Mucins
Gastric Mucins
Mucin-5B
Mucin-1
Mucin-4
Mucin-3
Goblet Cells
Mucus
Glycosylation
Antigens, Tumor-Associated, Carbohydrate
Oligosaccharides
Trachea
Periodic Acid-Schiff Reaction
Carbohydrates
Intestinal Mucosa
Carbohydrate Sequence
Physical characterization of a low-charge glycoform of the MUC5B mucin comprising the gel-phase of an asthmatic respiratory mucous plug. (1/105)
We have previously noted that sequential extraction of an asthmatic mucous exudate with 6 M guanidinium chloride yielded a fraction of the mucins that were most resistant to solubilization and of high Mr [Sheehan, Richardson, Fung, Howard and Thornton (1995) Am. J. Respir. Cell Mol. Biol. 13, 748-756]. Here we show that this mucin fraction is dominated (at least 96% of the total) by the low-charge glycoform of the MUC5B gene product. Seen in the electron microscope the mucins appeared mainly as compact 'island' structures composed of linear threads often emanating from globular 'nodes' rather than the discrete linear threads more typical of mucins that we have previously described. The effect of reducing agents was as expected for other gel-forming mucins, i.e. reduced subunits or monomers of Mr 3x10(6)) were produced within 15 min of treatment. Kinetic experiments on the cleavage of the intact mucins with the proteinase trypsin indicated two clear regimes of fragmentation. An initial rapid cleavage generated mucins ranging from Mr=4x10(6) to 30x10(6) that in the electron microscope appeared as polydisperse threads (500-3000 nm in length), similar to normal and other respiratory mucins that we have previously characterized. A subsequent slower fragmentation over many hours yielded a major fragment of Mr 3x10(6) and length 200-600 nm, very similar in size and Mr to the subunits obtained by reduction. The results suggest that the MUC5B mucin is assembled, first into polydisperse linear threads, which are then linked together via a protein-mediated process. This might involve part of the mucin polypeptide or an as yet unidentified protein(s). The high proteinase susceptibility of the linkage suggests that it might be a point of control for mucin size and thus mucus rheology. (+info)Salivary mucin MG1 is comprised almost entirely of different glycosylated forms of the MUC5B gene product. (2/105)
The MG1 population of mucins was isolated from human whole salivas by gel chromatography followed by isopycnic density gradient centrifugation. The reduced and alkylated MG1 mucins, separated by anion exchange chromatography, were of similar size (radius of gyration 55-64 nm) and molecular weight (2.5-2.9 x 10(6) Da). Two differently-charged populations of MG1 subunits were observed which showed different reactivity with monoclonal antibodies to glycan epitopes. Monosaccharide and amino acid compositional analyses indicated that the MG1 subunits had similar glycan structures on the same polypeptide. An antiserum recognizing the MUC5B mucin was reactive across the entire distribution, whereas antisera raised against the MUC2 and MUC5AC mucins showed no reactivity. Western blots of agarose gel electrophoresis of fractions across the anion exchange distribution indicated that the polypeptide underlying the mucins was the product of the MUC5B gene. Amino acid analysis and peptide mapping performed on the fragments produced by trypsin digestion of the two MG1 populations yielded data similar to that obtained for MUC5B mucin subunits prepared from respiratory mucus (Thornton et al., 1997) and confirmed that the MUC5B gene product was the predominant mucin polypeptide present. Isolation of the MG1 mucins from the secretions of the individual salivary glands (palatal, sublingual, and submandibular) indicate that the palatal gland is the source of the highly charged population of the MUC5B mucin. (+info)Regulation of human airway mucins by acrolein and inflammatory mediators. (3/105)
Bronchitis, asthma, and cystic fibrosis, marked by inflammation and mucus hypersecretion, can be caused or exacerbated by airway pathogens or irritants including acrolein, an aldehyde present in tobacco smoke. To determine whether acrolein and inflammatory mediators alter mucin gene expression, steady-state mRNA levels of two airway mucins, MUC5AC and MUC5B, were measured (by RT-PCR) in human lung carcinoma cells (NCI-H292). MUC5AC mRNA levels increased after >/=0.01 nM acrolein, 10 microM prostaglandin E2 or 15-hydroxyeicosatetraenoic acid, 1.0 nM tumor necrosis factor-alpha (TNF-alpha), or 10 nM phorbol 12-myristate 13-acetate (a protein kinase C activator). In contrast, MUC5B mRNA levels, although easily detected, were unaffected by these agonists, suggesting that irritants and associated inflammatory mediators increase mucin biosynthesis by inducing MUC5AC message levels, whereas MUC5B is constitutively expressed. When transcription was inhibited, TNF-alpha exposure increased MUC5AC message half-life compared with control level, suggesting that transcript stabilization is a major mechanism controlling increased MUC5AC message levels. Together, these findings imply that irritants like acrolein can directly and indirectly (via inflammatory mediators) increase airway mucin transcripts in epithelial cells. (+info)Inflammatory and epithelial responses during the development of ozone-induced mucous cell metaplasia in the nasal epithelium of rats. (4/105)
Rats repeatedly exposed to high ambient concentrations of ozone develop mucous cell metaplasia (MCM) in the nasal transitional epithelium (NTE). The present study was designed to determine the temporal relationships of ozone-induced inflammatory and epithelial responses and their correlation with subsequent MCM in the NTE of rats. Male F344/N rats were exposed to 0.5 ppm ozone, 8 h/day for 1, 2, or 3 days. Two h prior to sacrifice, all the rats were injected intraperitoneally with 5'-bromo-2-deoxyuridine (BrdU) to label epithelial cells undergoing DNA synthesis. Rats exposed to ozone for 1 or 2 days were killed 2 h after the exposure. Rats exposed to ozone for 3 days were killed 2 h or 1, 2, or 4 days after the exposure. Control rats were killed after a 7-day exposure to filtered air. One nasal passage from the anterior nasal cavity of each rat was fixed and processed for light microscopy to morphometrically determine the numeric densities of epithelial cells, neutrophils, and mucous cells, and the amount of intraepithelial mucosubstances in the NTE. The maxilloturbinate from the other nasal passage was processed for analysis of an airway mucin-specific gene (i.e., rMuc-5AC mRNA). Acute ozone exposure induced a rapid increase in rMuc-5AC mRNA levels prior to the onset of MCM, and the increased levels of rMuc-5AC mRNA persisted with MCM. Neutrophilic inflammation coincided with epithelial DNA synthesis and upregulation of rMuc-5AC, but was resolved when MCM first appeared in the NTE. The results of the present study suggest that upregulation of mucin mRNA by acute ozone exposure may be associated with the concurrent neutrophilic inflammation and epithelial hyperplasia in the NTE. Ozone-induced MCM may be dependent on these important pre-metaplastic responses (i.e., mucin mRNA upregulation, neutrophilic inflammation, and epithelial proliferation). (+info)Identification of MUC5B, MUC5AC and small amounts of MUC2 mucins in cystic fibrosis airway secretions. (5/105)
To investigate the genetic identities of the mucins secreted in cystic fibrosis (CF) airways, sputum was collected from five individuals. Samples were separated into gel and sol phases by high-speed centrifugation and the gel phase was extracted in 6 M guanidinium chloride. The 'insoluble' residue remaining after extraction of the gel phase was brought into solution by reduction/alkylation. Density-gradient centrifugation in CsCl revealed polydisperse distributions of sialic acid-containing mucins in the gel phase, insoluble residue and sol phase fractions and the degree of variation between the different individuals was low. Antibodies recognizing MUC5AC and MUC5B identified these mucins in each of the fractions. MUC2, however, was present only as a component of the insoluble residue from the gel which accounted for less than 4% by mass of the total mucins. MUC5B and MUC5AC from the gel phase were large oligomeric species composed of disulphide-bond linked subunits and MUC5B was present as two populations with different charge densities which are likely to correspond to MUC5B 'glycoforms'. The sol phase contained, in addition to MUC5AC and MUC5B, mainly smaller mucins which did not react with the antisera and which were probably degraded. MUC5AC appeared to be enriched in the sol, suggesting that this mucin may be more susceptible to proteolytic degradation than MUC5B. The mucins present in sputum remained broadly similar during acute exacerbation and following antibiotic treatment, although the relative amount of an acidic MUC5B glycoform was decreased during infection. (+info)Characterization of mucins from cultured normal human tracheobronchial epithelial cells. (6/105)
Early-passage normal human tracheobronchial epithelial (NHTBE) cells grown in air-liquid interface cultures in medium containing retinoids differentiate into a mucociliary epithelium over a 2- to 3-wk period and express increasing mRNA levels of the airway mucin genes MUC5AC and MUC5B as the cultures age; the levels of MUC2 mRNA were very low throughout the study. Using specific antibodies to MUC5AC and MUC5B mucins, we noted a gradual increase in these two mucins in the intracellular and apically secreted pools as a function of time. A low level of MUC2 mucin was detected, which did not change with time. The intracellular and apically secreted mucins isolated from day 14 and day 21 cultures by density gradient centrifugation were similar in density to those previously isolated from human respiratory mucus secretions. The sedimentation rate of the apically secreted mucins indicated that they were highly oligomerized, polydisperse macromolecules similar to those previously documented from in vivo secretions. In contrast, the cell-associated mucins from the cultured NHTBE cells were much smaller, possibly only monomers and dimers. Anion-exchange chromatography detected no differences in charge density between the reduced and carboxymethylated cell-associated and secreted forms of the MUC5AC and MUC5B mucins. The MUC5AC mucin was of similar charge density to its in vivo counterpart; however, MUC5B was more homogeneous than that found in vivo. Finally, evidence is presented for an intracellular NH(2)-terminal cleavage of the MUC5B mucins. These studies indicate that the mucins produced by cultured NHTBE cells are similar to those found in human airways, suggesting that this cell culture model is suited for studies of respiratory mucin biosynthesis, processing, and assembly. (+info)Sequence of the 5'-flanking region and promoter activity of the human mucin gene MUC5B in different phenotypes of colon cancer cells. (7/105)
Control of gene expression in intestinal cells is poorly understood. Molecular mechanisms that regulate transcription of cellular genes are the foundation for understanding developmental and differentiation events. Mucin gene expression has been shown to be altered in many intestinal diseases and especially cancers of the gastrointestinal tract. Towards understanding the transcriptional regulation of a member of the 11p15.5 human mucin gene cluster, we have characterized 3.55 kb of the 5'-flanking region of the human mucin gene MUC5B, including the promoter, the first two exons and the first intron. We report here the promoter activity of successively 5'-truncated sections of 956 bases of this region by fusing it to the coding region of a luciferase reporter gene. The transcription start site was determined by primer-extension analysis. The region upstream of the transcription start site is characterized by the presence of a TATA box at bases -32/-26, DNA-binding elements for transcription factors c-Myc, N-Myc, Sp1 and nuclear factor kappaB as well as putative activator protein (AP)-1-, cAMP-response-element-binding protein (CREB)-, hepatocyte nuclear factor (HNF)-1-, HNF-3-, TGT3-, gut-enriched Kruppel factor (GKLF)-, thyroid transcription factor (TTF)-1- and glucocorticoid receptor element (GRE)-binding sites. Intron 1 of MUC5B was also characterized, it is 2511 nucleotides long and contains a DNA segment of 259 bp in which are clustered eight tandemly repeated GA boxes and a CACCC box that bind Sp1. AP-2alpha and GATA-1 nuclear factors were also shown to bind to their respective cognate elements in intron 1. In transfection studies the MUC5B promoter showed a cell-specific activity as it is very active in mucus-secreting LS174T cells, whereas it is inactive in Caco-2 enterocytes and HT-29 STD (standard) undifferentiated cells. Within the promoter, maximal transcription activity was found in a segment covering the first 223 bp upstream of the transcription start site. Finally, in co-transfection experiments a transactivating effect of Sp1 on to MUC5B promoter was seen in LS174T and Caco-2 cells. (+info)Evolution of the large secreted gel-forming mucins. (8/105)
Mucins, the major component of mucus, contain tandemly repeated sequences that differ from one mucin to another. Considerable advances have been made in recent years in our knowledge of mucin genes. The availability of the complete genomic and cDNA sequences of MUC5B, one of the four human mucin genes clustered on chromosome 11, provides an exemplary model for studying the molecular evolution of large mucins. The emerging picture is one of expansion of mucin genes by gene duplications, followed by internal repeat expansion that strictly preserves frameshift. Computational and phylogenetic analyses have permitted the proposal of an evolutionary history of the four human mucin genes located on chromosome 11 from an ancestor gene common to the human von Willebrand factor gene and the suggestion of a model for the evolution of the repeat coding portion of the MUC5B gene from a hypothetical ancestral minigene. The characterization of MUC5B, a member of the large secreted gel-forming mucin family, offers a new model for the comparative study of the structure-function relationship within this important family. (+info)Mucins are high molecular weight, heavily glycosylated proteins that are the major components of mucus. They are produced and secreted by specialized epithelial cells in various organs, including the respiratory, gastrointestinal, and urogenital tracts, as well as the eyes and ears.
Mucins have a characteristic structure consisting of a protein backbone with numerous attached oligosaccharide side chains, which give them their gel-forming properties and provide a protective barrier against pathogens, environmental insults, and digestive enzymes. They also play important roles in lubrication, hydration, and cell signaling.
Mucins can be classified into two main groups based on their structure and function: secreted mucins and membrane-bound mucins. Secreted mucins are released from cells and form a physical barrier on the surface of mucosal tissues, while membrane-bound mucins are integrated into the cell membrane and participate in cell adhesion and signaling processes.
Abnormalities in mucin production or function have been implicated in various diseases, including chronic inflammation, cancer, and cystic fibrosis.
Gastric mucins refer to the mucin proteins that are produced and secreted by the mucus-secreting cells in the stomach lining, also known as gastric mucosa. These mucins are part of the gastric mucus layer that coats and protects the stomach from damage caused by digestive acids and enzymes, as well as from physical and chemical injuries.
Gastric mucins have a complex structure and are composed of large glycoprotein molecules that contain both protein and carbohydrate components. They form a gel-like substance that provides a physical barrier between the stomach lining and the gastric juices, preventing acid and enzymes from damaging the underlying tissues.
There are several types of gastric mucins, including MUC5AC and MUC6, which have different structures and functions. MUC5AC is the predominant mucin in the stomach and is produced by surface mucous cells, while MUC6 is produced by deeper glandular cells.
Abnormalities in gastric mucin production or composition can contribute to various gastrointestinal disorders, including gastritis, gastric ulcers, and gastric cancer.
Mucin-5B, also known as MUC5B, is a type of mucin protein that is heavily glycosylated and found in the respiratory tract. It is one of the major components of airway mucus, which helps to trap and remove inhaled particles and microorganisms from the lungs.
Mucin-5B is a large molecular weight gel-forming mucin that is produced by goblet cells and submucosal glands in the respiratory epithelium. It has a complex structure, consisting of a protein backbone with numerous oligosaccharide side chains that give it its gel-like properties.
Mutations in the MUC5B gene have been associated with several lung diseases, including chronic obstructive pulmonary disease (COPD), bronchiectasis, and idiopathic pulmonary fibrosis (IPF). In particular, a common genetic variant in the MUC5B promoter region has been identified as a significant risk factor for developing IPF.
Mucin-1, also known as MUC1, is a type of protein called a transmembrane mucin. It is heavily glycosylated and found on the surface of many types of epithelial cells, including those that line the respiratory, gastrointestinal, and urogenital tracts.
Mucin-1 has several functions, including:
* Protecting the underlying epithelial cells from damage caused by friction, chemicals, and microorganisms
* Helping to maintain the integrity of the mucosal barrier
* Acting as a receptor for various signaling molecules
* Participating in immune responses
In cancer, MUC1 can be overexpressed or aberrantly glycosylated, which can contribute to tumor growth and metastasis. As a result, MUC1 has been studied as a potential target for cancer immunotherapy.
Mucin-4, also known as "Podocalyxin-like" or "PODXL," is a type of transmembrane mucin protein that is heavily glycosylated. It is primarily expressed on the surface of certain types of cells, including epithelial and endothelial cells.
Mucin-4 is a large molecule with a molecular weight ranging from 150 to 250 kDa, depending on its degree of glycosylation. It has a extracellular domain that contains several N-linked glycans and O-linked oligosaccharides, which give it a highly extended structure and contribute to its ability to form protective barriers on the cell surface.
Mucin-4 is involved in various biological processes, such as providing a barrier function, regulating cell adhesion, and modulating immune responses. It has been implicated in several diseases, including cancer, where it can promote tumor growth and metastasis by facilitating cell migration and invasion. In the kidney, Mucin-4 is expressed on the surface of podocytes, which are specialized epithelial cells that play a critical role in maintaining the filtration barrier in the glomerulus. Mutations in the MUC16 gene, which encodes Mucin-4, have been associated with nephrotic syndrome, a kidney disorder characterized by proteinuria and edema.
Mucin-3, also known as MUC3A or CA15-3, is a type of mucin protein that is heavily glycosylated and found on the apical surface of epithelial cells in the gastrointestinal tract. It is a transmembrane protein that plays a role in protecting the epithelial surface from damage, infection, and inflammation. Mucin-3 has been identified as a tumor antigen and its expression is often upregulated in various types of cancer, including colon, pancreatic, and ovarian cancers. The soluble form of Mucin-3 can be measured in the blood and used as a tumor marker to monitor the progression of certain cancers.
I'm sorry for any confusion, but "Mucin-6" is not a widely recognized or established medical term. Mucins are high molecular weight glycoproteins that are the major component of mucus, which is produced by specialized epithelial cells in various organs. Each mucin is identified by a number, such as Mucin-1, Mucin-2, and so on, based on their order of discovery.
However, I couldn't find any reputable medical sources that mention "Mucin-6." It's possible that it may be a topic of ongoing research or that it might be referred to by another name. I would recommend consulting a specific scientific study or researcher for more accurate and detailed information.
Goblet cells are specialized epithelial cells that are located in various mucosal surfaces, including the respiratory and gastrointestinal tracts. They are named for their goblet-like shape, which is characterized by a narrow base and a wide, rounded top that contains secretory granules. These cells play an essential role in producing and secreting mucins, which are high molecular weight glycoproteins that form the gel-like component of mucus.
Mucus serves as a protective barrier for the underlying epithelial cells by trapping foreign particles, microorganisms, and toxins, preventing them from coming into contact with the epithelium. Goblet cells also help maintain the hydration of the mucosal surface, which is important for normal ciliary function in the respiratory tract and for the movement of food through the gastrointestinal tract.
In summary, goblet cells are secretory cells that produce and release mucins to form the mucus layer, providing a protective barrier and maintaining the homeostasis of mucosal surfaces.
Mucus is a viscous, slippery secretion produced by the mucous membranes that line various body cavities such as the respiratory and gastrointestinal tracts. It serves to lubricate and protect these surfaces from damage, infection, and foreign particles. Mucus contains water, proteins, salts, and other substances, including antibodies, enzymes, and glycoproteins called mucins that give it its characteristic gel-like consistency.
In the respiratory system, mucus traps inhaled particles such as dust, allergens, and pathogens, preventing them from reaching the lungs. The cilia, tiny hair-like structures lining the airways, move the mucus upward toward the throat, where it can be swallowed or expelled through coughing or sneezing. In the gastrointestinal tract, mucus helps protect the lining of the stomach and intestines from digestive enzymes and other harmful substances.
Excessive production of mucus can occur in various medical conditions such as allergies, respiratory infections, chronic lung diseases, and gastrointestinal disorders, leading to symptoms such as coughing, wheezing, nasal congestion, and diarrhea.
Sialomucins are a type of glycoprotein mucins that contain high amounts of sialic acid, which is a family of negatively charged sugars found on the surface of many cell types. These mucins are produced by the major salivary glands and are a major component of saliva. They play an important role in lubricating and protecting the oral cavity, as well as contributing to the mouth's ability to resist infection and damage.
Sialomucins have also been shown to have various biological functions, such as regulating cell adhesion, modulating immune responses, and serving as receptors for certain viruses and bacteria. Abnormalities in sialomucin expression or structure have been implicated in several diseases, including cancer, autoimmune disorders, and infectious diseases.
Glycosylation is the enzymatic process of adding a sugar group, or glycan, to a protein, lipid, or other organic molecule. This post-translational modification plays a crucial role in modulating various biological functions, such as protein stability, trafficking, and ligand binding. The structure and composition of the attached glycans can significantly influence the functional properties of the modified molecule, contributing to cell-cell recognition, signal transduction, and immune response regulation. Abnormal glycosylation patterns have been implicated in several disease states, including cancer, diabetes, and neurodegenerative disorders.
Tumor-associated carbohydrate antigens (TACAs) are a type of tumor antigen that are expressed on the surface of cancer cells. These antigens are abnormal forms of carbohydrates, also known as glycans, which are attached to proteins and lipids on the cell surface.
TACAs are often overexpressed or expressed in a different form on cancer cells compared to normal cells. This makes them attractive targets for cancer immunotherapy because they can be recognized by the immune system as foreign and elicit an immune response. Some examples of TACAs include gangliosides, fucosylated glycans, and sialylated glycans.
Tumor-associated carbohydrate antigens have been studied as potential targets for cancer vaccines, antibody therapies, and other immunotherapeutic approaches. However, their use as targets for cancer therapy is still in the early stages of research and development.
Oligosaccharides are complex carbohydrates composed of relatively small numbers (3-10) of monosaccharide units joined together by glycosidic linkages. They occur naturally in foods such as milk, fruits, vegetables, and legumes. In the body, oligosaccharides play important roles in various biological processes, including cell recognition, signaling, and protection against pathogens.
There are several types of oligosaccharides, classified based on their structures and functions. Some common examples include:
1. Disaccharides: These consist of two monosaccharide units, such as sucrose (glucose + fructose), lactose (glucose + galactose), and maltose (glucose + glucose).
2. Trisaccharides: These contain three monosaccharide units, like maltotriose (glucose + glucose + glucose) and raffinose (galactose + glucose + fructose).
3. Oligosaccharides found in human milk: Human milk contains unique oligosaccharides that serve as prebiotics, promoting the growth of beneficial bacteria in the gut. These oligosaccharides also help protect infants from pathogens by acting as decoy receptors and inhibiting bacterial adhesion to intestinal cells.
4. N-linked and O-linked glycans: These are oligosaccharides attached to proteins in the body, playing crucial roles in protein folding, stability, and function.
5. Plant-derived oligosaccharides: Fructooligosaccharides (FOS) and galactooligosaccharides (GOS) are examples of plant-derived oligosaccharides that serve as prebiotics, promoting the growth of beneficial gut bacteria.
Overall, oligosaccharides have significant impacts on human health and disease, particularly in relation to gastrointestinal function, immunity, and inflammation.
The trachea, also known as the windpipe, is a tube-like structure in the respiratory system that connects the larynx (voice box) to the bronchi (the two branches leading to each lung). It is composed of several incomplete rings of cartilage and smooth muscle, which provide support and flexibility. The trachea plays a crucial role in directing incoming air to the lungs during inspiration and outgoing air to the larynx during expiration.
The Periodic Acid-Schiff (PAS) reaction is a histological staining method used to detect the presence of certain carbohydrates, such as glycogen and glycoproteins, in tissues or cells. This technique involves treating the tissue with periodic acid, which oxidizes the vicinal hydroxyl groups in the carbohydrates, creating aldehydes. The aldehydes then react with Schiff's reagent, forming a magenta-colored complex that is visible under a microscope.
The PAS reaction is commonly used to identify and analyze various tissue components, such as basement membranes, fungal cell walls, and mucins in the respiratory and gastrointestinal tracts. It can also be used to diagnose certain medical conditions, like kidney diseases, where abnormal accumulations of carbohydrates occur in the renal tubules or glomeruli.
In summary, the Periodic Acid-Schiff reaction is a staining method that detects specific carbohydrates in tissues or cells, which can aid in diagnostic and research applications.
Carbohydrates are a major nutrient class consisting of organic compounds that primarily contain carbon, hydrogen, and oxygen atoms. They are classified as saccharides, which include monosaccharides (simple sugars), disaccharides (double sugars), oligosaccharides (short-chain sugars), and polysaccharides (complex carbohydrates).
Monosaccharides, such as glucose, fructose, and galactose, are the simplest form of carbohydrates. They consist of a single sugar molecule that cannot be broken down further by hydrolysis. Disaccharides, like sucrose (table sugar), lactose (milk sugar), and maltose (malt sugar), are formed from two monosaccharide units joined together.
Oligosaccharides contain a small number of monosaccharide units, typically less than 20, while polysaccharides consist of long chains of hundreds to thousands of monosaccharide units. Polysaccharides can be further classified into starch (found in plants), glycogen (found in animals), and non-starchy polysaccharides like cellulose, chitin, and pectin.
Carbohydrates play a crucial role in providing energy to the body, with glucose being the primary source of energy for most cells. They also serve as structural components in plants (cellulose) and animals (chitin), participate in various metabolic processes, and contribute to the taste, texture, and preservation of foods.
The intestinal mucosa is the innermost layer of the intestines, which comes into direct contact with digested food and microbes. It is a specialized epithelial tissue that plays crucial roles in nutrient absorption, barrier function, and immune defense. The intestinal mucosa is composed of several cell types, including absorptive enterocytes, mucus-secreting goblet cells, hormone-producing enteroendocrine cells, and immune cells such as lymphocytes and macrophages.
The surface of the intestinal mucosa is covered by a single layer of epithelial cells, which are joined together by tight junctions to form a protective barrier against harmful substances and microorganisms. This barrier also allows for the selective absorption of nutrients into the bloodstream. The intestinal mucosa also contains numerous lymphoid follicles, known as Peyer's patches, which are involved in immune surveillance and defense against pathogens.
In addition to its role in absorption and immunity, the intestinal mucosa is also capable of producing hormones that regulate digestion and metabolism. Dysfunction of the intestinal mucosa can lead to various gastrointestinal disorders, such as inflammatory bowel disease, celiac disease, and food allergies.
A "carbohydrate sequence" refers to the specific arrangement or order of monosaccharides (simple sugars) that make up a carbohydrate molecule, such as a polysaccharide or an oligosaccharide. Carbohydrates are often composed of repeating units of monosaccharides, and the sequence in which these units are arranged can have important implications for the function and properties of the carbohydrate.
For example, in glycoproteins (proteins that contain carbohydrate chains), the specific carbohydrate sequence can affect how the protein is processed and targeted within the cell, as well as its stability and activity. Similarly, in complex carbohydrates like starch or cellulose, the sequence of glucose units can determine whether the molecule is branched or unbranched, which can have implications for its digestibility and other properties.
Therefore, understanding the carbohydrate sequence is an important aspect of studying carbohydrate structure and function in biology and medicine.
The conjunctiva is the mucous membrane that lines the inner surface of the eyelids and covers the front part of the eye, also known as the sclera. It helps to keep the eye moist and protected from irritants. The conjunctiva can become inflamed or infected, leading to conditions such as conjunctivitis (pink eye).
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