1. Metabolism & Enzymatic Reactions
Chapter 8 (p )
Metabolism & Enzymatic Reactions

2. Thermodynamics
First Law
Second Law
Energy can be transferred and transformed, but it cannot be created or destroyed
Every energy transfer or transformation increases the entropy (disorder) of the universe
Energy is converted from sun  wheat  bread  ATP  nerve impulses
 ADP
Total amount of energy in a closed system is constant, however organisms are open systems that exchange energy with their environment.
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3. Free-Energy Change, G
Energy that can do work when temperature and pressure are uniform, as in a living cell
∆G = ∆H – T∆S
Gibbs free/available energy
H=total energy
T=temperature
S=entropy
Spontaneous reactions
Ball at top of slide has more energy at top (potential energy); H decreases as ball goes down
Molecules in closed container close together (more potential energy) will disperse into a given area; S increases
Bomb explodes when heat is added; T increases
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4. Amount of energy released (G  0) Amount of energy required (G  0)
Figure 8.6
(a) Exergonic reaction: energy released, spontaneous
Reactants
Amount of energy released (G  0)
Free energy
Energy
Products
Progress of the reaction
(b) Endergonic reaction: energy required, nonspontaneous
Products
G<0 spontaneous & exergonic
G<0 non-spontaneous & endergonic
G=0 equilibrium
Amount of energy required (G  0)
Free energy
Energy
Reactants
Progress of the reaction 4

6. Enzymes Lower Energy Barriers
Enzymes speed up metabolic reactions without being consumed by the reaction
Sucrose breaking down is a spontaneous exergonic reaction b/c bonds (chemical potential energy) are being broken and energy is released
Entropy is increasing as you split sucrose into glucose and fructose
Draw graph
Sugar doesn’t spontaneously break into pieces, giving off fire on your table
Activation energy is the amount of energy required to loosen bonds of molecules so that reaction can begin
Ea can be so high, that it can’t be achieved at room temperature (O2 + spark + gas = fire)
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8. Enzyme-substrate complex
Figure 8.14
Substrate
Active site
Induced fit
Enzyme
Enzyme-substrate complex
(a)
(b) 8

9. Substrates enter active site. 1
Substrates enter active site.
Substrates are held in active site by weak interactions. 2
Substrates
Enzyme-substrate complex
Active site can lower EA and speed up a reaction. 3
Active site is available for two new substrate molecules. 6
Figure 8.15 The active site and catalytic cycle of an enzyme.
Enzyme 5
Products are released.
Substrates are converted to products. 4
Products 9

10. Enzymatic “Activators”
Coenzymes
Cofactors
Non-protein, organic molecules
Bind near active site
Vitamins
NAD+
FAD+
Coenzyme A
Non-protein, small inorganic compounds & ions
Bound within protein’s tertiary structure
Mg, K, Ca, Zn, Fe, C

13. Optimal temperature for typical human enzyme (37°C)
Optimal temperature for enzyme of thermophilic (heat-tolerant) bacteria (77°C)
Rate of reaction
Figure 8.16 Environmental factors affecting enzyme activity. 20 40 60 80
100
120
Temperature (°C)
(a) Optimal temperature for two enzymes 13

14. Optimal pH for pepsin (stomach enzyme)
Figure 8.16b
Optimal pH for pepsin (stomach enzyme)
Optimal pH for trypsin (intestinal enzyme)
Rate of reaction
Figure 8.16 Environmental factors affecting enzyme activity. 1 2 3 4 5 6 7 8 9 10 pH
(b) Optimal pH for two enzymes 14