Biol 636 ch7 terms

Carbohydrate

Polyhydroxy aldehyde or ketone, or a compound that yields one on hydrolysis; many have the formula (CH2O)n

Monosaccharide

Single polyhydroxy aldehyde or ketone unit; the simplest sugar (e.g., glucose, fructose, ribose)

Oligosaccharide

Short chain of about 2-20 monosaccharides joined by glycosidic bonds

Disaccharide

Two monosaccharides joined by an O-glycosidic bond (e.g., sucrose, lactose, maltose)

Polysaccharide

Sugar polymer of more than ~20 monosaccharide units, linear or branched (e.g., starch, glycogen, cellulose)

Aldose

Monosaccharide whose carbonyl is an aldehyde at the end of the chain (e.g., glucose)

Ketose

Monosaccharide whose carbonyl is a ketone, usually at C-2 (e.g., fructose)

Enantiomer

One of a pair of non-superimposable mirror-image stereoisomers (e.g., D- and L-glucose)

Fischer projection formulas

Open-chain drawings with the carbon backbone vertical and the most oxidized carbon on top; horizontal bonds point toward the viewer, vertical bonds away

Epimers

Diastereomers that differ in configuration at only one chiral carbon (mannose is the C-2 epimer of glucose; galactose is the C-4 epimer)

Hemiacetal

Product of an aldehyde plus an alcohol; the functional group in ring-closed aldoses

Hemiketal

Product of a ketone plus an alcohol; the functional group in ring-closed ketoses

Anomers

Cyclic isomers that differ only in configuration at the anomeric carbon (alpha and beta)

Anomeric carbon

Carbonyl carbon that becomes a new chiral center on ring closure (C-1 of glucose); site of glycosidic bond formation

Pyranose

Six-membered sugar ring (five carbons and one oxygen)

Furanose

Five-membered sugar ring (four carbons and one oxygen)

Haworth perspective formulas

Ring drawings viewed edge-on, with substituents drawn above or below the ring plane

Mutarotation

Spontaneous interconversion of alpha and beta anomers in solution through the open-chain form until equilibrium (glucose: ~36% alpha, 64% beta)

Reducing sugar

Sugar with a free anomeric carbon that can reduce oxidizing agents such as Cu2+ (Fehling's, Benedict's)

O-glycosidic bonds

Acetal/ketal linkages formed when the anomeric carbon of one sugar bonds to a hydroxyl oxygen of another; stable in base, cleaved by acid

Reducing end

End of an oligo- or polysaccharide chain that has a free anomeric carbon

Hemoglobin glycation

Nonenzymatic attachment of glucose to hemoglobin; HbA1c reflects average blood glucose over the past 2-3 months

Glycan

Carbohydrate polymer or oligosaccharide, often attached to proteins or lipids; all of a cell's glycans make up its glycome

Homopolysaccharide

Polysaccharide made of one type of monosaccharide (e.g., starch, glycogen, cellulose)

Heteropolysaccharide

Polysaccharide containing two or more different monosaccharides (e.g., glycosaminoglycans)

Starch

Plant storage polysaccharide of glucose: amylose (unbranched alpha 1-4) and amylopectin (alpha 1-4 with alpha 1-6 branches every ~24-30 residues)

Glycogen

Animal storage polysaccharide of glucose: alpha 1-4 chains with alpha 1-6 branches every ~8-12 residues; abundant in liver and muscle

Cellulose

Unbranched beta(1-4) polymer of D-glucose; main structural polysaccharide of plant cell walls

Extracellular matrix (ECM)

Gel-like network outside cells made of glycosaminoglycans, proteoglycans, and fibrous proteins such as collagen

Glycosaminoglycan

Unbranched heteropolysaccharide of repeating disaccharides (amino sugar + uronic acid), often sulfated and negatively charged

Hyaluronan

Very large, unsulfated GAG of repeating GlcUA(beta1-3)GlcNAc, not attached to a core protein; lubricates joints and cushions tissue

Chondroitin sulfate

Sulfated GAG of glucuronic acid and N-acetylgalactosamine; gives tensile strength to cartilage, tendons, ligaments, and aorta walls

Heparan sulfate

Sulfated GAG on cell surfaces and in the ECM, attached to syndecans and glypicans; binds many extracellular signaling proteins

Glycoconjugate

Carbohydrate covalently linked to a protein or lipid, serving as an information carrier

Proteoglycan

Core protein covalently attached to one or more glycosaminoglycan chains

Glycoprotein

Protein with one or more oligosaccharides (smaller, often branched) covalently attached

Glycolipid

Membrane lipid with one or more carbohydrate units attached to its head group

Syndecan

Transmembrane proteoglycan whose extracellular domain carries heparan sulfate (sometimes chondroitin sulfate) chains

Glypican

Heparan sulfate proteoglycan tethered to the outer membrane leaflet by a GPI anchor

Glycomics

Systematic study of all glycans and glycoconjugates (the glycome) in a cell or organism

Ganglioside

Membrane sphingolipid whose head group is an oligosaccharide containing sialic acid

Lectin

Protein that binds specific carbohydrates with high affinity and specificity without modifying them; reads the "sugar code"

Selectins

Plasma membrane lectins that bind specific oligosaccharides to mediate cell-cell adhesion (e.g., leukocyte rolling at sites of injury or infection)