Biochemistry

1. UNIT-I
1.2 BIOENERGETICS
PRESENTED BY-
MS.PAYAL GAJANAN PILAJI

2. Bioenergetics or Biochemical thermodynamics
 Deals with the study of energy changes (transfer or utilization) in biochemical reaction.
 Bioenergetics means study of the transformation of energy in living organisms.
 The goal of bioenergetics is to describe how living organisms acquire and transform energy in
order to perform biological work.
 The study of metabolic pathways is thus essential to bioenergetics.
 In a living organism, chemical bonds are broken and made as part of the exchange and
transformation of energy.
 Energy is available for work (such as mechanical work) or for other processes (such as chemical
synthesis and anabolic processes in growth), when weak bonds are broken and stronger bonds are
made.
 The production of stronger bonds allows release of usable energy.

3.  Adenosine triphosphate (ATP) is the main "energy currency" for organisms; the goal of metabolic and
catabolic processes are to synthesize ATP from available starting materials (from the environment), and
to break- down ATP (into adenosine diphosphate (ADP) and inorganic phosphate) by utilizing it in
biological processes.
 In a cell, the ratio of ATP to ADP concentrations is known as the "energy charge" of the cell.
 A cell can use this energy charge to relay information about cellular needs; if there is more ATP than
ADP available, the cell can use ATP to do work, but if there is more ADP than ATP available, the cell
must synthesize ATP via oxidative phosphorylation.

4. 1. Exergonic Reaction
 Exergonic implies the release of energy from a spontaneous chemical reaction without any concomitant utilization of
energy.
 The reactions are significant in terms of biology as these reactions have an ability to perform work and include most of
the catabolic reactions in cellular respiration.
 Most of these reactions involve the breaking of bonds during the formation of reaction intermediates
 The release of free energy, G, in an exergonic reaction (at constant pressure and temperature) is denoted as
ΔG = G (products) – G (reactants )< 0
 This indicates that the products of the reaction have lower free energy than the reactants.
 Ex……
 Cellular respiration: Glucose is broken down in cells to produce water, carbon dioxide, and energy.
 Combustion of wood: Wood burns in the presence of oxygen to produce carbon dioxide, water, and heat.
Types of Bioenergetics Reactions

5. 2. Endergonic Reactions
 Endergonic in turn is the opposite of exergonic in being non-spontaneous and requires an input of free
energy.
 Most of the anabolic reactions like photosynthesis and DNA and protein synthesis are endergonic in
nature.
 The release of free energy, G, in an exergonic reaction (at constant pressure and temperature) is
denoted as
ΔG = G (products) – G (reactants) > 0
 This means that the products of the reaction have a higher free energy than the reactants.
 Ex……
 Photosynthesis: Plants take in sunlight, carbon dioxide, and water to produce glucose and oxygen.
 Synthesis of ATP: In cells, Adenosine diphosphate (ADP) combines with inorganic phosphate (Pi) to
produce ATP, absorbing energy in the process.

8. 3. Activation Energy
 Activation energy is the energy which must be available to a chemical system with potential
reactants to result in a chemical reaction.
 Activation energy may also be defined as the minimum energy required starting a chemical
reaction.
 While exergonic reactions are spontaneous in terms of energy, they may still require an initial
energy input, called the activation energy, to get started.
 Enzymes and catalysts can lower this activation energy, making the reaction proceed faster.
 Endergonic ones also have an activation energy, or a little push to get started. Catalysts or
enzymes can help reduce this initial energy barrier.

10.  Every living cell and organism must perform work to stay alive, to grow and to reproduce. The ability to
harvest energy from nutrients or photons of light and to channel it into biological work is the miracle of
life.
 1st Law of Thermodynamics: The energy of the universe remains constant.
 2nd Law of Thermodynamics: All spontaneous processes increase the entropy of the universe.
Bioenergetics Relationship Between Free Energy, Enthalpy & Entropy

11.  The Gibbs free energy (G) which is equal to the total amount of energy capable of doing work during a
process at constant temperature and pressure.
 It indicate the free energy change when the reactant or product are at conc. of 1 mol / l at pH 7.
o If ∆G is negative, then the process is spontaneous and termed exergonic.
o If ∆G is positive, then the process is nonspontaneous and termed endergonic.
o If ∆G is equal to zero, then the process has reached equilibrium.
 Under such conditions the relationships between the change in free energy, enthalpy and entropy can be
described by the expression
 where T is the temperature of the system in Kelvin. (K = 273 + ℃)
∆G = ∆H - T∆S
[∆G = Gibbs Free Energy; ∆H = Change in Enthalpy; T = Temperature in K; ∆S = Change in Entropy]
Gibbs free energy (G)

12.  The Enthalpy (H) which is the heat content of the system.
 Enthalpy is the amount of heat energy transferred (heat absorbed or emitted) in a chemical
process under constant pressure.
o When ∆H is negative the process produces heat and is termed exothermic.
o When ∆H is positive the process absorbs heat and is termed endothermic.
 The Entropy (S) is a quantitative expression of the degree of randomness or disorder of the
system.
 Entropy measures the amount of heat dispersed or transferred during a chemical process.
o When ∆S is positive then the disorder of the system has increased.
o When ∆S is negative then the disorder of the system has decreased.

14.  High energy compounds are also called energy-rich compounds.
 Compounds present in the biological system that when hydrolysed, produce free energy that is greater
or equal to that of ATP (△G is -7.3 kcal/mol) are termed high energy compounds.
 Low-energy compounds have an energy yield of less than -7.3 kcal/mol.
 High-energy bonds are found in the majority of high-energy compounds that produce energy upon
hydrolysis.
 Most of the high energy compounds contain phosphate groups and thus they are also termed high-
energy phosphates.
High energy compounds

15.  These high energy compounds are mainly classified into five groups:
1. Pyrophosphates
2. Acyl phosphate
3. Enol phosphate
4. Thiol phosphate
5. Phosphagens or guanido phosphates

17. 1. Pyrophosphates
 Pyrophosphate energy bonds are nothing but acid anhydride bonds. Condensation of acid groups
(primarily phosphoric acid) or their derivatives results in the formation of these bonds.
 ATP (△G = -7.3 kcal/mol) is an example of a pyrophosphate.
 It has two phosphoanhydride diphosphate bonds.
2. Acyl phosphates
 The reaction between the carboxylic acid group and the phosphate group forms a high energy bond in
this compound.
 1,3-bisphosphoglycerate (△G = -11.8 kcal/mol) is an example of acyl phosphate.

18. 3. Enol phosphates
 The enol phosphate bond is present here. It is formed when a phosphate group
binds to a hydroxyl group that is bound to a double-bonded carbon atom.
 As an example, consider phosphoenolpyruvate (△G = -14.8 kcal/mol).
4. Thiol phosphates
 There is no high energy phosphate bond here. Instead, a high energy thioester bond
is found here.
 Thioester bonds are formed by the reaction of thiol and carboxylic acid groups.
Acetyl CoA (△G = -7.7 kcal/mol) is an example.

19. 5. Phosphagens
 Guanidine phosphate bonds are present in phosphagens or guanido phosphates.
 The phosphate group is attached to the guanidine group to form it.
 Phosphocreatine (△G = -10.3 kcal/mol) is the most important compound with
this type of bond.

20.  Adenosine-5'-triphosphate (ATP) is a multifunctional nucleotide used in cells as a coenzyme.
 It is often called the "molecular unit of currency" of intracellular energy transfer.
 ATP transports chemical energy within cells for metabolism.
 It is produced by photophosphorylation and cellular respiration and used by enzymes and structural
proteins in many cellular processes, including biosynthetic reactions, motility, and cell division.
 The structure of this molecule consists of a purine base (adenine) attached to the 1' carbon atom of a
pentose sugar (ribose).
 Three phosphate groups are attached at the 5' carbon atom of the pentose sugar.
 It is the addition and removal of these phosphate groups that inter-convert ATP, ADP and AMP.
 When ATP is used in DNA synthesis, the ribose sugar is first converted to deoxyribose by
ribonucleotide reductase.
ADENOSINE TRIPHOSPHATE (ATP)

22.  The three main functions of ATP in cellular function are:
1. Transporting organic substances—such as sodium, calcium, potassium—
through the cell membrane.
2. Synthesizing chemical compounds, such as protein and cholesterol.
3. Supplying energy for mechanical work, such as muscle contraction

23.  The standard amount of energy released from hydrolysis of ATP can be calculated from the changes in
energy under non-natural (standard) conditions, then correcting to biological concentrations.
 The energy released by cleaving either a phosphate (Pi) or pyrophosphate (PPi) unit from ATP at standard
state of 1 M are:
Hydrolysis of ATP (exergonic)
 Associated with release of large amount of energy.
 ATP also act as donor of high energy phosphate to low energy compound to make then energy rich.
ATP + H2O → ADP + Pi + 7.3 Cal
 The hydrolysis of ATP to AMP releases -10.9 kcal/mol of energy
ATP + H2O → AMP + PPi
 Dehydration of ADP (endergonic)
ADP + Pi → ATP + H2O