Transcript Introduction to Metabolism

An Introduction
Section 8.1-8.3
Energy
 the ability to do work
Kinetic – energy due to movement
Potential – stored energy
Chemical potential energy is stored up in
the bonds of a molecule.
First Law of Thermodynamics
The total amount of energy in the universe is
constant.
Energy cannot be created or destroyed. It
can only be transformed.
Bond Energies
 Energy required to
make/break bonds
 Measured in kJ / mol
(kilojoules per mole)
 Double bonds require
more energy to break
than single bonds
 The greater the bond
energy, the more
stable the bond.
Bond Type
Average Bond
Energy (kJ/mol)
H-H
436
C-H
411
O-H
459
N-H
391
C-C
346
C-O
359
C=O
799
O=O
494
Bond Energies
exothermic reactions – NET energy released
endothermic reactions – NET energy absorbed
 energy is required to break bonds
 energy is released to form bonds
breaking > forming
endothermic
breaking < forming
exothermic
Potential Energy Diagram
EXOTHERMIC REACTION
A
B
C
D
Potential Energy (kJ)
Transition state
A
B
C
D
EA = Activation energy
Reactants
A
B
C
D
Products
Progress of the reaction
Figure 8.14
Potential Energy Diagram
The “molecule” that has the highest level of energy is
in its transition state.
 a stage in between the reactants and the products
Second Law of Thermodynamics
The universe is becoming more disordered.
entropy – a measure of randomness / disorder
 greater entropy = greater disorder
 metabolise glucose into CO2 and H2O
C6H12O6 + O2  CO2 + H2O + energy
Gibbs Free Energy
 Energy that can do work
 Heat is “useless” as it dissipates
DG = Gfinal - Ginitial
 DG is negative for spontaneous reactions
 DG is positive for reactions that require energy
 The change in free energy, ∆G during a biological
process
 Is related directly to the enthalpy (total energy) change
(∆H)
 and the change in entropy (∆S)
 Where T is temperature in Kelvins
∆G = ∆H – T∆S
Useable energy
Total energy
“Useless” energy – goes
Towards increasing
disorder
(e.g. heat)
Gibbs Free Energy
Exergonic reaction – spontaneous, - DG
Endergonic reaction – not spontaneous, + DG
C6H12O6 + 6O2  6CO2 + 6H2O
DG = -2870 kJ/mol
6CO2 + 6H2O  C6H12O6 + 6O2
DG = +2870 kJ/mol
 For a process to occur spontaneously (- ∆G)
 A process must give up enthalpy (decrease ∆H )
 Increase disorder (give up order) (increase T∆S)
 Or both
∆G = ∆H – T∆S
Potential Energy Diagram
DG
8.15
Effect of Enzymes of RR
 Enzymes lower the
Free energy
Course of
reaction
without
enzyme
activation energy
 How?
EA
without
enzyme
EA with
enzyme
is lower
Reactants
Course of
reaction
with enzyme
∆G is unaffected
by enzyme
Products
Progress of the reaction
 Orienting substrates
correctly
 Putting stress on
substrate bonds
 Providing a favorable
environment
 This increases the
rate of the reaction.
Equilibrium
Equilibrium reactions convert back and forth
with minimal energy.
For equilibrium reactions: DG = 0
Adenosine Triphosphate (ATP)
Phosphate Groups
adenine
(purine)
Ribose (has
O on second
carbon)
Adenosine Triphosphate
 ATP is the primary free energy source for cells
ATPase
ATP
H2O
DG = -31 kJ/mol
ADP + Pi
+ energy
Phosphorylation
ATP hydrolysis does not
occur on its own.
Often, the energy is
focused through
phosphorylation of
enzymes.
ATP is replenished
through cellular
respiration.
Energy Coupling
ATP hydrolysis to
ADP + P i yields energy
ATP synthesis from
ADP + P i requires energy
ATP
Energy from catabolism
Figure 8.12
Energy for cellular work
ADP + P
i
P
i
P
Motor protein
Protein moved
(a) Mechanical work: ATP phosphorylates motor proteins
Membrane
protein
ADP
+
ATP
P
P
Solute
P
Solute
transported
(b) Transport work: ATP phosphorylates transport proteins
P
Glu +
NH2
NH3
Reactants: Glutamic acid
and ammonia
Figure 8.11
Glu
+
P
i
Product (glutamine)
made
(c) Chemical work: ATP phosphorylates key reactants
i
i
Redox Reactions
 reactions involving electron transfer
Redox Reactions
Oxidation – chemical reaction where an atom loses
electrons
Reduction – chemical reaction where an atom gains
electrons
Loss
Electron
Oxidation
Gain
Electron
Reduction
LEO the lion says GER
Redox Reactions
Reducing Agent – substance that LOSES electrons; it
causes the other substance to be reduced
Oxidizing Agent – substances that GAIN electrons; it
causes the other substance to be oxidized
 Na is oxidized and is the reducing agent (electron
donor)
 Cl is reduced and is the oxidizing agent
becomes oxidized
(loses electron)
Na
+
Cl
Na+
+
becomes reduced
(gains electron)
Cl–
Redox in the Cell
Many metabolic processes consist of chains of redox
reactions.
A-
B-
C-
D-
A
B
C
D