Enymes Flashcards
How enzymes speed up reactions
Enzymes lower the activation energy of a chemical reaction often making reactions occur at a lower temperature than they usually do. This speeds up rate of reaction.
When a substrate fits into an enzymes active site it is know as a enzyme substrate complex. This lowers the activation energy because if two substrate molecules need to be joined being attached to the enzyme holds them closer together reducing any repulsion between the molecules so that they bond more easily.
If the enzyme is catalysing a breakdown reaction fitting into the active sites put strain on the bonds in the substrate so breaks down more easily.
The lock and key model vs the induced fit model
Enzymes only work with substrates that fit their active site the way a key only fits into a certain lock- complementary fit. The enzyme shape remained unchanged after enzyme activity. Evidence emerged that the active site should change in shape slightly .
The induced model suggests that the substrate does not only have to be the right shape for the active site but has to be bale to change the shape of the active site in the right way as well.
Enzyme properties
Enzyme properties are related to their tertiary structure. The active sites shape is determined by the enzymes tertiary structure which is in turn determined by the enzymes primary structure.
If the structure of the enzymes tertiary structure is altered in any way the shape of the active site will change
This means the substrate wont fit into the active site and the enzyme substrate complex will not longer form therefore no products.
The primary structure is determined by a gene if a mutation occurs in that gene it could alter the tertiary structure of the enzyme produced.
Effect of temp and how enzyme activity can be measured
The rate of an enzyme controlled reaction increases with temperature until optimum because more heat energy means more kinetic energy released meaning more frequent successful collisions between the active site and the substrate forming more es complexes. If the temp goes above around 45 the enzymes molecules vibrate more until the hydrogen bonds are broken causing a change in shape of the active site meaning it is no longer of a complementary fit to the substrate.
How enzyme activity can be measured
Measuring amount of end product at different times during experiment so reaction rate can be measured.
Measuring how fast the substrate can be broken down measuring amount of substrate left at different times during experiment.
Effect of PH
Optimum in most human enzymes = PH7
Above and below the optimum OH- and H+ ions can disrupt the hydrogen bonds and ionic bonds holding tertiary structure in place. Enzyme denatures active site changes shape.
Effect of substrate concentration
The higher the substrate concentration the faster the reaction, the more substrate molecules the more collisions with active site. Only true up until a saturation point after that all of the enzymes have been occupied. So adding more after saturation point makes no difference.
Effect of enzyme concentration
The more enzyme molecules in a solution the more frequent successful Collins between active site and substrate so increasing enzyme concentration increases rate of reaction. Unless substrate is limited therefore if all used up adding more enzymes will have no effect.
Competitive enzyme inhibitors
Similar shape to substrate molecules compete with substrate molecules to bind to active site but no reaction occurs
Instead they block the active site so the enzyme cannot reach it.
How much the enzyme is inhibited depends on the relative concentrations of the inhibitor and substrate.
If high concentration of inhibitor hardly any substrate will reach active site
If high substrate concentration substrate chance of reaching active site before the inhibitor increases.
Non competitive enzyme inhibitors
Inhibitor binds to the allotsteric binding site which changes the shape of the active site by changing tertiary structure. Cant overcome by increasing substrate concentration.
