Download Biochemistry Topic 7: High energy compounds and thermo

Biochemistry
Topic 7: High energy compounds and thermo dynamics of the living system
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The basic rule of thermodynamics is: ∆𝐺 = ∆𝐻 − 𝑇∆𝑆 = −𝑅𝑇𝑙𝑛𝐾𝑒𝑞 Gibbs-Helmholtz
equation Change in free enthalpy= change in heat – temperature times entropy change
Another important formula is ∆𝐺 0 = −𝑅𝑇 𝑙𝑛𝐾
All living cells require some source of free energy. In the human body ATP is the usual
supplier for energy, giving -30.5kJ by ATP -> ADP + Pi. If G is negative the reaction moves
forwards, if it is positive it will move backwards. The energy is obtained by the energy
difference between ATP and the Products ADP and Pi.
Humans obtain free energy by coupling their metabolism to the breakdown of some organic
molecules.
High energy compounds are substances which have a higher energy value than ATP.
The high energy compounds in our body are usually based on phosphate groups:
o Enolphosphates: Phosphoenolpyruvate: -61kJmol
o Anhydrids: 1,3-biphosphoglycerate: -49,3kJ/mol
o Phospoguanidine: creatinephosphate: -43.1kJ/mol
Other high energy compounds can be some thiol-esters involving CoA.
The greates supplier of the phosphate groups is the oxidative phosphorilation in the
mitochondria.
The full oxidation of glucose to CO2 yields -2840kJ for every mole of glucose. The glycolysis
itself contributes about 5.2% (-146kJ) of the entire energy stored in glucose. In total we get
about 30-32 ATP molecules from glucose.
ATP allows unfavorable thermodynamic reactions become favorable and happen inside the
cell.
Other energy is obtained by oxidation-reduction reactions