INTRO TO BIOENERGETICS,GLYCOLYSIS-UNIT 2.pdf

INCLUDES ENTHAPLY,ENTROPY,CATABOLISM,ANABOLISM,EMP PATHWAY

1. INTRODUCTION TO
BIOENERGETICS
PHYSIOLOGY-UNIT 2

2. BIOENERGETICS-INTRODUCTION
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.
- 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

3. METABOLISM
Metabolism is the total of all chemical reactions occurring in the cell.
Because chemical reactions either release or require energy, metabolism can be viewed as an
energy-balancing act.
Accordingly, metabolism can be divided into two classes of chemical reactions: those that release
energy and those that require energy.
CATABOLISM
In living cells, the enzyme-regulated chemical reactions that release energy are generally the ones involved
catabolism, the breakdown of complex organic compounds into simpler ones
.In the energy-conserving reactions or fueling reactions, the energy provided to the cell by its energy source
is released and conserved as ATP.
These reactions are called catabolic, or degradative, reactions,since they can involve the breakdown of
relatively large, complex organic molecules into smaller, simpler molecules.
Catabolic reactions are generally hydrolytic reactions (reactions which use water and in which chemical
bonds are broken), and they are exergonic (produce more energy than they consume).
An example of catabolism occurs when cells break down sugars into carbon dioxide and water.

4. ANABOLISM
Anabolism is the synthesis of complex organic molecules from simpler ones.
It involves a series ofsteps:
(1) conversion of the organism’s carbon source into a set of small molecules called precursor metabolites;
(2) synthesis of monomers and other building blocks (i.e., amino acids, nucleotides, simple carbohydrates, a
simple lipids) from the precursor metabolites;
(3) synthesis of macromolecules (i.e., proteins,nucleic acids, complex carbohydrates, and complex lipids); an
4) assembly of macromolecules into cellular structures.
Anabolism requires energy, which is transferred from the energy source to the synthetic systems of the c
by ATP.
Anabolism also requires a source of electrons stored in the form of reducing power. Reducing power is
needed because anabolism is a reductive process; that is, electrons are added to small molecules as they
used to build macromolecules

5. ENERGY
Energy may be most simply defined as the capacity to do work. This is because all physical and
chemical processes are the result of the application or movement of energy.
. In microbiology, energy transformations are measured in kilojoules (kJ), a unit of heat energy.
Living cells carry out three major types of work, and all are essential to life processes.
Chemical work involves the synthesis of complex biological molecules from much simpler precursors
(i.e., anabolism); energy is needed to increase the molecular complexity of a cell.
Transport work requires energy in order to take up nutrients, eliminate wastes, and maintain ion
balances.
Energy input is needed because molecules and ions often must be transported across cell membranes
against an electro chemical gradient.
For example, molecules move into a cell even though their concentration is higher internally.
Similarly a solute may be expelled from the cell against a concentration gradient.
The third type of work is mechanical work, perhaps the most familiar of the three.
Energy is required for cell motility and to move structures within cells.

6. FREE ENERGY
Free energy (abbreviated G), which is the energy available to do work.
The change in free energy during a reaction is expressed as ∆G0′, where the
symbol ∆ is read as “change in.”
The “0” and “prime” superscripts indicate that the free energy value is for standard
conditions: pH 7, 25°C, 1 atmosphere of pressure, and all reactants and products at
molar concentrations.
In 1878, Gibbs created the free energy function by combining the first and second
laws of thermodynamics in the form of following equation : ∆G = ∆ H – T∆S ... (3)
where, ∆ G = the change in free energy of a reacting system,1.
∆ H = the change in heat content or enthalpy of this system, 2.
T = the absolute temperature at which the process is taking place, 3.
and ∆ S = the change in entropy of this system4.

7. TYPES OF BIOENERGETICS REACTIONS
1. Exergonic Reaction -
If ∆G0′ for this reaction is negative in arithmetic sign, then the reaction will proceed with the
release of free energy, energy that the cell may conserve as ATP. Such energy-yielding
reactions are called exergonic.
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 as is evidently observed during respiratory pathways.
The bonds that are created during the formation of metabolites are stronger than the cleaved
bonds of the substrate.
- The release of free energy, G, in an exergonic reaction (at constant pressure and
temperature) is denoted as ΔG = Gproducts – Greactants < 0

8. 2. Endergonic Reactions
If ∆G0′ is positive, the reaction requires energy in order to
proceed. Such reactions are called endergonic.
- 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 =
Gproducts – Greactants > 0
o If ∆G is equal to zero, then the process has reached
equilibrium.

9. ENTHALPY
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.

10. ENTROPY
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.

11. REDOX REACTIONS
Oxidation is the removal of electrons (e−) from an atom or molecule,
a reaction that often produces energy.
Oxidation and reduction reactions are always coupled: each time
one substance is oxidized, another is simultaneously reduced.
The pairing of these reactions is called oxidation-reduction or a
redox reaction.
Oxidation-reduction (redox) reactions are those in which electrons
move from an electron donor to an electron acceptor.
The equilibrium constant for the reaction is called the standard
reduction potential (E0) and is a measure of the tendency of the
donor to lose electrons.

12. GLYCOLYSIS-INTRODUCTION
A nearly universal pathway for the catabolism of glucose is glycolysis, which breaks down glucose into
pyruvate.
Glycolysis is also called the Embden–Meyerhof–Parnas pathway for its major discoverers.
Whether glucose is fermented or respired, it travels through this pathway.
In fermentation, ATP is synthesized by substrate-level phosphorylation.
In this process, ATP is synthesized directly from energy-rich intermediates during steps in the catabolism of the
fermentable substrate .
This is in contrast to oxidative phosphorylation, which occurs in respiration; ATP is synthesized here at the
expense of the proton motive force .
The fermentable substrate in a fermentation is both the electron donor and electron acceptor; not all
compounds can be fermented, but sugars, especially hexoses such as glucose, are excellent fermentable
substrates.
The fermentation of glucose through the glycolytic pathway can be divided into three stages, each requiring
several independent enzymatic reactions. Stage I comprises “preparatory” reactions; these are not redox
reactions and do not release energy but instead form a key intermediate of the pathway. In Stage II, redox
reactions occur, energy is conserved, and two molecules of pyruvate are formed. In Stage III, redox balance is
achieved and fermentation products are formed
It is found in all major groups of microorganisms and functions in the presence or absence of O2.
The Embden-Meyerhof pathway occurs in the cytoplasmic matrix of procaryotes and eucaryotes.

13. REFER THE WHOLE DIAGRAM
IN PRESCOTT PAGE NUMBER
195

14. STAGE 1-PREPARATORY REACTIONS
In Stage I, glucose is phosphorylated by ATP, yielding glucose 6-
phosphate.
The latter is then isomerized to fructose 6-phosphate, and a second
phosphorylation leads to the production of fructose 1,6-
bisphosphate.
The enzyme aldolase then splits fructose 1,6-bisphosphate into two
3-carbon molecules, glyceraldehyde 3-phosphate and its isomer,
dihydroxyacetone phosphate, which is converted into
glyceraldehyde 3-phosphate.
To this point, all of the reactions, including the consumption of ATP,
have proceeded without any redox changes.

15. STAGE 11-PRODUCTION OF NADH,ATP AND PYRUVATE
The first redox reaction of glycolysis occurs in Stage II during the oxidation of glyceraldehyde 3-
phosphate to 1,3-bisphosphoglyceric acid.
In this reaction (which occurs twice, once for each of the two molecules of glyceraldehyde 3-
phosphate produced from glucose), the enzyme glyceraldehyde-3-phosphate dehydrogenase
reduces its coenzyme NAD+ to NADH.
Simultaneously, each glyceraldehyde 3-phosphate molecule is phosphorylated by the addition of a
molecule of inorganic phosphate.
This reaction, in which inorganic phosphate is converted to organic form, sets the stage for energy
conservation.
ATP formation is possible because 1,3-bisphosphoglyceric acid is an energy-rich compound .
ATP is then synthesized when (1) each molecule of 1,3-bisphosphoglyceric acid is converted to 3-
phosphoglyceric acid, and (2) each molecule of phosphoenolpyruvate is converted to pyruvate .
During Stages I and II of glycolysis, two ATP molecules are consumed and four ATP molecules are
synthesized
Thus, the net energy yield in glycolysis is two molecules of ATP per molecule of glucose fermented.

16. STAGE 111-REDOX BALANCE AND THE PRODUCTION OF
FERMENTATION
During the formation of two 1,3-bisphosphoglyceric acid molecules, two NAD+ are reduced to
NADH .
However, recall that NAD+ is only an electron shuttle, not a net (terminal) acceptor of electrons.
Thus, the NADH produced in glycolysis must be oxidized back to NAD+ in order for another round
of glycolysis to occur, and this is accomplished when pyruvate is reduced by NADH to fermentation
products .
For example, in fermentation by yeast, pyruvate is reduced to ethanol (ethyl alcohol) with the
subsequent production of carbon dioxide (CO2). By contrast, lactic acid bacteria reduce pyruvate to
lactate.
Many other possibilities for pyruvate reduction exist depending on the organism , but the end result
is the same: NADH is reoxidized to NAD+, and this allows earlier reactions of the pathway that
require NAD+ to continue.

17. OVERALL EQUATION
Glucose +2ADP+ 2Pi+ 2NAD ⎯⎯→ 2 pyruvate+ 2ATP+ 2NADH +2H
SUBSTRATE LEVEL PHOSPHORYLATION
Substrate-level phosphorylation is a metabolic reaction forming ATP or GTP
through the transfer of a phosphate group (PO43-) from a substrate to ADP or GDP
directly.
Being an exergonic reaction, it releases some free energy while breaking the
phosphate group from the substrate.
This released energy is utilized to phosphorylate the ADP or GDP.
In living cells, it occurs during glycolysis (in the cytoplasm) and the Krebs cycle (in
the mitochondria).
Thus, substrate-level phosphorylation takes place both in the presence and
absence of oxygen during glycolysis.
However, in the Krebs cycle, it happens strictly in an aerobic environment.

18. OXIDATIVE PHOSPHORYLATION
Oxidative phosphorylation, also known as electron transport-linked
phosphorylation, or terminal oxidation, is a metabolic pathway in
which ATPs are formed from ADP, when electrons move down an
electron transport chain (ETC) with the help of electron carriers like
NADH or FADH2, to oxygen.
This final step of cellular respiration occurs in the mitochondrial inner
membrane of eukaryotic cells. In prokaryotes, it takes place in the
cytoplasm.
The oxidative phosphorylation includes two closely connected
pathways that occur during aerobic cellular respiration: electron
transport chain (ETC) and chemiosmosis.