Chapter 11: Carbohydrates and Glycoproteins

Exam 3

monosaccharides

A single aldehyde or ketone that has two or more hydroxyl groups; monosaccharides are the simplest carbohydrates and are also called sugars

aldose

monosaccharide with aldehyde group

ketose

monosaccharide with keto group

isomers

molecules with an identical molecular formula but differ in arrangement

constitutional isomers

identical molecular formulas but differ in how the atoms are ordered

stereoisomers

differ in spatial arrangement but not bonding order

enantiomers

mirror images of each other

diastereoisomers

stereoisomers that are not mirror images of each other

epimers

A pair of molecules, each with more than one asymmetric center, that differ in configuration at only one such center

anomers

Isomers that differ at a new asymmetric carbon atom (anomeric carbon) generated by intramolecular hemiacetal or hemiketal formation

furanose

five-membered ring

pyranose

cyclic hemiacetal, a six-membered ring

anomeric carbon

new asymmetric carbon that was originally the carbonyl carbon in the open-chain form

• carbon that is bonded to directly 2 separate oxygen atoms

alpha-anomeric carbon

OH on carbon points down

beta-anomeric carbon

OH on carbon points up

linear to cyclic structure

1. OH of a carbon will attack the carbonyl carbon

2. O from attacking OH will be in the ring

3. carbonyl carbon becomes anomeric carbon

4. OH on anomeric carbon

5. terminal CH2OH points up in D-isomer sugars

pyranose ring

5C, 1O

furanose ring

4C, 1O

reducing sugar

sugar that converts into a form with a free aldehyde group that is readily oxidized and can reduce another compound

Fehling’s solution

test for presence of sugars by ability to reduce Cu2+ to Cu+

oligosaccharide

A carbohydrate composed of 2 to 12 monosaccharide units

disaccharide

A carbohydrate consisting of two sugars, usually joined by an O-glycosidic linkage

glycation

random, non-enzymatic addition of carbohydrate

glycosylation

specific, enzyme catalyzed addition of carbohydrate

Hb-A1C

amount of glycated hemoglobin, biomarker for the early onset and treatment of diabetes and other disorders

glycosidic linkage/bond

A covalent linkage between an aldehyde or ketone of a monosaccharide and an oxygen, nitrogen, or sulfur atom of another molecule

o-linked glycosidic bonds

anomeric carbon attached to O of alcohol

n-linked glycosidic bonds

anomeric carbon attached to N of amine

polysaccharides

A carbohydrate composed of a large number of covalently linked monosaccharide units

glycogen

A readily mobilized storage form of glucose in which the glucose monomers are linked by α-1,4-glycosidic linkages and in which there are branches (α-1,6-glycosidic linkages) at about every 12th residue

polysaccharides

large number of covalently linked monosaccharides

homopolysaccharides

only one monosaccharide repeatedly

heteropolysaccharides

2+ different monosaccharides

glycogen alpha 1,4

main chain

glycogen alpha 1,6

branch points

starch

A homopolysaccharide that is a storage form of glucose in plant chloroplasts. Amylopectin, the branched form of starch, has approximately one α-1,6 linkage per thirty α-1,4 linkages, whereas amylose is unbranched, composed of glucose residues in α-1,4 linkage

amylose

the unbranched type of starch, consists of glucose residues in α-1,4 linkage

amylopectin

the branched form, has about one α-1,6 linkage per 30 α-1,4 linkages

cellulose

An unbranched homopolysaccharide in plants, composed of glucose residues in β-1,4 linkage

chitin

structural polysaccharide of glucose in plants

• unbranched, beta (1,4) linkages

• N-acetylglucosamine

glycoforms

generic term for glycoslated proteins

3 main classes

1. glycoproteins

2. proteoglycans

3. mucins/mucoproteins

glycoproteins

A protein that has a specific carbohydrate moiety attached

proteoglycans

A protein containing one or more covalently linked glycosaminoglycan chains

mucins/mucoproteins

One of a class of glycoproteins, consisting mainly of carbohydrate, in which the protein component is extensively glycosylated to serine or threonine by N-acetylgalactosamine

endoplasmic reticulum (ER)

An extensive system of cytoplasmic membranes that comprises about half the total cell membrane

golgi complex

a stack of membranous sacs that constitute the major sorting center for proteins that reside in cell membranes and the lumen of organelles

glycosyltransferase

Any of a number of specific enzymes that catalyze the formation of glycosidic linkages

lectin

A protein with a high affinity for a specific sugar residue

• promote cell-cell interactions

selectin

A carbohydrate-binding protein that constrains immune-system cells to the site of injury in an inflammatory response by mediating cell–cell interactions