Enzymes are biological catalysts that speed up chemical reactions without being changed themselves. They are globular proteins that contain an active site where substrates bind and reactions occur. Enzymes lower the activation energy of reactions, allowing reactions to proceed more quickly. The lock-and-key and induced fit hypotheses describe how enzymes and substrates interact. An enzyme's activity can be affected by factors like temperature, pH, substrate and enzyme concentration. Enzymes can be immobilized to increase stability and allow continuous reaction processes. Common immobilization methods include cross-linking and adsorption.

1. Module 1
Section 1.2
Enzymes
AS Biology

2. Specification

3. Enzymes
 Enzymes are biological catalysts
 This means they speed up reactions without
being chemically changed themselves
 They are GLOBULAR proteins
 See notes on molecules to recall what these are

4. Enzyme Definitions
 Active site
 This is the region of the enzyme where catalysis
occurs and substrates fit
 Specificity
 An enzyme may catalyse only one, or else lots of
reactions. Its specificity determines this. An enzyme
that catalyses one reaction is a highly specific
enzyme.
 Affinity
 This is how strong an enzyme binds its substrates

5. Active Site
 The substrate is held in the active site by a
variety of bonds, such as hydrogen bonds and
electrostatic interactions

6. Enzyme Definitions
 Cofactors
 These are non-protein chemical compounds that
are bound to proteins and that are necessary for the
protein to have biological activity. “Helper
molecules” that are usually inorganic molecules.
Common examples include NAD+, FAD, Coenzmye
A, Mg2+
 Coenzymes
 A loosely bound cofactor, usually an organic
molecule
 Prosthetic group

7. Why do reactions take so long?
 For a reaction to occur, say A and B turning into C
 The rate will depend on how long A and B take to
associate and then turn into C
 This depends on how much energy you can
supply to make this happen – the ACTIVATION
ENERGY

8. Enzymes and Activation energy
 Enzymes function by lowering the activation
energy for reactions so that can be performed
easier

9. Enzyme-Substrate complex
 The enzyme binds both substrates, and lowers
the reactions activation energy
 This is called the ENZYME-SUBSTRATE
COMPLEX
 This allows the reaction to occur faster than if the
reactants were floating about free in solution

10. Models of enzyme action
 How enzymes work is quite an open area of
debate in biology!
 The main theories for how enzymes work are;
 The lock and key hypothesis
 The induced fit hypothesis

11. The lock-and-key hypothesis
 In this model;
 The reactants fit exactly into the enzyme active
site like a key fits into a lock. Once the catalysis
has occurred, the products are a different shape
and fit than the reagents and so they fall out of
the active site and the enzyme is free to start a
new reaction

12. The induced fit hypothesis
 In this model;
 The reagents don’t fit exactly into the enzymes
active site. But because enzymes are globular
proteins with flexible shapes, the enzyme
changes its active site shape to accommodate
the reagents

13. How can we make enzymes work
better?
 Because enzymes are proteins they are easily
affected by pH, temperature and concentrations
of starting materials

14. The effect of heat on enzyme
activity
 Enzymes are held together by hydrogen bonds and
other weak(ish) bonds
 At temperature above body temp (37 oC), these
bonds being to break and enzymes will no longer
function. But from 0 to 37, the enzyme activity will
steadily rise! Not all enzymes however are like this, it
depends on each particular enzymes OPTIMUM

15.  As complex, folded proteins, enzymes are susceptible
to changes in pH. Like with temperature, there is an
OPTIMUM pH for every enzyme
 For instance the enzymes in your stomach love being
at pH 1 or 2. Yet enzymes that are found in your blood
will only work well at pH 7.4-7.6. On either side of the
optimum pH the enzyme rate will decrease to 0 as the
pH is not optimum.
The effect of pH on enzyme activity

16.  Substrate means that thing that will be reacted
with and changed by the enzyme
 As you put in more substrate, the enzyme will
work and convert it to product! And this will
happen in a directly proportional way until ALL the
enzyme active sites are filled and the enzymes
The effect of substrate concentration
on enzyme activity

17.  Amount of enzyme will also affect a reactions
rate. As you put in more enzyme, the rate will
increase proportionally as there is nothing to slow
down the speed of the enzyme.
 Eventually however, the amount of substrate will
begin to limit the reaction and the graph will level
off.
The effect of enzyme concentration on
enzyme activity

18. Summary

19. Enzyme Inhibition
 Competitive inhibitors
These bind to the active site of the enzyme and prevent
substrates from binding and reacting.
 Non-competitive inhibitors
These bind anywhere on the enzyme EXCEPT the active
site. This changes the shape of the enzyme and the
active site and so stops substrate binding.

20. Enzyme Immobilisation
 Enzymes are a multi-million pound business
because they are cheap to make and can be
used for a multitude of purposes
 They can make reactions happen that would
otherwise take hours or days to happen without
the help of an enzyme
 One way to increase the efficiency of enzyme
catalysed reactions is to immobilise the enzymes
on solid supports in such a way that their active
site is easy to access

21. Methods of immobilisation

22. Why do we bother immobilising?
 Immobilising an enzyme allows for cost effective
usage of enzymes
 Immobilising can lead to;
 Increased enzyme stability
 Increased pH tolerance
 Increased temperature tolerance
 It allows continuous flow operation compared to
time consuming batch operation

23. Batch vs. Continuous culture

24. Problems with immobilising
 Reduced enzyme
efficiency in some
cases as the steps to
immobilise the
enzymes can damage
them
 Sometimes the
enzymes get attached
the wrong way around
which means that the
active site cannot be
accessed by the

25. Lactose-free milk
 An example of
immobilised enzyme
continuous culture is in
the production of lactose
free milk for people who
suffer lactose intolerance
or for cats

26. Clinistix
 Medical diagnostic
kits use immobilised
enzymes to text for
diabetes and kidney
failure
 Pregnancy tests also
use immobilised
enzymes that detect
human gonadotrophin
in urine