Characteristics of enzymes
- globular proteins=soluble in water+structure has a pocket/cleft=active site
- biological catalysts
- specific=1 enzyme only catalyses a single reaction
- sensitive to pH and temp
- very large molecules=amino acids fold in a specific way to give a particular 3rd structure=forms active site=very few amino acids form this (<10)
Role of enzymes
- catalyse anabolic (synthesis) and catabolic (breakdown) reactions
- work tgt to form a metabolic pathway
- without metabolic reaction would to slow to support life
Models of enzyme action
- lock and key (Fischer 1890)
Substrate(s) binds to enzyme’s active site
Substrate=key+complementary shape to enzyme=lock
Resultant complex=ESC —> EPC=product x complementary=product(s) leave active site - induced fit model
Enzymes=physically flexible structure
Substrate binding to enzyme=induces change in enzyme’s structure (and sum the substrate(s) )
Alternations favour a chemical reaction
Effect of pH on enzymes
- below and above the optimum pH of an enzyme, solutions with an excess of H+/OH- ions=cause H-bonds, etc to break=alters shape of active site=ESCs form less easily until they can’t form at all=enzyme has completely denatured
Investigating effect of pH on enzyme activity
Wear goggles and gloves
Enzymes have the potential to cause allergic reactions if they come into direct contact with skin
Place single drops of iodine solution in rows on the tile
Iodine solution is orange-brown
Label a test tube with the pH to be tested
Use the syringe to place 2cm3 of amylase in the test tube
Equal volume and concentration of enzyme should be used so these variables are controlled and the effect of changing pH can be measured
Add 1cm3 of buffer solution to the test tube using a syringe
Use another test tube to add 2cm3 of starch solution to the amylase and buffer solution, start the stopwatch whilst mixing using a pipette
Equal volume and concentration of the substrate (starch) should be used so these variables are controlled and the effect of changing pH can be measured
Mixing enables the enzymes and substrate to be equally mixed
After 10 seconds, use a pipette to place one drop of the mixture on the first drop of iodine, which should turn blue-black
This test indicates whether starch is still present
Wait another 10 seconds and place another drop of the mixture on the second drop of iodine
Repeat every 10 seconds until iodine solution remains orange-brown
When the solution remains orange-brown it means amylase has broken down all of the starch so nothing is left to react with the iodine
Repeat experiment at different pH values
The less time the iodine solution takes to remain orange-brown, the quicker all the starch has been digested and so the better the enzyme works at that pH
Effect of temp on enzyme
- low temp prevent reactions starting/slow them down
Molecules move slowly=less kinetic energy=less frequent successful collisions by enzyme+substrate=less ESCs formed
Substrates+enzymes collide with less energy=less likely for bonds to be formed or broken (stopping the reaction from occurring) - higher temp cause reactions to speed up
Molecules move more quickly=more kinetic energy=more frequent successful collisions bw substrate+active sites of enzymes=more ESCs formed
Substrates+enzymes collide with more energy=more likely for bonds to be formed or broken (allowing the reaction to occur)
If temp continue to increase past a certain point, enzyme rate significantly decreases
increased kinetic energy and vibration of the enzyme molecules puts a strain on them=weak H-bonds break=3rd structure changes=active site changes=x longer complementary
Temp coefficient
Temperature coefficient = (rate of reaction at (x + 10) °C) ÷ (rate of reaction at x °C)
Effect of enzyme conc
- higher the enzyme concentration=greater the number of active sites available=higher chance of ESCs forming
- however enough substrate has to be present
If there isn’t enough at a point, enzyme conc wont increase ROR= amount of substrate=limiting factor
Effect of substrate conc
- greater the substrate concentration, higher ROR
- more substrate=more likely ESCs form
- enzyme concentration remains fixed but the amount of substrate is increased past a point=all available active sites eventually become saturated and any further increase in substrate concentration will not increase the reaction rate
App vs holoenzymes
Apoenzyme=inactive enzyme
Holoenzyme=active enzyme due to sum added to it
Co-factors definition
Non-protein substance that allow enzymes to catalyse reactions
Types of cofactors (coenzyme)
- coenzymes=small organic, non-protein molecules that bind to the active site for a short period of time
Bind before/at the same time as the substrate binds
Changed in sum way like the substrate
Recycled to be used again
Often used to carry chemical grps bw enzymes involved in a sequence
Made from vitamins from ur diet
Types of cofactors (inorganic ion)
- sum ions increase ROR=binding of ion=affects charge distribution=ESCs form more easily
- changes active site to be more complementary to substrate
- amylase requires Cl- to breakdown starch to glucose
- carbonic anhydrase requires Zn2+ to form H2CO3
Types of cofactors (prosthetic groups)
- cofactors that are permanent parts of enzymes
- can be found in other proteins not just enzymes
- vital to enzyme function
- contribute to 3D shape
- haemoglobin and carbonic anhydrase
Competitive enzyme inhibitors
- fits into active site=substrate molecule x enter
- amount of inhibition depends on conc of substrate and inhibitor molecules
- more inhibitor molecules=more of them collide with active site
Non-competitive enzyme inhibitors
- binds to enzyme’s allosteric site=changes shape of active site=ESCs x form
- substrate conc has no effect on ROR
