| Term | Definition |
|---|
| Function of enzymes | biological catalysts, speed up reaction rate by lowering the activation energy (doesn't alter reaction equilibrium) |
| Features of enzyme catalysed reaction | Much faster reaction rate, much milder reaction conditions, reaction specificity, tightly regulated |
| Who came up with the lock and key hypothesis | Emil Fischer |
| 1. | Oxidoreductases: transfer of electrons |
| 2. | Transferases: group transfer reactions |
| 3. | Hydrolyases: hydrolysis reactions |
| 4. | Lyases: Addition of groups to double bonds |
| 5. | Isomerases: Transfer of groups within the molecule to yeild isomeric forms |
| 6. | Ligases: Formation of C-C, C-S, C-O, C-N bonds by condensation reactions coupled to ATP cleavage |
| Lock and Key | enzymes can differentiate between D and L forms of sugars. Explains enzyme specificity but not catalysis |
| Who came up with the Induced fit hypothesis | Koshland |
| Induced Fit | Enzyme doen't simply accept its substrate, it must also distort it to something close to the transition state. |
| Covalent catalysis | involves formation of highly reactive, short-lived intermediate which is covalently attached to the enzyme |
| Acid-base cataysis | H+ transfer by acidic or basic groups within the protein |
| Coenzymes | small organic molecules that bind to enzymes enable it to catalyse reactions |
| Holoenzyme | functional enzyme with its coenzyme and/or metal ion |
| Apoprotein | protein part of enzyme |
| What does the rate of a reation depend on? | concentration of rate limiting species (ES) |
| When substrate conc is in excess rate is proportional to... | enzyme conc |
| At low [S].. | V increases lineraly with increasing [S]- first order |
| At increasing [S]... | rate increases gradually until a plateau is reached (Vmax) where the enzymes active sites are all occupied. Rate dependent on substrate conc (zero order kinetics) |
| when [s]= Km | reaction proceeds at half its max velocity |
| At low [S] rate of reaction depends on... | [S] |
| at Vmax the enzyme is | saturated |
| Assumptions made with M-M kinetics | -conc of substrate much greater than conc of enzyme, -Conc of substrate doesn't change much during the intial stages of reaction, -Little product present |
| V= | Vmax[S] / Km + [S] |
| Km= equation | breakdown of ES/ Formation of ES K-1 + K2/ K1 |
| Lineweaver-Burk Plot | 1/V against 1/[S] |
| LBP x intc= | -1/Km |
| LMP Y intc= | 1/Vmax |
| Km definition | how tightly substrate is bound to enzyme, smaller: more tightly bound |
| Turnover no | moles of substrate converted to product per mole of enzyme per second |
| Kcat= | Vmax / [Et] |
| enzyme efficiency= | Kcat/Km: high value= high efficiency |
| Progress curve | [P] vs time |
| Michaelis menton graph | V / [S] |
| greatest efficiency when | high Kcat and low Km (high affinity) |
| units Kcat | per sec |
| units Km | mM |
| Km (graph)= | [Substrate] at Vmax/2 |
| LBP gradient | Km/V or [S]/V |
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