PH inside cells

What about amine bases In what form do they exist at the physiological pH inside cells—as the amine (A- = RNH2), or as the ammonium ion (HA = RNH3+) Let s take a 0.0010 Vf solution of methylamine at pH = 7.3, for example. According to Table 24.1, the pKa of methvlammonium ion is 10.64, so from the Henderson-Hasselbalch equation, we have... 

Another method for measuring the pH inside cells is to observe the phosphate shift in n.m.r. this procedure has an accuracy of 0.02 unit of pH (Navon etal., 1977). In another application of this method Robertses a/. (1980) found pH 7.1 for the cytoplasm of plant cells and 5.5 for the vacuoles. Their method was to note the chemical shift of the peak due to glucose 6-phosphate... 

When considering the formation of naturally occurring substances, whether simple amino-acids, sugars, or complex proteins, alkaloids, polyketides, terpenes or steroids, it should be remembered that all the reactions involved follow the normal laws of chemistry. One of the fascinating areas of chemistry today is trying to understand how these biosynthetic reactions occur. How it is that reactions we find extremely difficult in the laboratory are accomplished efficiently and quickly at room temperature and near neutral pH inside cells What kinds of organic chemical reactions can be used in living cells ... 

In addition to binding to sialic acid residues of the carbohydrate side chains of cellular proteins that the virus exploits as receptors, hemagglutinin has a second function in the infection of host cells. Viruses, bound to the plasma membrane via their membrane receptors, are taken into the cells by endocytosis. Proton pumps in the membrane of endocytic vesicles that now contain the bound viruses cause an accumulation of protons and a consequent lowering of the pH inside the vesicles. The acidic pH (below pH 6) allows hemagglutinin to fulfill its second role, namely, to act as a membrane fusogen by inducing the fusion of the viral envelope membrane with the membrane of the endosome. This expels the viral RNA into the cytoplasm, where it can begin to replicate. 

In acidic solution at low pH, a carboxylic acid is completely undissociated and exists entirely as RCO2H- In basic solution at high pH, a carboxylic acid is completely dissociated and exists entirely as RC02 - Inside living cells, however, the pH is neither acidic nor basic but is instead buffered to nearly neutral pH—in humans, to pH = 7.3, a value often referred to as physiological pH. In what form, then, do carboxylic acids exist inside cells The question is an important one for understanding the acid catalysts so often found in biological reactions. 

What is true for acetic acid is also true for other carboxylic acids at the ph ysiological pH that exists inside cells, carboxylic acids are almost entirely dissociated. To reflect this fact, we always refer to cellular carboxylic acids by the name of their anion—acetate, lactate, citrate, and so forth, rather than acetic acid, lactic acid, and citric acid. 

There are receptors (TfRs) on the surfaces of many cells for transferrin, it binds to these receptors and is internalized by receptor-mediated endocytosis (compare the fate of LDL Chapter 25). The acid pH inside the lysosome causes the iron to dissociate from the protein. The dissociated iron leaves the endosome via DMTl to enter the cytoplasm. Unlike the protein component of LDL, apoTf is not degraded within the lysosome. Instead, it remains associated with its receptor, returns to the plasma membrane, dissociates from its receptor, reenters the plasma, picks up more iron, and again delivers the iron to needy ceils. 

The fluorescence intensity of fluorescent proteins is pH dependent and most fluorescent proteins are less fluorescent at lower pH mainly because of a reduction in absorbance. Since the absorbance of the acceptor determines the FRET efficiency, changes in the acceptor absorbance spectrum due to pH variations can be wrongly interpreted as changes in FRET efficiency. Thus, a pKa well below physiological pH is recommended to prevent artifacts due to pH changes inside cells. This is especially challenging if the fluorescent proteins are to be targeted to acid cellular compartments, for example, endosomes, lysosomes, or plant vacuoles. 

Such a metabolic one-way street comes about in large part due the fact that certain chemical reactions are associated with a large energy change, which in chemical terms mean that the reaction is operating far away from its true equilibrium. Reactions of this nature are difficult to reverse under the conditions of pH, temperature and substrate concentration which exist inside cells and so become physiologically irreversible . 

Blood is the transport medium of the body. Plasma, which accounts for approximately 60% of the total volume, carries a wide range of small and medium-sized metabolites some are simply dissolved in solution (93% of the plasma is water), others are carried by specific carrier proteins. The chemical composition of the plasma is complex and reflects the chemical composition inside cells, which is why blood tests are so commonly used in diagnosis to see the biochemical events occurring in tissues. The formed cellular elements of the blood perform several functions defence against blood loss from bleeding (platelets, also called thrombocytes), defence against infection and immune surveillance (white cells, leucocytes), and gas transport and pH buffering (red cells, erythrocytes). 

The enzymatic catalysis of reactions is essential to living systems. Under biologically relevant conditions, uncatalyzed reactions tend to be slow—most biological molecules are quite stable in the neutral-pH, mild-temperature, aqueous environment inside cells. Furthermore, many common reactions in biochemistry entail chemical events that are unfavorable or unlikely in the cellular environment, such as the transient formation of unstable charged intermediates or the collision of two or more molecules in the precise orientation required for reaction. Reactions required to digest food, send nerve signals, or contract a muscle simply do not occur at a useful rate without catalysis. 

Because the pH inside a plant or animal cell is about 7, reduction potentials that apply at pH 0 are not particularly appropriate. For example, at pH 0, ascorbic acid (vitamin C) is a more powerful reducing agent than succinic acid. However, at pH 7, this order is reversed. It is the reducing strength at pH 7, not at pH 0, that is relevant to a living cell. 

The xanthenes exist in solution in several different forms depending on pH, as shown in Figure 2 and Table 1 [18]. The emission quantum yield of fluorescein depends on the acidity of the solution, the fluorescence intensity decreasing as the protonated forms of the dye come to predominate with decreasing pH. This pH sensitivity allows fluorescein derivatives to be employed as pH indicators, to measure the pH inside living cells [19-22], at water-lipid interfaces [23], and in the interior of phospholipid vesicles [24]. The sensitivity of fluorescein emission to the pH of the medium has also been used to measure lateral proton conductances at water-lipid interfaces [25-28] and proton translocation across phospholipid vesicles [29] and to determine the electrostatic potential of macromolecules [30, 31]. The pheno-... 

Organic acids may inhibit growth when present in the undissociated form because of their ability to change the pH inside the cell. The most efficient are benzoic acid and sorbic acid, but formic, acetic, and propionic acid also have this effect. The parabens, ie, -hydroxy benzoic acid esters, are also used because of their antimicrobial effect over a broad pH range. 

So, in aqueous solution cisplatin will loose Cl-, and an aqua or/and hydroxo (at high pH) ligand becomes coordinated. In the body, the Cl- concentration outside cells is rather high (about 100 mM), and therefore hydrolysis is largely prevented there. Inside cells, however, the Cl- concentration is about 4 mM, promoting the hydrolysis process. According to calculations by Martin35), the aquated species in the body fluids is present only for a few percent, whereas it amounts to about 50% of the total present inside the cell. 

In HeLa cells, the di-ferric transferrin-stimulated proton release is accompanied by an increase in the pH inside the cell as measured by change in fluorescence of the internal indicator BCECF incorporated into the cells (Figure 7). This alkalinization is consistent with exchanger activation to export protons. Most of the internal pH increase is inhibited by amiloride or dimethylamiloride (Mrkic et al., 1992 Yun et al., 1993). The internal change in pH is prevented if Cs+ is substituted for Na+ or Li+ in the external media (Toole-Simms, 1988). Ferricyanide-stimulated proton release by HeLa cells is not accompanied by an internal pH increase. The basis for this difference from di-ferric transferrin has not been investigated. It is possible that the rapid electron transport in response to ferricyanide leads to oxidation of sufficient NADH, which produces protons inside the cell, to counter... 

The motion of protons in water is extremely rapid, and no catalyst can manage this problem at low pH. Therefore, the known life that is found in acidic environments on Earth manages the low pH of its environment by pumping protons out of the cell. Although the pH of Rio Tinto outside the cells that five there is about 2, the pH inside the cells is well above 6, as it is in human cells. 

The pH of gastric juice is about 1.5. Assuming that the pH inside the cells of the gastric mucosa is 6.8, calculate the amount of energy required to secrete a mole of H ions. Assume T = 37 C. 

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