Enzyme ActionLearning objective: to describe different models forenzyme action and to investigate factors which control the rate of an enzyme reaction

18th October

Lock and Key

Active Site

YES ….this is an enzyme molecule --- VERY COMPLEX

BUT …..it only is shaped for ONE SUBSTRATE

enzyme animation

Exceptions to Lock and Key

However certain substances can bind to the enzyme at sites other than theActive site and modify its activity (inhibitors/co-factors)

Idea that the enzyme is flexible

Induced Fit

Enzyme reactions

enzyme + substrate enzyme-substrate complex

Enzyme reactions

enzyme + substrate enzyme-substrate complex

E +S ES

Enzyme reactions

enzyme + productenzyme-substrate complex

E +PES

enzyme + substrate enzyme-substrate complex

E +S ES

Catabolic – breaking apart

THERE ARE ALSO ENZYMES that BUILD substrates as well as take substrates apart as you have seen …

Anabolic - building up / combining

Enzyme activity

How fast an enzyme is workingRate of Reaction

Enzyme activity

How fast an enzyme is workingRate of Reaction

Rate of Reaction = Amount of substrate changed (or amount product formed) in a given period of time.

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Enzyme activity

Variable you are looking at

Enzyme activity

Four Variables

Enzyme activity

Four Variables

Temperature

pH

Enzyme Concentration

Substrate Concentration

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Temperature

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Temperature

0 20 30 5010 40 60

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Temperature

0 20 30 5010 40 60

40oC - denatures

5- 40oC Increase in Activity

<5oC - inactive

Effect of heat on enzyme activtyIf you heat the protein above its optimal temperature

bonds break meaning the protein loses it secondary and tertiary structure

Effect of heat on enzyme activty

Denaturing the protein

Effect of heat on enzyme activty

Denaturing the proteinACTIVE SITE CHANGES SHAPE

SO SUBSTRATE NO LONGER FITS

Even if temperature lowered – enzyme can’t regain its correct shape

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pH

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pH

1 3 42 5 6 7 8 9

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pH

1 3 42 5 6 7 8 9

Narrow pH optima

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pH

1 3 42 5 6 7 8 9

Narrow pH optima

WHY?

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pH

1 3 42 5 6 7 8 9

Narrow pH optima

Disrupt Ionic bonds - Structure

Effect charged residues at activesite

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Enzyme Concentration

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Enzyme Concentration

Enzyme Concentration

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Substrate Concentration

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Substrate Concentration

Substrate Concentration

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Substrate Concentration

Substrate Concentration

Active sites full- maximum turnover