Bioenergetics is the branch of biochemistry that focuses on
how cells transform energy, often by producing, storing or consuming adenosine
triphosphate (ATP). Bioenergetic processes, such as cellular respiration or
photosynthesis, are essential to most aspects of cellular metabolism, therefore
to life itself.
Laws
of Bioenergetics
1. Living cells use energy carriers
The first bioenergetics law states that living cells do not use
the acquired energy directly. Instead, the energy received from external
sources is first converted into energy carriers before performing cellular
works. Three energy carriers are known to date:
Adenosine triphosphate (ATP)
Considered the molecular
currency, ATP consists of adenine attached to one molecule of
ribose sugar at carbon one and a triphosphate group at carbon five, where
energy is stored in the phosphoanhydride bonds. Energy is released when
the triphosphate group of the ATP is broken up into di- and monophosphate,
resulting in adenosine diphosphate
(ADP) and adenosine monophosphate (AMP), respectively. ATP is found in all
types of living cells and is regarded as the universal sign of life. Most ATP
molecules are synthesized by a membrane-bound enzyme complex, coupled with the
translocation of hydrogen or sodium ions.
Proton or hydrogen ions (H+) potential difference
Potential differences of protons or hydrogen ions (H+) are
available as electrical and chemical potential differences. The chemical
potential difference results from the hydrogen ion concentration gradient,
while the electrical potential difference stems from membrane potential.
Electrical potential difference is generated because of charge separation
between the extracellular matrix and the intracellular cytosol.
Sodium ions (Na+) potential difference
Similar to the potential difference of hydrogen ions, sodium ion
potential differences exist in electrical and chemical form. It is typically
formed in association with cellular respiration and non-oxidative
decarboxylation and uses the potassium-proton (K+/H+) gradient as a buffering
system.
2. Living cells use at least two forms of energy carriers
The second law of bioenergetics states that all biological systems
have at least two forms of energy carriers.
3. The cellular energy carriers are interconvertible
The third law of bioenergetics is expanded from the second law. It
stipulates that energy carriers in one form can be converted to other forms
that exist in the cells.
Types
of Bioenergetic Reactions
Exergonic Reactions
Exergonic reactions refer to chemical reactions that release free energy when they are
complete. Hence, exergonic reactions can occur spontaneously in a closed system
subjected to stable temperature and pressure. From a metabolic point of
view, exergonic reactions are in the catabolic branch, where
macromolecules are dissimilated to smaller units. For example, starch and
glycogen are broken down into glucose, their basic monomeric
units.
Endergonic Reactions
In contrast to exergonic reactions, endergonic reactions are
processes that consume energy. This sort of reaction will not occur in a
thermostable closed system under constant pressure unless a sufficient amount
of energy is given to the system. From a metabolic point of view,
endergonic reactions are anabolic. In anabolism, the energy released
from catabolic reactions supplies the required energy for the synthesis of
biomolecules. Macromolecules such as proteins, carbohygrates, liids and
nucleic acid are polymer chains that store energy in living cells. They are eventually used as
reactants in catabolic reactions to supply the cells with energy.
Importance of Bioenergetics
The conversion of energy for cellular activities is a vital
process in any biological system. Failure to supply the required energy or
excessive energy is consequential to the well-being of the organisms. Moreover,
deficiency in the functioning of bioenergetic-related proteins can result in
tremendous outcomes. For instance, OXPHOS diseases refer to disorders that result from
disruptions or defects in oxidative phosphorylation, such as the activity of
enzymes. Examples of OXPHOS diseases include Leigh Syndrome, a progressive neurodegenerative disorder,
and Mohr-Tranebjærg syndrome,
also known as Deafness-dystonia-optic
neuronopathy (DDON) syndrome. DDON is an early hearing loss
condition that is associated with impaired vision and motor movement.
Similarly, ageing, according to the free-radical theory of aging, results from
the deterioration of bioenergetics activity. Specifically, the number of
reactive oxygen species (ROS) generated is increased as organisms age. ROS is
generated from the so-called ‘proton leak’ during
electron transfer reactions in cellular respiration. ROS generation leads to
free radicals that damage the mitochondria and decrease cellular activities and
mitochondrial function.
Bioenergetic
Models
Bioenergetic
models describe the factors affecting the growth of an individual over its
lifetime. The rate of change in average individual biomass (B′) is modeled as the sum of
weight-specific rates of physiological processes: consumption (C′), respiration (R′), egestion (F′), excretion (U′), and reproductive loss (G′): dB′dt=C′−R′+F′+U′+G′. These
process rates in turn are considered functions of other variables, such as
water temperature or food availability.
References
1.
Skulachev VP, Bogachev A V., Kasparinsky FO.
Principles of Bioenergetics. Berlin, Heidelberg: Springer Berlin Heidelberg;
2013. doi:10.1007/978-3-642-33430-6
2.
Nicholls DG, Ferguson SJ. Chemiosmotic energy
transduction. In: Bioenergetics. Elsevier; 2003:3-15.
doi:10.1016/B978-012518121-1/50003-8
3.
G. A. Bioenergetics Theory of Aging. In:
Bioenergetics. InTech; 2012. doi:10.5772/31410
4.
Mora D, Arioli S. Optimisation of Cell
Bioenergetics in Food-Associated Microorganisms. In: Bioenergetics. InTech;
2012. doi:10.5772/33232