CH 7 Study Guide

empirical formula of carbohydrates

(CH2O)n

hyaluron

(hyaluronic acid) alternating residues of D-glucuronic acid and N-acetylglucoasmine

steric factors and h-bonding influence homopolysaccharide folding (3)

1/ 3D structures stabilized by weak interactions w/in or b/t molecules 2/ h-bonding is especially important due to the high # of OH groups in polysaccharides 3/ free rotation about both C-O bonds linking residues is limited by steric hindrance by substituents

what makes sugar sweet? (2)

1/ TAS1R2 and TAS1R3 encode sweet-taste receptors 2/ binding of a compatible molecule generates a "sweet" electrical signal in the brain, which requires a steric match

chain-ring equilibrium and reducing (3)

1/ aldehydic monosaccharides are reducing agents 2/ Fehling's test 3/ Tollen's test

monosaccharides have asymmetric centers (4)

1/ all monosaccharides (except dihydroxyacetone) contain > 1 chiral carbon atom 2/ enantiomers 3/ in general, a molecule with n chiral centers can have 2n stereoisomers 4/ Fischer projections are used to represent 3D sugar structures on paper

different energetic conformation of a disaccharide (3)

1/ bulkiness and electronic effects at the anomeric carbon place constraints on psi and phi 2/ low-energy conformation is extended and maximizes h-bonding 3/ high-energy conformation is sterically hindered

other types of glycosaminoglycans (5)

1/ chondroitin sulfate, dermatan sulfate, keratan sulfate, and heparan sulfate differ from hyaluronan: -2/ generally much shorter polymers -3/ contain esterified sulfate groups -4/ covalently linked to specific proteins (proteoglycans) -5/ one or both monomer units differ from hyaluronan

D isomers (3)

1/ configuration at reference carbon is the same as D-glyceraldehyde 2/ on the right (dextro) in a projection formula 3/ most hexoses of living organisms

L isomers (2)

1/ configuration at reference carbon is the same as L-glyceraldehyde 2/ on the left (levo) in a projection formula

heteropolysaccharides (2)

1/ contain 2+ kinds of monomers 2/ provide extracellular support

homopolysaccharides (2)

1/ contain only a single monomeric sugar species 2/ serve as storage forms and structural elements

O-glycosidic bonds (3)

1/ covalent linkage joining two monosaccharides 2/ formed when a hydroxyl group of one sugar molecule reacts with the anomeric carbon of the other 3/ readily hydrolyzed by acid

hemiacetals or hemiketals (3)

1/ derivatives formed by a general reaction between alcohols and aldehydes or ketones 2/ product of the first alcohol molecule addition 3/ five- or six-membered ring forms if the -OH and carbonyl groups are on the same molecule

hemoglobin glycation in uncontrolled diabetes (4)

1/ diabetes is characterized by high blood [glucose] 2/ glycation 3/ glycosylation 4/ measurement of glycated hemoglobin is a better test to the progress of diabetes than blood [glucose] because its an outcome, not a symptom

colorimetric glucose analysis (4)

1/ enzymatic methods used to quantify glucose (reducing sugars) 2/ electrochemical detection is used in portable glucose sensors 3/ glucose oxidase catalyzes the conversion of glucose to glucono-D-lactone and hydrogen peroxide. 4/ hydrogen peroxide oxidizes organic molecules into highly colored cmpds whose concentration can be measured colorimetrically

glycoasminoglycans are heteropolysaccharides of the extracellular matrix (2)

1/ extracellular matrix 2/ basement membrane (specialized ECM) also contains heteropolysacchrides

furanoses (2)

1/ five-membered ring compounds 2/ form when the C-5 reacts with the keto group at C-2

reducing end (2)

1/ formation of a glycosidic bond renders a sugar nonreducing 2/ the end of a disaccharide or polysaccharide chain with a free anomeric carbon

extracellular matrix (ECM) (2)

1/ gel-like material in the extracellular space of tissues that holds cells together and provides a porous pathway for nutrient and O2 diffusion -2/ composed of an interlocking meshwork of heteropolysaccharides (ground substance) and fibrous proteins

glycoproteins (3)

1/ have one or several oligosaccharides joined covalently to a protein 2/ found on the outer face of the plasma membrane, in ECM, in blood, and in organelles (Golgi complexes, secretory granules, and lysosomes) 3/ oligosaccharide portions are heterogenous and rich in information

storage of glucose as polymers avoids high osmolarity (3)

1/ hepatocytes in the fed state store glycogen equivalent to a glucose concentration of 0.4 M 2/ 0.4 M glucose in the cytosol would elevate the osmolarity -3/ the resulting osmotic entry of water might rupture the cell

glycosaminoglycans (6)

1/ heteropolysaccharides in ECM 2/ linear polymers composed of repeating disaccharide units 3/ one monosaccharide is always either Glg-NAc or GaI-NAc and the other is usually a uronic acid 4/ unique to animals and bacteria 5/ except for hyaluronan, they contain esterified sulfate groups 6/ provide viscosity, adhesiveness, and tensile strength to the extracellular matrix

types of glycoaminoglycans (2)

1/ hyaluron 2/ the others

the common monosaccharides have cyclic structures (3)

1/ in aqueous solution, monosaccharides can form cyclic structures of 5- or 6-membered rings 2/ reaction between the aldehyde/ketone group and the hydroxyl group at C-5 or C-6 forms a hemiacetal linkage 3/ mutarotation

sugars can be phosphorylated (2)

1/ key intermediates in energy generation and biosynthesis 2/ phosphate keeps sugar inside the cell since sugar transporters are selective for neutral molecule only

three common disaccharides (2)

1/ lactose is a reducing disaccharide 2/ sucrose and trehalose are nonreducing sugars

chitin (2)

1/ linear homopolysaccharide composed of N-acetylglucosamine residues in (β1→4) linkage 2/ acetylated amino group makes chitin more hydrophobic and water-resistant than cellulose

haworth perspective formulas (3)

1/ more accurate representation of cyclic sugar structure than Fischer projections 2/ six-membered ring is tilted to make its plane almost perpendicular to that of the paper 3/ bonds closest to the reader are drawn thicker than those farther away

linear structure of cellulose (2)

1/ most stable conformation is a straight, extended chain 2/ each chair is turned 180° relative to its neighbors

glycogen (4)

1/ polymer of (α1→4)-linked glucose subunits, with (α1→6)-linked branches 2/ "animal starch" 3/ more extensively branched 4/ more compact than starch

acetal or ketal (2)

1/ product of the second alcohol molecule addition 2/ forms a glycosidic bond

conformational formulas for pyranoses (3)

1/ pyranose rings tends to assume either or two "chair" conformations 2/ interconvertible without breaking covalent bonds 3/ requires energy input to put a greater # of groups axial

α and β stereoisomeric configurations (4)

1/ reaction with the first alcohol molecule creates an additional chiral center (the carbonyl carbon) 2/ produces either of two stereoisomeric configuration: α and β 3/ anomers 4/ anomeric carbon

peptidoglycan (4)

1/ rigid component of bacterial cell walls 2/ reinforces the bacterial cell wall 3/ heteropolysaccharide of alternating (β1→4)-linked Glc-Nac and MurNAc residues 4/ cross-linked by short peptides

pyranoses (2)

1/ six-membered ring compounds 2/ form when the hydroxyl group at C-6 reacts with the keto group at C-2

phosphorylated derivatives (3)

1/ some sugar intermediates are phosphate esters eg. glucose 6-phosphate 2/ stable at neutral pH and bear a negative charge 3/ functions to trap sugar inside the cell because most cells do not have membrane transporters for phosphorylated sugars

some homopolysaccharides are storage forms of fuel (2)

1/ storage polysaccharides: starch in plant cells and glycogen in animal cells 2/ starch and glycogen molecules are heavily hydrated because they have many exposed hydroxyl groups available to h-bond

reducing sugars (4)

1/ sugars that are, or can form aldehydes 2/ undergo a characteristic redox reaction where free aldehyde groups react with Cu2+ under alkaline condition 3/ reduction of Cu2+ to Cu+ forms a brick-red precipitate 4/ ketoses that can tautomerize to form aldehydes are also reducing sugars

polysaccharides generally do not have defined lengths or molecular weights (3)

1/ this distinction b/t proteins and polysaccharides is a consequence of the mechanisms of assembly 2/ there is no template for polysaccharide synthesis 3/ the program for polysaccharide synthesis is intrinsic to the enzymes that catalyze the polymerization of monomer units

cellulose (6)

1/ tough, fibrous, water-insoluble substance 2/ intrachain h-bonds that produce straight, stable fibers that exclude water 3/ linear, unbranched homopolysaccharide, consisting of 10k to 15k D-glucose units 4/ glucose residues have the β configuration 5/ linked by (β1→4) glycosidic bonds 6/ animals do not have the enzyme to hydrolyze (β1→4) glycosidic bonds

trioses

3C backbone ex/ D-glyceraldehyde (aldotriose) & dihydroxyacetone (ketotriose)

tetroses

4C backbone

pentoses

5C backbone ex/ D-Ribose (aldopentose) component of RNA & 2-Deoxy-D-ribose (aldopentose) component of DNA

hexoses

6C backbone ex/ D-Glucose (aldohexose) & D-Fructose (ketohexose)

heptoses

7C backbone

Principle 3

storage of low molecular weight metabolites in polymeric form avoids the very high osmolarity that would result from storing them as individual monomers. if the glucose in liver glycogen were monomeric, the glucose concentration in liver would be so high that cells would swell and lyse from the entry of water by osmosis.

how can carbohydrates be joined to alcohols and amines?

glycosidic bonds such as N-glycosidic and O-glycosidic

two groups of stereoisomers

D and L isomers

organisms contain a variety of hexose derivatives

all groups equatorial in β-D-glucose

glycation

a non-enzymatic side rxn b/t the aldehyde of glucose and (Nu-) amines on proteins. causes proteins to malfunction.

Tollen's test

aldehyde can reduce Ag+ to Ag0

Fehling's test

aldehyde can reduce Cu2+ to Cu+

carbohydrates

aldehydes or ketones with at least two hydroxyl groups, or substances that yield such compounds on hydrolysis

how do sugar stereoisomers arise?

because many of the carbon atoms to which the hydroxyl groups are attached are chiral centers

glycoconjugate

biologically active molecule consisting of an informational carbohydrate joined to a protein or lipid

aldonic and uronic acids

both form stable intramolecular esters called lactones

Principle 1

carbohydrates can have multiple chiral carbons; the configuration of groups around each carbon atom determines how the compound interacts with other biomolecules. as we saw for L-amino acids in proteins, with rare exceptions, biological evolution selected one stereochemical series (d-series) for sugars.

aldose

carbonyl group is at an end of the carbon chain (in an aldehyde group)

ketose

carbonyl group is at any other position (in a ketone group)

some homopolysaccharides serve structural roles

cellulose

reference carbon

chiral center most distant from the carbonyl carbon

starch

contains two types of glucose polymer: amylose & amylopectin

converting D-hexose fischer projections to haworth perspective formulas (step 1)

draw the six-membered ring (five carbons, and one oxygen at the upper right)

uronic acids

form following oxidation at C-6

aldonic acids

form following oxidation of the carbonyl carbon of aldoses

naming reducing oligosaccharides (step 3)

indicate the parentheses the two carbon atoms joined by the glycosidic bond, with an arrow connecting the two numbers

anomers

isomeric forms of monosaccharides that differ only in their configuration about the hemiacetal or hemiketal carbon atom

amylopectin

larger than amylose with (α1→4) b/t glucose residues and highly branched due to (α1→6) linkages

amylose

long, unbranched chains of D-glucose residues connected by (α1→4) D-glucose linkages

hyaluronin in synovial fluid

lubricates and cushions during movement of joints and other tissues

Principle 2

monomeric subunits, monosaccharides, serve as the building blocks of large carbohydrate polymers. the specific sugar, the way the units are linked, and whether the polymer is branched determine its properties and thus its function.

glycans

most carbohydrates in nature occur as polysaccharides (Mr > 20k)

helical structure of starch and glycogen

most stable 3D structure for the (α1→4)-linked chains of starch and glycogen: six residues/turn

naming reducing oligosaccharides (step 2)

name the nonreducing residue using "furano" or "pyrano"

naming reducing oligosaccharides (step 4)

name the second residue and repeat for additional residues

converting D-hexose fischer projections to haworth perspective formulas (step 2)

number the carbons in a clockwise direction beginning with the anomeric carbon

disaccharides

oligosaccharides with two monosaccharide units ex/ sucrose (D-glucose and D-fructose)

carbohydrates can be joined to

phosphates, alcohols, and amines

converting D-hexose fischer projections to haworth perspective formulas (step 5)

place the aromeric hydroxyl group; for a β structure, the hydroxyl group is placed on the same side of the ring as C-6; for a α structure, it is placed on the opposite side

converting D-hexose fischer projections to haworth perspective formulas (step 3)

place the hydroxyl groups; hydroxyl groups on the right in a Fischer projection are placed pointing down and those on the left are placed pointing up

converting D-hexose fischer projections to haworth perspective formulas (step 4)

place the terminal - CH2OH group; project upward for the D enantiomer, downward for the L enantiomer

Principle 5

polysaccharides assume three-dimensional structures with the lowest-energy conformations, determined by covalent bonds, hydrogen bonds, charge interactions, and steric factors. starch folds into a helical structure stabilized by an internal hydrogen bonds; cellulose assumes an extended structure in which intermolecular hydrogen bonds are more important

oligosaccharides

short chains of monosaccharide units, or residues, joined by glycosidic bonds

monosaccharides

simple sugars, consist of a single polyhydroxyl aldehyde or ketone unit ex/ D-glucose

example of glucose polymers

starch and glycogen

enzymes that act on sugars are

stereospecific

epimers

sugar isomers that differ only in the configuration around one carbon atom

polysaccharides

sugar polymers with > 10 monosaccharide units ex/ cellulose (linear), glycogen (branched)

anomeric carbon

the carbonyl carbon atom

glycosylation

the intentional enzymatic addition of carbohydrates to biomolecules.

mutarotation

the interconversion of α and β anomers

Principle 4

the sequences of complex polysaccharides are determined by the intrinsic properties of the biosynthetic enzymes that add each monomeric unit to the growing polymer. this is in contrast with DNA, RNA, and proteins, which are synthesized on templates that direct their sequence.

enantiomers

two different optical isomers that are mirror images

naming reducing oligosaccharides (step 1)

with the nonreducing end on the left, give the configuration (α or β) at the anomeric carbon joining the first unit to the second