Enzymes

Overview

• Chemical reactions in the human body are controlled by enzymes.
• Discovered by Anselme Payen in 1833.
• Enzymes are proteins or RNA that speed up biochemical reactions by modifying substrates.
• Known for their specificity (selective binding and modifying).

Mode of Action

• Enzymes lower activation energy, aiding the start of reactions.
• Enzymes have an Active Site where substrates bind and reactions occur.
• The active site is unique to a specific substrate due to its specific amino acid arrangement.

Cofactors

• Some enzymes need non-protein parts called cofactors:
  • Cations: Positively charged metal ions that temporarily activate the enzyme.
  • Organic Molecules: Vitamins or their products (coenzymes) that temporarily join the enzyme-substrate complex.
  • Prosthetic Groups: Permanently bound to enzymes.
• Holoenzyme: Active enzyme + coenzyme.
• Apoenzyme: Inactive enzyme without coenzyme.

Models of Enzyme Action

• Lock and Key Hypothesis: Substrate fits precisely into the enzyme's active site, like a key in a lock.
• Induced Fit Hypothesis: Enzyme changes shape to bind the substrate more tightly upon interaction.

Environmental Effects on Enzymes

Temperature

• Optimal temperature: 37°C.
• Higher temperatures can denature enzymes.

pH

• Affects acidic/basic amino acids in the active site.
• Extreme pH values can denature enzymes.

Concentrations

• Enzyme Concentration: Higher concentrations increase reaction rate up to a limit.
• Substrate Concentration: Higher concentrations increase reaction rate up to a limit.

Inhibition of Enzyme Activity

• Competitive Inhibitors: Block active sites, preventing substrate binding.
• Non-competitive Inhibitors: Bind elsewhere on the enzyme, distorting its shape and inhibiting action.