Felix[1]..carbs 1

Definition: Carbohydrates are compounds containing carbon, hydrogen and oxygen. Carbohydrates are the most abundant organic compounds in the plant world. They account for approximately three-fourths of the dry weight of plants. Animals (including humans) get their carbohydrates by eating plants, but they do not store much of what they consume. In fact, less than 1% of the body weight of animals is made up of carbohydrates.

• The word carbohydrate means “hydrate of carbon” and derives from the formula Cx(H2O)y - x and y may or may not be equal and range in value from 3 to 12 or more. Two examples of carbohydrates with this general formula that can be written alternatively as hydrates of carbon are: glucose ( blood sugar): C6H12O6 sucrose (table sugar): C12H22C11  Most carbohydrates are polyhydroxyaldehydes, polyhydroketones, or compounds that yield them after hydrolysis. The simpler membears of the carohydrate family are often referred to as saccharides because of their sweet taste( Latin: saccharum, “sugar”)

Formation of a carbohydrate

FUNCTIONS: 

Carbohydrates are initially synthesized in plants from a complex series of reactions involving photosynthesis. •Store energy in the form of starch (photosynthesis in plants) or glycogen (in animals and humans). •Provide enaergy through metabolism pathways and cycles. •Supply carbon for synthesis of other compounds. •Form structural components in cells and

Classifications of carbohydrates Carbohydrates could be classified depending on the number of simple sugars they contain: Monosaccharides Disaccharides Oligosaccharides Polysaccharides

Monosaccharides Monosaccharides are simple sugars that could not be hydrolyzed further into smeller units under reasonably mild conditions.  Monosaccharides (from Greek monos: single, sacchar: sugar) are the simplest carbohydrates.. They consist of one sugar and are usually colorless, water-soluble, crystalline solids. Some monosaccharides have a sweet taste. Monosaccharides are the building blocks of disaccharides like sucrose (common sugar) and polysaccharides (such as cellulose and starch).

Monosaccharide nomenclature: Monosaccharides are classified by the number of carbon atoms they contain: The suffix “ose” indicates that a molecule is a carbohydrate, and the prefixes tri-, tetr-,pent-, and so forth indicate the number of carbon atoms in the chain. Triose, 3 carbon atoms Tetrose, 4 carbon atoms Pentose, 5 carbon atoms Hexose, 6 carbon atoms Heptose, 7 carbon atoms Octose, 8 carbon atoms Nonose, 9 carbon atoms Decose, 10 carbon atoms

Monosaccharides are also classified by the type of keto group they contain: Aldose, -CHO (aldehyde) Ketose, C=O (ketone)

or

D-glucose an aldose an aldohexose

or

D-fructose a ketose a ketohexose

Monosaccharides Common Carbohydrates Name

Derivation of name and Source

Glucose From Greek word for sweet wine; grape sugar, blood sugar, dextrose. Galactose Greek word for milk--"galact", found as a component of lactose in milk. Fructose Latin word for fruit--"fructus", also known as levulose, found in fruits and honey; sweetest sugar. Ribose

Ribose and Deoxyribose are found in the backbone structure of RNA and DNA, respectively.

Galactose is more commonly found in the disaccharide , lactose or milk sugar. It is found as the monosaccha ride in peas.

Amino Sugar amino sugar contains an amine group in place of a hydroxyl group.

Glucosamine

Disaccharides A disaccharide is a sugar (a carbohydrate) composed of two monosaccharides. 'Disaccharide' is one of the four chemical groupings of carbohydrates (monosaccharide, disaccharide, oligosaccharide, and polysaccharide).

Formation It is formed when two sugars are joined together and a molecule of water is removed. For example; milk sugar (lactose) is made from glucose and galactose whereas cane sugar ( sucrose) is made from glucose and fructose. The two monosaccharides are bonded via a dehydration reaction (also called a condensation reaction or dehydration synthesis) that leads to the loss of a molecule of water and formation of a glycosidic bond.

Depending on the monosaccharide constituents, disaccharides are sometimes crystalline, sometimes water-soluble, and sometimes sweettasting and sticky-feeling

Properties The glycosidic bond can be formed between any hydroxyl group on the component monosaccharide. So, even if both component sugars are the same (e.g., glucose), different bond combinations (regiochemistry) and stereochemistry (alpha- or beta-) result in disaccharides that are diastereoisomers with different chemical and physical properties.

Common disaccharides Disaccharides - contain two monosaccharides  Sucrose - French word for sugar--"sucre", a disaccharide containing glucose and fructose; table sugar, cane sugar, beet sugar.  Lactose - Latin word for milk--"lact"; a disaccharide found in milk containing glucose and galactose. Maltose - French word for "malt"; a disaccharide containing two units of glucose; found in germinating grains, used to make beer.

OLIGOSACCHARIDES An oligosaccharide is a saccharide polymer containing a small number (typically three to ten) of component sugars, also known as simple sugars.

Polysaccharides  Polysaccharides are relatively complex carbohydrates. They are polymers made up of many monosaccharides joined together by glycosidic bonds. They are therefore very large, often branched, macromolecules. They tend to be amorphous, insoluble in water, and have no sweet taste.  When all the monosaccharides in a polysaccharide are the same type the polysaccharide is called a homopolysaccharides. But when more than one type of monosaccharide is present they are called heteropolysaccharides.

Examples include storage polysaccharides such as starch and glycogen and structural polysaccharides such as cellulose and chitin. Polysaccharides have a general formula of Cn(H2O)n-1 where n is usually a large number between 200 and 2500. Considering that the repeating units in the polymer backbone are often six-carbon monosaccharides, the general formula can also be represented as (C6H10O5)n where n={40...3000}.

Storage polysaccharides Starches Starches are glucose polymers in which glucopyranose units are bonded by alpha-linkages. It is made up of a mixture of Amylose and Amylopectin. Amylose consists of a linear chain of several hundred glucose molecules, Amylopectin is a branched molecule made of several thousand glucose units. Starches are insoluble in water. They can be digested by hydrolysis, catalyzed by enzymes called amylases, which can break the alpha-linkages (glycosidic bonds). Humans and other animals have amylases, so they can digest starches. Potato, rice, wheat, and corn are major sources of starch in the human diet.

Glycogen  Glycogen is a branched polysaccharide found in nearly all animal cells and in certain protozoa and algae. In humans and other vertebrates it is principally stored in the liver and muscles and is the main form of stored carbohydrate in the body, acting as a reservoir of glucose (which the glycogen can be broken down into) for when the body is being starved of food. In an animal that has been fed well, as much as 10% of its liver weight may be glycogen. The liver’s glycogen store can be almost completely depleted during a 24 hour fast or during muscular exertion but glycogen is quickly re-synthesised from newly ingested carbohydrate.

Structural polysaccharides Cellulose The structural component of plants are formed primarily from cellulose. Wood is largely cellulose and lignin, while paper and cotton are nearly pure cellulose. Cellulose is a polymer made with repeated glucose units bonded together by beta-linkages. Humans and many other animals lack an enzyme to break the beta-linkages, so they do not digest cellulose. Certain animals can digest cellulose, because bacteria possessing the enzyme are present in their gut. The classic example is the termite.

Chitin Chitin is closely related in structure to cellulose, also being an unbranched polysaccharide. However, instead of the hydroxyl groups (-OH), the chains have the following structure – NH.CO.CH3 replacing it. Large amounts of chitin is found in the cuticles of arthropods, with smaller amounts being found in sponges, molluscs and annelids. Chitin can also be found in the cell walls of most fungi and in some green algae.

Acidic polysaccharides Acidic polysaccharides are polysaccharides that contain carboxyl groups, phosphate groups and/or sulfuric ester groups.