Class presentation

1. 3. The chemistry of life
3.6 Enzymes

2. Enzymes: are globular proteins that work as catalysts – they speed
up chemical reactions without being altered themselves.
Active site: a special region on the surface of the enzyme where
substrates bind.
Substrate: the substances that enzymes convert into products.

4. Lock and Key Hypothesis
• The substrate and the active site match each other
in two ways: structurally and chemically
a) Large globular protein
enzyme
b) Active Site where the
substrate combines to the
enzyme
c) Substrate which fits the
active site
d) Activated complex. The
substrate is weakened to
allow the reaction.
e)Unchanged enzyme/ re-
used at low concentrations
f) Product of the reaction

6. 3.6.3 Explain the effects of temperature, pH and
substrate concentration on enzyme activity.
• Explain means to give a detailed account of causes, reasons or mechanisms.
• Effect of temperature on the rate of an enzyme catalysed reaction:
• (a) As the temperature increases enzyme stability decreases. The kinetic energy of
the enzyme atoms increases causing vibrations in the enzyme molecule that lead
to the hydrogen bonds to breaking, shape changes in the active site.

7. 3.6.3 Explain the effects of temperature, pH and
substrate concentration on enzyme activity.
• Explain means to give a detailed account of causes, reasons or mechanisms.
• Effect of temperature on the rate of an enzyme catalysed reaction:
• (b) As the temperature increases the kinetic energy of the substrate and enzyme
molecules also increases. Therefore more collisions of the substrate with the active
site and the formation of activated complex's and product. The rate of reaction is
increasing.

8. 3.6.3 Explain the effects of temperature, pH and
substrate concentration on enzyme activity.
• Explain means to give a detailed account of causes, reasons or mechanisms.
• Effect of temperature on the rate of an enzyme catalysed reaction:
• (c) The optimal temperature (X) is the highest rate of reaction. Compromise
between decreasing enzyme stability and kinetic energy of the reactants.

9. 3.6.3 Explain the effects of temperature, pH and
substrate concentration on enzyme activity.
• Explain means to give a detailed account of causes, reasons or mechanisms.
• Effect of temperature on the rate of an enzyme catalysed reaction:
• (d) Higher temperature increases the kinetic energy of the enzyme atoms so much
that they break bonds, change shape of the active site.

11. 3.6.3 Explain the effects of temperature, pH and
substrate concentration on enzyme activity.
• pH also affects the rate of reaction of
an enzyme catalysed reaction.
• At the optimal pH (a) or (b) the
maximum rate of reaction is
achieved.
• Above or below the optimal pH the
rate decreases.
• The change in rate is because bonds
are made and broken which change
the shape of the active site and
therefore decrease the rate of
reaction.
• The two enzyme shown in the image
illustrate the fact that different
enzymes can have very different
optimal pH.
• e.g. Blue curve = pepsin (a)= pH3,
Red curve =salivary amylase (b)= pH
7.2

12. 3.6.3 Explain the effects of temperature, pH and
substrate concentration on enzyme activity.
• (a) As the substrate concentration
is increased the rate of reaction
increases.
• There are more collisions between
the substrate and the enzyme such
that more activated complex's are
formed and therefore product per
unit time.
• (b) Further increases in substrate
also increase the rate but
proportionately less than
previously.
• The number of occupied active site
is increasing and there is
competition for the active site.
• (c) The rate is constant.

13. Denaturation
• Definition: Denaturation is a structural change in
a protein that results in the loss (usually
permanent) of its biological properties.
Enzymes are globular proteins, affected
by temperature and pH. If the shape of
the active site is changed considerably,
the enzyme will not work.
High temperatures denature the enzyme
because the extra energy increases
vibration, breaking intra-molecular
bonds.
pH causes denaturation because it
breaks hydrogen bonds.

14. Lactose-free milk
• Production of lactose-free milk is an example of an
industrial process depending on biological methods
(biotechnology). These methods are of huge and increasing
economic importance.
• Lactose is a disaccharide (glucose + Galactose) milk sugar
• Around 90% of all humans show some kind of lactose
intolerance.
• People who are lactose intolerant can drink milk if it is
lactose free.
• Lactase is an enzyme extracted from yeast that can digest
the milk sugar to glucose and galactose.

15. Lactose-free milk
• Process:
• Milk is treated with
industrially-processed
lactase (obtained from
Aspergillus niger)
• Lactase is immobilized in
alginate beads to avoid
enzymes in the final
product.
• Milk is re-circulated until
all lactose has been
converted

16. AHL
7.6 ENZYMES

17. Metabolic pathways
• Chemical changes in living things often occur with
a number of intermediate stages.
• Each stage has its own enzyme.
• Catabolic pathways breakdown molecules
• Anabolic pathways build up molecules
• Metabolic pathways consist of chains and cycles
of enzyme-catalysed reactions.
• The product of one reaction is the reactant of the
next reaction.

18. Metabolic pathways
–Linear chain pathways
• Cycle pathways

19. Example: Blood clotting
Platelet/cell damage

21. Enzyme inhibitors
• Enzyme inhibitors are molecules that interact
in some way with the enzyme to prevent it
from working in the normal manner.
• There are a variety of types of inhibitors
including: nonspecific, irreversible, reversible -
competitive and noncompetitive.
• Poisons and drugs are examples of enzyme
inhibitors.

22. A competitive inhibitor
is any compound which
closely resembles the
chemical structure and
molecular geometry of
the substrate. A noncompetitive inhibitor is a substance that interacts with
the enzyme, but usually not at the active site.

24. Example of competitive inhibition
• Ethanol is metabolized Ethanol
in the body by oxidation
to acetaldehyde, which Oxidation
is in turn further
oxidized to acetic acid by
aldehyde oxidase
enzymes. Normally, the Acetaldehyde
second reaction is rapid Aldehyde
so that acetaldehyde oxidase
does not accumulate in
the body.
Acetic acid

25. Example of competitive inhibition
• A drug, disulfiram Ethanol
(Antabuse) inhibits the Oxidation
aldehyde oxidase which
causes the accumulation of
acetaldehyde with
subsequent unpleasant
Acetaldehyde
side-effects of nausea and Aldehyde
oxidase
vomiting.
• This drug is sometimes used
to help people overcome Acetic acid
the drinking habit.

27. Example of non-competitive inhibition
• ACE inhibitors help control blood
pressure.
• When blood pressure drops, the
vessels are constricted to reduce
the amount of blood.
• In people with hypertension or
heart failure, this reaction can
make their problem worse.
• ACE inhibitors are medications
that inhibit Angiotensin
Converting Enzyme – they
prevent increased blood pressure.

28. End-product inhibition
• It prevents a build-up of products
• Role of allosteric site: now it is the place
where the product can bind, causing a
conformational change in the enzyme’s active
site, temporarily inhibiting it.