The blue–white screen is a screening technique that allows for the rapid and convenient detection of recombinant bacteria in vector-based molecular cloning experiments. DNA of interest is ligated into a vector; the vector is inserted into a competent host cell viable for transformation, which are grown in the presence of X-gal. Cells transformed with vectors containing recombinant DNA will produce white colonies; this method of screening is performed using a suitable bacterial strain, but other organisms such as yeast may be used. Molecular cloning is one of the most used procedures in molecular biology. A gene of interest may be inserted into a plasmid vector via ligation, the plasmid is transformed into Escherichia coli cells. However, not all the plasmids transformed into cells may contain the desired gene insert, checking each individual colony for the presence of the insert is time-consuming, therefore a method for the detection of the insert would be useful for making this procedure less time- and labor-intensive.
One of the early methods developed for the detection of insert is blue-white screening which allows for identification of successful products of cloning reactions through the colour of the bacterial colony. The method is based on the principle of α-complementation of the β-galactosidase gene; this phenomenon of α-complementation was first demonstrated in work done by Agnes Ullmann in the laboratory of François Jacob and Jacques Monod, where the function of an inactive mutant β-galactosidase with deleted sequence was shown to be rescued by a fragment of β-galactosidase in which that same sequence, the α-donor peptide, is still intact. Langley et al. showed that the mutant non-functional β-galactosidase was lacking in part of its N-terminus with its residues 11—41 deleted, but it may be complemented by a peptide formed of residues 3—90 of β-galactosidase. M13 filamentous phage containing sequence coding for the first 145 amino acid was constructed by Messing et al. and α-complementation via the use of a vector was demonstrated by the formation of blue plaques when cells containing the inactive protein were infected by the phage and grown in plates containing X-gal.
The pUC series of plasmid cloning vectors by Vieira and Messing was developed from the M13 system and were the first plasmids constructed to take advantage of this screening method. In this method, DNA ligated into the plasmid disrupts the α peptide and therefore the complementation process, no functional β-galactosidase can form. Cells transformed with plasmid containing an insert therefore form white colonies, while cells transformed with plasmid without an insert form blue colonies. Β-galactosidase is a protein encoded by the lacZ gene of the lac operon, it exists as a homotetramer in its active state. However, a mutant β-galactosidase derived from the M15 strain of E. coli has its N-terminal residues 11—41 deleted and this mutant, the ω-peptide, is unable to form a tetramer and is inactive. This mutant form of protein however may return to its active tetrameric state in the presence of an N-terminal fragment of the protein, the α-peptide; the rescue of function of the mutant β-galactosidase by the α-peptide is called α-complementation.
In this method of screening, the host E. coli strain carries the lacZ deletion mutant which contains the ω-peptide, while the plasmids used carry the lacZα sequence which encodes the first 59 residues of β-galactosidase, the α-peptide. Neither is functional by itself. However, when the two peptides are expressed together, as when a plasmid containing the lacZα sequence is transformed into a lacZΔM15 cells, they form a functional β-galactosidase enzyme; the blue/white screening method works by disrupting this α-complementation process. The plasmid carries within the lacZα sequence an internal multiple cloning site; this MCS within the lacZα sequence can be cut by restriction enzymes so that the foreign DNA may be inserted within the lacZα gene, thereby disrupting the gene that produces α-peptide. In cells containing the plasmid with an insert, no functional β-galactosidase may be formed; the presence of an active β-galactosidase can be detected by X-gal, a colourless analog of lactose that may be cleaved by β-galactosidase to form 5-bromo-4-chloro-indoxyl, which spontaneously dimerizes and oxidizes to form a bright blue insoluble pigment 5,5'-dibromo-4,4'-dichloro-indigo.
This results in a characteristic blue colour in cells containing a functional β-galactosidase. Blue colonies therefore show that they may contain a vector with an uninterrupted lacZα, while white colonies, where X-gal is not hydrolyzed, indicate the presence of an insert in lacZα which disrupts the formation of an active β-galactosidase; the recombinant clones can be further analyzed by isolating and purifying small amounts of plasmid DNA from the transformed colonies and restriction enzymes can be used to cut the clone and determine if it has the fragment of interest. If the DNA is necessary to be sequenced, the plasmids from the colonies will need to be isolated at a point, whether to cut using restriction enzymes or performing other assays; the correct type of vector and competent cells are important considerations when planning a blue white screen. The plasmid must contain the lacZα, examples of such plasmids are pUC19 and pBluescript; the E. coli cell should contain the mutant lacZ gene with deleted sequence, some of the used cells with such genotype are JM109, DH5α, XL1-Blue.
It should be un
Glycoside hydrolases catalyze the hydrolysis of glycosidic bonds in complex sugars. They are common enzymes with roles in nature including degradation of biomass such as cellulose and starch, in anti-bacterial defense strategies, in pathogenesis mechanisms and in normal cellular function. Together with glycosyltransferases, glycosidases form the major catalytic machinery for the synthesis and breakage of glycosidic bonds. Glycoside hydrolases are found in all domains of life. In prokaryotes, they are found both as intracellular and extracellular enzymes that are involved in nutrient acquisition. One of the important occurrences of glycoside hydrolases in bacteria is the enzyme beta-galactosidase, involved in regulation of expression of the lac operon in E. coli. In higher organisms glycoside hydrolases are found within the endoplasmic reticulum and Golgi apparatus where they are involved in processing of N-linked glycoproteins, in the lysosome as enzymes involved in the degradation of carbohydrate structures.
Deficiency in specific lysosomal glycoside hydrolases can lead to a range of lysosomal storage disorders that result in developmental problems or death. Glycoside hydrolases are found in the intestinal tract and in saliva where they degrade complex carbohydrates such as lactose, starch and trehalose. In the gut they are found as glycosylphosphatidyl anchored enzymes on endothelial cells; the enzyme lactase is required for degradation of the milk sugar lactose and is present at high levels in infants, but in most populations will decrease after weaning or during infancy leading to lactose intolerance in adulthood. The enzyme O-GlcNAcase is involved in removal of N-acetylglucosamine groups from serine and threonine residues in the cytoplasm and nucleus of the cell; the glycoside hydrolases are involved in the degradation of glycogen in the body. Glycoside hydrolases are classified into EC 3.2.1 as enzymes catalyzing the hydrolysis of O- or S-glycosides. Glycoside hydrolases can be classified according to the stereochemical outcome of the hydrolysis reaction: thus they can be classified as either retaining or inverting enzymes.
Glycoside hydrolases can be classified as exo or endo acting, dependent upon whether they act at the end or in the middle of an oligo/polysaccharide chain. Glycoside hydrolases may be classified by sequence or structure based methods. Sequence-based classifications are among the most powerful predictive method for suggesting function for newly sequenced enzymes for which function has not been biochemically demonstrated. A classification system for glycosyl hydrolases, based on sequence similarity, has led to the definition of more than 100 different families; this classification is available on the CAZy web site. The database provides a series of updated sequence based classification that allow reliable prediction of mechanism, active site residues and possible substrates; the online database is supported by CAZypedia, an online encyclopedia of carbohydrate active enzymes. Based on three-dimensional structural similarities, the sequence-based families have been classified into'clans' of related structure.
Recent progress in glycosidase sequence analysis and 3D structure comparison has allowed the proposal of an extended hierarchical classification of the glycoside hydrolases. Inverting enzymes utilize two enzymic residues carboxylate residues, that act as acid and base as shown below for a β-glucosidase: Retaining glycosidases operate through a two-step mechanism, with each step resulting in inversion, for a net retention of stereochemistry. Again, two residues are involved, which are enzyme-borne carboxylates. One acts as the other as an acid/base. In the first step the nucleophile attacks the anomeric centre, resulting in the formation of a glycosyl enzyme intermediate, with acidic assistance provided by the acidic carboxylate. In the second step the now deprotonated acidic carboxylate acts as a base and assists a nucleophilic water to hydrolyze the glycosyl enzyme intermediate, giving the hydrolyzed product; the mechanism is illustrated below for hen egg white lysozyme. An alternative mechanism for hydrolysis with retention of stereochemistry can occur that proceeds through a nucleophilic residue, bound to the substrate, rather than being attached to the enzyme.
Such mechanisms are common for certain N-acetylhexosaminidases, which have an acetamido group capable of neighboring group participation to form an intermediate oxazoline or oxazolinium ion. Again, the mechanism proceeds in two steps through individual inversions to lead to a net retention of configuration. Glycoside hydrolases are named after the substrate that they act upon, thus glucosidases catalyze the hydrolysis of glucosides and xylanases catalyze the cleavage of the xylose based homopolymer xylan. Other examples include lactase, chitinase, maltase, invertase and lysozyme. Glycoside hydrolases are predicted to gain increasing roles as catalysts in biorefining applications in the future bioeconomy; these enzymes have a variety of uses including degradation of plant materials, in the food industry, in the paper and pulp industry. C
Aspergillus oryzae, known in English as koji, is a filamentous fungus used in Japan to ferment soybeans for making soy sauce and fermented bean paste, to saccharify rice, other grains, potatoes in the making of alcoholic beverages such as sake and shōchū. The domestication of A. oryzae occurred at least 2000 years ago. A. oryzae is used for the production of rice vinegars. Barley koji or rice koji are made by fermenting the grains with aspergillus oeryzae mold. Eiji Ichishima of Tohoku University called the kōji fungus a "national fungus" in the journal of the Brewing Society of Japan, because of its importance not only for making the koji for sake brewing, but for making the koji for miso, soy sauce, a range of other traditional Japanese foods, his proposal was approved at the society's annual meeting in 2006. It is different from Rhizopus used in Huangjiu. "Red kōji-kin" is a separate species, Monascus purpureus. Aspergillus was first mentioned in the Zhouli in China in 300 BCE, its development is a milestone in Chinese food technology, for it provides the conceptual framework for three major fermented soy foods: soy sauce, jiang / miso, douchi, not to mention grain-based wines and li.
The following properties of A. oryzae strains are important in rice saccharification for sake brewing: Growth: rapid mycelial growth on and into the rice kernels Enzymes: strong secretion of amylases. White was discovered at the beginning of the Taishō period when natural mutation and separation of some black kōji to white was observed; this effect was researched and white kōji was grown independently. White kōji is easy to cultivate and its enzymes promote rapid saccharization, it gives rise to a drink with a refreshing, sweet taste. Black is used in Okinawa to produce awamori, it produces plenty of citric acid. Of all three kōji, it most extracts the taste and character of the base ingredients, giving its shōchū a rich aroma with a sweet, mellow taste, its spores disperse covering production facilities and workers' clothes in a layer of black. Such issues led to it falling out of favour, but due to the development of new kuro-kōji in the mid-1980s, interest in black kōji resurged amongst honkaku shōchū makers because of the depth and quality of the taste it produced.
Several popular brands now explicitly state they use black kōji on their labels. Yellow is used to produce sake, at one time all honkaku shōchū. However, yellow kōji is sensitive to temperature; this makes it difficult to use in warmer regions such as Kyūshū, black and white kōji became more common. Its strength is that it gives rise to a rich, refreshing taste, so despite the difficulties and great skill required, it is still used by some manufacturers, it is popular amongst young people whom had no interest in strong potato shōchū, playing a role in its recent revival. Kept secret, the A. oryzae genome was released by a consortium of Japanese biotechnology companies in late 2005. The eight chromosomes together comprise 12 thousand predicted genes; the genome of A. oryzae is thus one-third larger than that of two related Aspergillus species, the genetics model organism A. nidulans and the dangerous A. fumigatus. Many of the extra genes present in A. oryzae are predicted to be involved in secondary metabolism.
The sequenced strain isolated in 1950 is called RIB40 or ATCC 42149. Resveratrol can be produced from its glucoside piceid through the process of fermentation by A. oryzae. Sake World's description of koji Aspergillus oryzae genome from the Database of Genomes Analysed at NITE
Enzymes are macromolecular biological catalysts. Enzymes accelerate chemical reactions; the molecules upon which enzymes may act are called substrates and the enzyme converts the substrates into different molecules known as products. All metabolic processes in the cell need enzyme catalysis in order to occur at rates fast enough to sustain life. Metabolic pathways depend upon enzymes to catalyze individual steps; the study of enzymes is called enzymology and a new field of pseudoenzyme analysis has grown up, recognising that during evolution, some enzymes have lost the ability to carry out biological catalysis, reflected in their amino acid sequences and unusual'pseudocatalytic' properties. Enzymes are known to catalyze more than 5,000 biochemical reaction types. Most enzymes are proteins; the latter are called ribozymes. Enzymes' specificity comes from their unique three-dimensional structures. Like all catalysts, enzymes increase the reaction rate by lowering its activation energy; some enzymes can make their conversion of substrate to product occur many millions of times faster.
An extreme example is orotidine 5'-phosphate decarboxylase, which allows a reaction that would otherwise take millions of years to occur in milliseconds. Chemically, enzymes are like any catalyst and are not consumed in chemical reactions, nor do they alter the equilibrium of a reaction. Enzymes differ from most other catalysts by being much more specific. Enzyme activity can be affected by other molecules: inhibitors are molecules that decrease enzyme activity, activators are molecules that increase activity. Many therapeutic drugs and poisons are enzyme inhibitors. An enzyme's activity decreases markedly outside its optimal temperature and pH, many enzymes are denatured when exposed to excessive heat, losing their structure and catalytic properties; some enzymes are used commercially, in the synthesis of antibiotics. Some household products use enzymes to speed up chemical reactions: enzymes in biological washing powders break down protein, starch or fat stains on clothes, enzymes in meat tenderizer break down proteins into smaller molecules, making the meat easier to chew.
By the late 17th and early 18th centuries, the digestion of meat by stomach secretions and the conversion of starch to sugars by plant extracts and saliva were known but the mechanisms by which these occurred had not been identified. French chemist Anselme Payen was the first to discover an enzyme, diastase, in 1833. A few decades when studying the fermentation of sugar to alcohol by yeast, Louis Pasteur concluded that this fermentation was caused by a vital force contained within the yeast cells called "ferments", which were thought to function only within living organisms, he wrote that "alcoholic fermentation is an act correlated with the life and organization of the yeast cells, not with the death or putrefaction of the cells."In 1877, German physiologist Wilhelm Kühne first used the term enzyme, which comes from Greek ἔνζυμον, "leavened" or "in yeast", to describe this process. The word enzyme was used to refer to nonliving substances such as pepsin, the word ferment was used to refer to chemical activity produced by living organisms.
Eduard Buchner submitted his first paper on the study of yeast extracts in 1897. In a series of experiments at the University of Berlin, he found that sugar was fermented by yeast extracts when there were no living yeast cells in the mixture, he named the enzyme that brought about the fermentation of sucrose "zymase". In 1907, he received the Nobel Prize in Chemistry for "his discovery of cell-free fermentation". Following Buchner's example, enzymes are named according to the reaction they carry out: the suffix -ase is combined with the name of the substrate or to the type of reaction; the biochemical identity of enzymes was still unknown in the early 1900s. Many scientists observed that enzymatic activity was associated with proteins, but others argued that proteins were carriers for the true enzymes and that proteins per se were incapable of catalysis. In 1926, James B. Sumner crystallized it; the conclusion that pure proteins can be enzymes was definitively demonstrated by John Howard Northrop and Wendell Meredith Stanley, who worked on the digestive enzymes pepsin and chymotrypsin.
These three scientists were awarded the 1946 Nobel Prize in Chemistry. The discovery that enzymes could be crystallized allowed their structures to be solved by x-ray crystallography; this was first done for lysozyme, an enzyme found in tears and egg whites that digests the coating of some bacteria. This high-resolution structure of lysozyme marked the beginning of the field of structural biology and the effort to understand how enzymes work at an atomic level of detail. An enzyme's name is derived from its substrate or the chemical reaction it catalyzes, with the word ending in -ase. Examples are alcohol dehydrogenase and DNA polymerase. Different enzymes that catalyze the same chemical reaction are called isozymes; the International Union of Biochemistry and Molecular Biology have developed a nomenclature for enzymes, the EC numbers. The first number broadly classifies the enzyme based on its mechanism; the top-level classification is: EC 1, Oxidoreductases: catalyze oxidation/reducti
Protein Data Bank
The Protein Data Bank is a database for the three-dimensional structural data of large biological molecules, such as proteins and nucleic acids. The data obtained by X-ray crystallography, NMR spectroscopy, or cryo-electron microscopy, submitted by biologists and biochemists from around the world, are accessible on the Internet via the websites of its member organisations; the PDB is overseen by an organization called the Worldwide Protein Data Bank, wwPDB. The PDB is a key in areas such as structural genomics. Most major scientific journals, some funding agencies, now require scientists to submit their structure data to the PDB. Many other databases use protein structures deposited in the PDB. For example, SCOP and CATH classify protein structures, while PDBsum provides a graphic overview of PDB entries using information from other sources, such as Gene ontology. Two forces converged to initiate the PDB: 1) a small but growing collection of sets of protein structure data determined by X-ray diffraction.
In 1969, with the sponsorship of Walter Hamilton at the Brookhaven National Laboratory, Edgar Meyer began to write software to store atomic coordinate files in a common format to make them available for geometric and graphical evaluation. By 1971, one of Meyer's programs, SEARCH, enabled researchers to remotely access information from the database to study protein structures offline. SEARCH was instrumental in enabling networking, thus marking the functional beginning of the PDB; the Protein Data Bank was announced in October 1971 in Nature New Biology as a joint venture between Cambridge Crystallographic Data Centre, UK and Brookhaven National Laboratory, USA. Upon Hamilton's death in 1973, Tom Koeztle took over direction of the PDB for the subsequent 20 years. In January 1994, Joel Sussman of Israel's Weizmann Institute of Science was appointed head of the PDB. In October 1998, the PDB was transferred to the Research Collaboratory for Structural Bioinformatics; the new director was Helen M. Berman of Rutgers University.
In 2003, with the formation of the wwPDB, the PDB became an international organization. The founding members are PDBe, RCSB, PDBj; the BMRB joined in 2006. Each of the four members of wwPDB can act as deposition, data processing and distribution centers for PDB data; the data processing refers to the fact that annotate each submitted entry. The data are automatically checked for plausibility; the PDB database is updated weekly. The PDB holdings list is updated weekly; as of 17 October 2018, the breakdown of current holdings is as follows: 120,052 structures in the PDB have a structure factor file. 9,734 structures have an NMR restraint file. 3,486 structures in the PDB have a chemical shifts file. 2,531 structures in the PDB have a 3DEM map file deposited in EM Data BankThese data show that most structures are determined by X-ray diffraction, but about 10% of structures are now determined by protein NMR. When using X-ray diffraction, approximations of the coordinates of the atoms of the protein are obtained, whereas estimations of the distances between pairs of atoms of the protein are found through NMR experiments.
Therefore, the final conformation of the protein is obtained, in the latter case, by solving a distance geometry problem. A few proteins are determined by cryo-electron microscopy; the significance of the structure factor files, mentioned above, is that, for PDB structures determined by X-ray diffraction that have a structure file, the electron density map may be viewed. The data of such structures is stored on the "electron density server". In the past, the number of structures in the PDB has grown at an exponential rate, passing the 100 registered structures milestone in 1982, the 1,000 in 1993, the 10,000 in 1999, the 100,000 in 2014. However, since 2007, the rate of accumulation of new protein structures appears to have plateaued; the file format used by the PDB was called the PDB file format. This original format was restricted by the width of computer punch cards to 80 characters per line. Around 1996, the "macromolecular Crystallographic Information file" format, mmCIF, an extension of the CIF format started to be phased in.
MmCIF is now the master format for the PDB archive. An XML version of this format, called PDBML, was described in 2005; the structure files can be downloaded in any of these three formats. In fact, individual files are downloaded into graphics packages using web addresses: For PDB format files, use, e.g. http://www.pdb.org/pdb/files/4hhb.pdb.gz or http://pdbe.org/download/4hhb For PDBML files, use, e.g. http://www.pdb.org/pdb/files/4hhb.xml.gz or http://pdbe.org/pdbml/4hhbThe "4hhb" is the PDB identifier. Each structure published in PDB receives a four-character alphanumeric identifier, its PDB ID; the structure files may be viewed using one of several free and open source computer programs, including Jmol, Pymol, VMD, Rasmol. Other non-free, shareware programs
Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. The various types of sugar are derived from different sources. Simple sugars are called monosaccharides and include glucose and galactose. "Table sugar" or "granulated sugar" refers to a disaccharide of glucose and fructose. In the body, sucrose is hydrolysed into glucose. Sugars are found in the tissues of most plants, but sucrose is concentrated in sugarcane and sugar beet, making them ideal for efficient commercial extraction to make refined sugar. Sugarcane originated in tropical Indian subcontinent and Southeast Asia, is known of from before 6,000 BP, sugar beet was first described in writing by Olivier de Serres and originated in southwestern and Southeast Europe along the Atlantic coasts and the Mediterranean Sea, in North Africa, Macaronesia, to Western Asia. In 2016, the combined world production of those two crops was about two billion tonnes. Other disaccharides include lactose. Longer chains of sugar molecules are called polysaccharides.
Some other chemical substances, such as glycerol and sugar alcohols, may have a sweet taste, but are not classified as sugar. Sucrose is used in prepared foods, is sometimes added to commercially available beverages, may be used by people as a sweetener for foods and beverages; the average person consumes about 24 kilograms of sugar each year, or 33.1 kilograms in developed countries, equivalent to over 260 food calories per day. As sugar consumption grew in the latter part of the 20th century, researchers began to examine whether a diet high in sugar refined sugar, was damaging to human health. Excessive consumption of sugar has been implicated in the onset of obesity, cardiovascular disease and tooth decay. Numerous studies have tried to clarify those implications, but with varying results because of the difficulty of finding populations for use as controls that consume little or no sugar. In 2015, the World Health Organization recommended that adults and children reduce their intake of free sugars to less than 10%, encouraged a reduction to below 5%, of their total energy intake.
The etymology reflects the spread of the commodity. From Sanskrit शर्करा, meaning "ground or candied sugar," "grit, gravel", came Persian shakar, whence Arabic سكر, whence Medieval Latin succarum, whence 12th-century French sucre, whence the English word sugar. Italian zucchero, Spanish azúcar, Portuguese açúcar came directly from Arabic, the Spanish and Portuguese words retaining the Arabic definite article; the earliest Greek word attested is σάκχαρις. The English word jaggery, a coarse brown sugar made from date palm sap or sugarcane juice, has a similar etymological origin: Portuguese jágara from the Malayalam ചക്കരാ, itself from the Sanskrit शर्करा. Sugar has been produced in the Indian subcontinent since ancient times and its cultivation spread from there into modern-day Afghanistan through the Khyber Pass, it was not plentiful or cheap in early times, in most parts of the world, honey was more used for sweetening. People chewed raw sugarcane to extract its sweetness. Sugarcane was a native of Southeast Asia.
Different species seem to have originated from different locations with Saccharum barberi originating in India and S. edule and S. officinarum coming from New Guinea. One of the earliest historical references to sugarcane is in Chinese manuscripts dating to 8th century BCE, which state that the use of sugarcane originated in India. In the tradition of Indian medicine, the sugarcane is known by the name Ikṣu and the sugarcane juice is known as Phāṇita, its varieties and characterics are defined in nighaṇṭus such as the Bhāvaprakāśa. Sugar remained unimportant until the Indians discovered methods of turning sugarcane juice into granulated crystals that were easier to store and to transport. Crystallized sugar was discovered by the time of the Imperial Guptas, around the 5th century CE. In the local Indian language, these crystals were called khanda, the source of the word candy. Indian sailors, who carried clarified butter and sugar as supplies, introduced knowledge of sugar along the various trade routes they travelled.
Traveling Buddhist monks took sugar crystallization methods to China. During the reign of Harsha in North India, Indian envoys in Tang China taught methods of cultivating sugarcane after Emperor Taizong of Tang made known his interest in sugar. China established its first sugarcane plantations in the seventh century. Chinese documents confirm at least two missions to India, initiated in 647 CE, to obtain technology for sugar refining. In the Indian subcontinent, the Middle East and China, sugar became a staple of cooking and desserts. Nearchus, admiral of Alexander of Macedonia, knew of sugar during the year 325 B. C. because of his participation in the campaign of India led by Alexander. The Greek physician Pedanius Dioscorides in the 1st century CE described sugar in his medical treatise De Materia Medica, Pliny the Elder, a 1st-century CE Roman, described sugar in his Natural History: "Sugar is made in Arabia as well, but Indian sugar is better, it is a kind of honey found in cane, white as gum, it crunches between the teeth.
It comes in lumps the size of a hazelnut. Sugar is used only for medical purposes." Crusaders brought sugar back to Europe after their campaigns in the Hol
Intestinal villi are small, finger-like projections that extend into the lumen of the small intestine. Each villus is 0.5–1.6 mm in length, has many microvilli projecting from the enterocytes of its epithelium which collectively form the striated or brush border. Each of these microvilli are much smaller than a single villus; the intestinal villi are much smaller than any of the circular folds in the intestine. Villi increase the internal surface area of the intestinal walls making available a greater surface area for absorption. An increased absorptive area is useful because digested nutrients pass into the semipermeable villi through diffusion, effective only at short distances. In other words, increased surface area decreases the average distance travelled by nutrient molecules, so effectiveness of diffusion increases; the villi are connected to the blood vessels so the circulating blood carries these nutrients away. Enterocytes, along with goblet cells, represent the principal cell types of the epithelium of the villi in the small intestine.
There, the villi and the microvilli increase intestinal absorptive surface area 30-fold and 600-fold providing exceptionally efficient absorption of nutrients in the lumen. There are enzymes on the surface for digestion. Villus capillaries collect amino acids and simple sugars taken up by the villi into the blood stream. Villus lacteals collect absorbed chylomicrons, which are lipoproteins composed of triglycerides and amphipathic proteins, are taken to the rest of the body through the lymph fluid. Villi are specialized for absorption in the small intestine as they have a thin wall, one cell thick, which enables a shorter diffusion path, they have a large surface area so there will be more efficient absorption of fatty acids and glycerol into the blood stream. They have a rich blood supply to keep a concentration gradient. C. W. Chan, Y. K. Leung and K. W. Chan. "Microscopic anatomy of the vasculature of the human intestinal villus - a study with review". Eur J Anat, 18: 291-301