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