Carbohydrate Basics and Classification
– Carbohydrates are compounds with the formula Cn(H2O)n.
– Monosaccharides like glucose and fructose have aldehyde or ketone structures with hydroxyl groups.
– Carbohydrates can be di-, oligo-, or polysaccharides.
– Monosaccharides classified by carbonyl group placement, carbon atom count, and chiral handedness.
– Carbohydrates are polyhydroxy compounds, including aldehydes, ketones, alcohols, and acids.
Carbohydrate Sources and Use in Living Organisms
– Monosaccharides are primary fuel sources for metabolism.
– Glucose is a primary energy source for most organisms.
– Carbohydrates are stored as glycogen in animals, starch in plants, and cellulose in cell walls.
– Different types of carbohydrates are metabolized at varying rates in organisms.
– Monosaccharides play roles in human metabolism, milk sugar, and glycoproteins.
Carbohydrate Nutrition and Health Effects
– Carbohydrates provide energy, with simple sugars yielding 3.87 kcal/g.
– Processed foods are high in carbohydrates, while unrefined foods have more fiber.
– Low-carb diets may miss health advantages of high-quality carbohydrates.
– Limited evidence on low-carb dieting in managing type 1 diabetes.
– Adverse effects and effectiveness of carbohydrate-restricted diets in weight loss.
Carbohydrate Metabolism and Catabolism
– Carbohydrate metabolism involves formation, breakdown, and interconversion of carbohydrates.
– Glycolysis and citric acid cycle are major pathways in monosaccharide catabolism.
– The human body stores 300-500g of carbohydrates, mainly in skeletal muscle.
– Oxidation of carbohydrates yields energy (16kJ/g).
– Some organisms cannot utilize all carbohydrate types due to enzyme limitations.
Carbohydrate Chemistry and Research
– Carbohydrate chemistry is a significant branch of organic chemistry.
– Key reactions involving carbohydrates include Amadori rearrangement and glycolipid formation.
– Research findings on whole grain diets, carbohydrate-restricted diets, and their impact on health.
– Various sources provide information on carbohydrate metabolism and chemistry.
– Studies on the effects of carbohydrates on health outcomes like cardiovascular disease prevention.
It has been suggested that Carbohydrate chemistry be merged into this article. (Discuss) Proposed since January 2024. |
A carbohydrate (/ˌkɑːrboʊˈhaɪdreɪt/) 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'), 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. 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 the word 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.
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 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.