Carbohydrates its function nd its classification
Answers
any of a large group of organic compounds occurring in foods and living tissues and including sugars, starch, and cellulose. They contain hydrogen and oxygen in the same ratio as water (2:1) and typically can be broken down to release energy in the animal body.
On the basis of the number of forming units, three major classes of carbohydrates can be defined: monosaccharides, oligosaccharides and polysaccharides.
Monosaccharides or simply sugars are formed by only one polyhydroxy aldehydeidic or ketonic unit.
The most abundant monosaccharide is D-glucose, also called dextrose.
Oligosaccharides are formed by short chains of monosaccharidic units (from 2 to 20) linked one to the next by chemical bounds, called glycosidic bounds.
The most abundant oligosaccharides are disaccharides, formed by two monosaccharides, and especially in the human diet the most important are sucrose (common table sugar), lactose and maltose. Within cells many oligosaccharides formed by three or more units do not find themselves as free molecules but linked to other ones, lipids or proteins, to form glycoconjugates.
Polysaccharides are polymers consisting of 20 to 107 monosaccharidic units; they differ each other for the monosaccharides recurring in the structure, for the length and the degree of branching of chains or for the type of links between units.
Whereas in the plant kingdom several types of polysaccharides are present, in vertebrates there are only a small number.
Polysaccharides are defined
omopolysaccharides if they contain only one type of monosaccharide as starch, glycogen and chitin;
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Carbohydrates, together with lipids, proteins and nucleic acids, are one of the four major classes of biologically essential organic molecules found in all living organisms.
Carbohydrates, all coming from the process of photosynthesis, represent the major part of organic substance on Earth, are the most abundant organic components in the major part of fruits, vegetables, legumes and cereal grains, carry out many functions in all living organisms and are the major energy source in a Mediterranean-type diet. Finally, they provide flavor and texture in many processed foods.
They are used as material for energy storage and production.
Starch and glycogen, respectively in plants and animals, are stored carbohydrates from which glucose can be mobilized for energy production. Glucose can supply energy both fueling ATP synthesis (ATP, the cell’s energy currency, has inside a phosphorylated sugar) and in the form of reducing power as NADPH.
It should be noted that glucose, used as energy source, “burns” without yielding metabolic wastes, being turned in CO2 and water, and of course releasing energy.
Monosaccharides supply 3.74 kcal/g, disaccharides 3.95 kcal/g, while starch 4.18 kcal/g; on average it is approached to 4 kcal/g.
They exert a protein-saving action: if present in adequate amount in daily nourishment, the body does not utilize proteins for energy purpose, an anti-economic and “polluting” fuel because it will need to eliminate nitrogen (ammonia) and sulfur present in some aminoacids.
Their presence is necessary for the normal lipid metabolism. More than 100 years ago Pasteur said: “Fats burn in the fire of carbohydrates“. This idea continues to receive confirmations from the recent scientific studies. Moreover, excess carbohydrates may be converted in fatty acids and triglycerides (processes that occur mostly in the liver).