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67-470: The COPII coat is responsible for the formation of vesicles from the endoplasmic reticulum (ER). These vesicles transport cargo proteins to the Golgi apparatus (in yeast) or the endoplasmic-reticulum-Golgi intermediate compartment (ERGIC, in mammals). Coat assembly is initiated when the cytosolic Ras GTPase Sar1 is activated by its guanine nucleotide exchange factor Sec12. Activated Sar1-GTP inserts itself into

134-501: A molecular mass of less than 300  Da . This mixture of small molecules is extraordinarily complex, as the variety of molecules that are involved in metabolism (the metabolites ) is immense. For example, up to 200,000 different small molecules might be made in plants, although not all these will be present in the same species, or in a single cell. Estimates of the number of metabolites in single cells such as E. coli and baker's yeast predict that under 1,000 are made. Most of

201-546: A 1:2:1 genotype ratio with the first two classes showing the (A) phenotype, and the last showing the (a) phenotype, thereby producing the 3:1 phenotype ratio. Mendel did not use the terms gene, allele, phenotype, genotype, homozygote, and heterozygote, all of which were introduced later. He did introduce the notation of capital and lowercase letters for dominant and recessive alleles, respectively, still in use today. In 1928, British population geneticist Ronald Fisher proposed that dominance acted based on natural selection through

268-488: A core of six beta strands flanked by three alpha helices , and two flexible "switch domains". Unlike other Ras GTPases, Sar1 inserts into membranes via an N-terminal helix (rather than myristoylation or prenylation ). These coat proteins are necessary but insufficient to direct or dock the vesicle to the correct target membrane. SNARE , cargo, and other proteins are also needed for these processes to occur. Pre-budding complex (composed of Sar1-GTP and Sec23/24) recruits

335-416: A given gene of any function; one allele can be dominant over a second allele of the same gene, recessive to a third, and co-dominant with a fourth. Additionally, one allele may be dominant for one trait but not others. Dominance differs from epistasis , the phenomenon of an allele of one gene masking the effect of alleles of a different gene. Gregor Johann Mendel , "The Father of Genetics", promulgated

402-409: A large central cavity that is isolated from the remainder of the cytosol. One example of such an enclosed compartment is the proteasome . Here, a set of subunits form a hollow barrel containing proteases that degrade cytosolic proteins. Since these would be damaging if they mixed freely with the remainder of the cytosol, the barrel is capped by a set of regulatory proteins that recognize proteins with

469-585: A low concentration of sodium ions. This difference in ion concentrations is critical for osmoregulation , since if the ion levels were the same inside a cell as outside, water would enter constantly by osmosis - since the levels of macromolecules inside cells are higher than their levels outside. Instead, sodium ions are expelled and potassium ions taken up by the Na⁺/K⁺-ATPase , potassium ions then flow down their concentration gradient through potassium-selection ion channels, this loss of positive charge creates

536-453: A membrane-bound H antigen. The I enzyme adds a galactose. The i allele produces no modification. Thus the I and I alleles are each dominant to i ( I I and I i individuals both have type A blood, and I I and I i individuals both have type B blood), but I I individuals have both modifications on their blood cells and thus have type AB blood, so the I and I alleles are said to be co-dominant. Another example occurs at

603-421: A much denser meshwork of actin fibres than the remainder of the cytosol. These microdomains could influence the distribution of large structures such as ribosomes and organelles within the cytosol by excluding them from some areas and concentrating them in others. The cytosol is the site of multiple cell processes. Examples of these processes include signal transduction from the cell membrane to sites within

670-537: A negative membrane potential . To balance this potential difference , negative chloride ions also exit the cell, through selective chloride channels. The loss of sodium and chloride ions compensates for the osmotic effect of the higher concentration of organic molecules inside the cell. Cells can deal with even larger osmotic changes by accumulating osmoprotectants such as betaines or trehalose in their cytosol. Some of these molecules can allow cells to survive being completely dried out and allow an organism to enter

737-406: A pink snapdragon flower. The pink snapdragon is the result of incomplete dominance. A similar type of incomplete dominance is found in the four o'clock plant wherein pink color is produced when true-bred parents of white and red flowers are crossed. In quantitative genetics , where phenotypes are measured and treated numerically, if a heterozygote's phenotype is exactly between (numerically) that of

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804-416: A set of proteins with similar functions, such as enzymes that carry out several steps in the same metabolic pathway. This organization can allow substrate channeling , which is when the product of one enzyme is passed directly to the next enzyme in a pathway without being released into solution. Channeling can make a pathway more rapid and efficient than it would be if the enzymes were randomly distributed in

871-677: A signal directing them for degradation (a ubiquitin tag) and feed them into the proteolytic cavity. Another large class of protein compartments are bacterial microcompartments , which are made of a protein shell that encapsulates various enzymes. These compartments are typically about 100–200 nanometres across and made of interlocking proteins. A well-understood example is the carboxysome , which contains enzymes involved in carbon fixation such as RuBisCO . Non-membrane bound organelles can form as biomolecular condensates , which arise by clustering, oligomerisation , or polymerisation of macromolecules to drive colloidal phase separation of

938-462: A state of suspended animation called cryptobiosis . In this state the cytosol and osmoprotectants become a glass-like solid that helps stabilize proteins and cell membranes from the damaging effects of desiccation. The low concentration of calcium in the cytosol allows calcium ions to function as a second messenger in calcium signaling . Here, a signal such as a hormone or an action potential opens calcium channel so that calcium floods into

1005-663: Is a key concept in Mendelian inheritance and classical genetics . Letters and Punnett squares are used to demonstrate the principles of dominance in teaching, and the upper-case letters are used to denote dominant alleles and lower-case letters are used for recessive alleles. An often quoted example of dominance is the inheritance of seed shape in peas . Peas may be round, associated with allele R , or wrinkled, associated with allele r . In this case, three combinations of alleles (genotypes) are possible: RR , Rr , and rr . The RR ( homozygous ) individuals have round peas, and

1072-466: Is extremely high, and approaches 200 mg/ml, occupying about 20–30% of the volume of the cytosol. However, measuring precisely how much protein is dissolved in cytosol in intact cells is difficult, since some proteins appear to be weakly associated with membranes or organelles in whole cells and are released into solution upon cell lysis . Indeed, in experiments where the plasma membrane of cells were carefully disrupted using saponin , without damaging

1139-562: Is lethal to mice in utero . In humans, a Sec23A variant causes Cranio-lenticulo-sutural dysplasia , while Sec23B variants are associated with the bone marrow disease congenital dyserythropoietic anemia type II and some cancers . Mice without Sec23B die soon after birth. Halperin-Birk syndrome (HLBKS), a rare autosomal recessive neurodevelopmental disorder, is caused by a null mutation in the SEC31A. CopII has three specific binding sites that can each be complexed. The adjacent picture (Sed5) uses

1206-443: Is one of the liquids found inside cells ( intracellular fluid (ICF)). It is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondrion into many compartments. In the eukaryotic cell , the cytosol is surrounded by the cell membrane and is part of the cytoplasm , which also comprises the mitochondria, plastids , and other organelles (but not their internal fluids and structures);

1273-645: Is regulated in part by Sec16A and Tango1 proteins, likely by concentrating Sec12 in a given location, so it can more efficiently activate Sar1. In mammals there are two Sar1 genes: SAR1A and SAR1B ( SAR1B was previously known as SARA2 ). In cultured mammalian cells the two Sar1 genes appear redundant; however, in animals SAR1B is uniquely required for the formation of large (over 1 micrometer across) COPII-coated vesicles. Similarly, mammals express two Sec23 genes: SEC23A and SEC23B . The two Sec23 isoforms have identical function but are expressed in different body tissues. Both Sec23 proteins can interact with any of

1340-451: Is that about 5% of this water is strongly bound in by solutes or macromolecules as water of solvation , while the majority has the same structure as pure water. This water of solvation is not active in osmosis and may have different solvent properties, so that some dissolved molecules are excluded, while others become concentrated. However, others argue that the effects of the high concentrations of macromolecules in cells extend throughout

1407-782: Is the phenomenon of one variant ( allele ) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome . The first variant is termed dominant and the second is called recessive . This state of having two different variants of the same gene on each chromosome is originally caused by a mutation in one of the genes, either new ( de novo ) or inherited . The terms autosomal dominant or autosomal recessive are used to describe gene variants on non-sex chromosomes ( autosomes ) and their associated traits, while those on sex chromosomes (allosomes) are termed X-linked dominant , X-linked recessive or Y-linked ; these have an inheritance and presentation pattern that depends on

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1474-510: Is when the effective concentration of other macromolecules is increased, since they have less volume to move in. This crowding effect can produce large changes in both the rates and the position of chemical equilibrium of reactions in the cytosol. It is particularly important in its ability to alter dissociation constants by favoring the association of macromolecules, such as when multiple proteins come together to form protein complexes , or when DNA-binding proteins bind to their targets in

1541-417: The rr (homozygous) individuals have wrinkled peas. In Rr ( heterozygous ) individuals, the R allele masks the presence of the r allele, so these individuals also have round peas. Thus, allele R is dominant over allele r , and allele r is recessive to allele R . Dominance is not inherent to an allele or its traits ( phenotype ). It is a strictly relative effect between two alleles of

1608-451: The cell nucleus is separate. The cytosol is thus a liquid matrix around the organelles. In prokaryotes , most of the chemical reactions of metabolism take place in the cytosol, while a few take place in membranes or in the periplasmic space . In eukaryotes, while many metabolic pathways still occur in the cytosol, others take place within organelles. The cytosol is a complex mixture of substances dissolved in water. Although water forms

1675-422: The genome . Although the components of the cytosol are not separated into regions by cell membranes, these components do not always mix randomly and several levels of organization can localize specific molecules to defined sites within the cytosol. Although small molecules diffuse rapidly in the cytosol, concentration gradients can still be produced within this compartment. A well-studied example of these are

1742-553: The "calcium sparks" that are produced for a short period in the region around an open calcium channel . These are about 2  micrometres in diameter and last for only a few milliseconds , although several sparks can merge to form larger gradients, called "calcium waves". Concentration gradients of other small molecules, such as oxygen and adenosine triphosphate may be produced in cells around clusters of mitochondria , although these are less well understood. Proteins can associate to form protein complexes , these often contain

1809-569: The ER membrane, binding preferentially to areas of membrane curvature. As Sar1-GTP inserts into the membrane, it recruits Sec23 and Sec24 to make up the inner cage. Once the inner coat is assembled, the outer coat proteins Sec13 and Sec31 are recruited to the budding vesicle. Hydrolysis of the Sar1 GTP to GDP promotes disassembly of the coat. Some proteins are found to be responsible for selectively packaging cargos into COPII vesicles. More recent research suggests

1876-636: The F1 generation are self-pollinated, the phenotypic and genotypic ratio of the F2 generation will be 1:2:1 (Red:Spotted:White). These ratios are the same as those for incomplete dominance. Again, this classical terminology is inappropriate – in reality, such cases should not be said to exhibit dominance at all. Dominance can be influenced by various genetic interactions and it is essential to evaluate them when determining phenotypic outcomes. Multiple alleles , epistasis and pleiotropic genes are some factors that might influence

1943-479: The Sec22 t-SNARE complex to bind. This site is more strongly bound, and therefore is more favored. (Embo) Mutations the threonine at position 39 to asparagine generates a dominant negative Sar1A bound permanently to GDP; mutating histidine 79 to glycine generates a constitutively active Sar1A, with GTP hydrolysis slowed dramatically. Cytosol The cytosol , also known as cytoplasmic matrix or groundplasm ,

2010-568: The Sec23/Sec24-Sar1 complex participates in cargo selection. For example, Erv29p in Saccharomyces cerevisiae is found to be necessary for packaging glycosylated pro-α-factor. Sec24 proteins recognize various cargo proteins, packaging them into the budding vesicles. The COPII coat consists of an inner layer – a flexible meshwork of Sar1, Sec23, and Sec24 – and an outer layer made of Sec13 and Sec31. Sar1 resembles other Ras-family GTPases, with

2077-418: The cell, such as the cell nucleus , or organelles. This compartment is also the site of many of the processes of cytokinesis , after the breakdown of the nuclear membrane in mitosis . Another major function of cytosol is to transport metabolites from their site of production to where they are used. This is relatively simple for water-soluble molecules, such as amino acids, which can diffuse rapidly through

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2144-401: The contribution of modifier genes . In 1929, American geneticist Sewall Wright responded by stating that dominance is simply a physiological consequence of metabolic pathways and the relative necessity of the gene involved. In complete dominance, the effect of one allele in a heterozygous genotype completely masks the effect of the other. The allele that masks are considered dominant to

2211-443: The cytoplasm or nucleus. Although the cytoskeleton is not part of the cytosol, the presence of this network of filaments restricts the diffusion of large particles in the cell. For example, in several studies tracer particles larger than about 25  nanometres (about the size of a ribosome ) were excluded from parts of the cytosol around the edges of the cell and next to the nucleus. These "excluding compartments" may contain

2278-451: The cytoplasm that is contained within organelles. Due to the possibility of confusion between the use of the word "cytosol" to refer to both extracts of cells and the soluble part of the cytoplasm in intact cells, the phrase "aqueous cytoplasm" has been used to describe the liquid contents of the cytoplasm of living cells. Prior to this, other terms, including hyaloplasm , were used for the cell fluid, not always synonymously, as its nature

2345-410: The cytoskeleton by motor proteins . The cytosol is the site of most metabolism in prokaryotes, and a large proportion of the metabolism of eukaryotes. For instance, in mammals about half of the proteins in the cell are localized to the cytosol. The most complete data are available in yeast, where metabolic reconstructions indicate that the majority of both metabolic processes and metabolites occur in

2412-504: The cytosol and that water in cells behaves very differently from the water in dilute solutions. These ideas include the proposal that cells contain zones of low and high-density water, which could have widespread effects on the structures and functions of the other parts of the cell. However, the use of advanced nuclear magnetic resonance methods to directly measure the mobility of water in living cells contradicts this idea, as it suggests that 85% of cell water acts like that pure water, while

2479-566: The cytosol contains the cell's genome , within a structure known as a nucleoid . This is an irregular mass of DNA and associated proteins that control the transcription and replication of the bacterial chromosome and plasmids . In eukaryotes the genome is held within the cell nucleus , which is separated from the cytosol by nuclear pores that block the free diffusion of any molecule larger than about 10  nanometres in diameter. This high concentration of macromolecules in cytosol causes an effect called macromolecular crowding , which

2546-433: The cytosol is water , which makes up about 70% of the total volume of a typical cell. The pH of the intracellular fluid is 7.4. while human cytosolic pH ranges between 7.0 and 7.4, and is usually higher if a cell is growing. The viscosity of cytoplasm is roughly the same as pure water, although diffusion of small molecules through this liquid is about fourfold slower than in pure water, due mostly to collisions with

2613-412: The cytosol, and can also prevent the release of unstable reaction intermediates. Although a wide variety of metabolic pathways involve enzymes that are tightly bound to each other, others may involve more loosely associated complexes that are very difficult to study outside the cell. Consequently, the importance of these complexes for metabolism in general remains unclear. Some protein complexes contain

2680-407: The cytosol. However, hydrophobic molecules, such as fatty acids or sterols , can be transported through the cytosol by specific binding proteins, which shuttle these molecules between cell membranes. Molecules taken into the cell by endocytosis or on their way to be secreted can also be transported through the cytosol inside vesicles , which are small spheres of lipids that are moved along

2747-409: The cytosol. Major metabolic pathways that occur in the cytosol in animals are protein biosynthesis , the pentose phosphate pathway , glycolysis and gluconeogenesis . The localization of pathways can be different in other organisms, for instance fatty acid synthesis occurs in chloroplasts in plants and in apicoplasts in apicomplexa . Dominant negative In genetics , dominance

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2814-407: The cytosol. This sudden increase in cytosolic calcium activates other signalling molecules, such as calmodulin and protein kinase C . Other ions such as chloride and potassium may also have signaling functions in the cytosol, but these are not well understood. Protein molecules that do not bind to cell membranes or the cytoskeleton are dissolved in the cytosol. The amount of protein in cells

2881-534: The dominant gene. However, if the F1-generation is further crossed with the F1-generation (heterozygote crossed with heterozygote) the offspring (F2-generation) will present the phenotype associated with the dominant gene ¾ times. Although heterozygote monohybrid crossing can result in two phenotype variants, it can result in three genotype variants -  homozygote dominant, heterozygote and homozygote recessive, respectively. In dihybrid inheritance we look at

2948-648: The flexible Sec13p/31p complex, characterized by polymerization of the Sec13/31 complex with other Sec13/31 complexes to form a cuboctahedron with a broader lattice than its Clathrin vesicle analog. The formation of the cuboctahedron deforms the ER membrane and detaches the COPII vesicle (alongside cargo proteins and v-SNAREs), completing the COPII vesicle budding process. The signal(s) that triggers Sec12 to initiate COPII assembly remains unclear, though some regulators of coat formation are now known. The frequency of COPII formation

3015-547: The four Sec24 proteins: SEC24A, SEC24B, SEC24C, and SEC24D. Lethal or pathogenic variants of most COPII proteins have been described. Loss of Sar1B in mice results in death soon after birth. In humans, inheriting two copies of certain SAR1B variants results in Chylomicron retention disease , and loss of Sar1B causes a combination of chylomicron retention disease and the neuromuscular disorder Marinesco–Sjögren syndrome . Loss of Sec23A

3082-406: The idea of dominance in the 1860s. However, it was not widely known until the early twentieth century. Mendel observed that, for a variety of traits of garden peas having to do with the appearance of seeds, seed pods, and plants, there were two discrete phenotypes, such as round versus wrinkled seeds, yellow versus green seeds, red versus white flowers or tall versus short plants. When bred separately,

3149-417: The inheritance of two pairs of genes simultaneous. Assuming here that the two pairs of genes are located at non-homologous chromosomes, such that they are not coupled genes (see genetic linkage ) but instead inherited independently. Consider now the cross between parents (P-generation) of genotypes homozygote dominant and recessive, respectively. The offspring (F1-generation) will always heterozygous and present

3216-585: The large majority of the cytosol, its structure and properties within cells is not well understood. The concentrations of ions such as sodium and potassium in the cytosol are different to those in the extracellular fluid ; these differences in ion levels are important in processes such as osmoregulation , cell signaling , and the generation of action potentials in excitable cells such as endocrine, nerve and muscle cells. The cytosol also contains large amounts of macromolecules , which can alter how molecules behave, through macromolecular crowding . Although it

3283-399: The large numbers of macromolecules in the cytosol. Studies in the brine shrimp have examined how water affects cell functions; these saw that a 20% reduction in the amount of water in a cell inhibits metabolism, with metabolism decreasing progressively as the cell dries out and all metabolic activity halting when the water level reaches 70% below normal. Although water is vital for life,

3350-485: The level of dominance the alleles expresses towards each other. Pleiotropic genes are genes where one single gene affects two or more characters (phenotype). This means that a gene can have a dominant effect on one trait, but a more recessive effect on another trait. Epistasis is interactions between multiple alleles at different loci. Easily said, several genes for one phenotype. The dominance relationship between alleles involved in epistatic interactions can influence

3417-450: The locus for the beta-globin component of hemoglobin , where the three molecular phenotypes of Hb /Hb , Hb /Hb , and Hb /Hb are all distinguishable by protein electrophoresis . (The medical condition produced by the heterozygous genotype is called sickle-cell trait and is a milder condition distinguishable from sickle-cell anemia , thus the alleles show incomplete dominance concerning anemia, see above). For most gene loci at

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3484-455: The molecular level, both alleles are expressed co-dominantly, because both are transcribed into RNA . Co-dominance, where allelic products co-exist in the phenotype, is different from incomplete dominance, where the quantitative interaction of allele products produces an intermediate phenotype. For example, in co-dominance, a red homozygous flower and a white homozygous flower will produce offspring that have red and white spots. When plants of

3551-418: The other allele, and the masked allele is considered recessive . When we only look at one trait determined by one pair of genes, we call it monohybrid inheritance . If the crossing is done between parents (P-generation, F0-generation) who are homozygote dominant and homozygote recessive, the offspring (F1-generation) will always have the heterozygote genotype and always present the phenotype associated with

3618-407: The other cell membranes, only about one quarter of cell protein was released. These cells were also able to synthesize proteins if given ATP and amino acids, implying that many of the enzymes in cytosol are bound to the cytoskeleton. However, the idea that the majority of the proteins in cells are tightly bound in a network called the microtrabecular lattice is now seen as unlikely. In prokaryotes

3685-470: The parental hybrid plants. Mendel reasoned that each parent in the first cross was a homozygote for different alleles (one parent AA and the other parent aa), that each contributed one allele to the offspring, with the result that all of these hybrids were heterozygotes (Aa), and that one of the two alleles in the hybrid cross dominated expression of the other: A masked a. The final cross between two heterozygotes (Aa X Aa) would produce AA, Aa, and aa offspring in

3752-496: The phenotype and neither allele masks another. For example, in the ABO blood group system , chemical modifications to a glycoprotein (the H antigen) on the surfaces of blood cells are controlled by three alleles, two of which are co-dominant to each other ( I , I ) and dominant over the recessive i at the ABO locus . The I and I alleles produce different modifications. The enzyme coded for by I adds an N-acetylgalactosamine to

3819-462: The phenotype associated with the dominant allele variant. However, when crossing the F1-generation there are four possible phenotypic possibilities and the phenotypical ratio for the F2-generation will always be 9:3:3:1. Incomplete dominance (also called partial dominance , semi-dominance , intermediate inheritance , or occasionally incorrectly co-dominance in reptile genetics ) occurs when

3886-404: The phenotype of the heterozygous genotype is distinct from and often intermediate to the phenotypes of the homozygous genotypes. The phenotypic result often appears as a blended form of characteristics in the heterozygous state. For example, the snapdragon flower color is homozygous for either red or white. When the red homozygous flower is paired with the white homozygous flower, the result yields

3953-535: The phenotypic outcome. Although any individual of a diploid organism has at most two different alleles at a given locus, most genes exist in a large number of allelic versions in the population as a whole. This is called polymorphism , and is caused by mutations. Polymorphism can have an effect on the dominance relationship and phenotype, which is observed in the ABO blood group system . The gene responsible for human blood type have three alleles; A, B, and O, and their interactions result in different blood types based on

4020-427: The plants always produced the same phenotypes, generation after generation. However, when lines with different phenotypes were crossed (interbred), one and only one of the parental phenotypes showed up in the offspring (green, round, red, or tall). However, when these hybrid plants were crossed, the offspring plants showed the two original phenotypes, in a characteristic 3:1 ratio, the more common phenotype being that of

4087-421: The remainder is less mobile and probably bound to macromolecules. The concentrations of the other ions in cytosol are quite different from those in extracellular fluid and the cytosol also contains much higher amounts of charged macromolecules such as proteins and nucleic acids than the outside of the cell structure. In contrast to extracellular fluid, cytosol has a high concentration of potassium ions and

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4154-456: The sex of both the parent and the child (see Sex linkage ). Since there is only one copy of the Y chromosome , Y-linked traits cannot be dominant or recessive. Additionally, there are other forms of dominance, such as incomplete dominance , in which a gene variant has a partial effect compared to when it is present on both chromosomes, and co-dominance , in which different variants on each chromosome both show their associated traits. Dominance

4221-449: The structure of this water in the cytosol is not well understood, mostly because methods such as nuclear magnetic resonance spectroscopy only give information on the average structure of water, and cannot measure local variations at the microscopic scale. Even the structure of pure water is poorly understood, due to the ability of water to form structures such as water clusters through hydrogen bonds . The classic view of water in cells

4288-420: The two homozygotes, the phenotype is said to exhibit no dominance at all, i.e. dominance exists only when the heterozygote's phenotype measure lies closer to one homozygote than the other. When plants of the F 1 generation are self-pollinated, the phenotypic and genotypic ratio of the F 2 generation will be 1:2:1 (Red:Pink:White). Co-dominance occurs when the contributions of both alleles are visible in

4355-454: Was first introduced in 1965 by H. A. Lardy, and initially referred to the liquid that was produced by breaking cells apart and pelleting all the insoluble components by ultracentrifugation . Such a soluble cell extract is not identical to the soluble part of the cell cytoplasm and is usually called a cytoplasmic fraction. The term cytosol is now used to refer to the liquid phase of the cytoplasm in an intact cell. This excludes any part of

4422-427: Was not well understood (see protoplasm ). The proportion of cell volume that is cytosol varies: for example while this compartment forms the bulk of cell structure in bacteria , in plant cells the main compartment is the large central vacuole . The cytosol consists mostly of water, dissolved ions, small molecules, and large water-soluble molecules (such as proteins). The majority of these non-protein molecules have

4489-401: Was once thought to be a simple solution of molecules, the cytosol has multiple levels of organization. These include concentration gradients of small molecules such as calcium , large complexes of enzymes that act together and take part in metabolic pathways , and protein complexes such as proteasomes and carboxysomes that enclose and separate parts of the cytosol. The term "cytosol"

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