Carbohydrate chemistry

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Carbohydrate chemistry is a subdiscipline of chemistry primarily concerned with the detection, synthesis, structure, and function of carbohydrates. [1] Due to the general structure of carbohydrates, their synthesis is often preoccupied with the selective formation of glycosidic linkages and the selective reaction of hydroxyl groups; as a result, it relies heavily on the use of protecting groups.



Individual saccharide residues are termed monosaccharides.

Carbohydrate synthesis

Carbohydrate synthesis is a sub-field of organic chemistry concerned specifically with the generation of natural and unnatural carbohydrate structures. This can include the synthesis of monosaccharide residues or structures containing more than one monosaccharide, known as oligosaccharides.

Glycosidic bond formation

Protecting groups


Reactions of carbohydrates

Carbohydrates are reactants in many organic reactions. For example:

Functions of carbohydrates

Carbohydrates have four major functions within the body:

  1. Energy supply, particularly for the brain in the form of glucose
  2. Avoiding the breakdown of amino acids for energy
  3. Avoiding ketosis from the breakdown of fatty acids
  4. Cellular and protein recognition

Energy supply, particularly for the brain in the form of glucose

Avoiding the breakdown of amino acids for energy

Avoiding ketosis from the breakdown of fatty acids

Cellular and protein recognition

Glycoprotein hormones may be removed by the liver from the bloodstream when the passage of time causes the breaking-off of carbohydrates from the glycoproteins.[ citation needed ]

See also

Carbohydrate structure

Carbohydrate function and biology

Related Research Articles

Biochemistry Study of chemical processes in living organisms

Biochemistry or biological chemistry, is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology and metabolism. Over the last decades of the 20th century, biochemistry has become successful at explaining living processes through these three disciplines. Almost all areas of the life sciences are being uncovered and developed through biochemical methodology and research. Biochemistry focuses on understanding the chemical basis which allows biological molecules to give rise to the processes that occur within living cells and between cells, in turn relating greatly to the understanding of tissues and organs, as well as organism structure and function. Biochemistry is closely related to molecular biology, which is the study of the molecular mechanisms of biological phenomena.

Carbohydrate Organic compound that consists only of carbon, hydrogen, and oxygen

A carbohydrate is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula Cm(H2O)n (where m may or may not be different from n). However, not all carbohydrates conform to this precise stoichiometric definition (e.g., uronic acids, deoxy-sugars such as fucose), nor are all chemicals that do conform to this definition automatically classified as carbohydrates (e.g. formaldehyde and acetic acid).

Disaccharide Complex sugar

A disaccharide is the sugar formed when two monosaccharides are joined by glycosidic linkage. Like monosaccharides, disaccharides are simple sugars soluble in water. Three common examples are sucrose, lactose, and maltose.

Polysaccharide Long carbohydrate polymers comprising starch, glycogen, cellulose, and chitin

Polysaccharides, or polycarbohydrates, are the most abundant carbohydrates found in food. They are long chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with water (hydrolysis) using amylase enzymes as catalyst, which produces constituent sugars. They range in structure from linear to highly branched. Examples include storage polysaccharides such as starch, glycogen and galactogen and structural polysaccharides such as cellulose and chitin.

A glycosidic bond or glycosidic linkage is a type of covalent bond that joins a carbohydrate (sugar) molecule to another group, which may or may not be another carbohydrate.

Glycoprotein Protein with oligosaccharide modifications

Glycoproteins are proteins which contain oligosaccharide chains (glycans) covalently attached to amino acid side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycosylation. Secreted extracellular proteins are often glycosylated.

In polymer science, the polymer chain or simply backbone of a polymer is the main chain of a polymer. Polymers are often classified according to the elements in the main chains. The character of the backbone, i.e. its flexibility, determines the properties of the polymer. For example, in polysiloxanes (silicone), the backbone chain is very flexible, which results in a very low glass transition temperature of −123 °C. The polymers with rigid backbones are prone to crystallization in thin films and in solution. Crystallization in its turn affects the optical properties of the polymers, its optical band gap and electronic levels.

Glycosylation is the reaction in which a carbohydrate, i.e. a glycosyl donor, is attached to a hydroxyl or other functional group of another molecule in order to form a glycoconjugate. In biology, glycosylation usually refers to an enzyme-catalysed reaction, whereas glycation may refer to a non-enzymatic reaction. Glycosylation is a form of co-translational and post-translational modification. Glycans serve a variety of structural and functional roles in membrane and secreted proteins. The majority of proteins synthesized in the rough endoplasmic reticulum undergo glycosylation. Glycosylation is also present in the cytoplasm and nucleus as the O-GlcNAc modification. Aglycosylation is a feature of engineered antibodies to bypass glycosylation. Five classes of glycans are produced:

An oligosaccharide is a saccharide polymer containing a small number of monosaccharides. Oligosaccharides can have many functions including cell recognition and cell binding. For example, glycolipids have an important role in the immune response.

Glycoside Molecule in which a sugar is bound to another functional group

In chemistry, a glycoside is a molecule in which a sugar is bound to another functional group via a glycosidic bond. Glycosides play numerous important roles in living organisms. Many plants store chemicals in the form of inactive glycosides. These can be activated by enzyme hydrolysis, which causes the sugar part to be broken off, making the chemical available for use. Many such plant glycosides are used as medications. Several species of Heliconius butterfly are capable of incorporating these plant compounds as a form of chemical defense against predators. In animals and humans, poisons are often bound to sugar molecules as part of their elimination from the body.

Amino sugar

In organic chemistry, an amino sugar is a sugar molecule in which a hydroxyl group has been replaced with an amine group. More than 60 amino sugars are known, with one of the most abundant being N-Acetyl-d-glucosamine, which is the main component of chitin.

Reducing sugar Sugars that contain free OH group at the anomeric carbon atom

A reducing sugar is any sugar that is capable of acting as a reducing agent. In an alkaline solution, a reducing sugar forms some aldehyde or ketone, which allows it to act as a reducing agent, for example in Benedict's reagent. In such a reaction, the sugar becomes a carboxylic acid.

Glycal is a name for cyclic enol ether derivatives of sugars having a double bond between carbon atoms 1 and 2 of the ring. The term “glycal” should not be used for an unsaturated sugar that has a double bond in any position other than between carbon atoms 1 and 2.

An Endoglycosidase is an enzyme that releases oligosaccharides from glycoproteins or glycolipids. It may also cleave polysaccharide chains between residues that are not the terminal residue, although releasing oligosaccharides from conjugated protein and lipid molecules is more common.

The terms glycans and polysaccharides are defined by IUPAC as synonyms meaning "compounds consisting of a large number of monosaccharides linked glycosidically". However, in practice the term glycan may also be used to refer to the carbohydrate portion of a glycoconjugate, such as a glycoprotein, glycolipid, or a proteoglycan, even if the carbohydrate is only an oligosaccharide. Glycans usually consist solely of O-glycosidic linkages of monosaccharides. For example, cellulose is a glycan composed of β-1,4-linked D-glucose, and chitin is a glycan composed of β-1,4-linked N-acetyl-D-glucosamine. Glycans can be homo- or heteropolymers of monosaccharide residues, and can be linear or branched.

Glycopeptides are peptides that contain carbohydrate moieties (glycans) covalently attached to the side chains of the amino acid residues that constitute the peptide.

A glycosyl donor is a carbohydrate mono- or oligosaccharide that will react with a suitable glycosyl acceptor to form a new glycosidic bond. By convention, the donor is the member of this pair that contains the resulting anomeric carbon of the new glycosidic bond. The resulting reaction is referred to as a glycosylation or chemical glycosylation.


An oxocarbeniumion is a chemical species characterized by a central sp2-hybridized carbon, an oxygen substituent, and an overall positive charge that is delocalized between the central carbon and oxygen atoms. A oxocarbenium ion is represented by two limiting resonance structures, one in the form of a carbenium ion with the positive charge on carbon and the other in the form of an oxonium species with the formal charge on oxygen. As a resonance hybrid, the true structure falls between the two. Compared to neutral carbonyl compounds like ketones or esters, the carbenium ion form is a larger contributor to the structure. They are common reactive intermediates in the hydrolysis of glycosidic bonds, and are a commonly used strategy for chemical glycosylation. These ions have since been proposed as reactive intermediates in a wide range of chemical transformations, and have been utilized in the total synthesis of several natural products. In addition, they commonly appear in mechanisms of enzyme-catalyzed biosynthesis and hydrolysis of carbohydrates in nature. Anthocyanins are natural flavylium dyes, which are stabilized oxocarbenium compounds. Anthocyanins are responsible for the colors of a wide variety of common flowers such as pansies and edible plants such as eggplant and blueberry.

Carbohydrate synthesis is a sub-field of organic chemistry concerned specifically with the generation of natural and unnatural carbohydrate structures. This can include the synthesis of monosaccharide residues or structures containing more than one monosaccharide, known as oligosaccharides.

<i>N</i>-linked glycosylation

N-linked glycosylation, is the attachment of an oligosaccharide, a carbohydrate consisting of several sugar molecules, sometimes also referred to as glycan, to a nitrogen atom, in a process called N-glycosylation, studied in biochemistry. This type of linkage is important for both the structure and function of many eukaryotic proteins. The N-linked glycosylation process occurs in eukaryotes and widely in archaea, but very rarely in bacteria. The nature of N-linked glycans attached to a glycoprotein is determined by the protein and the cell in which it is expressed. It also varies across species. Different species synthesize different types of N-linked glycan.


  1. Ruppersberg, Klaus; Rautenstrauch, Hanne; Thomsen, Stefan (5 April 2022). "Know Thy Carbs! Safer Carbohydrate Detection Methods for School Labs – Part 1". ChemistryViews. doi:10.1002/chemv.202200022.