China
Africa
Explore chapters and articles related to this topic
The Chemical Work of Biosynthesis
Published in Jean-Louis Burgot, Thermodynamics in Bioenergetics, 2019
Living cells use the chemical energy of ATP to perform the chemical work of biosynthesizing cellular components from precursor molecules. They use the common intermediate principle. We have seen that this principle makes possible the conservation of oxidation-reduction energy as the phosphate bond energy of ATP. Recall, for example, the formation of sucrose from glucose and fructose (Chapter 33). Glucose-1-phosphate is formed by the enzymatic transfer of a phosphate group from ATP to glucose. The bond between glucose and phosphate has about the same Gibbs energy of hydrolysis as the glucosidic bond which links fructose and glucose in sucrose. Once formed, glucose-1-phosphate reacts enzymatically with fructose to produce sucrose. The latter is readily formed. The overall reaction is downhill. Its ∆G’ is frankly negative (∆G’ = −6270 J mol–1): ATP + glucose→ADP + glucose-1-phosphateglucose-1-phosphate + fructose→sucrose + phosphate
Applications in Biology
Published in Gabriel A. Wainer, Discrete-Event Modeling and Simulation, 2017
We also considered the formation of UDP-glucose, which can be attached to glucose chains that can be acted upon by glycogen synthesis. Glucose enters the cells by facilitated diffusion, and then the cell modifies glucose by phosphorylation, as shown in Figure 8.11. Glucose-6-phosphate is used in the synthesis of glycogen: glucose-6-phosphate is first isomerized to glucose-1-phosphate by the enzyme phosphoglucomutase, as seen in Figure 8.12. UDP-glucose has the ability to attach its glucose part to glucose chains. This new chain can be acted upon during glycogen synthesis, as seen in Figure 8.13. Figure 8.14 shows this process in our CD++ simulation.
Cellulose – A Sustainable Material for Biomedical Applications
Published in Ashwani Kumar, Mangey Ram, Yogesh Kumar Singla, Advanced Materials for Biomechanical Applications, 2022
N. Vignesh, K. Chandraraj, S.P. Suriyaraj, R. Selvakumar
The synthesis of BC proceeds through a bottom-up approach wherein the glucose monomers taken up by the bacteria are assembled into cellulose through metabolic pathways inside the cell (Figure 4.1b). Initially, glucose is phosphorylated to glucose-6-phosphate by glucokinase. The isomerization of glucose-6-phosphate to glucose-1-phosphate is catalyzed by phosphoglucomutase. Further, glucose-1-phosphate is converted into uridine diphosphate glucose (UDPG) by UDPG pyrophosphorylase. The polymerization of glucose into cellulose is finally catalyzed by cellulose synthase through the formation of linear β-1,4-glucan chains [30]. The synthesized cellulose present in the form of protofibrils is secreted across the cell wall through transporters (Figure 4.1c). In the extracellular medium, the secreted protofibrils aggregate into microfibrils, which further organize into a desired nanostructure like a pellicle or mat depending on the culture condition [25].The production of BC is simple, as it requires optimum physical conditions like pH, temperature and aeration for the growth of the bacterial strain. Moreover, the secreted BC is treated with alkali to produce cellulose polymorph II for increasing the pore size, surface area and elasticity of the material [37]. Besides, the elevated porosity of BC facilitates its application as a precursor material for aerogel preparation (Figure 4.1d). To improve the properties of BC, in situ modification of its structure has been reported in many studies. Unlike an external chemical treatment, in situ modification refers to an alteration in the chemical composition of BC through the supplementation of additives in the growth medium. As a result, the desired components are incorporated into the structure of BC during microbial synthesis [38]. BC conjugates produced using additives such as polyvinyl alcohol, hydroxyapatite, chitosan, heparin and dextrin have been used for developing cardiovascular soft tissue, bone regeneration scaffold, antimicrobial membrane, anticoagulant wound dressing material and blood transfusion membrane respectively [29]. Eventhough BC is associated with intriguing properties and environmentally friendly production, the requirements of a large vessel, continuous aeration and longer process time are the major limitations hindering the commercial feasibility (Table 4.2).
Comparative proteomic analysis revealed the metabolic mechanism of excessive exopolysaccharide synthesis by Bacillus mucilaginosus under CaCO3 addition
Published in Preparative Biochemistry & Biotechnology, 2019
Hongyu Xu, Zhiwen Zhang, Hui Li, Yujie Yan, Jinsong Shi, Zhenghong Xu
Exopolysaccharides are water-soluble polysaccharides that are secreted by special microorganisms outside the cell walls in the growth and metabolism and are easily separated from the cells and secreted into the environment.[1,2] The enzymes involved in the synthesis of extracellular polysaccharides are located at different sites of the microbial cells and can be divided into the following four different types. The first enzyme type is located intracellularly and composed primarily of kinases and mutases. The other typical enzymes are glucokinase, phosphoglucose mutase, and glucose, which produce glucose-6-phosphate under the action of glucokinase. Glucose-1-phosphate is formed by the action of phosphoglucose mutase. Most of the glyconucleotide precursors required for the synthesis of extracellular polysaccharides are derived from glucose-1-phosphate; thus, phosphorylation is important for the synthesis of extracellular polysaccharides.[3] Recent studies highlighted a signaling activity for the exopolysaccharides produced by the Bacillus subtilis eps operon. This polymer is recognized by the extracellular domain of a tyrosine kinase that activates its own synthetic pathway.[4] The second type of enzyme is located intracellularly and includes UDP–glucose pyrophosphorylase (UGP) and various epimerases. UGP catalyzes glucose-1-phosphate as an important precursor for the polysaccharide synthesis of UDP–glucose. Under the action of epimerase, UDP–glucose can produce other sugar nucleotide precursors.[5] The third type of enzyme is mostly located in cell membranes, such as glycosyltransferases. The sugar nucleotides are transported to a glycosyl lipid carrier and then assembled into oligosaccharide repeat units with the participation of a glycosyltransferase.[6] The fourth type of enzyme is located in the cell membrane or extracellularly and presumably associated with bacterial extracellular polysaccharide polymerization. After a macromolecular polysaccharide is produced, it is secreted extracellularly to form a mucin polysaccharide or attached to the surface of the cell to form a capsular polysaccharide.[7]