2.4 Conduct a practical investigation to model the action of enzymes in cells

Enzymes and Metabolism

• Metabolism is the chemical processes that occur in an organism

• The speed at which these reactions occur at is called the metabolic rate

• Enzymes maintain the metabolic rate

• Enzymes are biological catalysts (found in living cells, and control the rate of reactions without being used up or changing themselves)

• Each acts on a specific substrate, breaking it down (catabolism) or synthesising it into more complex molecules (anabolism)

• Enzymes are proteins made of polypeptide, which fold to form the unique 3D structure 

  • This 3D structure is determined by the amino acid chains in polypeptides

• The 3D structure results in a unique active site, which fits the enzyme’s specific substrate and binds them together, forming an enzyme-substrate complex

Lock and Key Model

1. Substrate is drawn into the active site on the enzyme, which is a perfect fit

2. Enzyme-substrate complex is formed and reaction occurs

3. Product is released and enzyme remains unchanged

Induced Fit Model

1. Substrate is drawn into the active site on the enzyme, which is a slightly different shape to the substrate

2. Enzyme-substrate complex is formed, temporarily changing the enzyme’s shape, and reaction occurs

3. Product is released and the enzyme’s active site reverts to its original shape

Extra Information

• Enzymes are not used up in reactions, so are only required in small amounts

• Enzymes end in -ase and are often named after their substrate, eg. maltose and maltase, lactose and lactase, pectin and pectinase, lipids and lipases, proteins and proteases

  • Some don’t follow this convention, eg. hydrogen peroxide and catalase

• Enzymes have narrow ranges of optimum conditions (temperature, pH)

• Deviation from these optimum conditions lower the enzyme’s rate of activity, and can cause the active site to change shape and the enzyme to denature

• Due to enzymes’ sensitivity, cells must keep their internal environment constant