Energetics of metabolism
Metabolism
Metabolism = all the chemical reactions that occur in the body.
Sun
sugar
everything
organic products
O2
photosynthetic
autotrophs
heterotrophs
CO2, H2O
degradation
synthesis
The complexity of metabolism
Energy has to abide by the laws of thermodynamics
First law of thermodynamics: energy may change form or be transported but
can not be created or destroyed. This is also know as the principle of
conservation of energy.
Second law of thermodynamics: in all natural processes, the entropy of
universe increases.
Transfer or transformation of energy in a cell releases heat.
Increase in entropy Increase
stability
What is ordered and what is disordered?
Greater
entropy
All these pathways are go to one direction to increase disorder of universe.
Free energy (∆G)
Free energy: energy, that is released in a system.
∆G = ∆H - T ∆S
It can tell us something
how a reaction proceeds
∆G= Gibb’s free energy
∆H= change in enthalphy, heat content of the reaction
∆S= change in entropy
T= absolute temperature, in Kelvin
∆G<0 (exergonic) reaction proceeds forward, energy is released or transformed
∆G>0 (endergonic) energy is needed for reaction to occur
Free energy (∆G)
Energy changes in exergonic and energonic reactions.
Exergonic Reaction (Spontaneous)
 Decrease in Gibbs free energy (-G)
 Increase in stability
 Downhill (toward center of gravity
well, e.g., of Earth)
 Movement towards equilibrium
 Coupled to ATP production (ADP
phosphorylation)
 Catabolism
Endergonic reaction (Non-Spontaneous)

Increase in Gibbs free energy (+G)
 Decrease in stability
 Not Spontaneous
 Uphill
 Movement away from equilibrium
 Coupled to ATP utilization
 Anabolism
Single-step system
Metabolism and equilibrium
No work can be performed!
water intake
(b) An opened hydrolectric system
outflow
Energy can be generated and utilized in the body.
Metabolism and equilibrium
Cellular respiration: glucose is broken down in a series of reactions that
power the work of cell.
The product of each reaction becomes the reactant for the next, no recation reaches equilibrium.
Cellular respiration
Cells convert biochemical energy from nutrients into adenosine
triphosphate (ATP), and then release waste products (CO2 and water).
Steps of cellular respiration:
1. Glycolysis
2. Citric acid cycle
3. Oxidative phosphorylation
Cellular respiration
Cellular work
Energy reuired for:
 chemical work
 transport work
 mechanikal work
Coupling of exergonic and endergonic reactions
e.g.
Exergonic and endergonic reactions can be coupled to overcome endergonic
reactions.
Structure and hydrolysis of ATP
ATP hydrolysis coupled reactions
Summery of metabolic coupling
Endergonic
reaction
Exergonic
reaction
Exergonic
reaction
Endergonic
reaction
Exergonic processes drive endergonic processes.
Thank you for your attention!