METABOLISM

The concept of metabolism• Metabolism = all the chemical reactions

taken place inside the living organisms• Metabolic reactions produce different

life processes, e.g. – photosynthesis– respiration– movement– growth– reproduction

Types of metabolism

• Catabolism : – breaking down of complex organic

molecules into simpler molecules, e.g. respiration

Types of metabolism

• Anabolism– building up of complex organic

molecules from simple molecules, e.g. photosynthesis

Control of metabolism

• Metabolic reactions can be controlled and speeded up by enzymes– metabolic reactions would be too slow

to occur if no enzymes are present!

Mechanism of enzyme action• Each enzyme has an active site

Mechanism of enzyme action

• Place where substrate binds with the enzyme

• Each enzyme only allows its specific substrate to fit with its active site exactly

• The enzyme and substrate molecules combine to form a temporary structure called enzyme-substrate complex

Mechanism of enzyme action

• The product molecules are then formed and they escape from the active site

Mechanism of enzyme action

• The product molecules are then formed and they escape from the active site

Mechanism of enzyme action

• The active site is free to attach to other substrate molecules

This hypothesis to explain the This hypothesis to explain the specificity of enzyme action is specificity of enzyme action is

calledcalled

•Biological catalyst

Nature and properties of enzymes

•Proteins in nature•Specific in action

– one kind of enzyme will catalyse only one kind of chemical reaction

Biological

found within living organisms

catalyst

substance which can speed up a chemical reaction

Nature and properties of enzymes• Catalyse reversible reaction in

both directions• Action affected by temperature

and pH– high temperature and extreme pH

can denature enzymes protein in nature

Effect of temperature on enzyme activity• Low temperature : low kinetic energy possessed

by the substrate and enzyme molecules

Lower reaction rate (and enzyme activity)The enzyme becomes inactive

Effect of temperature on enzyme activity• Higher temperature : more kinetic

energy possessed by the substrate and enzyme molecules

Higher reaction rate (and enzyme activity)

Effect of temperature on enzyme activity• The temperature which allows the

highest enzyme activity is called the optimum temperature

Effect of temperature on enzyme activity

• At temperature higher than the optimum temperature, the shape of the active site is changed

substrate can no longer bind to the active site of the enzyme

The enzyme is said to be denatured

Graph showing effect of temperature on enzyme activity

Effect of temperature on enzyme activity• Enzymes become inactive but not

denatured at low temperaturesThey can regain catalytic function when

the temperature increases

Effect of temperature on enzyme activity• Denaturation is a permanent processWhen an enzyme is denatured, its catalytic

function is lost permanently, and cannot be restored even it is put in lower temperature

Effect of temperature on enzyme activity• Different enzymes may have different

optimum temperature• The optimum temperature of many

enzymes in human body is not 37oC, even though this is our body temperature!– Our body temperature can provide a

better environment for the enzymes in our bodies to work

Effect of pH on enzyme activity• Optimum pH : the pH value at which

the enzyme has the highest activity• Different enzymes may have

different optimum pHs• pH of medium higher or lower than

optimum pH can denature the enzyme