Enzymes

• Enzyme inhibitors can be competitive or non-competitive.
• Lock and key model of enzyme-substrate interaction:

  • The shape of the substrate is complementary to the shape of the enzyme's active site
  • The substrate fits into the active site like a key into a lock
• Induced fit model:

  • The active site of the enzyme changes shape slightly to fit the substrate, even if they are not fully complementary in shape
• Enzymes speed up reactions by lowering the activation energy needed for the reaction to occur
• Enzyme-substrate interaction process:

  1. Substrate collides with the enzyme molecule

  2. Substrate binds to the active site of the enzyme, forming an enzyme-substrate complex

  3. The reaction occurs

  4. Products are released and the enzyme is free to bind to another substrate
• Co-enzymes definition

  Co-enzymes are organic molecules that when present increase the activity of an enzyme e.g. vitamins
• Factors affecting rate of enzyme controlled reactions include temperature, pH, concentration of reactants and presence of activators/inhibitors
• Optimum temperature varies from one enzyme to another but most enzymes have optimum temperatures around body temp (37°C)
• Inactive precursors are non-working enzymes that are synthesised to prevent cell damage
• Examples of a competitive inhibitor: carbon monoxide competes with oxygen for haemoglobin
• In end product inhibition the final product in the pathway inhibits an early- stage enzyme

  This causes a reduced rate of the metabolic pathway

  Its used to regulate metabolic pathways

  It's an example of a negative feedback and of a non competitive inhibition
• At high temperatures, the shape of the enzyme is affected as the ionic bonds holding the enzyme together break, a process known as denaturation
• The denature of enzymes occurs above the optimal pH level for the enzyme, affecting its active site where hydrogen bonds are crucial for enzyme-substrate interactions
• Competitive inhibitors are molecules that bind to the enzyme's active site, preventing the substrate from binding and decreasing the rate of the reaction
• When competitive inhibitors are present, the reaction can still happen, but at a decreased rate until it reaches Vmax
• Non competitive inhibitors bind to the allosteric site of the enzyme causing it to change its tertiary structure making the active site no longer complementary to the substrate.

  Thus decreases the rate of reaction
• The temperature coefficient (Q₁₀) indicates how much the rate of reaction increases when the temperature rises by 10°C
• Cofactors definition

  Cofactors are inorganic ions e.g. chlorine ion is a cofactor for amylase
• Prosthetic groups definition

  Prosthetic groups are tightly bound non amino acid component necessary for enzyme activity e.g. Zn2+ on carbonic anhydrase