2.11 Energy in Metabolic Processes

The energy relationships in metabolic processes

The Sum of all biochemical reactions of a living being is known as the metabolism and it consists of all catabolic and anabolic reactions.

Catabolism is the breaking down of complex molecules into simple molecules by releasing free energy. Therefore it is an exergonic reaction. Anabolism is making complex molecules from simple molecules by absorbing free energy. Hence it is an endergonic reaction.

Biochemical reactions involved in the usage of energy released by catabolic reactions in the living system are called anabolic reactions. ATP acts as the energy carrier in all living organisms including the simplest bacteria. Therefore the ATP is known as the universal currency of energy transactions.

Energy can be defined as the capacity to do work. All living organisms require energy for their living process in many ways. Such processes are;

?       Synthesis of substances

?       Active transport across the plasma membrane

?       Transmission of nerve impulses

?       Muscle contraction

?       Beating of cilia and flagella

?       Bioluminescence

?       Electrical discharges.

The idea of the energy relations of living systems in the biosphere is composed of the following steps.

?       Energy flows into biological systems from the environment through solar radiation. (Primary energy source is the Sun)

?     Light energy is captured in the cells having photosynthetic pigments (chlorophyll) by the process of photosynthesis and stored as chemical energy in the organic compounds such as carbohydrates

?       Captured energy in organic food is transformed into chemical energy in ATP by a process called cellular respiration.

?       The energy stored in ATP is utilized in various energy-requiring processes.

ATP (Adenosine Tri Phosphate)

ATP is a nucleotide, consisting of,

? Ribose- sugar

? Adenine - nitrogenous base

? A chain of three phosphate groups.

During the hydrolysis of ATP, ADP and Pi are produced. As a result, very high energy is released. This is because the reactants (ATP and water) contain more energy than products (ADP and Pi). Therefore it yields energy and is an exergonic reaction.

When ATP is hydrolyzed, the free energy yield of each of the two end phosphate groups is -30.5kJ/mol.

Most biological reactions use the energy released during the breaking of the terminal phosphate bond. ATP is mobile. Therefore it can carry energy to anywhere in the cell, for any energy-consuming reaction.

ATP can be produced within living cells within a short period of time, using ADP, inorganic phosphate (Pi) and energy. The production of ATP within cells is called phosphorylation. According to the energy, source phosphorylation is divided as;

i. Photophosphorylation – synthesis of ATP using solar energy in photosynthesis

ii. Substrate phosphorylation – synthesis of ATP using the energy released by the breaking down of complex molecules into simple ones.

iii. Oxidative phosphorylation – synthesis of ATP using the energy released as a result of the oxidation of molecules.

In living cells energy in ATP is transformed into various energy forms which are used for different functions.

References

•  "Adenosine 5'-triphosphate disodium salt Product Information" (PDF). Sigma. Archived (PDF) from the original on 2019-03-23. Retrieved 2019-03-22.
• Knowles, J. R. (1980). "Enzyme-catalyzed phosphoryl transfer reactions". Annu. Rev. Biochem. 49: 877–919. doi:10.1146/annurev.bi.49.070180.004305. PMID 6250450.
• T?rnroth-Horsefield, S.; Neutze, R. (December 2008). "Opening and closing the metabolite gate". Proc. Natl. Acad. Sci. USA. 105 (50): 19565–19566. Bibcode:2008PNAS..10519565T. doi:10.1073/pnas.0810654106. PMC 2604989. PMID 19073922.
• Storer, A.; Cornish-Bowden, A. (1976). "Concentration of MgATP2? and other ions in solution. Calculation of the true concentrations of species present in mixtures of associating ions". Biochem. J. 159 (1): 1–5. doi:10.1042/bj1590001. PMC 1164030. PMID 11772.
• Wilson, J.; Chin, A. (1991). "Chelation of divalent cations by ATP, studied by titration calorimetry". Anal. Biochem. 193 (1): 16–19. doi:10.1016/0003-2697(91)90036-S. PMID 1645933.
• Garfinkel, L.; Altschuld, R.; Garfinkel, D. (1986). "Magnesium in cardiac energy metabolism". J. Mol. Cell. Cardiol. 18 (10): 1003–1013. doi:10.1016/S0022-2828(86)80289-9. PMID 3537318.
• Saylor, P.; Wang, C.; Hirai, T.; Adams, J. (1998). "A second magnesium ion is critical for ATP binding in the kinase domain of the oncoprotein v-Fps". Biochemistry. 37 (36): 12624–12630. doi:10.1021/bi9812672. PMID 9730835.
• Lin, X.; Ayrapetov, M; Sun, G. (2005). "Characterization of the interactions between the active site of a protein tyrosine kinase and a divalent metal activator". BMC Biochem. 6: 25. doi:10.1186/1471-2091-6-25. PMC 1316873. PMID 16305747.
• Budavari, Susan, ed. (2001), The Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals (13th ed.), Merck, ISBN 0911910131
• Ferguson, S. J.; Nicholls, David; Ferguson, Stuart (2002). Bioenergetics 3 (3rd ed.). San Diego, CA: Academic. ISBN 978-0-12-518121-1.
• G.C.E. (Advanced Level) - Biology - Grade 12 - Resource Book - Department of Science, Faculty of Science and Technology, LK
• Adenosine triphosphate. (2022, November 16). In Wikipedia. https://en.wikipedia.org/wiki/Adenosine_triphosphate