Chapter 10: Carbohydrates

Flashcards covering key carbohydrate functional groups, structures, and biological roles from the lecture notes.

Carbohydrates

Carbon-based molecules rich in hydroxyl groups, having an aldehyde or ketone in acyclic forms, with hydrogen and oxygen in a 2:1 ratio.

Monosaccharides

Aldehydes or ketones that contain two or more hydroxyl groups; the simplest carbohydrates, with the smallest composed of three carbons.

Sugar

A generic name for sweet, soluble carbohydrates, primarily mono- and disaccharides.

Anomeric Carbon

C1 carbon in monosaccharide rings, which becomes a new chiral center upon cyclization.

Alpha (α) conformation (for D sugars)

The hydroxyl group at C1 is below the plane of the ring when drawn in standard Haworth projection.

Beta (β) conformation (for D sugars)

The hydroxyl group at C1 is above the plane of the ring when drawn in standard Haworth projection.

D stereoisomer (Fischer projection)

The hydroxyl group on the bottom chiral center points right, common form in biology.

L stereoisomer (Fischer projection)

The hydroxyl group on the bottom chiral center points left.

Hemiacetal

Formed when an aldehyde reacts with a hydroxyl group, a characteristic of cyclic forms of aldoses.

Hemiketal

Formed when a ketone reacts with a hydroxyl group, a characteristic of cyclic forms of ketoses.

Anomers

Isomers of monosaccharides that differ only in the configuration at the anomeric carbon (α or β form).

Glycosidic Bonds

Covalent bonds formed when monosaccharides react with other molecules via their hydroxyl groups, most commonly with alcohols, amines, and phosphates.

Oligosaccharides

Carbohydrates containing two or more monosaccharides linked by O-glycosidic bonds.

Disaccharides

Oligosaccharides composed of two monosaccharide units, such as maltose, sucrose, and lactose.

Sucrase

An enzyme that cleaves the disaccharide sucrose (table sugar).

Lactase

An enzyme that cleaves the disaccharide lactose (milk sugar); poor expression causes lactose intolerance.

Maltase

An enzyme that cleaves the disaccharide maltose.

Glycosyltransferases

Enzymes that catalyze the formation of glycosidic bonds, typically using a UDP-donor.

Polysaccharides

Large polymeric carbohydrates composed of many monosaccharide units, such as glycogen and starch.

Glycogen

A highly branched storage form of glucose in animals, with α-1,4-glycosidic bonds and α-1,6-glycosidic branches every ~10 glucose units.

Starch

A storage form of glucose in plants, consisting of amylose (unbranched) and amylopectin (branched).

Amylose

The unbranched component of starch, composed of glucose units linked by α-1,4-glycosidic bonds.

Amylopectin

The branched component of starch, with α-1,4-glycosidic bonds and α-1,6-glycosidic branches approximately every 30 glucose units.

Cellulose

A structural polysaccharide in plant cell walls, composed of glucose monomers linked by β-1,4-glycosidic bonds, forming strong, insoluble fibrils.

Glycoproteins

Proteins to which carbohydrates are attached, where the protein is the largest component by weight, playing various roles in membranes and secretion.

Proteoglycans

Proteins attached to glycosaminoglycans, where carbohydrates make up the majority of the weight; play structural roles or act as lubricants.

Mucins (Mucoproteins)

Proteins that are predominantly carbohydrate, characteristically attached by N-acetylgalactosamine, often serving as lubricants in mucus and saliva.

N-linked carbohydrate

A carbohydrate attached to the nitrogen atom of an asparagine (Asn) side chain, typically with a common pentasaccharide core.

O-linked carbohydrate

A carbohydrate attached to the oxygen atom of a serine (Ser) or threonine (Thr) side chain, often starting with N-acetylgalactosamine, N-acetylglucosamine, or galactose.

ABO Blood Groups

Reflect the specificity of glycosyltransferases, based on varying oligosaccharide patterns (antigens) attached to membrane proteins and lipids on red blood cells.

O (H) Antigen

The oligosaccharide foundation common to all ABO blood groups, which is Gal-GlcNAc-Gal-Fuc.

A Antigen

Formed when N-acetylgalactosamine is added to the O antigen by a specific glycosyltransferase.

B Antigen

Formed when galactose is added to the O antigen by a specific glycosyltransferase.

Glycosaminoglycans

Polysaccharides composed of repeating disaccharide units with carboxylate and/or sulfate modifications, making them negatively charged and capable of binding large amounts of water.

Aggrecan

A proteoglycan that, along with collagen, is a key component of cartilage; its glycosaminoglycan component cushions joints by reversibly binding and releasing water.

Hyaluronan (Hyaluronic acid)

A nonsulfated glycosaminoglycan, an important component of cartilage.

Reducing form of sugar

The open-chain form of a sugar that can react with oxidants, a minor form in aqueous solution.