2. Enzymes
3.6.1 Define enzyme and active site.
3.6.2 Explain enzyme–substrate specificity. The lock-and-key
model can be used as a basis for the explanation. Refer to the
3D structure. The induced-fit model is not expected at SL.
3.6.3 Explain the effects of temperature, pH and substrate
concentration on enzyme activity.
3. Enzymes
3.6.4 Define denaturation.
Denaturation is a structural change in a protein that results in the
loss (usually permanent) of its biological properties. Refer only to
heat and pH as agents.
3.6.5 Explain the use of lactase in the production of lactose-free
milk.
4. Enzymes
Catalysts are substances which speed up chemical reactions.
Enzymes are Biological Catalysts.
– They speed up reactions that occur inside living systems.
Enzymes are Proteins Macromolecules.
Enzymes are globular proteins which have a unique shape.
Enzymes remain unchanged in the chemical reaction to be used
over and over again.
Without enzymes, many chemical reactions occur very slowly.
By making some enzymes, cells can control what chemical
reactions occur in their cytoplasm.
5. Enzymes are Specific for their Substrate
The reactants in enzyme catalysed reactions are called substrates.
An important aspect of enzyme function is that enzymes are highly
specific for a particular reaction.
They have a specific active site for binding with substrates.
– Substrates are the reacting molecules in the reaction.
The Active Site of the enzyme is a groove or cleft on the surface of the
enzyme into which the substrate molecule can bind.
Many enzyme names end in –ase
– Eg: amylase, catalase, sucrase, lipase
6. Enzymes – Lock and Key
This is an
example of the
Lock and Key
model of
Enzyme action.
7. Factors Affecting Enzyme Activity.
Most chemical reactions in a cell would occur very slowly or not
at all if it were not for special catalysts called enzymes.
Catalysts are substances that alter the rate of a chemical
reaction without being altered themselves.
The main factors affecting enzyme activity include:
– temperature.
– pH.
– substrate concentration.
8. Temperature & Enzymes
At low temperatures, there is little enzyme activity because the
molecules have little energy and little movement.
At high temperatures (above 50°C) the delicate 3D structure of
the protein can be altered.
The enzyme is denatured.
This happens when the tertiary structure is changed, altering the
active site.
The substrate molecules can no longer bind to the active site of
the enzyme.
Enzymes have optimum temperatures in which they work best.
9. Temperature & Enzymes
Ref: Biology, Allott
At high temperatures
enzymes are
denatured and stop
working. This is
because heat causes
vibrations inside
enzymes which break
bonds needed to
maintain the structure
of the enzyme.
Enzyme activity increases as temperature
increases. This is because collisions
between substrate and enzyme active
sites happen more frequently at higher
temperatures due to faster molecular
motion.
10. pH & Enzymes
Most enzymes work best around neutral, ph 6-8.
Some enzymes work best in acidic conditions:
– Pepsin – a digestive enzyme in your stomach pH-2
Some enzymes work best in alkaline conditions:
– Trypsin – enzyme made in the pancreas for breaking down protein pH- 8
In the wrong pH conditions for an enzyme, the tertiary structure of
the enzyme changes, affecting the shape of the active site
(denatured).
Once again, substrate molecules will not be able to bind to the
active site of the enzyme.
Different enzymes have their optimum operating pH.
11. pH & Enzymes
Ref: Biology, Allott
Optimum pH at which the
enzyme activity is fastest.
As pH increases or decreases from the optimum,
enzyme activity is reduced.
Both acids and alkalis can denature enzymes.
12. Substrate Concentration & Enzymes
At low substrate concentrations, enzyme activity is
directly proportional to substrate concentration. This is
because random collisions between substrate and active
site happen more frequently with higher substrate
concentration
At high substrate
concentrations, all the
active sites of the
enzymes are fully
occupied, so increasing
substrate concentration
has no effect.
Ref: Biology, Allott
13. Denaturation
Denaturation is changing the structure of an enzyme (or other
protein) so that it can no longer carry out its function.
Denaturation is usually permanent.
Denaturation can be caused by high temperatures and extremes
of pH.
Denaturing is caused when the bonds that form the tertiary
structure of a protein are broken. The protein loses its shape and
hence cannot function normally.
14. Use of Pectinase in Fruit Juice Production
Pectin is a complex carbohydrate found in the cell walls of plants.
Pectinase is the enzyme that breaks down pectin.
Pectinase is obtained by culturing a fungus (Aspergillus niger). The fungus grows
on fruits where it uses pectinase to soften the cell walls of the fruit so that it can
grow through it.
Fruits juices are produced by crushing the fruit to separate the liquid juice from the
solid pulp. When ripe fruits are crushed, pectin forms links between the cell wall
and the cytoplasm of the fruit cells, making the juice viscous and more difficult to
separate from the pulp.
Pectinase is added during crushing of fruit to break down the pectin and increase
the volume of juice obtained.
Pectinase also makes the juice less cloudy by helping solids suspended in the juice
to settle and be separated from the fluid.
15. Use of Protease in Biological
Washing Powder.
Protease enzymes break down proteins into soluble peptides or amino acids.
Laundry washing powders that contain protease are called biological washing
powders.
Protease is obtained by culturing a bacterium (Bacillus licheniformis), that is
adapted to grow in alkaline conditions. The protease has a high optimum pH of
between 9 and 10.
Detergents in laundry washing powders remove fats and oils during the washing of
clothes, but much of the dirt is made of proteins. If protease is added to the
washing powder, this protein is digested during the wash.
If protease is not used, protein stains can only be removed by using a very high
temperature wash. Protease allows much lower temperatures to be used, with
lower energy use and less risk of shrinkage of clothes or loss of coloured dyes.
16. Lactose intolerance
Lactose is a dissacharide sugar found in mammalian milk.
Lactase is the enzyme that breaks down lactose.
People unable to produce lactase fail to digest milk sugar.
As a result, bacteria in the large intestine feed on the
lactose, producing fatty acids and methane, causing
diarrhoea and flatulance
Such people are said to be lactose intolerant (common in
the Orient, Arabia and India)
Such people may be prescribed lactose-free milk, supplied
by the application of enzyme technology
18. Use of lactase in lactose-free
milk production
The enzyme lactase is obtained from bacteria and
purified
The enzyme is immobilised in a resin
Milk is passed through a column containing
immobilised lactase
Lactose-free milk is the product
The enzyme preparation can be re-used repeatedly
to produce large quantities of the product
19. Advantages
Lactose intolerant patients can
digest their food
Lactose free products can be
prepared for special diets
Lactase is used to hydrolyse
lactose in ice cream into glucose
and galactose to give it a sweeter
flavour
Stoney Creek Dairy
20. IBO guide:
3.6.1 Define enzyme and active site.
3.6.2 Explain enzyme–substrate specificity. The lock-and-key
model can be used as a basis for the explanation. Refer to the
3D structure. The induced-fit model is not expected at SL.
3.6.3 Explain the effects of temperature, pH and substrate
concentration on enzyme activity.
Aim 7: Enzyme activity could be measured using data loggers
such as pressure sensors, pH sensors or colorimeters.
Aim 8: The effects of environmental acid rain could be discussed.
21. IBO guide:
3.6.4 Define denaturation.
Denaturation is a structural change in a protein that results in the
loss (usually permanent) of its biological properties. Refer only to
heat and pH as agents.
3.6.5 Explain the use of lactase in the production of lactose-free
milk.
Aim 8: 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.
