Enzymes are proteins that act as biological catalysts and speed up chemical reactions by lowering their activation energy. They have an active site that binds specifically to substrate molecules. The lock and key hypothesis states that the shape of the active site matches that of the substrate. Enzymes only work on specific substrates and are not used up in reactions. They are denatured and unable to function if the conditions of temperature or pH move outside their optimum ranges.

1. Biological catalysts

2.  A protein which acts as a catalyst, which
speeds up the rate of
reaction.
*All proteins are composed of sub-units
called amino acids.
*Proteins contain the elements carbon,
hydrogen, oxygen, nitrogen and sulphur.

3. Enzymes are special proteins
*There are hundreds of different enzymes but
*With the right enzyme present, the reaction happens
10
faster
each enzyme
speeds up only one kind of reaction
*Like all proteins, each enzyme molecule has a particular shape
*Any substance an enzyme acts on is called a substrate

4. enzyme
substrate A
substrate B
The substrate molecules fit the shape of the enzyme
12

5. 13

6. substrates combine temporarily with enzyme
enzyme joins substrates together
14

7. new compound released
by enzyme
enzyme unchanged
and ready for
next reaction
15

8. The last 4 slides show how an enzyme is involved in
combining substrates to create a larger molecule ANABOLISM
(a sucrose molecule from glucose + fructose)
The next sequence shows how an enzyme can help to
break a large molecule into smaller molecules CATABOLISM
(a sucrose molecule into glucose and
fructose molecules)
16

9. the shape of the substrate
molecule fits the enzyme shapethis is called
the active site
of the enzyme
17

10. substrate combines
temporarily with enzyme
enzyme will break
molecule here
18

11. substrate splits and
separates from enzyme
19

12. end-products
enzyme ready for
next reaction
20

13. They always produce the same end products
Although they take part in the reaction, they are not used up
Because enzymes are proteins, they are denatured by heat
or some chemicals
Denaturing involves a change of shape in the enzyme
molecule so that it cannot combine with the substrate
Individual enzymes work best at a particular temperature
and pH (acidity or alkalinity)
21

14. this substrate cannot combine
with this enzyme
this substrate cannot combine
with this enzyme
22

15. enzyme
denatured
by heat
denatured enzyme cannot combine with substrate
enzyme +
substrate
23

16.  A catalyst is a substance that speeds up the rate of
a chemical reaction but is not itself changed by the
reaction.

17.  Proteins are long molecules that are folded into a specific shape.
catalase amylase trypsinpepsin
Enzymes are proteins

18. Active site:
Enzyme

19. Active site:
The site on the
enzyme where the
reaction occurs
Enzyme
Substrate molecules

20. Active site:
The site on the
enzyme where the
reaction occurs
Enzyme
Product molecules

22.  The lock and key hypothesis states that the active site specifically
matches the shape of the substrate molecule
enzyme
Each enzyme is specific to one substrate molecule
or type of molecule
active site

23.  Enzymes will usually react with
only one substance.This can be
explained by the 'lock and key'
theory. If this theory is correct,
which of the following
substances, represented by P,
Q, R and S would be acted on
by enzyme A?

24.  Enzymes will usually react with
only one substance.This can be
explained by the 'lock and key'
theory. If this theory is correct,
which of the following
substances, represented by P,
Q, R and S would be acted on
by enzyme A?

25.  At low temperatures enzyme controlled reactions go slowly
because the molecules have low kinetic energy.
The rate of an enzyme controlled reaction is
affected by temperature

26. But this only occurs up to the
optimum temperature
(usually about 40oC)
The temperature at which
the rate of reaction is
fastest is known as the
optimum temperature
When temperature increases the reaction also
increases as the molecules have more kinetic energy

27. After the optimum temperature the heat causes
the enzyme to denature
 This means that cross linkages break and the enzyme changes
properties and shape and the active site no longer matches the
shape of the substrate molecule
+ than 40° C => cross linkages break down/loses shape and properties DENATURALIZATION

28. (HOW HOT SHOULD HE BE?)

29. Rate
Of
Reaction
Temperature/oC
0 10 20 30 40 50 60 70
Optimum temperature
Enzyme
is denaturing
Rate of reaction of an enzyme reaction changes
at different temperatures
Molecules gain
kinetic energy

30.  PH is a measure of ACIDITY (-7) or
ALKALINITY (+7)and is a mathematical
method for expressing the concentration of
H+ ions in solution.
 Most enzymes work best at a ph of 7/They
are affected by extremes of ph --
Exceptions: pepsin ph2 amylase ph 7 or +7

31.  Enzymes prefer to work at an optimum pH. Outside of its pH range
the enzyme is denatured.
Rate
Of
Reaction
pH
1 2 3 4 5 6 7 8 9 10 11 12
pepsin amylase
The activity and shape of enzymes is also
affected by pH
Optimum pH

32.  Proteases break down the coloured, insoluble proteins that
cause stains to smaller, colourless soluble polypeptides.
 Can wash at lower temperatures

33.  Pectinase break down substances in
apple cell walls and enable greater
juice extraction.
 Lactase breaks down lactose in milk
into glucose and galactose.
This makes milk drinkable for lactose
intolerant people.

34. a) membrane system
b) mitochondria
c) special vacuoles
d) cytoplasm

35.  Keywords:
enzyme
active sitesubstrate product
denaturetemperature
pH
optimum
catalase amylase
trypsin pepsinpectinase
lactase
protease
catalyst catalyse protein