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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
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