Introduction to Carbohydrates

Monosaccharides are simple sugars that cannot be hydrolyzed into simpler forms. They come in various types based on the number of carbon atoms (3-7) and the presence of an aldehyde or ketone group. D-glucose is the most abundant monosaccharide in nature.

Disaccharides are formed from the condensation of two monosaccharide units, with the bond being a glycosidic bond. Examples include lactose (glucose + galactose), maltose (glucose + glucose), sucrose (glucose + fructose), and trehalose (glucose + glucose).

Oligosaccharides are formed from 3 to 10 monosaccharide units, and they are not digestible by human enzymes.

Polysaccharides are formed from more than 10 monosaccharide units, and they may be linear or branched polymers. Glycogen is an example of a branched glucose polymer. Starches are another type of polysaccharide. Foods with a polysaccharide structure, which are not digested by human enzymes, form the main component of dietary fiber.

Monosaccharides can be classified as D- or L-isomers based on the arrangement of atoms around the asymmetric carbon atom. D-isomers have the -OH group on the bottom-most chiral center (opposite direction to aldehyde structure) on the right-hand side of the Fischer projection, while L-isomers have it on the left-hand side.

Monosaccharides can also exist as pyranose or furanose ring structures, with alpha- or beta-anomers.

Epimers are isomers that differ as a result of variations in the configuration of the -OH and -H on carbon atoms 2, 3, and 4 of glucose. Mannose and galactose are important epimers of glucose.

Aldose-ketose isomerism refers to the ability of aldoses to be converted into ketoses, and vice versa. Reducing 6C sugars, such as glucose, galactose, and mannose, are important in this context.

Monosaccharides have physiological importance, as they are intermediates in glycolysis and the pentose phosphate pathway. Carboxylic acid derivatives of glucose are also important, as they play a role in the formation of glycosaminoglycans.

Glycosides are formed by condensation between the hydroxyl group of the anomeric carbon of a monosaccharide and a second compound, with the resulting compound being named based on the second group. Cardiac glycosides and antibiotics are examples of glycosides.

Deoxy sugars are monosaccharides in which one hydroxyl group has been replaced by hydrogen. Deoxyribose is an example of a deoxy sugar.

Amino sugars, also known as hexosamines, are components of glycoproteins, gangliosides, and glycosaminoglycans, and they contain an amino group attached to the sugar ring. Antibiotics such as erythromycine contain amino sugars.

Disaccharides are sugars composed of two monosaccharide residues linked by a glycoside bond. Examples include sucrose, lactose, and maltose.

The important disaccharides in the body are maltose, sucrose, and lactose. 24 Carbohydrates are essential macromolecules, serving structural and storage functions as polysaccharides.

Polysaccharides include glycans in cell walls, lubricants in joints, and storage polysaccharides.

Starch is the storage polysaccharide in plants. It is a homopolymer of glucose with helical structures and α1 → 4 and α1 → 6 linkages.

Glycogen is the storage polysaccharide in animals. It is a highly branched structure made of α-D-glucopyranose residues in α1 → 4 linkages with branching by α1 → 6 bonds.

Inulin is a polysaccharide of fructose found in plants, used for determining glomerular filtration rate but has no nutritional value.

Cellulose is a structural polysaccharide in plant cell walls, made of β-D-glucopyranose units linked by β1 → 4 bonds, insoluble, and the major component of dietary fiber.

Chitin is a structural polysaccharide in crustacean and insect exoskeletons and in mushrooms, made of β-D-glucopyranose units linked by β1 → 4 bonds.

Pectin is a polysaccharide in fruits.

The glycemic index measures the digestibility of a starchy food based on the extent it raises blood glucose concentration. It ranges from 0-100% for readily hydrolyzed starches.

Glycoconjugates are carbohydrates covalently joined to proteins or lipids and play a role in cell-cell recognition and adhesion.

Proteoglycans are large glycosaminoglycan (GAG) molecules attached to proteins, and they provide hydration and cushioning to tissues.

Glycosaminoglycans (GAGs) are complex carbohydrates, containing amino sugars and uronic acids, and may be attached to proteins to form proteoglycans.

There are various types of GAGs: hyaluronic acid, chondroitin sulfate, keratan sulfate I, II, heparin, heparan sulfate, and dermatan sulfate.

Glycoproteins are proteins with oligosaccharide chains, and glycosylation is a common posttranslational modification.

Sialic acids are derivatives of neuraminic acid and are present in many glycoproteins.

Glycoconjugates, including proteoglycans and glycoproteins, are crucial for cellular communication and function, and their structures are used for diagnosis and treatment in medicine.