Amylase + Carbohydrase enzymes break down Starch → Sugar (simple)
- Protease enzymes break down Proteins → Amino acids
- Lipase enzymes break down Lipids (fats and oils) → Fatty acids + Glycerol
EXAMPLES:
- Catalase: An enzyme that breaks down hydrogen peroxide (H₂O₂).
→ Hydrogen peroxide + Catalase → Oxygen + Water
- Amylase: An enzyme that breaks down starch into maltose in the mouth and small intestine. Carbohydrase
- Pepsin: An enzyme that breaks down proteins into the beginning of amino acids. Protease is found in the stomach.
- Pancreatic Lipase: The pancreas produces this enzyme, which is present in digestive fluid.
- Catalase: A common enzyme that breaks down hydrogen peroxide.
Effects
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Temperature:
- As temperature increases, the enzyme and substrate molecules have more kinetic energy. This means they move faster, and there are more frequent successful collisions between the substrates and the active sites of the enzymes. ESCs go on here.
- At temperatures above the optimum, enzymes denature. They have too much kinetic energy, so their shape changes. The active site is no longer complementary to the substrate, so the reaction stops.
- The rate, or how quickly the reaction occurs, increases as the temperature rises.
Effects of pH:
- If the pH is too far from the optimum, it denatures.
- All enzymes have a specific optimum pH at which they function optimally.
→ Pepsin works best at pH 2.
→ Salivary amylase works well at pH 6.
→ Alkaline phosphatase works well at pH 9.
Effect of Different Substrate and Enzyme Concentration:
- To investigate this, you need to create different concentrations of the substrate. You can achieve this by diluting a substrate solution.
- As the concentration of the substrate increases, the rate of reaction also increases. The graph ends in a plateau; due to the increased amount of the substrate, all active sites were occupied, and the enzyme couldn't work any faster.
- At low substrate concentration, not all active sites are being occupied.
- When all active sites are occupied, the reaction reaches its fastest rate and plateaus.
Q10 Values
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- Q₁₀ is the equation used to calculate the effect of temperature on the rate of an enzyme-controlled reaction.
- Q₁₀ can help you work out whether a reaction is enzyme-controlled or not.
- Enzyme-controlled reactions have a Q₁₀ of 2 (only between 5°C and optimum).
- If the Q value is greater than 2, then an increase of 10°C in temperature results in a doubling of the reaction rate.
Enzyme Concentration:
- As the concentration of the enzyme increases, the reaction also increases due to the availability of more active sites.
- The rate stops increasing when there are more active sites than the number of substrate molecules available.
