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THE BHP WIRE —
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Explore the people, places, events, achievements, struggles and stories that shaped our journey.
Movements, leaders, victories and the continuing fight for equality.
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Meet the people whose lives, choices and achievements shaped the journey.
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In August 1908, a white mob attacked Springfield, Illinois’s Black community, destroying homes and businesses and lynching two Black men. National outrage over the violence helped spur the movement that created the NAACP the following year.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
 | This article may be too technical for most readers to understand. (March 2020) |
Intracellular pH (pHi) is the measure of the acidity or basicity (i.e., pH) of intracellular fluid. The pHi plays a critical role in membrane transport and other intracellular processes. In an environment with the improper pHi, biological cells may have compromised function.[1][2] Therefore, pHi is closely regulated in order to ensure proper cellular function, controlled cell growth, and normal cellular processes.[3] The mechanisms that regulate pHi are usually considered to be plasma membrane transporters of which two main types exist — those that are dependent and those that are independent of the concentration of bicarbonate (HCO−
3). Physiologically normal intracellular pH is most commonly between 7.0 and 7.4, though there is variability between tissues (e.g., mammalian skeletal muscle tends to have a pHi of 6.8–7.1).[4][5] There is also pH variation across different organelles, which can span from around 4.5 to 8.0.[6][7] pHi can be measured in a number of different ways.[3][8]
Intracellular pH is typically lower than extracellular pH due to lower concentrations of HCO3−.[9] A rise of extracellular (e.g., serum) partial pressure of carbon dioxide (pCO2) above 45 mmHg leads to formation of carbonic acid, which causes a decrease of pHi as it dissociates:[10]
Since biological cells contain fluid that can act as a buffer, pHi can be maintained fairly well within a certain range.[11] Cells adjust their pHi accordingly upon an increase in acidity or basicity, usually with the help of CO2 or HCO3– sensors present in the membrane of the cell.[3] These sensors can permit H+ to pass through the cell membrane accordingly, allowing for pHi to be interrelated with extracellular pH in this respect.[12]
Major intracellular buffer systems include those involving proteins or phosphates. Since the proteins have acidic and basic regions, they can serve as both proton donors or acceptors in order to maintain a relatively stable intracellular pH. In the case of a phosphate buffer, substantial quantities of weak acid and conjugate weak base (H2PO4– and HPO42–) can accept or donate protons accordingly in order to conserve intracellular pH:[13][14]
The pH within a particular organelle is tailored for its specific function.
For example, lysosomes have a relatively low pH of 4.5.[6] Additionally, fluorescence microscopy techniques have indicated that phagosomes also have a relatively low internal pH.[15] Since these are both degradative organelles that engulf and break down other substances, they require high internal acidity in order to successfully perform their intended function.[15]
In contrast to the relatively low pH inside lysosomes and phagosomes, the mitochondrial matrix has an internal pH of around 8.0, which is approximately 0.9 pH units higher than that of inside intermembrane space.[6][16] Since oxidative phosphorylation must occur inside the mitochondria, this pH discrepancy is necessary to create a gradient across the membrane. This membrane potential is ultimately what allows for the mitochondria to generate large quantities of ATP.[17]
There are several common ways in which intracellular pH (pHi) can be measured including with a microelectrode, dye that is sensitive to pH, or with nuclear magnetic resonance techniques.[18][19] For measuring pH inside of organelles, a technique utilizing pH-sensitive green fluorescent proteins (GFPs) may be used.[20]
Overall, all three methods have their own advantages and disadvantages. Using dyes is perhaps the easiest and fairly precise, while NMR presents the challenge of being relatively less precise.[18] Furthermore, using a microelectrode may be challenging in situations where the cells are too small, or the intactness of the cell membrane should remain undisturbed.[19] GFPs are unique in that they provide a noninvasive way of determining pH inside different organelles, yet this method is not the most quantitatively precise way of determining pH.[21]
The microelectrode method for measuring pHi consists of placing a very small electrode into the cell's cytosol by making a very small hole in the plasma membrane of the cell.[19] Since the microelectrode has fluid with a high H+ concentration inside, relative to the outside of the electrode, there is a potential created due to the pH discrepancy between the inside and outside of the electrode.[18][19] From this voltage difference, and a predetermined pH for the fluid inside the electrode, one can determine the intracellular pH (pHi) of the cell of interest.[19]
Another way to measure Intracellular pH (pHi) is with dyes that are sensitive to pH, and fluoresce differently at various pH values.[15][22] This technique, which makes use of fluorescence spectroscopy, consists of adding this special dye to the cytosol of a cell.[18][19] By exciting the dye in the cell with energy from light, and measuring the wavelength of light released by the photon as it returns to its native energy state, one can determine the type of dye present, and relate that to the intracellular pH of the given cell.[18][19]
In addition to using pH-sensitive electrodes and dyes to measure pHi, Nuclear Magnetic Resonance (NMR) spectroscopy can also be used to quantify pHi.[19] NMR, typically speaking, reveals information about the inside of a cell by placing the cell in an environment with a potent magnetic field.[18][19] Based on the ratio between the concentrations of protonated, compared to deprotonated, forms of phosphate compounds in a given cell, the internal pH of the cell can be determined.[18] Additionally, NMR may also be used to reveal the presence of intracellular sodium, which can also provide information about the pHi.[23]
Using NMR Spectroscopy, it has been determined that lymphocytes maintain a constant internal pH of 7.17± 0.06, though, like all cells, the intracellular pH changes in the same direction as extracellular pH.[24]
To determine the pH inside organelles, pH-sensitive GFPs are often used as part of a noninvasive and effective technique.[20] By using cDNA as a template along with the appropriate primers, the GFP gene can be expressed in the cytosol, and the proteins produced can target specific regions within the cell, such as the mitochondria, golgi apparatus, cytoplasm, and endoplasmic reticulum.[21] If certain GFP mutants that are highly sensitive to pH in intracellular environments are used in these experiments, the relative amount of resulting fluorescence can reveal the approximate surrounding pH.[21][25]
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Source: Wikipedia. Article content is retrieved live through the MediaWiki API.
Intracellular pH (pHi) is the measure of the acidity or basicity (i.e., pH) of intracellular fluid. The pHi plays a critical role in membrane transport and other intracellular processes. In an environment with the improper pHi, biological cells may have compromised function. Therefore, pHi is closely regulated in order to ensure proper cellular function, controlled cell growth, and normal cellular processes. The mechanisms that regulate pHi are usually considered to be plasma membrane transporters of which two main types exist — those that are dependent and those that are independent of the concentration of bicarbonate (HCO−3). Physiologically normal intracellular pH is most commonly between 7.0 and 7.4, though there is variability between tissues (e.g., mammalian skeletal muscle tends to have a pHi of 6.8–7.1). There is also pH variation across different organelles, which can span from around 4.5 to 8.0. pHi can be measured in a number of different ways.
Every organism requires energy to be active. However, to obtain energy from its outside environment, cells must not only retrieve molecules from their surroundings but also break them down. This process is known as intracellular digestion. In its broadest sense, intracellular digestion is the breakdown of substances within the cytoplasm of a cell. In detail, a phagocyte's duty is obtaining food particles and digesting it in a vacuole. For example, following phagocytosis, the ingested particle (or phagosome) fuses with a lysosome containing hydrolytic enzymes to form a phagolysosome; the pathogens or food particles within the phagosome are then digested by the lysosome's enzymes. Intracellular digestion can also refer to the process in which animals that lack a digestive tract bring food items into the cell for the purposes of digestion for nutritional needs. This kind of intracellular digestion occurs in many unicellular protozoans, in Pycnogonida, in some molluscs, Cnidaria and Porifera. There is another type of digestion, called extracellular digestion. In amphioxus, digestion is both extracellular and intracellular.
Intracellular transport is the movement of vesicles and substances within a cell. Intracellular transport is required for maintaining homeostasis within the cell by responding to physiological signals. Proteins synthesized in the cytosol are distributed to their respective organelles, according to their specific amino acid's sorting sequence. Eukaryotic cells transport packets of components to particular intracellular locations by attaching them to molecular motors that haul them along microtubules and actin filaments. Since intracellular transport heavily relies on microtubules for movement, the components of the cytoskeleton play a vital role in trafficking vesicles between organelles and the plasma membrane by providing mechanical support. Through this pathway, it is possible to facilitate the movement of essential molecules such as membrane‐bounded vesicles and organelles, mRNA, and chromosomes. Intracellular transport is unique to eukaryotic cells because they possess organelles enclosed in membranes that need to be mediated for exchange of cargo to take place. Conversely, in prokaryotic cells, there is no need for this specialized transport mechanism because there are no membranous organelles and compartments to traffic between. Prokaryotes are able to subsist by allowing materials to enter the cell via simple diffusion. Intracellular transport is more specialized than diffusion; it is a multifaceted process which utilizes transport vesicles. Transport vesicles are small structures within the cell consisting of a fluid enclosed by a lipid bilayer that hold cargo. These vesicles will typically execute cargo loading and vesicle budding, vesicle transport, the binding of the vesicle to a target membrane and the fusion of the vesicle membranes to target membrane. To ensure that these vesicles embark in the right direction and to further organize the cell, special motor proteins attach to cargo-filled vesicles and carry them along the cytoskeleton. For example, they have to ensure that lysosomal enzymes are transferred specifically to the golgi apparatus and not to another part of the cell which could lead to deleterious effects.
Intracellular bacteria are bacteria that have the capability to enter and survive within the cells of the host organism. These bacteria include many different pathogens that live in the cytoplasm and nuclei of the host cell's they inhabit. Mycobacterium tuberculosis is an example of an intracellular bacterial species. There are two types of intracellular bacteria: facultative intracellular bacteria, which can grow extracellularly or intracellularly, and obligate intracellular bacteria, which can grow only intracellularly.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Shirley Chisholm, elected in 1968.
