Carbohydrate

Lactose is a disaccharide found in animal milk. It consists of a molecule of D-galactose and a molecule of D-glucose bonded by beta-1-4 glycosidic linkage.

In organic chemistry, a carbohydrate (/ˌkɑːrbˈhdrt/) is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula Cm(H2O)n (where m may or may not be different from n), which does not mean the H has covalent bonds with O (for example with CH2O, H has a covalent bond with C but not with O). However, not all carbohydrates conform to this precise stoichiometric definition (e.g., uronic acids, deoxy-sugars such as fucose), nor are all chemicals that do conform to this definition automatically classified as carbohydrates (e.g. formaldehyde and acetic acid).

The term is most common in biochemistry, where it is a synonym of saccharide (from Ancient Greek σάκχαρον (sákkharon) 'sugar'[1]), a group that includes sugars, starch, and cellulose. The saccharides are divided into four chemical groups: monosaccharides, disaccharides, oligosaccharides, and polysaccharides. Monosaccharides and disaccharides, the smallest (lower molecular weight) carbohydrates, are commonly referred to as sugars.[2] While the scientific nomenclature of carbohydrates is complex, the names of the monosaccharides and disaccharides very often end in the suffix -ose, which was originally taken from glucose (from Ancient Greek γλεῦκος (gleûkos) 'wine, must'), and is used for almost all sugars, e.g. fructose (fruit sugar), sucrose (cane or beet sugar), ribose, lactose (milk sugar), etc.

Carbohydrates perform numerous roles in living organisms. Polysaccharides serve as an energy store (e.g. starch and glycogen) and as structural components (e.g. cellulose in plants and chitin in arthropods). The 5-carbon monosaccharide ribose is an important component of coenzymes (e.g. ATP, FAD and NAD) and the backbone of the genetic molecule known as RNA. The related deoxyribose is a component of DNA. Saccharides and their derivatives include many other important biomolecules that play key roles in the immune system, fertilization, preventing pathogenesis, blood clotting, and development.[3]

Carbohydrates are central to nutrition and are found in a wide variety of natural and processed foods. Starch is a polysaccharide and is abundant in cereals (wheat, maize, rice), potatoes, and processed food based on cereal flour, such as bread, pizza or pasta. Sugars appear in human diet mainly as table sugar (sucrose, extracted from sugarcane or sugar beets), lactose (abundant in milk), glucose and fructose, both of which occur naturally in honey, many fruits, and some vegetables. Table sugar, milk, or honey are often added to drinks and many prepared foods such as jam, biscuits and cakes.

Cellulose, a polysaccharide found in the cell walls of all plants, is one of the main components of insoluble dietary fiber. Although it is not digestible by humans, cellulose and insoluble dietary fiber generally help maintain a healthy digestive system[4] by facilitating bowel movements. Other polysaccharides contained in dietary fiber include resistant starch and inulin, which feed some bacteria in the microbiota of the large intestine, and are metabolized by these bacteria to yield short-chain fatty acids.[5][6]

  1. ^ Avenas P (2012). "Etymology of main polysaccharide names" (PDF). In Navard P (ed.). The European Polysaccharide Network of Excellence (EPNOE). Wien: Springer-Verlag. Archived from the original (PDF) on February 9, 2018. Retrieved January 28, 2018.
  2. ^ Flitsch SL, Ulijn RV (January 2003). "Sugars tied to the spot". Nature. 421 (6920): 219–20. Bibcode:2003Natur.421..219F. doi:10.1038/421219a. PMID 12529622. S2CID 4421938.
  3. ^ Maton A, Hopkins J, McLaughlin CW, Johnson S, Warner MQ, LaHart D, Wright JD (1993). Human Biology and Health. Englewood Cliffs, New Jersey: Prentice Hall. pp. 52–59. ISBN 978-0-13-981176-0.
  4. ^ USDA National Nutrient Database, 2015, p. 14
  5. ^ Cummings, John H. (2001). The Effect of Dietary Fiber on Fecal Weight and Composition (3rd ed.). Boca Raton, Florida: CRC Press. p. 184. ISBN 978-0-8493-2387-4. Archived from the original on April 2, 2019. Retrieved April 24, 2022.
  6. ^ Byrne CS, Chambers ES, Morrison DJ, Frost G (September 2015). "The role of short chain fatty acids in appetite regulation and energy homeostasis". International Journal of Obesity. 39 (9): 1331–8. doi:10.1038/ijo.2015.84. PMC 4564526. PMID 25971927.

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