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.

1. EnzymesBy: Chen Dewei (2P304)

2. Introduction of EnzymesBiological catalysts which speed up biological reactions by lowering the activation energy required for them to take placeMostly made up of proteinsNot used up or chemically changed at the end of the biological reaction

3. Introduction of Enzymes (Cont.)Can be used again and againProduced only when neededCatalyse reversible reactionsE + S ⇌ ES -> EP ⇌ E + P (E= Enzyme, S= Substrate, P=Product)

4. Enzyme-Catalysed ReactionsAnabolic reactionsSynthesis of simpler substances into complex onesAmino acids -> Polypeptides -> ProteinsCatabolic reactionsBreakdown of complex substances into simpler onesHydrogen peroxide -> Oxygen + Water2H2O2-> O2 + 2H2OTo prevent the poisonous effect of hydrogen peroxide

5. Classification of EnzymesHydrolases (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)

6. Types of HydrolasesCarbohydrasesDigest carbohydratesAmylase (starch)Maltase (maltose)Sucrase (sucrose)ProteasesDigest proteinsPepsinErepsinLipasesDigest fatsLipase

7. Characteristics of EnzymesSpeed up chemical reactionsSmall amount is needed to catalyse a reaction because enzymes can be used again and againThe shapes of the active sites make enzymes highly specific, meaning they can only interact with 1 type of substrate to form an enzyme-substrate complexPresented using the ‘lock and key’ hypothesis

8. “Lock and Key” HypothesisThe active site of an enzyme molecule = lock; substrate molecule that the enzyme acts on = keyWhen the enzyme and substrate molecules are bound together, they form an enzyme-substrate complexSubstrate molecule is subsequently converted into productsProduct molecules leave the active siteEnzyme molecule is free to bind with more substrate molecules

9. “Induced Fit” ModelEnzyme molecule can undergo adjustments at its active siteBinds more tightly with substrate moleculeFacilitates binding at active site and speeds up rate of chemical reaction

10. TemperaturepHConcentrations of substrates in enzymatic reactionsFactors Which Affect Enzyme Activity

11. TemperatureOptimum 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 activityKinetic energy of particles increasesIncreases the chance of substrate molecules fitting into the active sites of enzyme moleculesMore rapid formation of enzyme-substrate complexesIncrease in formation of products

12. Temperature (Cont.)When temperature exceeds the optimum temperature of enzyme activity, it starts to fall rapidlyH-H bonds in enzymes break, leading to the denaturation of enzymesUnique 3-dimensional structure lostDenaturation is irreversible

13. pHOptimum pH = maximum activityMost enzymes lose their abilities to catalyse reactions at pH 3 and 11Extreme 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 substrateElectrostatic repulsion occursInhibits the formation of enzyme-substrate complex

15. Substrate and Enzyme ConcentrationsSubstrate concentration increases -> rate of reaction increasesSaturation of enzyme molecules (all being made use of)Reaction cannot take placeIncrease in enzyme concentration will increase the rate of reaction again

16. CoenzymesNot made up of protein (unlike enzymes)Organic compoundsBind with enzymes before the latter can catalyse reactions

17. Referenceshttp://users.rcn.com/jkimball.ma.ultranet/BiologyPages/E/Enzymes.htmlhttp://www.elmhurst.edu/~chm/vchembook/570enzymes.htmlhttp://www.mrothery.co.uk/studentswork/student%20presentations/Enzyme%20Activity.ppt

18. End of Presentation