Carbohydrates ( ) are biomolecules composed of carbon atoms (C), hydrogen (H) and oxygen (O), usually with a 2: 1 hydrogen-oxygen atom ratio (such as in water); in other words, with the empirical formula C m (H 2 O) n (where m may be different from n ). This formula applies to monosaccharides. Some exceptions exist; for example, deoxyribose, a sugar component of DNA, has an empirical formula C 5 H 10 O 4 . Carbohydrates are technically carbon hydrates; structurally more accurately to see them as aldosis and ketosis.
This term is most common in biochemistry, where it is a synonym of 'saccharide', a group that includes sugar, starch, and cellulose. Sakarida is divided into four chemical groups: monosaccharides, disaccharides, oligosaccharides, and polysaccharides. Monosaccharides and disaccharides, the smallest carbohydrates (low molecular weight), commonly referred to as sugar. The word saccharide comes from the Greek word ???????? ( sÃÆ'¡kkharon ), which means "sugar". While the complex scientific nomenclature of carbohydrates, the names of monosaccharides and disaccharides very often end in a suffix -like, in fructose monosaccharides (fruit sugar) and glucose (grape sugar) and sucrose disaccharides (sugar cane) and lactose (milk sugar).
Carbohydrates play many roles in living organisms. Polysaccharides function for energy storage (eg starch and glycogen) and as structural components (eg cellulose in plants and chitin in arthropods). 5-carbon monosaccharide ribose is an important component of coenzymes (eg ATP, FAD and NAD) and the backbone of a genetic molecule known as RNA. Deoxyribose linked is a component of DNA. Saccharides and its derivatives include many other important biomolecules that play a key role in the immune system, fertilizing, preventing pathogenesis, blood clotting, and development.
Carbohydrates are found in a wide variety of foods. Important sources are cereals (wheat, corn, rice), potatoes, cane, fruit, table sugar (sucrose), bread, milk, etc. Starch and sugar are important carbohydrates in our diet. Starch contains lots of potatoes, corn, rice and other cereals. Sugars appear in our diet primarily as sucrose (table sugar), which is added to drinks and many ready-to-eat foods such as jams, biscuits and cakes, and glucose and fructose that occur naturally in many fruits and vegetables.
Glycogen is a carbohydrate found in the liver and muscles (as an energy source). Cellulose in the cell wall of all plant tissues is carbohydrates. It is important in our diet as fiber that helps maintain a healthy digestive system.
Video Carbohydrate
Terminology
In scientific literature, the term "carbohydrate" has many synonyms, such as "sugar" (in the broad sense), "saccharide", "ose", "glucida", "carbon hydrate" or "polyhydroxy compound with aldehyde or ketone".. Some of these terms, especially "carbohydrates" and "sugars", are also used with other meanings.
In food science and in many informal contexts, the term "carbohydrate" often means foods rich in complex starchy carbohydrates (like cereals, breads and pasta) or simple carbohydrates, like sugar (found in candies, jams, and desserts).
Often in lists of nutritional information, such as the USDA National Nutrition Database, the term "carbohydrate" (or "carbohydrate by difference") is used for everything other than water, protein, fat, ash, and ethanol. These include chemical compounds such as acetic acid or lactate, which are not usually considered carbohydrates. It also includes dietary fiber which is a carbohydrate but does not contribute much in the way food energy (kilocalories), although it is often included in the calculation of total energy of food as if it were sugar.
In a narrow sense, "sugar" is used for sweet and soluble carbohydrates, many of which are used in food.
Maps Carbohydrate
Structure
Previously the name "carbohydrate" was used in chemistry for any compound with the formula C m (H 2 O) n . Following this definition, some chemists consider formalin (CH 2 O) as the simplest carbohydrate, while others claim that the title is for glycolaldehyde. Today, the term is generally understood in terms of biochemistry, which does not include compounds with only one or two carbons and includes many biological carbohydrates that deviate from this formula. For example, while the above representative formula seems to be catching commonly known carbohydrates, carbohydrates everywhere and abundant often deviate from this. For example, carbohydrates often feature chemical groups such as: N -acetyl (eg chitin), sulfates (eg glycosaminoglycans), carboxylic acids (eg sialic acid) and deoxy modifications (eg fucose and sialic acid).
Natural saccharides are generally made of simple carbohydrates called monosaccharides with the general formula (CH 2 O) n where n is three or more. Typical monosaccharides have the structure of H- (CHOH) x (C = O) - (CHOH) y -H , that is, aldehydes or ketones with many hydroxyl groups added, usually one on each carbon atom which is not part of the aldehyde or ketone functional group. Examples of monosaccharides are glucose, fructose, and glyceraldehyde. However, some biological substances commonly referred to as "monosaccharides" are inconsistent with this formula (eg uronic acid and deoxy oils such as fucose) and there are many chemicals in accordance with this formula but are not considered monosaccharides (eg CH formaldehyde). 2 O and inositol (CH 2 O) 6 ).
The open chain form of the monosaccharides often coexists with the closed-ring form in which the carbonyl group carbonyl aldehyde/ketone (C = O) and the hydroxyl group (-OH) reacts to form hemiasetal with a new C-O-C bridge.
Monosaccharides can be linked together into what are called polysaccharides (or oligosaccharides) in various ways. Many carbohydrates contain one or more modified monosaccharide units that already have one or more groups that are replaced or removed. For example, deoxyribose, a DNA component, is a modified version of ribose; chitin consists of a repeating unit of N-acetyl glucosamine, a form of glucose containing nitrogen.
Division
Carbohydrates are polyhydroxy aldehydes, ketones, alcohols, acids, their simple derivatives and their polymers have an acetal-type connection. They can be classified according to their degree of polymerization, and can be divided initially into three main groups, namely sugar, oligosaccharides and polysaccharides
DP * = Polymerization rate
Monosaccharides
Monosaccharides are the simplest carbohydrates because they can not be hydrolyzed into smaller carbohydrates. They are aldehydes or ketones with two or more hydroxyl groups. The general chemical formula of unmodified monosaccharides is (CoH 2 O) n , literally "carbon hydrate". Monosaccharides are important fuel molecules as well as building blocks for nucleic acids. The smallest monosaccharides, which are n = 3, dihydroxyacetone and D- and L-glyceraldehyde.
Monosaccharide Classification
Monosaccharides are classified according to three different characteristics: the placement of the carbonyl group, the number of carbon atoms they contain, and their chiral saturation. If the carbonyl group is an aldehyde, the monosaccharide is aldose; if the carbonyl group is a ketone, the monosaccharide is ketose. The monosaccharides with three carbon atoms are called trioses, with four called tetroses, five are called pentoses, six are hexoses, and so on. These two classification systems are often combined. For example, glucose is aldohexose (six-carbon aldehyde), ribose is aldopentose (five-carbon aldehyde), and fructose is ketohexose (six carbon ketone).
Each carbon atom containing a hydroxyl group (-OH), with the exception of the first and last carbon, is asymmetric, making it the stereo centers with two possible configurations (R or S) respectively. Because of this asymmetry, a number of isomers may exist for certain monosaccharide formulas. Using the rule of Le Bel-van't Hoff, aldohexose D-glucose, for example, has the formula (CÃ, Â · H 2 O) 6 , of which four of the six carbonic atoms is stereogenic, making D-glucose one of 2 4 = 16 possible stereoisomers. In the case of glyceraldehydes, aldotriose, there is a possible pair of stereoisomers, which are enantiomers and epimers. 1, 3-dihydroxyacetone, ketose associated with aldose glyceraldehyde, is a symmetrical molecule with no stereo centers. The assignment of D or L is made in accordance with the asymmetrical orientation of the farthest carbon from the carbonyl group: in the standard Fischer projection if the hydroxyl group is to the right of its molecule is sugar D, otherwise it is sugar L. The "D-" and "L-" prefixes should not be equated with "d-" or "l-", which indicates the direction that sugar rotates the polarized light of the plane. The use of "d-" and "l-" is no longer followed in carbohydrate chemistry.
Isomerism perpendicular chain
The aldehyde or ketone group of the monosaccharide straight chain will react reversibly with the hydroxyl group at different carbon atoms to form hemiasetal or hemiketal, forming a heterocyclic ring with an oxygen bridge between two carbon atoms. Rings with five and six atoms are called furanose and pyranose forms, respectively, and are present in equilibrium with straight-chain shapes.
During the conversion from a straight chain form to a cyclic form, carbon-containing carbonyl carbon, called an anomic carbon, becomes a stereogenic center with two possible configurations: The oxygen atom can take a position above or below the ring plane. The likelihood of the resulting stereoisomer pair is called anomers. In ? anomer , the substituent -OH on the anomeric carbon is located on the opposite side (trans) ring of the side branch CH 2 OH. Alternative form, where the substituent CH 2 OH and the anomeric hydroxyl are on the same side (cis) of the ring plane, called ? anomer .
Use in living organism
Monosaccharide is the main source of fuel for metabolism, which is used both as a source of energy (glucose becomes the most important in nature) and in biosynthesis. When monosaccharides are not immediately required by many cells, they are often converted into more efficient forms of space, often polysaccharides. In many animals, including humans, this form of storage is glycogen, especially in the liver and muscle cells. In plants, starch is used for the same purpose. The most abundant carbohydrates, cellulose, are the structural components of plant cell walls and many forms of algae. Ribose is an RNA component. Deoksiribose is a component of DNA. Lyxose is a component of lyxoflavin found in the human heart. Ribulose and xylulose occur in the path of pentosa phosphate. Galactose, a component of lactose milk sugar, is found in galactolipids in plant cell membranes and glycoproteins in many tissues. Mannose occurs in human metabolism, especially in certain glycosylated proteins. Fructose, or fruit sugar, is found in many plants and in humans, metabolized in the liver, absorbed directly into the intestines during digestion, and is found in semen. Trehalose, the main insect sugar, is rapidly hydrolyzed into two glucose molecules to support continuous flight.
Disaccharides
The two joined monosaccharides are called disaccharides and these are the simplest polysaccharides. Examples include sucrose and lactose. They consist of two monosaccharide units bonded together by covalent bonds known as glycosidic links formed by dehydration reaction, resulting in the loss of hydrogen atoms from one monosaccharide and hydroxyl group from the other. The unmodified disaccharide formula is C 12 H 22 O 11 . Although there are many types of disaccharides, a handful of disaccharides are essential.
Sucrose, pictured on the right, is the most abundant disaccharide, and the main form in which carbohydrates are transported in plants. It consists of one D-glucose molecule and one D-fructose molecule. The systematic name for sucrose, O -? - D-glucopyranosyl- (1-> 2) -D-fructofuranoside, shows four things:
- Monosaccharides: glucose and fructose
- The type of their ring: glucose is pyranose and fructose is furanose
- How are they linked together: oxygen on carbon number 1 (C1) from? -D-glucose associated with C2 from D-fructose.
- The -oside suffix indicates that the anomeric carbon of the two monosaccharides participates in the glycosidic bond.
Lactose, a disaccharide composed of one D-galactose molecule and one D-glucose molecule, occurs naturally in mammalian milk. The systematic name for lactose is O -? - D-galactopyranosyl- (1-> 4) -D-glucopyranose. Other important disaccharides include maltose (two related D-glucoses? -1,4) and cellulobiose (two related D-glucoses? -1,4). Disaccharides can be classified into two types: reduced and non-reduction disaccharides. If the functional group exists in bonding with another sugar unit, this is called disaccharide or biose reduction.
Nutrition
Carbohydrates consumed in food produce 3.87 kilocalories of energy per gram for simple sugars, and 3.57 to 4.12 kilocalories per gram for complex carbohydrates in most other foods. Relatively high carbohydrate levels are related to processed foods or processed foods made from plants, including candies, cookies and candies, table sugar, honey, soft drinks, bread and crackers, jams and fruit products, pasta and breakfast cereals. Lower carbohydrate amounts are usually associated with unrefined foods, including nuts, tubers, rice, and unrefined fruit. Animal-based foods generally have the lowest carbohydrate levels, although milk does contain a high proportion of lactose.
Organisms usually can not metabolize all types of carbohydrates to produce energy. Glucose is an almost universal and accessible source of energy. Many organisms also have the ability to metabolize monosaccharides and other disaccharides but glucose is often metabolized first. In Escherichia coli , for example, the lac operon will express the enzyme for lactose digestion when present, but if both lactose and glucose are present lac the operon is suppressed, producing glucose used first (see : Diauxie). Polysaccharides are also a common source of energy. Many organisms can easily break down starch into glucose; most organisms, however, can not metabolize cellulose or other polysaccharides such as chitin and arabinoxylans. This type of carbohydrate can be metabolized by some bacteria and protists. Ruminants and termites, for example, use microorganisms to process cellulose. Although these complex carbohydrates are not easily digested, they represent an important dietary element for humans, called dietary fiber. Fiber improves digestion, among other benefits.
Based on the effect on risk of heart disease and obesity in healthy middle-aged adults, the Institute of Medicine recommends that American and Canadian adults earn between 45-65% of the food energy of wheat carbohydrates. The Food and Agriculture Organization and the World Health Organization jointly recommend that the national dietary guidelines set 55-75% of the total energy intake of carbohydrates, but only 10% directly from sugar (their term for simple carbohydrates).
Classification
Nutritionists often refer to carbohydrates as simple or complex. However, the exact differences between these groups can be ambiguous. The term "complex carbohydrates" was first used in the US Senate Select Committee on the publication of the Nutrition and Human Needs Dietary Destination for the United States (1977) where it was meant to differentiate sugars from other carbohydrates ( which is considered superior in terms of nutrition). However, the report includes "fruits, vegetables and grains" in complex carbohydrate columns, despite the fact that these may contain sugars as well as polysaccharides. This confusion continues as today some nutritionists use complex carbohydrate terms to refer to any kind of undigested saccharide that exists throughout the diet, where fiber, vitamins and minerals are also found (compared to refined carbohydrates, which provide energy but little other nutrients). The use of standards, however, is to classify carbohydrates chemically: simple if they are sugars (monosaccharides and disaccharides) and complexes if they are polysaccharides (or oligosaccharides).
In any case, simple and complex chemical distinctions have little value to determine the nutritional quality of carbohydrates. Some simple carbohydrates (eg fructose) raise blood glucose slowly, while some complex carbohydrates (starch), especially when processed, increase blood sugar quickly. Digestive speed is determined by a variety of factors including other nutrients that are consumed with carbohydrates, how foods are prepared, individual differences in metabolism, and carbohydrate chemistry.
The USDA's Dietary Guidelines for Americans 2010 calls for moderate-to high carb consumption from a balanced diet that includes six servings of one serving of whole grain food, at least half of the whole grain source and the rest from enriched.
The glycemic index (GI) and the concept of glycemic load have been developed to characterize food behavior during human digestion. They rank foods rich in carbohydrates based on their speed and magnitude of the effect on blood glucose levels. The glycemic index is a measure of how quickly food glucose is absorbed, while glycemic load is a measure of total glucose that can be absorbed in food. The insulin index is a newer, similar classification method that rates foods based on their effect on blood insulin levels, caused by glucose (or starch) and some amino acids in the diet.
Dietary restriction of carbohydrate diet
Carbohydrates are a common source of energy in living organisms; However, there is no single carbohydrate which is an essential nutrient in humans. Humans can derive all their energy needs from proteins and fats, although the potential for some of the health-negative effects of extreme carbohydrate restrictions remains, since the issue has not been widely studied. However, in the case of digested fiber-carbohydrate diet that is not a source of energy - inadequate intake can cause a significant increase in mortality.
Following a diet consisting of very low daily carbohydrates for several days will usually result in higher levels of the blood ketone body than isocaloric diets with similar protein content. This relatively high level of body ketone is commonly known as ketosis and is often very confused with the fatal conditions commonly found in people with type 1 diabetes known as diabetic ketoacidosis. A person suffering from ketoacidosis will have a higher rate of blood ketone bodies along with high blood sugar, dehydration and electrolyte imbalances.
Long-chain fatty acids can not cross the blood-brain barrier, but the liver can break it down to produce ketones. However, the middle-chain octanoic and heptanoic acid fatty acids may cross the barrier and are used by the brain, which usually depends on glucose for its energy. Gluconeogenesis allows humans to synthesize some glucose from specific amino acids: from the glycerol backbone in triglycerides and in some cases from fatty acids.
Metabolism
Carbohydrate metabolism shows the various biochemical processes responsible for the formation, breakdown and interconversion of carbohydrates in living organisms.
The most important carbohydrates are glucose, simple sugars (monosaccharides) that are metabolized by almost all known organisms. Glucose and other carbohydrates are part of various metabolic pathways across the species: plants synthesize carbohydrates from carbon dioxide and water with photosynthesis store internally absorbed energy, often in the form of starch or lipids. Plant components are consumed by animals and fungi, and are used as fuel for cell respiration. The oxidation of one gram of carbohydrate produces about 9 kJ (4 kcal) of energy, while the oxidation of one gram of lipid yields about 38 kJ (9 kcal). The human body stores between 300 and 500 g of carbohydrates depending on weight, with skeletal muscle contributing to most of the storage. Energy derived from metabolism (eg, glucose oxidation) is usually stored temporarily in cells in the form of ATP. Organisms capable of anaerobic and aerobic respiration that metabolize glucose and oxygen (aerobes) to release energy with carbon dioxide and water as a by-product.
Catabolism
Catabolism is a metabolic reaction that cells undergo breaking bigger molecules, extracting energy. There are two main metabolic pathways of monosaccharide catabolism: glycolysis and citric acid cycle.
In glycolysis, oligo/polysaccharide is first split into smaller monosaccharides by an enzyme called glycoside hydrolase. The monosaccharide unit can then enter the monosaccharide cathodism. ATP 2 investments are needed at the first step of glycolysis to phosphorylate Glucose to Glucose 6-Phosphate (G6P) and Fructose 6-Phosphate (F6P) to Fructose 1,6-bisphosphate (FBP), thereby inducing forward reactions to be irreversible. In some cases, as in humans, not all types of carbohydrates can be used because the required digestive and metabolic enzymes do not exist.
Carbohydrate Chemistry
Chemical carbohydrates are a large and economically important branch of organic chemistry. Some of the major organic reactions that involve carbohydrates are:
- Carbohydrate assetization
- Cyanohydrin Reaction
- Lobry de Bruyn-van Ekenstein's Transformation
- Amadori rearrangement
- Nefek reaction
- Wohl degradation
- Koenigs-Knorr Reaction
- Carbohydrate digestion
See also
References
Source
- "Raw food compensation, processed, prepared" (PDF) . United States Department of Agriculture. September 2015 . Retrieved October 30, 2016 . Ã,
External links
- Carbohydrates, including interactive models and animations (Requires Chime MDL)
- IUPAC-IUBMB Joint Commission on Biochemistry Nomenclature (JCBN): Nomenclature of Karbo
- Detailed carbs
- Carbohydrates and Glycosylation - Virtual Library of Biochemistry, Molecular Biology, and Cell Biology
- Glycomics Gateway Functional, a collaboration between Consortium for Functional Glycomics and Nature Publishing Group
Source of the article : Wikipedia
0 Comments