2.1.4 Enzymes
(a) the role of enzymes in catalysing reactions that affect metabolism at a
cellular and whole organism level
Enzyme: a biological catalyst that speed up metabolic reactions in living organisms and remains
unchanged at the end of the reaction
A small amount of catalyst can catalyse the conversion of a large number of substrate molecules
into product. The number of reactions per second is known as an enzymes turnover number.
Enzymes are more specific than chemical catalysts and work at conditions needed to sustain life
e.g. pH7.
Active site: indented area on the surface of an enzyme molecule, with a shape complementary to
the shape of the substrate molecule
Enzymes have a specific area consisting of around 6-10 amino
acids known as the active site. Its tertiary structure is therefore
important as its shape is complementary to the substrate
molecule. They are globular proteins.
Enzymes have an effect on both structure (e.g. collagen
production) and function (e.g. respiration).
(b) the role of enzymes in catalysing both intracellular and extracellular
reactions
Intracellular Enzymes
Some metabolic reactions are part of a metabolic pathway, which is a series of reactions where
each step is catalysed by a specific enzyme to produce a specific product. Each product is an
intermediate acting as a substrate for the next enzyme. The reactants, intermediates and
products are known as metabolites. Respiration and photosynthesis are both metabolic
pathways.
Catabolic: metabolites are broken down to smaller molecules and release energy
Anabolic: energy is used to synthesise larger molecules from smaller ones
Catalase
Catalase is an enzyme that protects cells from damage by reactive oxygen by breaking down
H2O2. It has a high turnover number of 6 million per second and is found in small vesicles called
peroxisomes. White blood cells ingest pathogens then use catalase to help kill the invading
microbe.
Optimum temperature: 45˚C
Optimum pH: 7
(a) the role of enzymes in catalysing reactions that affect metabolism at a
cellular and whole organism level
Enzyme: a biological catalyst that speed up metabolic reactions in living organisms and remains
unchanged at the end of the reaction
A small amount of catalyst can catalyse the conversion of a large number of substrate molecules
into product. The number of reactions per second is known as an enzymes turnover number.
Enzymes are more specific than chemical catalysts and work at conditions needed to sustain life
e.g. pH7.
Active site: indented area on the surface of an enzyme molecule, with a shape complementary to
the shape of the substrate molecule
Enzymes have a specific area consisting of around 6-10 amino
acids known as the active site. Its tertiary structure is therefore
important as its shape is complementary to the substrate
molecule. They are globular proteins.
Enzymes have an effect on both structure (e.g. collagen
production) and function (e.g. respiration).
(b) the role of enzymes in catalysing both intracellular and extracellular
reactions
Intracellular Enzymes
Some metabolic reactions are part of a metabolic pathway, which is a series of reactions where
each step is catalysed by a specific enzyme to produce a specific product. Each product is an
intermediate acting as a substrate for the next enzyme. The reactants, intermediates and
products are known as metabolites. Respiration and photosynthesis are both metabolic
pathways.
Catabolic: metabolites are broken down to smaller molecules and release energy
Anabolic: energy is used to synthesise larger molecules from smaller ones
Catalase
Catalase is an enzyme that protects cells from damage by reactive oxygen by breaking down
H2O2. It has a high turnover number of 6 million per second and is found in small vesicles called
peroxisomes. White blood cells ingest pathogens then use catalase to help kill the invading
microbe.
Optimum temperature: 45˚C
Optimum pH: 7
