Bioenergetics and biological oxidation, aide to oxidative phosphorylation- For medical students

1. BIOENERGETICS
Prof. (Dr.) V.P.ACHARY
BIOENERGETICS

2. What is Bioenergetics???
 Also known as Biochemical thermodynamics
 Study of energy changes accompanying
biochemical reactions
 Exergonic & Endergonic reactions
 Concerned with the initial and final states of
energy components of the reactants
 Not concerned with the mechanism of the
reactions
 Predicts feasibility of a reaction
 Kinetics- predicts rate of reaction

3. Why do we need energy???
 Co-ordinate the metabolic reactions for our
sustenance
 Metabolic reactions require energy

4.  Modern organisms use the chemical energy in
fuels (carbonhydrates, lipids) to bring about
the synthesis of complex macromolecules
from simple precursors
 Convert the chemical energy into
concentration gradients and electrical
gradients, into motion and heat, and, in a few
organisms into light (fireflies, some deep-sea
fishes)

5. Why should a doctor know about
Bioenergetics???
 Nutritional diseases- Starvation, PEM, Obesity
 Metabolic diseases- DM, Insulin resistance
 Hormonal diseases- Hypo- and hyper
thyroidism
 Growth and reproduction
 Molecular level-Transport across membranes,
enzyme catalysis, DNA binding, protein
stability etc also utilize the laws of
thermodynamics

6. 1st lawofthermodynamics
In any physical or chemical change, the
total energy of a system, including its
surroundings remains constant.
∆E= Q-W
Q= heat absorbed by the system
W= work done
Law of conservation of energy
Biological energy transductions obey the laws of
thermodynamics

7. 2ndlawofthermodynamics
The total entropy of a system must increase
if a process is to occur spontaneously.
Entropy- degree of randomness
 Entropy becomes maximum as it
approaches the equilibrium
 Enthalpy- heat content
 Entropy is that fraction of heat that is not
available for useful work

8. Gibb’sFreeEnergy
 Available to perform useful work
 Combining 1st & 2nd law of thermodynamics
 ∆ G/ Chemical potential
 Determines spontaneity of a reaction
 Negative- reaction is spontaneous
∆G= ∆H -T∆S
For most biochemical reactions, ∆H = ∆E
Hence, ∆G= ∆E -T∆S

9. Standard free energy change
 DGo' = standard free energy change (at pH 7, 1M
reactants & products); R = gas constant; T =
temp.
 Free energy change under standard conditions

10.  ∆ G = 0 ; reaction at equilibrium
 ∆ G negative ; forward reaction
 ∆ G positive ; backward reaction
 Highly exergonic- reaction goes into
completion ; irreversible
 Reversible reactions- ∆ G = 0

11. Exothermic & exergonic- are they
same??
 ∆H – for heat
 When negative- exothermic
 When positive- endothermic
 When 0- isothermic
 Biological systems are essentially
isothermic

12. Energeticallyunfavorablereactionscoupled
withfavorableonestomakethemhappen
 Glucose +Pi → Glucose-6-P………….(1)
 ATP + H2O → ADP + Pi ………………….(2)
 Glucose + ATP → Glucose-6-P + ADP … (3)
DGo‘ for reaction 1, 2 & 3 are +13.8, - 30.5 &
-16.7 KJ/mole
Catabolic reactions- exergonic
Anabolic reactions- endergonic

13. ATP-energycurrency
 ATP ADP + Pi; ∆G0 = -7.3 Kcal/mole
 ADP AMP + Pi; ∆G0 = -7.3 Kcal/mole
 AMP Adenosine + Pi
∆G0 =-3.4 Kcal/mole
It’s a stable molecule in absence of the enzymes

14. ATP cycle
 ATP – major interlinking product
between exergonic and endergonic
reactions
 ATP-ADP cycle
 3 sources of ̴P taking part in energy
conservation- 3 SLP sites, Oxidative
Phosphorylation

17. 5 groups of high-energy compounds
1. Pyrophosphates – ATP
2. Acyl phosphates – 1, 3- BPG
3. Enol phosphate – PEP
4. Thio esters–Acetyl CoA
5. Phosphagens -- Phosphocreatine

18. BiologicalOxidation
Oxidation- removal of electrons
Reduction- gain of electrons
Electron donator- reducing agent/ reductant;
gets oxidized itself
Fe++ (reduced)  Fe+++ (oxidized) + e-
Electron acceptor- oxidizing agent/ oxidant;
gets reduced itself
Two important e- carriers in metabolism: NAD+
& FAD

19. NAD+, Nicotinamide Adenine
Dinucleotide, is an electron acceptor in
catabolic pathways.
The Nicotinamide ring, derived from the
vitamin niacin, accepts 2 e- & 1 H+ (a
hydride) in going to the reduced state,
NADH.
NADP+/NADPH is similar except for Pi.
NADPH is e- donor in synthetic pathways.

20. The electron transfer reaction may be
summarized as :
NAD+ + 2e- + H+  NADH
It may also be written as:
NAD+ + 2e- + 2H+  NADH + H+

21. Redox couple
 When a substance exists both in the reduced and
oxidized state, the pair is called a redox couple
 Redox potential- Electromotive force measured
by (EMF)
 Positive redox potential- higher affinity for e
than H+
 Negative redox potential- lower affinity for e
than H+

22. Redox potential
 Analogous expression of standard free energy
 Eo’
 Redox couple
 Electron flows from one redox couple to another
in the direction of more positive system
 ↑negativity- ↑tendency to lose electrons
(more affinity towards H)
 ↑positivity- ↑ tendency to accept electrons

23. The more negative redox potential represents a greater tendency to
lose electrons

24. Substrate level phosphorylation
 Energy from a high energy compound
is directly transferred to nucleoside
diphosphate to form NTP
 3 steps
 1,3 –BPG (Glycolysis)
 Phosphoenolpyruvate (Glycolysis)
 Succinyl CoA (TCA cycle)

25. Do not pretend- be
Do not promise- act
Do not dream- realise

26. For more ppt on Medical Biochemistry please visit
www.vpacharya.com