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X-Nuclei MRI and Energy Metabolism
Published in Guillaume Madelin, X-Nuclei Magnetic Resonance Imaging, 2022
In this book, we will define cellular energy metabolism as the set of enzyme-mediated chemical reactions that occur in living organisms to synthesize energy carriers and utilize their stored energy in order to grow and reproduce, maintain their structures, and respond to environmental changes. We will also focus on the energy metabolism in eukaryotic cells only. Eukaryotes are cells that contain a nucleus and organelles, such as mitochondria, enclosed by a plasma membrane, and which make plants and animals [1–5, 10–12]. The main energy carrier in living cells is the adenosine triphosphate (ATP). It can be synthesized in cells during cellular respiration, and hydrolyzed into adenosine diphosphate (ADP) to release its energy and enable a wide range of biochemical reactions to maintain a transmembrane electrochemical gradient for ion homeostasis; allow nerve excitation and muscle contraction; synthesize proteins, DNA, and RNA; and serve as substrate for kinase enzymes involved in signal transduction. Enzymes play a crucial role in energy metabolism. They act as catalysts to allow energetic reactions to proceed efficiently and rapidly, and to allow the regulation of metabolic pathways in response to changes in the cellular environment or to signals from other cells [1–5, 10–12].
Cultivation and Conversion of Algae for Wastewater Treatment and Biofuel Production
Published in Sonil Nanda, Prakash Kumar Sarangi, Dai-Viet N. Vo, Fuel Processing and Energy Utilization, 2019
Priyanka Yadav, Sivamohan N. Reddy, Sonil Nanda
Microalgae assimilated the fixed N2 as ammonium-nitrogen, nitrate-nitrogen, and nitrite-nitrogen. The assimilation of nitrogen requires its reduction to ammonium-nitrogen in a two-step process in the presence of nitrate and nitrite reductases enzymes. In the initial step, the nitrate-nitrogen reduces to nitrite-nitrogen by the nitrate reductase enzyme in the presence of NADPH as a reducing agent. Furthermore, nitrite-nitrogen is reduced to ammonium-nitrogen by the nitrite reductase enzyme, which further uses ferredoxin to catalyze the electron transfer reactions. Ammonium-nitrogen formed by the reduction of nitrate-nitrogen and nitrite-nitrogen is further converted into amino acids by the glutamine synthetase-glutamate synthase pathway in the presence of the glutamine synthase enzyme. Phosphorus enters microalgae cells through the plasma membrane in the form of HPO42− and H2PO4−. Further, phosphate-phosphorus is converted into organic compounds by processes such as phosphorylation, oxidative phosphorylation, and photophosphorylation. In these processes, adenosine diphosphate (ADP) is converted into ATP by an energy input (Martinez et al. 1999).
Work Capacity, Stress, Fatigue, and Recovery
Published in R. S. Bridger, Introduction to Human Factors and Ergonomics, 2017
Energy for muscle contraction (and for many other bodily processes) comes from the breakdown of a substance known as adenosine triphosphate (ATP). By breaking one of the phosphate bonds, ATP is converted into adenosine diphosphate (ADP) and energy is made available inside the cell. Astrand and Rodahl (1977) liken ATP to a rechargeable battery pack—a short-term store of directly available energy. For the cell to continue functioning, the ADP must be reconverted to ATP so that energy can continue to be made available when required. A second phosphate compound, known as creatine phosphate, acts like a backup energy store to recharge the ADP to ATP.
Microbial fuel cells: a sustainable solution for bioelectricity generation and wastewater treatment
Published in Biofuels, 2019
Har Mohan Singh, Atin K. Pathak, Kapil Chopra, V.V. Tyagi, Sanjeev Anand, Richa Kothari
Microorganisms can use a wide spectrum of organic compounds (carbohydrates, proteins, lipids) as carbon and energy sources. These compounds can perform as electron donors in citric acid chain reactions and form energy carrier adenosine triphosphate (ATP) molecules before cyclic chain reactions. The conglomerated carbohydrates, proteins and lipids break into their constituting monomers and form acetyl coenzyme A (CoA) by glycolysis. The CoA molecule initiates the citric acid cycle and oxidation reactions occur jointly with reduction of nicotinamide adenine dinucleotide (NAD+) and flavin adenine dinucleotide (FAD) and form nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FADH2) as electron carriers. The citric acid cycle is completed in the cytoplasm and cell membrane with the assistance of electron carriers NADH and FADH2 (Figure 2). The cell membrane passes to terminal electron acceptor through various complex membrane intermediates and ATP synthase transmembrane protein is used to convert adenosine diphosphate (ADP) to ATP. These ATP molecules act as the chemical currency of living organisms and the production process represents respiration. In the anodic compartment, a bacterial cell replaces an electrode as the terminal electron acceptor. The mechanism of the cell membrane is shown in Figure 3 [11].
Microalgae: a cheap tool for wastewater abatement and biomass recovery
Published in Environmental Technology Reviews, 2022
Haruna Saidu, Jibrin Mohammed Ndejiko, Nafiatu Abdullahi, Aisha Bello Mahmoud, Shaza Eva Mohamad
The mechanism of nitrogen uptake involving nitrogen assimilation is simple. Nitrogen is an essential requirement for the growth of microalgae. It forms the precursor molecule for the synthesis of amino acids, nucleic acids, and nitrogen-containing compounds. Organic nitrogen transpires in the form of protein, peptide, enzyme, or chlorophyll, energy transfer molecules (ADP and ATP) and genetic material (RNA, DNA) [4]. Organic nitrogen is derived from inorganic sources such as nitrate, nitrite, and ammonium. Organisms converted inorganic nitrogen into organic nitrogen via nitrogen fixation (e.g. Cyanobacteria) and assimilation (e.g. all eukaryotic microalgae). In the eukaryotic cell, inorganic nitrogen is translocated via the plasma membrane and become oxidized. Subsequently, the oxidized inorganic nitrogen becomes reduced to ammonia and integrated into an amino acid. Nitrate reductase uses two electrons from nicotinamide adenine dinucleotide phosphate (NADPH) to convert nitrate to nitrite, while nitrite reductase converts nitrite to ammonia by transferring six (6) electrons to the reaction chain. This implies that all forms of nitrogen must be converted to ammonia prior to integration into an amino acid. Glutamine synthase catalyzes the conversion of ammonia into amino acid glutamine in a cellular fluid (Figure 2). Unlike nitrogen, phosphorus provides the main source of energy for microalgal cells. During metabolic processes, inorganic phosphorus in the form of orthophosphates is integrated into organic compounds via phosphorylation by the formation of adenosine triphosphate (ATP) from adenosine diphosphate (ADP) for energy generation. Transportation takes place actively across the plasma membrane of the microalgal cell [65]. In fact, in another literature, it was reported that although microalgae utilized organic or inorganic nitrogen, but it prefers ammonium at a certain limited concentration. This is because a high amount of ammonium causes an increase in pH value, thereby affecting the growth of microalgae due to toxicity [1]. Wastewater having high pH value of more than 10 can alter the water chemistry, thereby causing ammonia assimilation and rapid precipitation of phosphate in the form of calcium phosphate [4]. These two scenarios could clarify the established link between nitrogen and phosphate removal. Here, it means that phosphate and nitrogen were removed by chemical precipitation and algal assimilation. Microalgae activity was the reason behind the two removals. The most critical factors that have a direct effect on microalgae growth for nitrogen and phosphorus removal are temperature, pH and nutrients. Microalgae density at the inception of the growth depend on nutrients availability whereas an increase in the rate of cell growth relies on light intensity. Thus, to increase the microalgae cell density, the cultivation period also needs to be increased. Although an increase in cell density might cause a shading effect, mixotrophic group of microalgae sources other alternative carbon and energy sources for growth apart from light.