Carbohydrates: Structure, Classification, and Functions

Flashcards covering the definitions, classifications, structures, and functions of carbohydrates including monosaccharides, disaccharides, oligosaccharides, and polysaccharides.

Carbohydrates

Biomolecules containing a group of naturally occurring carbonyl compounds (aldehydes or ketones) and several hydroxyl groups, consisting of carbon (C), hydrogen (H), and oxygen (O) atoms.

Empirical formula of Carbohydrates

$C_m(H_2O)_n$ or $(CH_2O)_n$, usually with a hydrogen-oxygen atom ratio of $2:1$.

Monosaccharides

The simplest form of carbohydrates consisting of one sugar molecule which can be present as linear chains or ring-shaped molecules.

Anomeric carbon

Carbon-1 in a sugar ring that becomes asymmetric during the process of ring formation.

Alpha ($\alpha$) position

An arrangement where the hydroxyl group ($-OH$) is below the plane of carbon number 1 in a sugar ring.

Beta ($\beta$) position

An arrangement where the hydroxyl group ($-OH$) is above the plane of carbon number 1 in a sugar ring.

Glucose ($C_6H_{12}O_6$)

An important source of energy in humans and plants; plants synthesize it using carbon dioxide and water.

Galactose

A monosaccharide found in milk sugar (lactose).

Fructose

A monosaccharide found in fruits and honey that provides sweetness.

Ribose

A monosaccharide that serves as a structural element of nucleic acids and some coenzymes.

Mannose

A constituent of mucoproteins and glycoproteins required for the proper functioning of the body.

Disaccharides

Carbohydrates consisting of two sugar units joined together by a covalent bond through a dehydration reaction.

Glycosidic bond

The covalent bond formed between two sugar molecules when the hydroxyl group of one combines with the hydrogen of another, releasing water.

Sucrose

A non-reducing disaccharide composed of one D-glucose molecule and one D-fructose molecule; systematic name is $0$-$\alpha$-D-glucopyranosyl-($1-2$)-D-fructofuranoside.

Lactose

A disaccharide composed of one D-galactose molecule and one D-glucose molecule; systematic name is $0$-$\beta$-D-galactopyranosyl-($1-4$)-D-glucopyranose.

Maltose

A reducing disaccharide composed of two glucose units joined by an $\alpha$-1,4 linkage.

Reducing sugar

A disaccharide that has a free hemiacetal unit serving as a reducing aldehyde group, such as maltose and cellobiose.

Non-reducing Sugar

Disaccharides that do not have a free hemiacetal because they bond through an acetal linkage between their anomeric centers, such as sucrose and trehalose.

Oligosaccharides

Compounds that yield $3$ to $10$ molecules of monosaccharides upon hydrolysis, normally present as glycans linked to lipids or proteins.

Glycosylation

The process in which a carbohydrate is covalently attached to an organic molecule, creating structures such as glycoproteins and glycolipids.

N-Linked Oligosaccharides

Attachment of oligosaccharides to asparagine via a beta linkage to the amine nitrogen of the side chain.

O-Linked Oligosaccharides

Attachment of oligosaccharides to threonine or serine on the hydroxyl group of the side chain, occurring in the Golgi apparatus.

Polysaccharides

A chain of more than $10$ carbohydrates joined through glycosidic bonds, also known as glycans.

Homopolysaccharides

Polysaccharides composed of repeating units of only one type of monomer, such as cellulose, starch, and glycogen.

Cellulose

A linear, unbranched homopolysaccharide of glucose units joined by $\beta$ 1-4 linkages; a major structural component in the biosphere.

Starch

A plant storage polysaccharide made of D-glucose units with $\alpha$-linkages, composed of amylose ($15$-$20$%) and amylopectin ($80$-$85$%).

Amylose

A component of starch consisting of unbranched chains of glucose with $1-4$ glycosidic bonds.

Amylopectin

A branched component of starch containing both $1-4$ and $1-6$ glycosidic bonds, with branches occurring approximately every $20$ subunits.

Glycogen

A highly branched storage polysaccharide in animals, bacteria, and fungi with $1-4$ and $1-6$ bonds and branches every $10$ subunits.

Heteropolysaccharides

Polysaccharides composed of two or more repeating units of different types of monomers, such as peptidoglycan and agarose.

Peptidoglycan

A heteropolymer of alternating units of N-acetylglucosamine (NAG) and N-acetylmuramic acids (NAM), linked by $\beta$-1,4-glycosidic linkages.

Glycosaminoglycans (GAG)

Negatively charged unbranched heteropolysaccharides composed of repeating disaccharide units, such as hyaluronic acid and heparin.

Chitin

A structural homopolysaccharide involved in the synthesis of fungal cell walls and animal structures.

Agarose

A polysaccharide composed of repeating units of agarobiose, which consists of D-galactose and $3,6$-anhydro-L-galactopyranose.