Biochemistry: Carbohydrates, Reactions, and Polysaccharides

This set covers the fundamental vocabulary of carbohydrate biochemistry, including structure, isomerism, reactions, and the specific composition of various disaccharides and polysaccharides.

Carbohydrate

A polyhydroxyaldehyde or polyhydroxyketone, or a substance that gives these compounds on hydrolysis.

General Formula of Carbohydrates

$C_n(H_2O)_n$, where $n$ varies from $3$ to $8$.

Monosaccharides

The simplest form of carbohydrates, characterized by one carbonyl group and one or more hydroxyl groups; they serve as the building blocks for all carbohydrates.

Aldose

A monosaccharide that is a polyhydroxyl aldehyde.

Ketose

A monosaccharide that is a polyhydroxyl ketone.

Trioses

The smallest molecules regarded as monosaccharides ($n = 3$), including Glyceraldehyde (aldose) and Dihydroxyacetone (ketone).

Aldopentoses

Five-carbon monosaccharides ($5C$), such as Ribose and deoxyribose, which are key components of RNA and DNA.

Fischer Projections

A 2D representation where the carbon chain is vertical, horizontal lines represent bonds projecting forward, and vertical lines represent bonds projecting to the rear.

Enantiomers

Stereoisomers that have mirror image molecules, such as D-glyceraldehyde and L-glyceraldehyde.

Diastereomers

Stereoisomers that are non-superimposable and non-mirror images of each other.

Epimers

Isomers that differ in configuration at only one chiral carbon.

Hemiacetal

A compound formed from the reaction of an aldehyde and an alcohol, containing a hydroxyl and an ether group on the same carbon atom.

Anomeric Carbon

The new chiral center formed from the carbonyl carbon when a sugar cyclizes.

Mutarotation

The process where $\alpha$ and $\beta$ forms of a sugar interconvert through the open-chain form.

$\alpha$-anomer

A cyclic sugar isomer where the $-OH$ on the anomeric carbon is on the opposite side of the ring from the $-CH_2OH$ group.

$\beta$-anomer

A cyclic sugar isomer where the $-OH$ on the anomeric carbon is on the same side of the ring as the $-CH_2OH$ group.

Haworth Projections

Representations that depict sugars as planar rings viewed edge-on, where five-membered rings are furanoses and six-membered rings are pyranoses.

Reducing Sugar

A sugar that reduces an oxidizing agent (like Tollen's, Benedict's, or Fehling's reagent) and is itself oxidized.

Lactone

A cyclic ester formed by the oxidation of a cyclic hemiacetal.

Aldonic Acid

The product formed when the aldehyde at $C1$ of an aldose is oxidized to a carboxyl group (e.g., Gluconic acid).

Alduronic Acid (Uronic Acid)

The product formed when the primary alcohol at $C6$ is oxidized to a carboxylic acid, requiring enzymes.

Aldaric Acid

The product formed when both $C1$ and $C6$ are oxidized to carboxylic acids using powerful agents like nitric acid.

Glycosidic Bond

The bond between an alcohol group and the anomeric carbon of a sugar, forming an acetal or ketal.

Sucrose

A disaccharide composed of Glucose and Fructose connected by an $\alpha-1,2$-glycosidic linkage.

Lactose

Milk sugar; a disaccharide composed of Galactose and Glucose joined by a $\beta-1,4$-glycosidic linkage.

Maltose

Malt sugar; a disaccharide consisting of two Glucose units linked by an $\alpha-1,4$-glycosidic linkage.

Cellobiose

A disaccharide consisting of two Glucose units joined by a $\beta-1,4$-glycosidic linkage; the repeating unit of cellulose.

Cellulose

A major structural component of plants consisting of linear polymers of D-glucose joined by $\beta-1,4$-glycosidic linkages.

Amylose

A component of starch consisting of unbranched chains of $\alpha$-D-glucose joined by $\alpha-1,4$-glycosidic linkages.

Amylopectin

A highly branched starch polymer with $\alpha-1,4$ bonds in the chain and $\alpha-1,6$ glycosidic bonds at branching points.

Starch-iodine Test

A test where iodine molecules insert into the helical structure of amylose, creating a dark blue or blue-black charge transfer complex.

Chitin

A structural polymer of $N$-acetyl-$\beta$-D-glucosamine linked by $\beta-1,4$-glycosidic linkages, found in arthropod exoskeletons.

Peptidoglycan

A structural layer in bacterial cell walls consisting of repeating $NAM$ and $NAG$ units joined by $\beta-1,4$-glycosidic linkages and tetrapeptide chains.

Glycosaminoglycans

Polysaccharides containing amino sugars and negative charges (Sulfate/Carboxylate) that serve as lubricants and shock absorbers in joints.

Glycoproteins

Molecules on cell surfaces consisting of carbohydrates conjugated to proteins, essential for intercellular communication and blood group antigens.