Concentration gradients. primary active transport. “Active transport is the movement of molecules across a membrane from a region of lower concentration to a region of higher concentration against the concentration gradient, often assisted by enzymes and requires energy” “Passive transport is the movement of ions and molecules across the cell membrane without requiring energy.” Examples of such substances that are carried across the cell membrane by primary active transport include metal ions, are Na+, K+, Mg2+, and Ca2+. are synthesized from cholesterol in hepatocytes. Luis Reuss, in Seldin and Giebisch's The Kidney (Fourth Edition), 2008. The H+/ATP stoichiometry of the plasma membrane ATPase is 1 for several eukaryotes, including N. crassa (Perlin et al., 1986) and S. cerevisiae (Malpartida and Serrano, 1981). This chapter first describes the mechanisms that mediate apical membrane H secretion and then discusses possible backleak mechanisms. The best established example of the group translocation systems is the phosphotransferase system (PTS), by which certain sugars are transported in bacteria. PMCA is the plasma membrane Ca-ATPase; SERCA is the smooth endoplasmic reticulum Ca-ATPase; SPCA is the secretory pathway Ca-ATPase. Cells use the breakdown of ATP for primary active transport. Some are located on the plasma membrane of specific cell types; others, such as the smooth endoplasmic reticulum Ca-ATPase (SERCA), are located on subcellular organelles. This ATPase is probably working only in the direction of ATP hydrolysis, and it normally has a stoichiometric ratio of 1 H+/ATP. This portal blood returns to the liver and the bile acids are taken up from the sinusoidal blood by a Na+-dependent cotransporter that links bile acid uptake to Na+ entry (NTCP=SLC10A1, see Figure 8.4.7) and by a second mechanism on the basolateral membrane that does not require Na+ (OATP=SLCO1B3, see Figure 8.4.7). To prevent the bile acids from solubilizing the liver cells, the cytoplasmic bile acid concentration must be kept low. Studies have shown that some pathologic conditions lead to a change in P-gp expression. Figure 8.4.7. The primary active transport system uses ATP to move a substance, such as an ion, into the cell, and often at the same time, a second substance is moved out of the cell. Substances that are transported across the cell membrane by primary active transport include metal ions, such as Na +, K +, Mg 2+, and Ca 2+.These charged particles require ion pumps or ion channels to cross membranes and distribute through the body. They typically exhibit a critical micellar concentration, or CMC. There are two main forms of coupled transport: antiport and symport. AP® is a registered trademark of the College Board, which has not reviewed this resource. Among these are gastric H+-ATPase that is responsible for acidification of the stomach contents; Na+,K+-ATPase that is responsible for maintaining ionic gradients in most cells; PMCA (for plasma membrane calcium ATPase), responsible for pumping Ca2+ out of cells; and the SERCA family of pumps, where SERCA stands for smooth endoplasmic reticulum Ca2+ ATPase, which is responsible for removing Ca2+ from the cytosol of a variety of cell types and placing it in storage in internal sacs within cells. The primary bile acids are synthesized in the liver cells from cholesterol and are excreted into the bile as such. This degradation of cholesterol is the largest metabolic sink for cholesterol in the body. As several antiepileptic drugs are substrates for P-gp, drug resistance was another phenomenon that is observed in these patients. Thus, the synthesis of the bile acids is under negative feedback control. Primary active transport, also called direct active transport, directly uses chemical energy (such as from adenosine triphosphate or ATP in case of cell membrane) to transport all species of solutes across a membrane against their concentration gradient. In eukaryotes the F0F1-ATPase is located in the mitochondria, but they also possess a plasma membrane ATPase belonging to another class of ATPases. Primary active transport moves ions across a membrane and creates a difference in charge across that membrane. Primary and secondary active transport. In this process of transportation, the sodium ions are moved to the outside of the cell and potassium ions are moved to the inside of the cell. The primary bile acids are secreted into the bile by a primary active transport mechanism. In primary active transport, there is a direct coupling of energy such as ATP. Results indicated that P-gp is highly expressed in brain capillaries . Alternatively, the transport process may be coupled to another transport process with a downhill concentration gradient (secondary active transport). For example, in a study conducted with PD patients, the P-gp activity was decreased. Substances moved in primary active transport are Na +, K +, Mg 2+, and Ca2 +. Bile acids are synthesized in the liver, secreted into the bile, and stored temporarily in the gallbladder. In primary active transport, specialized trans-membrane proteins recognize the presence of a substance that needs to be transported and serve as pumps, powered by the chemical energy ATP, to carry the desired biochemicals across. Joseph Feher, in Quantitative Human Physiology, 2012, There are a variety of primary active transport pumps encoded by the human genome. In many ( but not all ) secondary active transport have catalytic activity ; they are glutathione.... 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