4.4 Cofactors, Coenzymes and
Prosthetic Groups
First review @November 20, 2023
Practise Q's Done
The difference between cofactors and enzymes
some enzymes need non-protein ‘helpers’ in order to carry out their function as biological
catalyst
these helpers may transfer atoms/ groups from one reaction to another during a
multi-step pathway, or they form part of an enzyme active site
these helpers are called cofactors, if it is an organic molecule then it is called a
coenzyme
inorganic cofactors are obtained through diet as minerals: iron, calcium, chloride and
zinc ions
e.g. amylase contains a chloride ion that is necessary for the formation of a correctly
shaped active site
many coenzymes are derived from vitamins e.g. vitamin B3 is used to synthesise
nicotinamide adenine dinucleotide (NAD)— a coenzyme responsible for the transfer of
hydrogen atoms between molecules involved in respiration
NADP plays a similar role in photosynthesis and is also derived from vitamin B3
vitamin B5 is also used to make a coenzyme, coenzyme A— this is essential in the
breakdown of fatty acids and carbohydrates in respiration
Prosthetic groups
prosthetic groups, e.g. iron ion in haemoglobin, are cofactors— required by certain
enzymes to catalyse reactions
prosthetic groups are tightly bound to the enzyme and are a permanent feature, unlike
other cofactors
e.g. zinc ions form an important part of the structure of carbonic anhydrase— this
enzyme is necessary for the metabolism of carbon dioxide
4.4 Cofactors, Coenzymes and Prosthetic Groups 1
Prosthetic Groups
First review @November 20, 2023
Practise Q's Done
The difference between cofactors and enzymes
some enzymes need non-protein ‘helpers’ in order to carry out their function as biological
catalyst
these helpers may transfer atoms/ groups from one reaction to another during a
multi-step pathway, or they form part of an enzyme active site
these helpers are called cofactors, if it is an organic molecule then it is called a
coenzyme
inorganic cofactors are obtained through diet as minerals: iron, calcium, chloride and
zinc ions
e.g. amylase contains a chloride ion that is necessary for the formation of a correctly
shaped active site
many coenzymes are derived from vitamins e.g. vitamin B3 is used to synthesise
nicotinamide adenine dinucleotide (NAD)— a coenzyme responsible for the transfer of
hydrogen atoms between molecules involved in respiration
NADP plays a similar role in photosynthesis and is also derived from vitamin B3
vitamin B5 is also used to make a coenzyme, coenzyme A— this is essential in the
breakdown of fatty acids and carbohydrates in respiration
Prosthetic groups
prosthetic groups, e.g. iron ion in haemoglobin, are cofactors— required by certain
enzymes to catalyse reactions
prosthetic groups are tightly bound to the enzyme and are a permanent feature, unlike
other cofactors
e.g. zinc ions form an important part of the structure of carbonic anhydrase— this
enzyme is necessary for the metabolism of carbon dioxide
4.4 Cofactors, Coenzymes and Prosthetic Groups 1
