1. CHAPTER 3
ENZYMES
Leonardus, S.Si.

2. Mode of action of enzymes Factors that affect enzyme action
Content
Mode of action of enzymes
Factors that affect enzyme action

3. Learning Outcomes
Candidates should be able to:
(a) explain that enzymes are globular proteins that catalyse metabolic reactions;
(b) explain the mode of action of enzymes in terms of an active site, enzyme/substrate complex, lowering of activation energy and enzyme specificity;

4. Learning Outcomes
(c) [PA] follow the progress of an enzyme-catalysed reaction by measuring rates of formation of products(for example, using catalase) or rates of disappearance of substrate (for example, using amylase);
(d) [PA] investigate and explain the effects of temperature, pH, enzyme concentration and substrate concentration on the rate of enzyme-catalysed reactions;

5. Learning Outcomes
(e) explain the effects of competitive and non-competitive inhibitors on the rate of enzyme activity;
(f) use the knowledge gained in this section in new situations or to solve related problems.

6. Introduction
Enzyme name is usually end in –ase eg. Amylase, lipase, etc
Enzymes are used in several processes such as food manufacture, production of pharmaceuticals and chemicals, analytical methods and medical research
Without enzyme most of the reaction inside the cell cannot occur.
They don’t change the nature of the products reactions that they catalyse.

7. Introduction
A small amount of enzymes can bring about a lot of substrate to became product. This is because the enzyme is not destroyed by the reaction it catalyse.
All enzyme reactions are reversible.

8. Characteristics of Enzymes
Enzymes are globular proteins, which act as catalysts (speed up the metabolic reaction)
Enzymes are globular proteins enzyme molecule coiled into a precise 3D structure that hydrophilic R-chain on the outside to make sure enzyme soluble
Enzymes can be defined as biological catalysts
All enzymes are globular proteins. They dissolve freely in water and function independently in the protoplasm of the cell, outside the cell or attached to the membrane

9. Characteristics of Enzymes
Enzyme are globular proteins
Protein

10. Enzyme are globular proteins
Characteristics of Enzymes
Enzyme are globular proteins
back

11. Characteristics of Enzymes
Enzymes work by lowering the activation energy for the reaction that is catalyzed
An uncatalyzed reaction
requires a higher activation
energy than does a
catalyzed reaction
There is no difference
in free energy
between catalyzed
and uncatalyzed
reactions
Activation Energy is the energy required for a reactant or substrate to start a reaction.
Enzim mengkatalis reaksi dengan meningkatkan kecepatan reaksi.
Meningkatkan kec reaksi dilakukan dgn menurunkan energi aktivasi (energi yg diperlukan utk melakukan reaksi)

12. Characteristics of Enzymes
Activation Energy is the energy required for a reactant or substrate to start a reaction.
Enzim mengkatalis reaksi dengan meningkatkan kecepatan reaksi.
Meningkatkan kec reaksi dilakukan dgn menurunkan energi aktivasi (energi yg diperlukan utk melakukan reaksi)

13. Characteristics of Enzymes
Each enzyme acts on only one specific substrate, because there has to be a perfect match between the shape of the substrate and the shape of the enzyme’s active site to form an enzyme-substrate complex
ex: Hexokinase only acts on all hexoses. Glucokinase only acts on glucose not fructose.

14. Characteristics of Enzymes
Enzymes work specifically

15. Characteristics of Enzymes
Enzymes work specifically

16. Characteristics of Enzymes
Enzymes work specifically
Enzyme-substrate complex bind at active site

17. Enzyme work
There are two hypotheses have been put forward to explain enzyme activity:
Lock-and-key hypotheses
Induced-fit hypotheses

18. Lock-and-key hypotheses
Enzyme work
Lock-and-key hypotheses
Proposed by Emil Fischer (1890)
Theory: enzyme had a particular shape into which the substrate(s) fit exactly. i.o.w. the shape of the substrate is complementary to the shape of the active site of the enzyme
Substrate=key, enzyme=lock
i.o.w. : in other words

19. Enzyme work

20. Enzyme work Induced-fit hypotheses Proposed by Daniel Koshland (1959)
Theory: the initial shape of the active site of an enzyme might not be complementary to the shape of the substrate. Binding of the substrate to the active site induces a conformational change in the shape of the enzyme, which enables the substrate to fit more snugly into the active site. i.o.w. the active site has a shape complementary to that of the substrate only after the substrate is bound
Active site=flexible
After product getting loose, the active site back at first
i.o.w. : in other words
Induce: membujuk
Snugly: pas

21. Enzyme work

22. Enzyme work
Lock-and-key and induced fit model

23. Enzyme activity
The activity of an enzyme is the measure of how well it catalyses its specific
Factors affecting enzyme activity :
Enzyme concentration
Substrate concentration
Temperature pH
Presence of inhibitors

24. 1. Enzyme concentration Enzyme activity
The active site can be reused for several times, unless the substrate is limited, the rate of reaction will increase linear by increasing amount of enzyme

25. 2. Substrate concentration
Enzyme activity
2. Substrate concentration
At lower substrate concentration, some enzyme molecules have their active site “free”
When substrate is increased then the all active sites of enzyme molecules are “occupied”
Vmax is the rate of enzyme catalyzed reaction when all active site are saturated with substrate
Vmax

26. 3. Temperature Enzyme activity 3 Rate Of Reaction 2 4 1
Rate Of Reaction
Temperature/oC 3 4 1 2
At low temperatures, the reaction takes place only very slowly
As temperature continues to increase, the speed of movement of the substrat and enzyme molecules also continues to increase
The temperature at which an enzyme catalyses a reaction at the maximum rate is called the optimum temperature, at about C
At high temperature, enzyme loses the catalytic ability, known as denaturation (irreversible)

27. Optimal temperature of thermophilic bacteria
Enzyme activity
Optimal temperature of thermophilic bacteria

28. 4. pH (potential hydrogen)
Enzyme activity
4. pH (potential hydrogen)
Enzymes prefer to work at an optimum pH. Outside of its can cause denaturation of an enzyme
Most enzymes work fastest at a pH of somewhere around 7
However, such as the protease, pepsin, which is found in the acidic condition of the stomach, have different optimum pH
pepsin
amylase
Optimum pH
Rate Of Reaction pH

29. Optimal pH of some enzymes
Enzyme activity
Optimal pH of some enzymes

30. Optimal pH of some enzymes
Enzyme activity
Optimal pH of some enzymes

31. 5. Presence of Inhibitors
Enzyme activity
5. Presence of Inhibitors
An inhibitor is a substance that prevents an enzyme from catalysing its reaction. It is an inorganic or organic compound that slows down or stops enzyme reaction
Inhibitors:
Reversible Inhibitors
Competitive inhibitors
Non-competitive inhibitors
Irreversible inhibitors

32. Enzyme activity
REVERSIBLE COMPETITIVE INHIBITORS. These competitors are not the substrate molecule and they thus compete with the substrate. If they are in high concentration they may essentially inactivate the enzyme. These are not damage the enzyme only form low-binding with the enzyme
IRREVERSIBLE COMPETITIVE INHIBITORS. The competitor and substrate both compete for the active site but the competitor occupies the active site permanently thus deactivating the enzyme.
Carbon monoxide is an irreversible competitive inhibitor of hemoglobin. Oxygen is the substrate. Penicillin is an irreversible competitive inhibitor. heavy metals, cyanide, nerve gas, and arsenic

33. Enzyme activity
COMPETITIVE INHIBITORS are molecules that bind reversibly or irreversibly to the active site. Most naturally occuring competitive inhibitors are irreversible.
it is a chemical that competes with the substrate molecule to bind the active site of the enzyme
the inhibitor molecule is similar in structure to the substrate molecule.

34. succinic dehydrogenase is the enzyme
Enzyme activity
SUCCINIC ACID  FUMARIC ACID
succinic dehydrogenase is the enzyme

35. Enzyme activity

36. Enzyme activity
2. NON-COMPETITIVE INHIBITORS have no structural similarity with the substrate, the inhibitor and substrate do not compete for space in the active site. the inhibitor reacts with some other part of the enzyme molecule. It may be reversible or irreversible. Reversible non-competitive inhibition is a major metabolic control mechanism

37. Enzyme activity
2. NON-COMPETITIVE INHIBITORS The inhibitor and the substrate do not compete for the same site. If the regulatory site is occupied by the inhibitor then the shape of the active site is changed so that the substrate molecules cannot fit and react. This type of inhibition, often called allosteric control

38. Enzyme activity

39. Enzyme activity

40. End Product Inhibition

41. Enzyme activity
Feedback Inhibition

42. Sitation
Longman A-level Course in Biology, Core Syllabus, Vol.1, Hoh Yin Kiong, pp
Cambridge AS and A Level Biology, 2nd ed., Mary Jones & Friends, pp