Enzymes and Biotechnology
notes at end of 2.)
Aspects of the vitamin, food and drugs GCSE chemistry are on the "Extra
Organic Chemistry" page.
Living cells use chemical
reactions to produce new materials.
Living things produce catalysts called enzymes which allow chemical
reactions to occur quite quickly at ordinary temperatures and pressures.
Enzymes are powerful 'biochemical catalysts' and are widely used in the
food industry and are being used more and more to manufacture many other
chemicals. These biological catalysts promote most of the reactions in
The names of enzymes end
in ...ase e.g. amylase, protease, invertase, isomerase etc.
Cells contain protein
molecules that act as biological or biochemical catalysts, they are
known as ENZYMES.
The chemical reactions
brought about by living cells are quite fast in conditions that are
warm rather than hot.
This is because the cells use these enzyme catalysts.
and lock' mechanism is explained later on.
Enzymes are protein molecules which are usually
damaged by temperatures above about 45º C. Although not damaged by
lower temperatures, the reactions may be too slow to be of any use.
(see rates notes at the end of
Different enzymes work
best at different pH values.
The enzymes in yeast cells
(living organism's) convert
sugar into ethanol ('alcohol') and carbon dioxide in the brewing and
drinks industry. A
similar process is used to convert sugar cane into ethanol and
distilled to use as biofuel.
glucose ==> ethanol and carbon dioxide in water and the absence of air.
==> 2C2H5OH(aq) + CO2(g)
This process occurs
efficiently between 25 to 55oC and is
called fermentation and is used to produce the
alcohol in beer and wine. The carbon dioxide dissolved in the
final alcoholic drink produces the fizz!
on raising agents in cooking: It is this reaction
producing bubbles of carbon dioxide which make dough mixtures rise in the
kitchen or food industry when yeast is used in baking bread or
cake making etc.
A simple laboratory
test for carbon dioxide is that it forms a milky precipitate with
However other enzymes
in living material can also catalyse oxidation with the oxygen in
air. When alcoholic drinks turn sour it is due to the alcohol
being oxidised to the weak organic acid ethanoic acid, commonly
know as 'vinegar'!
Enzymes are involved
in the following processes in the home
enzymes are used to bring about reactions at normal temperatures and
pressures that would otherwise require more expensive and more energy demanding
break down proteins and are used to
'pre-digest' the protein in some baby foods.
used to convert starch syrup into sugar syrup.
is used to make the sugar
for soft chocolates.
Isomerase* is used to
convert glucose syrup into fructose syrup, which is much sweeter
and therefore can be used in smaller quantities e.g. in slimming foods.
breaks down insoluble pectin polysaccharides and so is used in
clarify fruit juices.
Amylases break down carbohydrates and
break down fats.
are used in genetic
engineering and penicillin production.
The dairy industry
uses enzymes made by microorganisms (bacteria) to
produce yoghurt and cheese from milk.
in biological detergents help break down staining food
processes often depend on the immobilization of the enzyme:
Rates of Reaction - kinetics of Enzymes (full
rates of reaction notes)
Concentration: If either the substrate reactant
e.g. sugar, or
the yeast cell (enzyme) concentration is increased, the rate of reaction
increases in a simple proportional way. However, if the concentration of
enzyme is low but the substrate concentration is very high, the rate of
reaction rises to a maximum and then stays constant. This
is because the maximum number of catalyst sites for the 'key and lock' mechanism
are in use and the rate of reaction depends on the rate of diffusion of
substrate in and product out.
This would be the graph for an enzyme with
an optimum pH of 7.0
What is the optimum pH of an enzyme?
pH effect: The structure of the protein enzyme
can depends on how acid or alkaline the reaction medium is, that is, it is
pH dependent. If it is too acid or too alkaline, the structure of the protein
is changed and it is 'denatured' and becomes less effective. In the
optimum pH range, the enzyme catalysis is at its most efficient.
If the enzyme does not have the correct 'lock' structure, it
cannot function efficiently by accepting the 'key' substrate molecule. Most enzymes have an optimum pH of between 4
and 9, and quite frequently near the neutral point of 7.
enzyme pepsin has a peak at pH2 and can operate in the very acid
(hydrochloric) conditions of the stomach to help breakdown proteins for
digestion in the small intestine.
|Amylase (pancreas) enzyme
||6.7 - 7.0
||A pancreatic enzyme that
catalyzes the breakdown/hydrolysis of starch into soluble sugars
that can readily be digested and metabolised for energy
|Amylase (malt) enzyme
||4.6 - 5.2
breakdown/hydrolysis of starch into soluble sugars in malt
||Catalyses the breakdown of
potentially harmful hydrogen peroxide to water and oxygen.
Important in respiration/metabolism chemistry.
==> 2H2O(l) + O2(g)
breakdown/hydrolysis of sucrose into fructose + glucose, the
resulting mixture is 'inverted sugar syrup'.
+ H2O ==> C6H12O6 +
|Lipase (pancreas) enzyme
||Lipases catalyse the breakdown
dietary fats, oils, triglycerides etc. into digestible molecules
in the human digestion system.
|Lipase (stomach) enzyme
||4.0 - 5.0
||As above, but note the
significantly different optimum pH in the acid stomach juices,
to optimum pH in the alkaline fluids of the pancreas.
||6.1 - 6.8
||Breaks down malt sugars.
||1.5 - 2.0
breakdown/hydrolysis of proteins into smaller peptide fragments.
||7.8 - 8.7
breakdown/hydrolysis of proteins into amino acids. Note again,
the significantly different optimum pH to similarly functioning
||Catalyzes the breakdown of urea
into ammonia and carbon dioxide.
+ H2O(l) ==> 2NH3(aq)
|Note in the
data/information table above, that there are several instances,
amongst many, where two different enzymes perform the same
function, BUT at very different optimum pHs. This results in
versatility ie where same chemistry is needed in different
organs of the body - which incidentally, functions very nicely
with its ~3000 different enzymes. Almost every chemical reaction
in living organisms requires a specific catalyst or enzyme.
What is the optimum temperature of an enzyme?
Temperature: The structure of the protein enzyme can
depend the temperature. If the enzyme does not have the correct 'lock'
structure, it cannot function efficiently. The shape of the graph is
due to two factors. (1) The initial rise in rate of reaction is what you
normally expect for any chemical reaction. The increase in temperature
increases the average kinetic energy (KE) of the molecules to increase the chance of
the product forming from the higher KE 'fruitful collisions. (2) However as the
temperature rises further, the increasing thermal vibration of the enzyme
molecule causes its structure to break down (denature) and so the 'lock'
is damaged so the enzyme is less efficient (see key-lock below). This may
be due to the failure of weak intermolecular forces or actual
ionic/covalent bonds, but the 3D molecular structure of the
enzyme is changed so that the substrate molecule cannot 'dock in' to be
changed into products. The optimum temperature for
the fastest rate of reaction is often around 30-40oC (note our
body temperature is about 37oC, no coincidence!). Eventually at high
temperatures the enzyme ceases to function.
enzyme biochemical catalysis
E = free
= free substrate reactant molecule, E-S
= enzyme-reactant complex, E-P
= enzyme-product complex, E
= free enzyme, P
= free product
The enzyme is a complex
protein molecule, but there is a particular site where the reactant
molecule 'docks in' by random collision. The enzyme is sometimes referred to as the
and the initial reactant substrate molecule as the 'key', hence this is called
the 'key and lock' mechanism. This is also explains why enzymes are
very specific - you need the right molecular key for a particular
Once the 'reactant-enzyme
complex' is formed the enzyme function changes the reactant molecule
into the new product molecule.
The 'enzyme-new molecule
complex' breaks down to free the new product molecule and the enzyme
who's reactive site can now be re-used by another reactant molecule.
1. Compared to the
un-catalysed reaction, the enzyme provides a 'chemical change
route' with a much lower activation energy, and
so this greatly increases the rate of reaction as more molecules
have enough kinetic energy to react at the same temperature.
2. The products are shown as
two molecules, because there are quite often two products for each
step of the breakdown of a bigger molecule into smaller molecules e.g.
protein to 'smaller protein' + amino acid,
starch to 'smaller starch' plus a glucose molecule
etc. But there can be just one
product molecule e.g. when isomerase changes glucose into fructose.
There can also be two substrate reactant molecules being combined
to form a bigger molecule or a long natural polymer molecule like
starch being broken down to small sugar molecules. In other words there are lots of
3. Many drugs
work by blocking the sites normally used by enzymes. The
molecular key (the drug) goes onto the reactive enzyme site, but
stays there, so inhibiting enzyme activity which promotes harmful
chemical-organism effects in the body. The harmful effect might be
the production of toxic chemicals from a bacteria or the
reproduction of a harmful organism etc.
4. "Rates of
Reaction Notes" fully
explains all the factors affecting the rate of any chemical
reaction, including explaining experimental methods and reaction
profile diagrams and activation energy.
5. Different reactions
need different enzymes, and also if enzymes, which bring about the same
chemical change, are quite likely to have different optimum rate pH's or
temperatures. this phenomena is known as the specificity of
enzymes is related to the unique structure of each enzyme and its
'reactivity' limited to interaction with particular substrate
Advanced chemistry notes on Enzyme structure on the stereochemistry
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