Cytoplasmic inclusion

Last updated

Cytoplasmic inclusions are diverse intracellular [1] non-living substances [2] that are not bound by membranes. Inclusions are stored nutrients, secretory products, and pigment granules. Examples of inclusions are glycogen granules in the liver and muscle cells, lipid droplets in fat cells, pigment granules in certain cells of skin and hair, and crystals of various types. [3] Cytoplasmic inclusions are an example of a biomolecular condensate arising by liquid-solid, liquid-gel or liquid-liquid phase separation.

These structures were first observed by O. F. Müller in 1786. [1] Cytoplasmic inclusions are cytoplasmic molecular aggregates such as pigments organic polymers and crystal. Fat droplets and glycogen granules are examples of cytoplasmic inclusion.

Examples

Glycogen granules in Spermiogenesis in Pleurogenidae (Digenea) Parasite130059-fig7 Spermiogenesis in Pleurogenidae (Digenea).tif
Glycogen granules in Spermiogenesis in Pleurogenidae (Digenea)

Glycogen : Glycogen is the most common form of glucose in animals and is especially abundant in cells of muscles, and liver. It appears in electron micrograph as clusters, or a rosette of beta particles that resemble ribosomes, located near the smooth endoplasmic reticulum. [3] Glycogen is an important energy source of the cell; therefore, it will be available on demand. The enzymes responsible for glycogenolysis degrade glycogen into individual molecules of glucose and can be utilized by multiple organs of the body. [4] [2]

Lipids : Lipids are triglycerides in storage form is the common form of inclusions, not only are stored in specialized cells (adipocytes) but also are located as individuals droplets in various cell type especially hepatocytes. [3] These are fluid at body temperature and appear in living cells as refractile spherical droplets. Lipid yields more than twice as many calories per gram as does carbohydrate. On demand, they serve as a local store of energy and a potential source of short carbon chains that are used by the cell in its synthesis of membranes and other lipid containing structural components or secretory products. [3] [4]

Crystals : Crystalline inclusions have long been recognized as normal constituents of certain cell types such as Sertoli cells and Leydig cells of the human testis, and occasionally in macrophages. [4] It is believed that these structures are crystalline forms of certain proteins which is located everywhere in the cell such as in nucleus, mitochondria, endoplasmic reticulum, Golgi body, and free in cytoplasmic matrix. [3] [4]

Pigments : The most common pigment in the body, besides hemoglobin of red blood cells is melanin, manufactured by melanocytes of the skin and hair, pigments cells of the retina and specialized nerve cells in the substantia nigra of the brain. [3] These pigments have protective functions in skin and aid in the sense of sight in the retina but their functions in neurons is not understood completely. Furthermore, cardiac tissue and central nervous system neurons shows yellow to brown pigment called lipofuscin, some believed that they have lysosomal activity. [4]

Related Research Articles

Biological membrane enclosing or separating membrane that acts as a selectively permeable barrier within living thing

A biological membrane, biomembrane or cell membrane is a selectively permeable membrane that separates cell from the external environment or creates intracellular compartments. Biological membranes, in the form of eukaryotic cell membranes, consist of a phospholipid bilayer with embedded, integral and peripheral proteins used in communication and transportation of chemicals and ions. The bulk of lipid in a cell membrane provides a fluid matrix for proteins to rotate and laterally diffuse for physiological functioning. Proteins are adapted to high membrane fluidity environment of lipid bilayer with the presence of an annular lipid shell, consisting of lipid molecules bound tightly to surface of integral membrane proteins. The cell membranes are different from the isolating tissues formed by layers of cells, such as mucous membranes, basement membranes, and serous membranes.

Cytoplasm Material within a cell

In cell biology, the cytoplasm is all of the material within a cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. The main components of the cytoplasm are cytosol – a gel-like substance, the organelles – the cell's internal sub-structures, and various cytoplasmic inclusions. The cytoplasm is about 80% water and usually colorless.

Endoplasmic reticulum Irregular network of membranes coterminous with the outer nuclear membrane in eukaryote cytoplasm that form a meshwork of tubular channels, often expanded into cisternae

The endoplasmic reticulum (ER) is a type of organelle made up of two subunits – rough endoplasmic reticulum (RER), and smooth endoplasmic reticulum (SER). The endoplasmic reticulum is found in most eukaryotic cells and forms an interconnected network of flattened, membrane-enclosed sacs known as cisternae, and tubular structures in the SER. The membranes of the ER are continuous with the outer nuclear membrane. The endoplasmic reticulum is not found in red blood cells, or spermatozoa.

Endomembrane system A collection of membranous structures involved in transport within the cell. The main components of the endomembrane system are endoplasmic reticulum, Golgi bodies, vesicles, cell membrane and nuclear envelope.

The endomembrane system is composed of the different membranes that are suspended in the cytoplasm within a eukaryotic cell. These membranes divide the cell into functional and structural compartments, or organelles. In eukaryotes the organelles of the endomembrane system include: the nuclear membrane, the endoplasmic reticulum, the Golgi apparatus, lysosomes, vesicles, endosomes, and plasma (cell) membrane among others. The system is defined more accurately as the set of membranes that form a single functional and developmental unit, either being connected directly, or exchanging material through vesicle transport. Importantly, the endomembrane system does not include the membranes of chloroplasts or mitochondria, but might have evolved from the latter.

Glycogen glucose polymer used as energy store in animals

Glycogen is a multibranched polysaccharide of glucose that serves as a form of energy storage in animals, fungi, and bacteria. The polysaccharide structure represents the main storage form of glucose in the body.

Leydig cell Androgen-producing cell adjacent to the seminiferous tubules of the testicle

Leydig cells, also known as interstitial cells of Leydig, are found adjacent to the seminiferous tubules in the testicle. They produce testosterone in the presence of luteinizing hormone (LH). Leydig cells are polyhedral in shape, and have a large prominent nucleus, an eosinophilic cytoplasm and numerous lipid-filled vesicles.

Hepatocyte liver cell type

A hepatocyte is a cell of the main parenchymal tissue of the liver. Hepatocytes make up 55-65% of the liver's mass. These cells are involved in:

Glucose 6-phosphate small group of chemical compounds

Glucose 6-phosphate is a glucose sugar phosphorylated at the hydroxy group on carbon 6. This dianion is very common in cells as the majority of glucose entering a cell will become phosphorylated in this way.

Sarcoplasm Cytoplasm of a muscle cell, including the sarcoplasmic reticulum.

Sarcoplasm is the cytoplasm of a myocyte. It is comparable to the cytoplasm of other cells, but it contains unusually large amounts of glycosomes and significant amounts of myoglobin, an oxygen-binding protein. The calcium ion concentration in sarcoplasma is also a special element of the muscle fiber; it is the means by which muscle contractions take place and are regulated.

Fatty acid metabolism consists of catabolic processes that generate energy, and anabolic processes that create biologically important molecules (triglycerides, phospholipids, second messengers, local hormones and ketone bodies). Fatty acids are a family of molecules classified within the lipid macronutrient class. One role of fatty acids in animal metabolism is energy production, captured in the form of adenosine triphosphate (ATP). When compared to other macronutrient classes (carbohydrates and protein), fatty acids yield the most ATP on an energy per gram basis, when they are completely oxidized to CO2 and water by beta oxidation and the citric acid cycle. Fatty acids (mainly in the form of triglycerides) are therefore the foremost storage form of fuel in most animals, and to a lesser extent in plants. In addition, fatty acids are important components of the phospholipids that form the phospholipid bilayers out of which all the membranes of the cell are constructed (the plasma membrane and other membranes that enclose all the organelles within the cells, such as the nucleus, the mitochondria, endoplasmic reticulum, and the Golgi apparatus). Fatty acids can also be cleaved, or partially cleaved, from their chemical attachments in the cell membrane to form second messengers within the cell, and local hormones in the immediate vicinity of the cell. The prostaglandins made from arachidonic acid stored in the cell membrane, are probably the most well known group of these local hormones.

Lipofuscin

Lipofuscin is the name given to fine yellow-brown pigment granules composed of lipid-containing residues of lysosomal digestion. It is considered to be one of the aging or "wear-and-tear" pigments, found in the liver, kidney, heart muscle, retina, adrenals, nerve cells, and ganglion cells. It is specifically arranged around the nucleus, and is a type of lipochrome.

Endoplasm

Endoplasm generally refers to the inner, dense part of a cell's cytoplasm. This is opposed to the ectoplasm which is the outer (non-granulated) layer of the cytoplasm, which is typically watery and immediately adjacent to the plasma membrane. These two terms are mainly used to describe the cytoplasm of the amoeba, a protozoan, eukaryotic cell. The nucleus is separated from the endoplasm by the nuclear envelope. The different makeups/viscosities of the endoplasm and ectoplasm contribute to the amoeba's locomotion through the formation of a pseudopod. However, other types of cells have cytoplasm divided into endo- and ectoplasm. The endoplasm, along with its granules, contains water, nucleic acids amino acids, carbohydrates, inorganic ions, lipids, enzymes, and other molecular compounds. It is the site of most cellular processes as it houses the organelles that make up the endomembrane system, as well as those that stand alone. The endoplasm is necessary for most metabolic activities, including cell division.

Cerebroside class of compounds

Cerebrosides is the common name for a group of glycosphingolipids called monoglycosylceramides which are important components in animal muscle and nerve cell membranes.

Glucose 6-phosphatase InterPro Family

Glucose 6-phosphatase is an enzyme that hydrolyzes glucose 6-phosphate, resulting in the creation of a phosphate group and free glucose. Glucose is then exported from the cell via glucose transporter membrane proteins. This catalysis completes the final step in gluconeogenesis and therefore plays a key role in the homeostatic regulation of blood glucose levels.

Glycosome Organelle containing glycolytic enzymes in some protists

The glycosome is a membrane-enclosed organelle that contains the glycolytic enzymes. The term was first used by Scott and Still in 1968 after they realized that the glycogen in the cell was not static but rather a dynamic molecule. It is found in a few species of protozoa including the Kinetoplastida which include the suborders Trypanosomatida and Bodonina, most notably in the human pathogenic trypanosomes, which can cause sleeping sickness, Chagas's disease, and leishmaniasis. The organelle is bounded by a single membrane and contains a dense proteinaceous matrix. It is believed to have evolved from the peroxisome. This has been verified by work done on Leishmania genetics.

Outline of cell biology Overview of and topical guide to cell biology

The following outline is provided as an overview of and topical guide to cell biology:

The insulin transduction pathway is a biochemical pathway by which insulin increases the uptake of glucose into fat and muscle cells and reduces the synthesis of glucose in the liver and hence is involved in maintaining glucose homeostasis. This pathway is also influenced by fed versus fasting states, stress levels, and a variety of other hormones.

Lipotoxicity is a metabolic syndrome that results from the accumulation of lipid intermediates in non-adipose tissue, leading to cellular dysfunction and death. The tissues normally affected include the kidneys, liver, heart and skeletal muscle. Lipotoxicity is believed to have a role in heart failure, obesity, and diabetes, and is estimated to affect approximately 25% of the adult American population.

Seipin is a homo-oligomeric integral membrane protein in the endoplasmic reticulum (ER) that concentrates at junctions with cytoplasmic lipid droplets (LDs). Alternatively, seipin can be referred to as Bernardinelli-Seip congenital lipodystrophy type 2 protein (BSCL2), and it is encoded by the corresponding gene of the same name, i.e. BSCL2. At protein level, seipin is expressed in cortical neurons in the frontal lobes, as well as motor neurons in the spinal cord. It is highly expressed in areas like the brain, testis and adipose tissue. Seipin's function is still unclear but it has been localized close to lipid droplets, and cells knocked out in seipin which have anomalous droplets. Hence, recent evidence suggests that seipin plays a crucial role in lipid droplet biogenesis.

Biomolecular condensate class of non-membrane bound organelles and organelle subdomains

Biomolecular condensates are a class of non-membrane bound organelles and organelle subdomains. As with other organelles, biomolecular condensates are specialized subunits of the cell. However, unlike many organelles, biomolecular condensate composition is not controlled by a bounding membrane. Instead they can form through a range of different processes, the most well-known of which is phase separation of proteins, RNA and other biopolymers into colloids, liquid crystals, solid crystals or aggregates.

References

  1. 1 2 Shively, J. M. (ed.). (2006). Microbiology Monographs Vol. 1: Inclusions in Prokaryotes. Berlin, Heidelberg: Springer-Verlag. link.
  2. 1 2 Peter S. Amenta (1 January 1997). Histology: from normal microanatomy to pathology. PICCIN. pp. 17–. ISBN   978-88-299-1195-0 . Retrieved 25 November 2010.
  3. 1 2 3 4 5 6 Leslie P. Gartner and James L. Hiatt ; Text book of Histology; 3rd edition
  4. 1 2 3 4 5 Fawcett; The cell, 2nd edition