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BIOENERGETICS

BIOENERGETICS. By: Ms. Preeti S. Salve. KLE College of Pharmacy, Belagavi A constituent Unit of KLE Academy of Higher Education and Research Nehru Nagar, Belagavi – 590 010, Karnataka, India

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BIOENERGETICS

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  1. BIOENERGETICS By: Ms. PreetiS. Salve KLE College of Pharmacy, Belagavi A constituent Unit of KLE Academy of Higher Education and Research Nehru Nagar, Belagavi– 590 010, Karnataka, India Phone: 0831-2471399;Fax: 0831-2472387; Web:http://www.klepharm.eduE-mail: principal@klepharm.edu

  2. Bioenergetics / Biochemical thermodynamics • It is the study of energy changes accompanying biochemical reactions • It describes the transfer and utilization of energy in biological systems • It is concerned with the initial and final energy states of reaction components and not the reaction mechanism or the time required for the chemical reaction

  3. Free energy • It is the energy actually available to do work (utilizable energy) • Change in free energy (∆G) predicts whether a chemical reaction is feasible/favourable • Reactions can occur simultaneously if they are accompanied by decrease in free energy • ∆G approaches zero as reaction proceeds to equilibrium

  4. During a chemical reaction, heat may be released or absorbed • Enthalpy(∆H)is a measure of the change in heat content of the reactants, compared to products • Entropy (∆S) represents a change in the randomness or disorder of reactants and products • Entropy reaches a maximum as the reaction approaches equilibrium • The reactions of biological systems involve a temporary decrease in entropy

  5. Laws of thermodynamics • 1st law: Energy can neither be created nor be destroyed, but can be converted from one form to another • 2nd law: Total entropy of a system must increase is a process has to occur simultaneously

  6. Combining the two laws of thermodynamics, Gibbs in 1878, came up with the following equation • The relation between the change in free energy (∆G), enthalpy (∆H) and entropy (∆S) is expressed as – ∆G = ∆H – T ∆S where, ∆G = the change in free energy of a reacting system ∆H = the change in heat content or enthalpy of this system T = the absolute temperature in Kelvin at which the process is taking place ∆S = the change in entropy of this system

  7. Free energy change • ∆G predicts the change in free energy and thus the direction of the reaction, at any specified concentration of the reactants and products • Standard free energy ∆G° is the energy change when the reactants and products are at a concentration of 1 mol/L

  8. Negative and positive ∆G Consider the reaction: • If ∆G is a negative number --- Net loss of energy --- Reaction proceeds spontaneously --- A is converted to B --- Reaction is exergonic • If ∆G is a positive number --- Net gain of energy --- Reaction does not proceed spontaneously from B to A --- Reaction is endergonic --- Energy must be supplied to the reactants

  9. e.g. Hydrolysis of ATP --- Exergonic reaction • Reversal of the reaction (ADP + Pi ATP) is endergonic and occurs only when there is a supply of energy of atleast 7.3 cal/mol (∆G° is positive) • If ∆G = 0, reaction is in equilibrium --- Free energy of the forward reaction ( ) is equal in magnitude but opposite in sign to that of backward reaction ( )

  10. ∆G is dependent on the actual concentration of reactants and products • At constant temperature and pressure, the following relation can be derived

  11. ∆G is an additive value for pathways • Biochemical pathways involve a series of reactions • Free energy change is an additive value for such reactions • The sum of ∆G determines whether a particular pathway will proceed or not. • If the sum of ∆G of individual reactions is negative, the pathway can operate. • This happens despite the fact that some of the individual reactions may have positive ∆G

  12. Determination of ∆G from equilibrium constant • For a reaction, • The equation can be written as • At equilibrium, there is no net conversion of A to B. Hence, ∆G = 0 • Where, Keq = Equilibrium constant

  13. By evaluating the constants we get, • R = 1.987 cal/mol-degree, • 25°C = 298°T • ln X = 2.303 log 10x • Substituting these values in previous equation, ∆G° = – (1.987) (298) (2.303) log 10 Keq = – 1363 log 10 Keq • If the concentration of both reactants and products at equilibrium can be measured, the Keq and in turn the ∆G° of the reaction can be calculated

  14. Determination of ∆G from reduction potential • ∆G of a reaction which involves an oxidation-reduction process may be related to the difference in oxidation-reduction potentials (∆E°) of the reactants • Reducing agent – Substance that donates an electron and gets oxidized • Fe+++ is an oxidising agent – Accepts an electron and gets reduced

  15. These reactions in which the electrons are indicated as being accepted or donated but the donor or acceptor have not been mentioned are called as half reactions • Various oxidation-reduction systems have certain reduction potential values

  16. The relation between change in free energy and reduction potential is given as – ∆G = – nF . ∆E° Where, • n = Number of electrons transferred in a redox reaction • F = Faraday’s constant = 23,063 cal/v equiv • ∆E° = difference in reduction potential of oxidising and reducing agents i.e. (E° of half reaction containing oxidising agent) – (E° of half reaction containing reducing agent)

  17. High energy compounds • Certain compounds are encountered in the biological system which, on hydrolysis, yield energy • High-energy compounds or energy rich compounds – substances which possess sufficient free energy to liberate at least 7 cal/mol at pH 7.0 • Low-energy compounds – Compounds which liberate less than 7.0 cal/mol (lower than ATP hydrolysis to ADP + Pi)

  18. Classification of high energy compounds

  19. Adenosine triphosphate (ATP) • Adenosine triphosphate (ATP) is the energy currency of the cell, the most important high-energy molecule in the living cells • It consists of an adenine, a ribose and a triphosphate moiety • ATP is a high-energy compound due to the presence of two phosphoanhydride bonds in the triphosphate unit.

  20. Structure of ATP

  21. ATP synthesis • ATP can be synthesized by two methods – 1. Oxidative phosphorylation • It is the major source of ATP in aerobic organisms • It is linked with the mitochondrial electron transport chain

  22. ATP synthesis 2. Substrate level phosphorylation • ATP can be directly synthesized during substrate oxidation in the metabolism • High-energy compounds like phosphoenolpyruvate and 1,3-bisphosphoglycerate (intermediates of glycolysis) and succinylCoA (of citric acid cycle) can transfer high-energy phosphate to finally produce ATP

  23. Biological significance of ATP • The hydrolysis of ATP is associated with the release of large amount of energy – ATP + H2O ADP + Pi + 7.3 Cal The energy liberated is utilized for various processes like muscle contraction, active transport etc • ATP can also act as a donor of high-energy phosphate to low-energy compounds, to make them energy rich ADP can accept high-energy phosphate from the compounds possessing higher free energy content to form ATP

  24. ATP is required for synthesis of nuclosidetriphosphates • The cyclic phosphodiestercAMP is formed from ATP in a reaction catalysed by adenylylcyclase. cAMP, which is a second messenger participates in different regulatory functions of the cell

  25. Thank you

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