1. Metabolism
Chapter 8

2. I. Thermodynamics

3. Metabolism
All the chemical reactions in an organism

4. Catabolic pathways Break down complex molecules into simpler molecules
Releases energy
Examples?
Digestive enzymes break down food to release energy

5. Anabolic pathway Build complex molecules from simple molecules
Consume energy
Example: Body links amino acids to form muscle in response to exercise

6. Energy
The ability to do work

7. Kinetic energy
Energy of movement

8. Potential energy Stored energy as a result of position or structure
Chemical energy – form of potential energy stored in molecules.
On the platform, a diver
has more potential energy.
Diving converts potential
energy to kinetic energy.
Climbing up converts kinetic
energy of muscle movement
to potential energy.
In the water, a diver has
less potential energy.
Figure 8.2

9. An example of energy conversion
Figure 8.3 
First law of thermodynamics: Energy can be transferred or transformed but
Neither created nor destroyed. For
example, the chemical (potential) energy
in food will be converted to the kinetic
energy of the cheetah’s movement in (b).
(a)
Chemical
energy

10. Thermodynamics Study of energy transformation in matter
First law: energy cannot be created or destroyed, only transferred or transformed
2nd law: Energy that is transferred or transformed increases entropy or the amount of disorder or randomness in the universe

11. The Second Law of Thermodynamics
Figure 8.3 
Second law of thermodynamics: Every energy transfer or transformation increases
the disorder (entropy) of the universe. For example, disorder is added to the cheetah’s
surroundings in the form of heat and the small molecules that are the by-products
of metabolism.
(b)
Heat
co2
H2O +

12. II. Free energy

13. III. ATP - Adenine Phosphate groups Ribose Figure 8.8 NH2 HC CH C N OOH N C HC
NH2
Adenine
Ribose
Phosphate groups - CH

14. Energy coupling
Use of exergonic process to drive an endergonic one

15. ATP Primary source of energy for coupling
Made up of adenine bound to ribose and three phosphate groups
When ATP is hydrolyzed energy is released in an endergonic reation

16. Energy is released from ATP When the terminal phosphate bond is broken
Figure 8.9 P
Adenosine triphosphate (ATP)
H2O +
Energy
Inorganic phosphate
Adenosine diphosphate (ADP)
P i
ATP drives endergonic reactions
By phosphorylation, transferring a phosphate to other molecules

17. ADP When ATP is hydrolyzed it become ADP
How many phophates does ADP have?
ATP synthesis from
ADP + P i requires energy
ATP
ADP + P i
Energy for cellular work
(endergonic, energy-
consuming processes)
Energy from catabolism
(exergonic, energy yielding
processes)
ATP hydrolysis to
ADP + P i yields energy
Figure 8.12

18. IV. Enzymes

19. Catalyst
Changes the rate of a chemical reaction without being altered in the process

20. Enzymes Macromolecules that are biological catalysts
Considered proteins

21. Activation energy
Amount of energy it takes to start a reaction, or the amount of energy it takes to break the bonds of reactant molecules
Enzymes speed up reactions by LOWERING activation energy

22. Exergonic reaction – energy released
Progress of the reaction
Products
Course of
reaction
without
enzyme
Reactants
with enzyme EA
EA with
is lower
∆G is unaffected
by enzyme
Free energy
Figure 8.15

23. Endergonic reaction – energy required

24. Parts of enzymes Substrate: enzyme reactants
Active sites: site where substrate binds
Enzyme substrate complex: formed when the substrate and enzyme bind
After substrate binds it is converted into products which are released from the enzyme

25. Figure 8.16
Substate
Active site
Enzyme
(a)

26. Induced fit of a substrate
Brings chemical groups of the active site into positions that enhance their ability to catalyze the chemical reaction
Figure 8.16
(b)
Enzyme- substrate
complex

27. The catalytic cycle of an enzyme
Substrates
Products
Enzyme
Enzyme-substrate
complex
1 Substrates enter active site; enzyme
changes shape so its active site
embraces the substrates (induced fit).
2 Substrates held in
active site by weak
interactions, such as
hydrogen bonds and
ionic bonds.
3 Active site (and R groups of
its amino acids) can lower EA
and speed up a reaction by
• acting as a template for
substrate orientation,
• stressing the substrates
and stabilizing the
transition state,
• providing a favorable
microenvironment,
• participating directly in the
catalytic reaction.
4 Substrates are
Converted into
Products.
5 Products are
Released.
6 Active site
Is available for
two new substrate
Mole.
Figure 8.17

28. Enzyme activity
Activity of an enzyme can be affected by several factors:
Changes in
Temperature pH
Changes in temperature and pH can change the shape of the enzyme, making it less effective

29. Cofactors Non-protein helpers
Include metals like zinc, iron and copper
Function to allow catalysis to occur

30. Coenzymes
Organic cofactors such as vitamins

31. Competitive inhibitors
Reversible inhibitors that compete with the substrate for the active site
Very similar to normal substrate
Figure 8.19
(b) Competitive inhibition
A competitive
inhibitor mimics the
substrate, competing
for the active site.
Competitive
inhibitor
A substrate can
bind normally to the
active site of an
enzyme.
Substrate
Active site
Enzyme
(a) Normal binding

32. Noncompetitive inhibitors
Prevent enzyme activity by binding to anotehr part of the enzyme
Cause change in shape
Figure 8.19
A noncompetitive
inhibitor binds to the
enzyme away from
the active site, altering
the conformation of
the enzyme so that its
active site no longer
functions.
Noncompetitive inhibitor
(c) Noncompetitive inhibition

33. V. Enzyme activity regulation

34. Allosteric site
Specific binding site other than the active site where regulators bind and change the shape of the enzyme.
Can either stimulate OR inhibit the activity

35. Figure 8.20 Allosteric activater stabilizes active from
Stabilized inactive form
Allosteric activater stabilizes active from
Allosteric enyzme with four subunits
Active site (one of four)
Regulatory site (one of four)
Active form
Activator
Stabilized active form
Allosteric activater stabilizes active form
Inhibitor
Inactive form
Non- functional active site
(a) Allosteric activators and inhibitors. In the cell, activators and inhibitors dissociate when at low concentrations. The enzyme can then oscillate again.
Oscillation
Figure 8.20

36. Feedback inhibition
The end product of an enzymatic pathway can switch off the pathway by binding to the allosteric site (the result!)
Increases efficiency of pathway by turning off when the end product accumulates in the cell.

37. Feedback inhibition Figure 8.21 Initial substrate (threonine)
Active site available
Isoleucine used up by cell
Feedback inhibition
Isoleucine binds to allosteric site
Active site of enzyme 1 no longer binds threonine; pathway is switched off
Initial substrate (threonine)
Threonine in active site
Enzyme 1 (threonine deaminase)
Intermediate A
Intermediate B
Intermediate C
Intermediate D
Enzyme 2
Enzyme 3
Enzyme 4
Enzyme 5
End product (isoleucine)
Figure 8.21