MAINTAINING A BALANCE

HSC CourseCore Topic 1

- Factors Affecting Activity of Enzymes

Enzyme activityHow fast an enzyme is working = Rate 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

Factors Affecting Enzyme Activity

Temperature pH Substrate concentration Presence of activators

Coenzymes Cofactors

Presence of enzyme inhibitors

TemperatureThe effect: Most enzymes work

best at certain temperatures i.e. 370C in mammals.

The speed of the reaction decreases if the temperature varies from this level.

The activity of most enzymes increases as temperature increase.

Why does it happen?

Increased temperaturecauses molecules to

move more rapidly which in

turn causes more collisions between molecules.

This increases the chances

of the substrate colliding

with the enzyme’s active

site.

Denaturing If the temperature

rises above a certain level, the enzyme denatures (changes it shape so its active site is no longer correctly exposed) to become inactive and can no longer bind with the substrate.

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Temperature

0 20 30 5010 40 60

40oC - denatures

5- 40oC Increase in Activity

<5oC - inactive

Each enzyme has it own optimal temperature. The hydrogen bonds holding proteins together are broken by high temperatures and this disrupts their three dimensional shape.

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pH

1 3 42 5 6 7 8 9

pH

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1 3 42 5 6 7 8 9

Narrow pH optima

pH

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1 3 42 5 6 7 8 9

Narrow pH optima

WHY?

pH

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pH

1 3 42 5 6 7 8 9

Narrow pH optima

Outside this range also disrupt bonding of protein molecule Changes structure/shape and therefore alters the active site.

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Enzyme Concentration

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Enzyme Concentration

Enzyme Concentration

As enzyme concentration increses, rate of reaction increases.

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Substrate Concentration

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Substrate Concentration

Substrate Concentration

As substrate concentration increases, reaction rate increases until all active sites are filled. After this point, the reaction plateaus and can not proceed any faster. This point is called enzyme saturation point.

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Substrate Concentration

Substrate Concentration

Active sites full- maximum turnover

Presence of Activators

Coenzymes and Cofactors

Coenzymes – Organic molecules that may be required for enzyme activity

Cofactors – Inorganic molecules that may be required for enzyme activity

Presence of Enzyme Inhibitors

Other molecules that block the active site of enzymes. The stop the substrate from binding to the active site.