Summary of the some of the main groups of enzymes and the uses of co-enzymes, as well as the reaction profile of an enzymatic reaction.
Goes into detail about the 3 general mechanisms through which enzymes promotes catalysis (General acid-base, metal ion and covalent catalysis).
Covers how p...
Enzymes can be split into 6 main Reaction energetics In a reaction, enzymes will form a
groups based on its function: For a favourable reaction, ∆ G is number of complexes (which
Oxidoreductase – oxidation- negative (products have less free distinguishes them from chemical
reduction where oxygen and energy than the reactants). The catalysts). They also provide a
hydrogen are lost or gained. speed of a reaction is determined by specific space for the substrate
Cytochrome oxidase ∆ G ‡ . The higher the activation where the reaction is more
Transferase – transfer of functional energy, the slower the reaction. The favourable through tight binding –
groups e.g amino acid group. relationship between the activation the active site. The enzyme lowers
Acetate kinase energy and the reaction rate constant the activation energy without being
Hydrolase – hydrolysis (addition of is given by the Arrhenius equation used up in the process (ES and EP
H20 to substrate). Lipase, sucrase. K= A e−∆ G ‡ / RT (∆ G ‡ high = K low. are reaction intermediates), and all
Lysase – removal of groups without As the transition state in a reaction is the reactions are reversible.
hydrolysis. Oxalate decarboxylase unstable, anything which stabilises The enzyme and substrate bind to
Isomerase – rearrangement of this will speed up the reaction as it make an ES complex (little peak due
atoms within a molecule. Glucose- will lower the ∆ G ‡ . Catalysts do to energy need e.g to free-up the
phosphate isomerase. this, but note that they can’t make an active site/prepare substrate. The
Ligase – joining of two molecules unfavourable reaction favourable. enzyme enters its transition state
(using energy usually derived from complex ES‡, before forming the EP.
ATP breakdown). DNA ligase The last rise in G is due to the need
ES‡ of energy to break the bonds
between the enzyme and product in
EP. The largest peak gives you the
Co-enzyme: non-protein organic EP
energy of ES‡.
molecules required for catalysis e.g FAD
Note that enzymes don’t bind to the
and NAD+
substrate or product as this would
Co-factor: inorganic substances ES
mean that the free energy of ES
required for catalysis e.g metal ions
decreases so the difference between
Holoenzyme: combination of a protein
ES and ES‡ is larger giving a larger
with its co-enzyme/co-factor. Enzymes and Co- activation energy. They do however
Apoenzyme: The protein without its co-
bind tightly in the transition state to
enzyme enzymes stabilise it. This state is stabilised by
Co-enzymes/co-factors allow enzymes
the same forces that stabilise
to access chemistries that amino acid
protein folding.
side chains can’t access. Many of the
common co-enzymes are vitamins and
so have a dietary requirement. Too
much or too little can cause harm. E.g.
Niacin deficiency can cause pellagra,
and in large doses can damage the liver.
Common co-enzymes:
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