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Microbial Remediation of Persistent Organic Pollutants
Published in Narendra Kumar, Vertika Shukla, Persistent Organic Pollutants in the Environment, 2021
Bacteria import nutrients for growth from their environment and export metabolites by the processes of passive transport, active transport, and group translocation. Passive transport is a naturally occurring phenomenon and does not require the cell to expend energy, as substances move from an area of higher concentration to an area of lower concentration by a process called diffusion. Only small molecules like oxygen and carbon dioxide or lipid-soluble chemicals diffuse freely through the cytoplasmic membrane using this process. On the other hand, active transport uses transmembrane proteins to transport a substance against a concentration or electrochemical gradient, for which the cell has to spend some ATP molecules. These transport mechanisms make up the mass transport system of a bacterial cell. This mass transport, of the pollutant to the bacterial cell, is the rate-controlling step in the process of biodegradation. When a pollutant is lipophilic in nature, a bacterium can speed up its mass transport by production of surfactant (Mateju, 2016).
Computational Modeling of Transepithelial Endogenous Electric Signals
Published in Ben Greenebaum, Frank Barnes, Biological and Medical Aspects of Electromagnetic Fields, 2018
Somen Baidya, Ahmed M. Hassan, Min Zhao
In passive transport, ions move from regions of high concentration to regions of lower concentration. Similarly, positive ions move in the same direction as the incident electric field, whereas negative ions move in the opposite direction. However, in some cases, ions can move in the opposite direction of the electric field or from regions of low concentration to regions of higher concentration. This process is called active transport because it involves ion pumps that consume energy in the form of adenosine tri-phosphate (ATP). The main active pump which is present in the majority of cells is the 3Na+/2K+ ATPase pump that uses hydrolysis to pump three Sodium (Na+) ions out of the cell and two potassium (K+) ions into the cell. This is performed against the concentration gradient since typically the extracellular medium contains more Na+ and fewer K+ ions than the intracellular medium. Driving Na+ out of the cell in the opposite direction of the concentration gradient facilitates transport of several proteins, glucose, and other nutrients into the cell [2,45,46].
Toxicity and Toxins
Published in Gary S. Moore, Kathleen A. Bell, Living with the Earth, 2018
Gary S. Moore, Kathleen A. Bell
Not all molecules can passively diffuse from a high to low concentration. Generally, the chemical nature (basic or acidic), electrical charge, and the size and shape of the molecules determine their ability to passively diffuse across the membrane. Some molecules such as amino acids and sugars require specialized carrier proteins to be transported across a membrane. No high-energy phosphate such as adenosine triphosphate (ATP) is required in this process and so it is referred to as facilitated diffusion. When ATP is required in conjunction with special carrier proteins to move molecules through a membrane against a concentration gradient (i.e., from low concentration to high concentration), this process is called active transport. Typically, about 40 percent of the ATP in a human body cell is consumed in this process of actively transporting molecules across the cell membrane. This process is important in nerve impulse conduction in which sodium and potassium are actively transported across the nerve cell membrane by the sodium-potassium ATPase pump. The energy from ATP is required because three sodium ions are actively transported out for every two potassium ions actively transported in.4,5
Zinc(II)-Schiff base complex functionalized on gold nanospheres: synthesis, characterization, anticancer study and interaction with proteins
Published in Journal of Coordination Chemistry, 2022
Yin Zhuang Ng, Kong Wai Tan, Lip Yong Chung, Fatimah Salim, May Lee Low, Ing Hong Ooi, Foo Win Yip, Chew Hee Ng
Differentiated human intestinal cells (Caco-2 cells) are commonly used to study permeability of drugs and nanoparticles, and they can be grown in transwell insert (Supplementary Figure S1) to form a model intestinal epithelial monolayer [58, 59]. Using this method, studies have shown that different nanoparticles could be transported across this type of epithelial monolayer [60, 61]. There are four main routes for nutrients and drug transport across Caco-2 cells: (i) passive paracellular route, (ii) active transport by transporter, (iii) transcytosis and (iv) passive transcellular route through the cell.