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Powerpoint presentation on Enzymes In Accordance with the CXC CAPE Syllabus
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ENZYMES PART II- FACTORS AFFECTING ENZYME ACTION
OBJECTIVESExplain the effects of pH, temperature, enzyme concentration and substrate concentration on enzyme action
Explain the effects of competitive and non-competitive inhibitors on enzyme activity
Investigate the effects of temperature and substrate concentration on enzyme activity
TEMPERATUREAs temperature increases, the kinetic energy of the enzyme and substrate molecules also increase
There is a greater chance of collision
Enzymes are inactive at low temperatures
Enzyme activity increases until an optimum temperature is obtained
TEMPERATUREIf the temperature goes beyond the optimum, the secondary and tertiary structures of the enzymes will be denatured or destroyed.
Bonding interactions are disrupted and the active site is lost.
Enzyme activity will be reduced
TEMPERATURE
TEMPERATUREA is the optimum temperature
TEMPERATUREThe change in rate of reaction for each 10C rise in temperature is called the temperature coeffecient, Q10
Q10 = rate of reaction at (x+10C)rate of reaction at x
*An example will be given for calculation purposes
pHEnzymes have an optimum pH at which they work best
Deviations from the optimum can cause bonds to be broken (especially hydrogen and ionic bonds), so the enzyme becomes denatured
These bonds contribute to the stability of the tertiary structure of the enzyme
Extremes in pH change the shape of the enzymes and their active sites
pH
CONCENTRATION OF ENZYMESGiven that all other factors remain constant, the rate of an enzyme-catalysed reaction is directly proportional to the concentration of the enzymes present.
SUBSTRATE CONCENTRATIONAs the substrate concentration increases, so will the rate of reaction
However, a point is reached where all the active sites become filled with substrates and there is no further increase in rate (Vmax)
Products will have to be released from the active sites for new ES complexes to form
SUBSTRATE CONCENTRATION
INHIBITORSThese are chemicals which reduce the rate of an enzyme-catalysed reaction
They can change the shape of the active site directly or indirectly
May be competitive or non-competitive
They are either reversible or irreversible
INHIBITORSCOMPETITIVEHas a shape resembling the normal substrate
Competes with the substrate to occupy the active site
INHIBITORS
INHIBITORSNON COMPETITIVEThey do not attach to the active site
Bind with the enzyme elsewhere but causes a change in the shape of the active site
Prevents the formation of ES complex
INHIBITORS
INHIBITORS
INHIBITORS
EXAMPLES OF INHIBITORSAntibiotics called sulphonamides act as competitive inhibitors
Their shape resembles para-aminobenzoate (PAB) which harmful bacteria use to make folic acid, which involves enzyme action
If folic acid is not made, the bacteria will die
EXAMPLES OF INHIBITORSHeavy metals like mercury and arsenic may completely inhibit enzymes
They combine permanently with sulphydryl groups
May cause precipitation of the enzyme molecules
EXAMPLES OF INHIBITORSThe enzyme succinic dehydrogenase converts succinate to fumarate in the Krebs Cycle (involved in respiration)
Malonate fits into the enzymes active site
Competitive inhibition results
EXAMPLES OF INHIBITIONAcetylcholinesterase breaks down the neurotransmitter acetylcholine at the synapses.
-Organophosphates found in nerve gases or insecticides inhibit this enzyme in a non-competitive way
EXAMPLES OF INHIBITORSPyrethroids paralyse insects by keeping the sodium channels open in neuronal membranes.
Pyrethroids inhibit oxidase enzymes
Organisms cannot metabolise the substance
Lethality persists
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