Biological Reactions are Regulated by Enzymes

Biological Reactions are Regulated by Enzymes

Understanding Enzymes

  • Enzymes are specialised proteins acting as biological catalysts to speed up the rate of reactions in cells.
  • Each enzyme has a particular active site that fits with its specific substrate akin to a lock and key model, leading to its specificity.
  • Enzymes function best at an optimum pH and temperature, deviations from which can result in a decrease in activity or denaturation.

Enzyme-Substrate Interactions

  • An enzyme and its substrate form a temporary enzyme-substrate complex to lower the activation energy for the reaction.
  • The changed shape of the active site after substrate binding is described by the induced fit model, leading to a transition state where the reaction occurs.
  • Once the reaction is complete, the product is released and the enzyme is free to catalyse another reaction, thus demonstrating their reusability.

Roles of Enzymes in Metabolic Pathways

  • Enzymes are integral in anabolic (building up) and catabolic (breaking down) metabolic pathways.
  • They assist in the synthesis of molecules such as proteins, DNA, RNA and polysaccharides in anabolic pathways.
  • In catabolic pathways, enzymes facilitate the breakdown of complex molecules to smaller ones releasing energy, such as in respiration and digestion.

Regulatory Mechanisms

  • The activity of enzymes can be regulated by factors such as the availability of substrates or enzyme inhibitors.
  • In competitive inhibition, molecules similar to the substrate bind to the active site of an enzyme preventing substrate binding.
  • In non-competitive inhibition, the inhibitor binds to an allosteric site (sites other than the active site) causing a structural change in the enzyme rendering it non-functional.
  • Feedback inhibition occurs when the product of a reaction inhibits the enzyme that produced it, helping to maintain homeostasis.

Clinical Significance of Enzymes

  • Malfunction or deficiency of enzymes can lead to pathological conditions. For instance, phenylketonuria results from a deficiency of the enzyme that metabolises phenylalanine.
  • Enzymes are used for therapeutic purposes, such as digestive enzymes in cystic fibrosis and DNA polymerase in PCR for DNA replication.
  • Understanding enzyme kinetics and regulation is vital for the design of effective therapeutic drugs.