Enzymes are biological catalysts that are mostly proteins. They are highly specific and only work within a narrow pH and temperature range. Enzymes catalyze reactions by lowering the activation energy through mechanisms like lock-and-key or induced fit. Their activity depends on factors like substrate concentration, inhibitors, temperature, and pH. The Michaelis constant Km and maximum reaction rate Vmax can be determined graphically and provide information about enzyme-substrate binding and activity levels.
2. What?
• Enzymes are biological
catalysts.
• Enzymes increase rate of reaction by
providing an alternate pathway with
lower activation energy.
• They are responsible for thousands of
methabolic processes in living orgnisms.
3. B.7.1 Describe the characteristics of
biological catalysts (enzymes).
• Enzymes are proteins (mostly)
• Highly specific for their substrates
• Work in narrow pH range and temperature
• Enzyme activity depends on their tertiary and
quaternary structure.
• Work by either lock and key mechanism or by
induced fit model (enzymes change shape to fit
shape of substrate)
4. B.7.2 Compare inorganic catalysts and
biological catalysts (enzymes).
Inorganic catalysts Biological catalysts (enzymes)
Mineral ions/simple inorganic molecules Globular proteins (complex organic
molecules)
Can catalyze several different reactions Catalyze specific typesof reactions
(substrate specific)
Wider range, less sensitive to pH or
temperature changes
Narrow pH and temperature range
Increase rates by fractions Increase rates by 10^3-10^6
Are not regulated by other molecules Are regulated by specific molecules
(cofactors)
Are not synthesized in living cells Are synthesized in living cells by
ribosomes
Increase rate of reaction by lowering activation energy
5. B.7.3 Describe the relationship between
substrate concentration and enzyme
activity.
• At low [S] (substrate conc.) rate of reaction is
proportional to [S], 1st order,as there are active
sites available for binding.
• As [S] further increases, rate increase slows
down and eventually stops, due to occupation of
active sites.
• At very high [S], rate is constant (max rate), 0th
reaction order (unaffected), because all
enzymes are saturated with substrates.
6.
7. B.7.4 Determine Vmax and the value of the Michaelis
constant (Km) by graphical means and explain its
significance.
• Vmax: maximum rate of reaction, when
enzyme is saturated with substrate
• Km: is the concentration of substrate
which permits the enzyme to achieve half
Vmax. (experimentally determined)
The higher Km, the lower enzyme's activity.
8.
9. Importance of determining Km
• The Km of an enzyme, relative to the
concentration of its substrate under
normal conditions permits prediction of
whether or not the rate of formation of
product will be affected by the availability
of substrate.
10. An enzyme with a low Km relative to the physiological concentration of
substrate, is normally saturated with substrate, and will act at a more or less
constant rate, regardless of variations in the concentration of substrate within
the physiological range.
11. An enzyme with a high Km relative to the physiological concentration of
substrate, as shown above, is not normally saturated with substrate and
its activity will vary as the concentration of substrate varies, so that the
rate of formation of product will depend on the availability of substrate.
12. If two enzymes, in different pathways, compete for the
same substrate, then knowing the values of Km and Vmax
for both enzymes permits prediction of the metabolic fate of
the substrate and the relative amount that will flow through
each pathway under various conditions.
13. B.7.5 Describe the mechanism of enzyme action,
including enzyme substrate complex, active site
and induced fit model.
GENERAL PRINCIPLE
1. Substrate binds to active site of enzyme
2. Enzyme-substrate complex forms
3. Products + unchanged enzyme
14.
15. Induced fit model
• Specific substrate interacts with the active
site of enzyme, and both slightly change
their shape to fit together.
16.
17. B.7.6 Compare competitive inhibition and
non-competitive inhibition.
• Inhibitor: chemical that prevents substrate
binding to enzyme; deactivates enzyme.
• Competitve: when a inhibitor chemically
resembles substrate and therefore can bind to
enzyme's active site instead of substrate.
• Non-competitive: compound binds to other site
than active site what alters the shape of active
site thus preventing the binding between
substrate and enzyme.
18.
19. B.7.7 State and explain the effects of heavymetal
ions, temperature changes and pH changes on enzyme
activity.
Heavy metal ions:
• React irreversibly with -SH group by replacing H
atom and forming a covalent bond between S
atom and the heavy metal ion
• Ion poisons enzyme by binding to active site
• Ion disrupts folding of enzyme, structure
alterations
->> Lead to stuctural changes, reduction in activity
Heavy metal examples: mercury, chromium,
thalium, lead, zink, nickel.
20. Temperature changes
• Increacing temperature increases rate of
enzymatic reaction, i.e. product formation, until a
certain point. According to collision theory,
increased temperatures result in more frequent
collisions between enzyme and substrate.
• Rate of reacion drops sharply when certain
denaturation temperature is reached, i.e.
enzyme disintegrates, since hydrogen and other
non-covalent bonds are broken.
21.
22. pH changes
• At narrow pH range, enzyme is active.
• Deviations from optimum pH cause
denaturation of enzyme.
