Enzymes are biological catalysts that speed up biochemical reactions by lowering their activation energy. They are mostly proteins and are not used up in the reactions they catalyze. Enzymes can catalyze both anabolic reactions that build up complex molecules and catabolic reactions that break down complex molecules. They are classified based on the type of reaction they catalyze such as hydrolases, oxidoreductases, transferases, lyases, isomerases, and ligases. Enzyme activity is affected by factors like temperature, pH, and substrate and enzyme concentrations, with most enzymes having an optimal temperature and pH at which their activity is highest before they become irreversibly denatured.
2. Introduction of Enzymes Biological catalysts which speed up biological reactions by lowering the activation energy required for them to take place Mostly made up of proteins Not used up or chemically changed at the end of the biological reaction
3. Introduction of Enzymes (Cont.) Can be used again and again Produced only when needed Catalyse reversible reactions E + S ⇌ ES -> EP ⇌ E + P (E= Enzyme, S= Substrate, P=Product)
4. Enzyme-Catalysed Reactions Anabolic reactions Synthesis of simpler substances into complex ones Amino acids -> Polypeptides -> Proteins Catabolic reactions Breakdown of complex substances into simpler ones Hydrogen peroxide -> Oxygen + Water 2H2O2-> O2 + 2H2O To prevent the poisonous effect of hydrogen peroxide
5. Classification of Enzymes Hydrolases (Hydrolysis) Catalyse hydrolytic reactions in the body (eg. Of digestion) Oxidoreductoases (Oxidation – Reduction) Transferases (Transfer groups of atoms) Lyases (Add/Remove atoms to/from a double bond) Isomerases (Rearrange atoms) Ligases (Combine molecules using ATP)
7. Characteristics of Enzymes Speed up chemical reactions Small amount is needed to catalyse a reaction because enzymes can be used again and again The shapes of the active sites make enzymes highly specific, meaning they can only interact with 1 type of substrate to form an enzyme-substrate complex Presented using the ‘lock and key’ hypothesis
8. “Lock and Key” Hypothesis The active site of an enzyme molecule = lock; substrate molecule that the enzyme acts on = key When the enzyme and substrate molecules are bound together, they form an enzyme-substrate complex Substrate molecule is subsequently converted into products Product molecules leave the active site Enzyme molecule is free to bind with more substrate molecules
9. “Induced Fit” Model Enzyme molecule can undergo adjustments at its active site Binds more tightly with substrate molecule Facilitates binding at active site and speeds up rate of chemical reaction
11. Temperature Optimum temperature – the temperature at which an enzyme is the most active (can catalyse the most number of reactions per second) Rise in temperature (till optimum) -> Increase in enzyme activity Kinetic energy of particles increases Increases the chance of substrate molecules fitting into the active sites of enzyme molecules More rapid formation of enzyme-substrate complexes Increase in formation of products
12. Temperature (Cont.) When temperature exceeds the optimum temperature of enzyme activity, it starts to fall rapidly H-H bonds in enzymes break, leading to the denaturation of enzymes Unique 3-dimensional structure lost Denaturation is irreversible
13. pH Optimum pH = maximum activity Most enzymes lose their abilities to catalyse reactions at pH 3 and 11 Extreme changes in pH of a solution will denature the enzyme, just like temperature
14. pH (cont.) Slight changes in pH is enough to change the electrostatic charges of the active site of enzyme and substrate Electrostatic repulsion occurs Inhibits the formation of enzyme-substrate complex
15. Substrate and Enzyme Concentrations Substrate concentration increases -> rate of reaction increases Saturation of enzyme molecules (all being made use of) Reaction cannot take place Increase in enzyme concentration will increase the rate of reaction again
16. Coenzymes Not made up of protein (unlike enzymes) Organic compounds Bind with enzymes before the latter can catalyse reactions
