Enzymes – the story so far

1. Enzymes – the story so far • Enzymes are biological catalysts • Speed up reactions • Lower the energy needed to make reactions proceed • Enzymes react with substrates - very specific • Substrates have a structure complimentary to the active site of the enzyme (‘lock & key’) • Reaction complete = enzyme is unchanged • Can help ‘build-up’ or ‘breakdown’ reactions

3. Enzymes ctd. • Can be intracellular or extracellular • All made of protein, most globular • Amino acid sequence, and bonding between them, determines active site shape All have an active site

4. Factors affecting enzymes • Temperature: • Increasing temp makes atoms vibrate • above 40oC, vibrations break chemical bonds holding enzyme together • Structure unravels, active site is lost • = denatured • pH: • All enzymes have an optimum pH • Mostly close to neutral (5-9) • exceptions • - pepsin (2-3) • - alkaline phosphatase/phosphorylase (10)

5. Factors affecting enzymes • Enzyme concentration: • - enzyme-substrate reaction is very brief • - enzyme then moves on to the next substrate molecule • Turnover Number: • - no. of substrate molecules which an enzyme acts on in a given time • range: 100-4000 per second • Increased enzyme conc. = increased reaction rate • This will increase at a steady rate as long as there is substrate present

6. Factors Affecting Enzymes • Substrate Concentration: • Increasing substrate conc. will increase reaction rate • - more substrates binding with active sites • After a certain point all the active sites will be filled • Therefore increasing substrate conc. will no longer have an effect

7. Inhibitors • Competitive: • - compete directly for enzyme’s active site • - have a structure very similar to that of the substrate • - active site gets blocked • - reaction rate goes down as more sites get blocked by inhibitor • - increasing substrate conc. can return reaction rate to normal

8. Inhibitors • Non-Competitive: • - Don’t combine with active site • - Attach to another region on the enzyme • - This results in the active site structure being altered indirectly • e.g cyanide, heavy metals • - increasing substrate conc. will not return reaction rate to normal

9. Activation of Enzymes • Co-Factor: • A non-protein substance which helps to activate an enzyme • e.g. Zn, Fe, Cu, Mg • Often helps the substrate to fit the active site • Some are known as Co-Enzymes • These are mostly made of vitamins • e.g. Vitamin B - transfers Hydrogen during aerobic respiration

10. Other Enzymes • Many digestive enzymes start off inactive • In the gut they’re activated by enzyme activators • e.g. trypsin & chymotrypsin in the pancreas • - both protein digesting enzymes • - if permanently active, could digest the pancreas itself • InactiveActivatorActive enzyme • trypsinogen+ enterokinase trypsin • Chymotrypsinogen + trypsin chymotrypsin + trypsin

11. Inborn Errors of Metabolism (PKU) • Metabolism - sum of all the chemical reactions in the body • Products of one reaction often go into another reaction • All reactions controlled by enzymes • If a genetic fault occurs, the enzymes are not produced correctly • Intermediate metabolites accumulate and cause disorders • e.g. albinism, PKU