Chapter Note: Enzymes | Biology for GCSE/IGCSE - Year 11 PDF Download

 Page 1


Enzymes
? A catalyst is a substance that increases the rate of a chemical reaction but is not involved/used up in
the reaction
? Enzymes are proteins that function as a biological catalysts
? The function of enzymes is to catalyse metabolic reactions
? Properties of enzymes
? All enzymes are proteins
? Enzymes are made inactive by high temperatures
? Enzymes work best at a particular temperature
¦ Enzymes found in human body work best at 37 - 40 degree celsius
? Enzymes work best at a particular pH
¦ Some work best in acidic conditions while others work best in neutral or alkaline
conditions
? Enzymes are catalysts
? Enzymes are specific
¦ Each kind of enzymes will only catalyse one kind of chemical reaction
E n z y m e S u b s t r a t e P r o d u c t
Carbohydrase Carbohydrate
Amylase Starch Maltose
Maltase Maltose Glucose
Sucrase Sucrose Glucose and fructose
Lipases Fats/ lipids Fatty acids/ glycerol
Protease Proteans Polyperate/ amino acids
? Lock and key mechanism
? An enzyme works by allowing the molecule of the substance on which it is acting to fit into it.
The fit has to be perfect. The enzyme is like a lock and the molecule fits in like a key.
? The molecule that the enzyme wants to help change in called a substrate
? Every enzyme has an active site (amylase has a dent in it, it is its active site). The starch fits into the
active site of amylase, forming an enzyme-substrate complex.
? Enzyme activity
? Substrate enters active site
? Enzyme-substrate complex forms
? Reaction occurs
? Products form and leave active site
? Optimum temperature
? This is the temperature at which there is maximum ROR. This is best temperature for an
enzyme
Page 2


Enzymes
? A catalyst is a substance that increases the rate of a chemical reaction but is not involved/used up in
the reaction
? Enzymes are proteins that function as a biological catalysts
? The function of enzymes is to catalyse metabolic reactions
? Properties of enzymes
? All enzymes are proteins
? Enzymes are made inactive by high temperatures
? Enzymes work best at a particular temperature
¦ Enzymes found in human body work best at 37 - 40 degree celsius
? Enzymes work best at a particular pH
¦ Some work best in acidic conditions while others work best in neutral or alkaline
conditions
? Enzymes are catalysts
? Enzymes are specific
¦ Each kind of enzymes will only catalyse one kind of chemical reaction
E n z y m e S u b s t r a t e P r o d u c t
Carbohydrase Carbohydrate
Amylase Starch Maltose
Maltase Maltose Glucose
Sucrase Sucrose Glucose and fructose
Lipases Fats/ lipids Fatty acids/ glycerol
Protease Proteans Polyperate/ amino acids
? Lock and key mechanism
? An enzyme works by allowing the molecule of the substance on which it is acting to fit into it.
The fit has to be perfect. The enzyme is like a lock and the molecule fits in like a key.
? The molecule that the enzyme wants to help change in called a substrate
? Every enzyme has an active site (amylase has a dent in it, it is its active site). The starch fits into the
active site of amylase, forming an enzyme-substrate complex.
? Enzyme activity
? Substrate enters active site
? Enzyme-substrate complex forms
? Reaction occurs
? Products form and leave active site
? Optimum temperature
? This is the temperature at which there is maximum ROR. This is best temperature for an
enzyme
? Effect of temperature on ROR of enzyme
? At first increasing the temperature will increase the ROR because the molecules of the enzyme
and the substrate will have greater kinetic energy. They move around quickly and there are
more collisions. Therefore, more substrate molecules will fit into their respective active sites,
and the reaction will take place.
? As temperature continues to increase, the bonds holding the enzyme molecule together start to
break down. This changes the shape of the active site, so the substrate can no longer fit. The
enzyme has been denatured and it can no longer catalyze the reaction.
? Effect of pH on ROR of enzyme
? Many of the chemical bonds holding the structure of the enzyme are weak bonds. If these bonds
that hold the enzyme molecule in shape are broken by changes in ph, then the shape of the
active site can be altered. When the ROR is zero, the shape of the active site has changed so
much that the substrate molecules will no longer fit
? At these values of pH enzymes are denatured. Small changes in pH can affect the ROR without
denaturing the enzyme, but at the extremes of its pH range an enzyme becomes unstable and
denatures.
? Pepsin
? Requires acidic environment (pH 2)
? Found in stomach
? Amylase
? Mouth/salivary gland, duodenum
? Requires 7pH (neutral)