Carbohydrate Chemistry: Concepts, Structure, Properties, and Functions

1. Concept:

Carbohydrates, also known as saccharides, are a vital class of organic compounds that play a major role in providing energy for living organisms. They are found in all living organisms and exist in a variety of forms.

2. Structure:

• Monosaccharides:

• The basic building blocks of carbohydrates.

• General formula: (CH2O)n, where n ≥ 3.

• Functional groups: An aldehyde or ketone group, along with multiple hydroxyl groups.

• Examples:

• Triose: D-glyceraldehyde (aldehyde), Dihydroxyacetone (ketone)

• Pentose: Ribose (CHO), Deoxyribose (lacks OH at C2), D-ribulose (CO), D-xylulose (CO)

• Hexose: Glucose (CHO), Fructose (CO), Galactose (epimer of glucose at C4), Mannose (epimer of glucose at C2)

• Optical Isomers: All monosaccharides (except dihydroxyacetone) exhibit optical isomerism.

• Ring Structure: Monosaccharides can exist in both open-chain and cyclic forms.

• Pyranose ring: 6-membered ring, formed by a bond between C1 and C5 with an oxygen atom.

• Furanose ring: 5-membered ring, formed by a bond between C1 and C4 with an oxygen atom.

• Disaccharides:

• Formed by the linkage of two monosaccharides via a glycosidic bond.

• Examples:

• Maltose: 2 α-D-glucose units linked by a 1,4-glycosidic bond.

• Lactose: β-D-galactose linked to α-D-glucose via a 1,4-β-galactosidic bond.

• Sucrose: α-D-glucose linked to β-D-fructose via a 1,2-α-β-glycosidic bond.

• Polysaccharides:

• Formed by the linkage of many monosaccharides via glycosidic bonds.

• Examples:

• Starch: Amylose (linear chain, α-1,4-glycosidic bond) and Amylopectin (branched chain, α-1,4-glycosidic and α-1,6-glycosidic bonds).

• Glycogen: Similar to amylopectin but with more branching.

• Cellulose: β-D-glucose linked by β-1,4-glycosidic bonds.

• Dextran: α-D-glucose linked by α-1,6-glycosidic bonds.

• Inulin: Fructose units linked together.

• Mucopolysaccharides: Contain osamines and uronic acids.

• Glycoproteins: Proteins linked to oligosaccharide chains.

• Glycolipids: Complex polysaccharides found in cell membranes.

3. Properties:

• Physical properties:

• Generally soluble in water, with a sweet taste (except cellulose).

• Solubility and sweetness vary depending on the structure of the carbohydrate.

• Reducing properties:

• Monosaccharides can reduce heavy metals (Cu2+, Hg2+) in alkaline conditions, forming the corresponding acid.

• This reaction is used for qualitative and quantitative analysis of sugars, like Fehling’s reagent which forms Cu2O (reddish-brown precipitate).

• Oxidation properties:

• Monosaccharides can be oxidized to form the corresponding acid (e.g., glucose to gluconic acid).

• Esterification reactions:

• Carbohydrates can react with inorganic and organic acids, with ester-phosphates being particularly significant.

• Glycosidic bond formation:

• Formed by the reaction of the hemiacetal OH group of a monosaccharide with the OH group of another molecule.

4. Functions:

• Energy source: Carbohydrates are the primary energy source for living organisms.

• Structural component: Carbohydrates form important structures like plant cell walls (cellulose), cartilage (chondroitin sulfate), and cell membranes.

• Protection: Mucopolysaccharides provide protection for organs and tissues.

• Body fluids: Carbohydrates are found in bodily fluids like blood, urine, and saliva.

• Biological activity: Glycoproteins and glycolipids play crucial roles in the biological activity of cells.

• Pharmaceuticals: Carbohydrates are used in the production of medications (e.g., Dextran).

Note:

• Carbohydrates are a diverse group of compounds with a wide range of functions.

• The structure of a carbohydrate determines its properties and function.

• Carbohydrates are essential for the life processes of all living organisms.

Additional information:

• Uronic acids:

• Function: Detoxify the body, conjugate with bilirubin in the liver, and form complex polysaccharides.

• Examples: Galacturonic acid, glucuronic acid.

• Phosphate esters:

• Function: Act as metabolic intermediates and activated forms of carbohydrate metabolic substrates.

• Examples: Glucose-6-phosphate, fructose-1,6-bisphosphate.

• Osamines:

• Function: Form complex polysaccharides.

• Examples: Glucosamine, galactosamine.

• Sialic acids:

• Function: Found in complex polysaccharides of animal cell membranes.

• Examples: Neuraminic acid.

• Glycoproteins:

• Function: Biological activity, antigens, cellular structures.

• Examples: Hormones FSH, LH, TSH, blood group antigens A, B, O.

• Glycolipids:

• Function: Cellular structures, cell recognition.

• Examples: Glycolipids found in red blood cell membranes.

• Dextran:

• Function: Blood plasma substitute in medicine.

• Inulin:

• Function: Used to assess glomerular filtration rate.

• Mucopolysaccharides:

• Function: Structural components of animal tissue ground substance.

• Examples: Hyaluronic acid, chondroitin sulfate, heparin.

Hope this additional information is helpful to you!