• What is an enzyme?

• Enzyme actions

• ‘Lock and key’ hypothesis

• Effect of temperature on enzyme action

• Effect of pH on enzyme action

• Uses of enzymes in daily life

• protein

Protein

• a catalyst: speeds up chemical reactions in the body

• no change after a reaction

• a little amount is enough• specific

• works within a narrow range of pH and temperature

no changereused again

catalyst

What is an enzyme?

can be reused

Enzyme action: catabolic action

Enzym e Enzym e

enzyme-substrate complex

products

enzyme can be reused again

Enzym e

active site

substrate

Enzyme action: anabolic action

enzyme can be reused again

active site

substratesproductenzyme-substrate

complex

Enzym e Enzym e Enzym e

‘Lock and key’ hypothesis• Explains the specificityspecificity of enzyme actions

• Each key opens only one lock

• Each enzyme acts on one or a few substrates that fits into its active site

‘Lock and key’ hypothesis

key = enzyme

lock = substrate

lock and key =enzyme-substrate complex key has no

change

lock is open

Effect of temperature on enzyme action

• Works slowly at low temperature (inactive)

• Does not work at high temperature (denatured)

• Works best at a narrow range of temperature (optimum temperature)

Enzyme activity increases with a rise in temperatureIt then decreases with a further increase in temperature.

Effect of temperature on enzyme action

Temperature (oC)

Rate of enzyme action(arbitrary unit)

The optimum temperature is about 40 oC for most enzymes in human body.

until it reaches a maximum (the optimum temperature).

Enzyme activity increases with pH until a maximum (the optimum pH), then decreases as pH increases.

pH

Rate of enzyme action(arbitrary unit)

Different enzymes have their own optimum pH.

Effect of pH on enzyme action

• washing powder

• cleaning solution of contact lens

• meat tenderizers

Uses of enzymes in daily life

Enzymes• are special proteins that speed up chemical

reactions inside organisms (a biological catalyst)• take part in both catabolic and anabolic reactions• are specific• whose specificity explained by ‘lock and key’

hypothesis• whose activity changes with temperature and pH

Summary