This document discusses bioenergetics, which is the study of energy changes that accompany biochemical reactions. It examines exergonic and endergonic reactions, and how bioenergetics can predict the feasibility and rate of reactions based on initial and final energy states. Modern organisms use chemical energy from fuels like carbohydrates and lipids to power metabolic reactions and generate concentration gradients, motion, heat, and light. A doctor's understanding of bioenergetics is important for diseases related to nutrition, metabolism, hormones, growth, and molecular processes involving energy. The document outlines the first and second laws of thermodynamics, Gibbs free energy, redox couples, ATP as the energy currency, electron carriers, substrate-level phosphorylation

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