Year 11 GK Biology – Enzymes Study Notes

Year 11 GK Biology – Enzymes

What are Enzymes?

• Enzymes are proteins (specifically compact proteins) that catalyze metabolic reactions while remaining unchanged at the end of the reaction.

• Like all globular proteins, enzyme molecules are coiled into a precise three-dimensional shape.

• The R groups (side-chains) are hydrophilic, located on the outside of the molecule, ensuring that enzymes are soluble in water.

• Enzymes are known as biological catalysts because they catalyze almost every metabolic reaction within a living organism, making them essential for life.

Types of Enzymes

Intracellular and Extracellular Enzymes

1. Intracellular Enzymes
      - Location of enzyme action: Operate within cells.
      - Examples: DNA polymerase (enzyme that synthesizes DNA in the nucleus).

2. Extracellular Enzymes
      - Location of enzyme action: Catalyze reactions outside cells.
      - Examples: Digestive enzymes, Fungi (which digest decomposing substrates before absorbing nutrients).

Mode of Action of Enzymes

Lock and Key Hypothesis

• The active site of an enzyme is the specific region where another molecule can bind, which is termed the substrate.

• In this analogy, the substrate is likened to a key that fits into the lock (the active site of the enzyme).

• Temporary bonds form between the substrate and some R groups of the amino acids in the enzyme.   

Enzyme-Substrate Complex

• Enzymes have a specific shape that only fits corresponding complementary substrates.

• Each enzyme typically interacts with a single type of substrate molecule due to the unique shape of the active site.

Induced Fit Hypothesis

• Unlike the lock-and-key model, in the induced fit hypothesis, both the enzyme and the substrate can adapt their shapes to ensure a perfect fit, enhancing catalytic efficiency.

• Example of an induced fit enzyme: Lysozyme
     - Lysozyme serves as a natural defense against bacteria, found in tears, saliva, and other secretions. It hydrolyzes polysaccharide chains forming bacterial cell walls.

Lowering of Activation Energy

Activation Energy Definition

• Activation energy is defined as the minimum amount of energy needed for a reaction to commence.

• A higher activation energy signifies a more challenging reaction scenario.

• Chemical reactions are often heated to provide energy to overcome activation energy thresholds.

How Enzymes Decrease Activation Energy

• Enzymes lower activation energy by positioning substrates closer, facilitating easier reactions at much lower temperatures than usually required.

Factors Affecting Enzyme Activity

1. Temperature:
      - Enzyme activity is affected by temperature variations.    - At low temperatures, enzymes may become deactivated.    - As temperatures rise, the rate of enzyme reaction typically increases until reaching an optimum temperature.    - Beyond this optimum temperature, enzymes may denature, rendering the active site incapable of binding to the substrate.

Denaturation of Enzymes

• Upon exceeding optimal conditions, the shape of the active site alters leading to its inability to interact with the substrate effectively.

• This results in a loss of enzymatic activity as the functional conformation of the enzyme is disrupted.