China
Africa
Explore chapters and articles related to this topic
Whence Dynamical Systems
Published in LM Pismen, Working with Dynamical Systems, 2020
The ion transport combines diffusion, driven by the concentration gradient ∇ci of a particular ion, and migration, driven by the potential gradient ∇ϕ. The ion flux j is defined, therefore, by the Nernst—Planck equation ji=−D∇ci−T−1nFci∇ϕ,where n is the ion charge and F is the Faraday number. This equation contains already a spatial dependence of the concentration and potential, and the concentration distribution can be computed by solving the equation c˙i=∇⋅ji.
39K
Published in Guillaume Madelin, X-Nuclei Magnetic Resonance Imaging, 2022
As for sodium, potassium concentrations in cells are therefore very sensitive to changes in the metabolic state of tissues and the integrity of cell membranes. The potassium influx and outflux in cells can occur by several routes, such as voltage-gated K+ channels (which are the most widely distributed type of ion channel and are found in almost all living organisms), the Na+/Ca2+-K+ exchanger, the Na+-K+/2Cl− and K+-Cl− cotransporters, and, most importantly, through the Na+/K+-ATPase. The Na+/K+-ATPase (also called sodium–potassium pump) is present within the membrane of every animal cell. It is a plasma membrane-associated protein complex that is expressed in most eukaryotic cells and can be considered either an enzyme (ATPase) or an ion transporter. Its main function is to maintain the sodium and potassium gradients across the membrane by pumping three intracellular sodium ions out of the cell and two extracellular potassium ions within the cell. This ion transport is performed against the electrochemical Na+ and K+ gradients existing across the cell membrane and therefore requires energy, provided by adenosine triphosphate (ATP) hydrolysis. These high electrochemical sodium and potassium gradients are essential to protect the cell from bursting as a result of osmotic swelling. They regulate the cell volume and help maintain the resting cell membrane potential that can be used for transmitting nerve impulses (Na+ and K+ have to be actively pumped back after an excitation event of a nerve or muscle membrane potential) and for pumping ions (protons, calcium, chloride, phosphate), metabolites (glucose, amino acids), or neurotransmitters (glutamate) across the cell membrane. Regulation of Na+/K+-ATPase therefore plays a key role in the etiology of some pathological processes. When the demand for ATP exceeds its production (when cell membrane leaks overwhelm the pumping capacity), the ATP supply for the Na+/K+-ATPase will be insufficient to maintain the electrochemical potassium gradient and thus a variation of intracellular potassium concentration can be observed, leading to changes in osmolarity and eventually leading to cell death. Typical concentrations of potassium in the human body are listed in Table 6.2.
Cyanobacteria mediated heavy metal removal: a review on mechanism, biosynthesis, and removal capability
Published in Environmental Technology Reviews, 2021
Abdullah Al-Amin, Fahmida Parvin, Joydeep Chakraborty, Yong-Ick Kim
The circadian clock is cyanobacterial intrinsic timekeeping machinery that depends on diurnal light and dark cycles [114]. The circadian clock regulates the metabolic and genetic function of cyanobacteria [114]. Clark et al., [115] established the functionality of the circadian clock on cyanobacterial growth. The circadian gene expressions are regulated by a transcription factor, RpaA, which also regulates ATP production pathways. This implicates the metabolic cross-talk between ATP production and the circadian clock [116]. It has been established that the circadian clock influences most cellular transcription promoters [98]. A few examples of enzymes under such regulation that are of interest in the current review are ABC protein transporter (Ppa), metal ion transporter (metH), Metallothionine (SmtA), and copper transporting p-type ATPase (ctaA). Thus, genetic engineering of circadian clock can enhance the ability to switch ‘on’ promoters and consequently expression of mRNA regulated by the circadian clock instead of controlled by 12-hour light/ dark. Although the molecular mechanisms of the cyanobacterial circadian system are well characterized, substantial literature for its ecological benefits is not available yet. The circadian clock may have a key role in the biogeography of the two most abundant marine cyanobacteria – Prochlorococcus, (low-latitude open ocean), and Synechococcus (high-latitude and coastal waters). While Synechococcus has a circadian clock exhibiting free-running rhythms, it is absent in Prochlorococcus [117]. Synechocystis sp. PCC 6803 promoters have also been studied extensively for the purpose of engineered circadian clock [118]. The reason to study this organism is that its circadian clock regulates gene expression at the genome-scale. The potential application of an engineered circadian clock in regulation and effective heavy metal ion sequestration is yet to be explored. Application of circadian clock in cyanobacterial metal ion sequestration application might disclose the molecular-level mechanisms of cyanobacteria to sequester metal ions and different defense mechanisms.