Carbohydrate Structure/Function

Carbohydrates

"Compound containing carbon, hydrogen, and oxygen in the approximate ratio of C:2H:O (e.g., sugars, starches, and cellulose)" Carbohydrates are "carbon hydrates" Equivalents of carbon and water Most abundant class of biological molecules

Lactone

(a cyclic ester with the carbonyl group @ C1). When an aldose is in ring form and it oxidizes

Three types of stereoisomers

1) Enantiomers 2) Diastereomers 3) Epimers

What two reagents are used to detect presence of reducing sugars?

1) Tollen's reagent - Ag(NH3)+ (oxidizing agent) 2) Benedict's reagent - CuO2

Furanose rings

5 membered carbon ring structures

Pyranose rings

6-atom ring structures

What sugars can be oxidized?

Aldoses can be oxidized (open up to open chain form, oxidized to C acid). Common reducing agents include Benedict's reagent and Tollen's reagent. *ketoses can be oxidized when they undergo tautomerization* **one of the most impt biochemical rxns in the human body is oxidation of carbohydrates to yield E

D and L glyceraldehyde

All monosaccharides are assigned D or L configuration based on rlt to glyceraldehyde D and L/ Fischer projections are very common for sugars D/L designation at configuration @ highest numbered asymmetric center D/L do not specify the sign of rotation of plane polarized light (that is d and l)- ie they are not directly related to the (+) and (-) designations denoting optical rotation. Mnemonic: L OH is on LEFT

What digests amylose

Alpha amylase and Beta. Beta cleaves at non

Alpha anomer, Beta anomer

Beta anomer "beside" hydroxy is on same side as dangling CH2OH on highest numbered chiral carbon If flipped hydroxy to bottom, alpha anomer.

Polysaccharides

Carbohydrates that are made up of more than two monosaccharides

Ketoses

Carbohydrates that contain a ketone at C-2

Aldoses

Carbohydrates that contain an aldehyde at C-1

Glycosidic linkages

The linkages between the anomeric C of one sugar with any of the hydroxyl groups of another sugar. Three common bonding arrangements Way we attach these to one another is acetal/ ketal like. Typically when you want to couple, carbon (hidden carbonyl- carbon attached to two O) and an alcohol moiety. Appearance of swapping/ linking O together. Condensation/ dehydration because losing elements of H2O (like amide bond). Condensation/ dehydration rxn (reverse is hydrolysis)

Cellulose

The main structural component for plant cell walls and is the main source of fiber in humans. Composed of long chains of B glucose polymers with 1-4 linkages. H bonds hold the polymer chains together for support. Humans can digest bc they lack cellulase enzyme responsible for hydrolyzing cellulose to glucose monomers.

Sucrose

glucose + fructose linked by (b- glucose- a-fructose 1,1 bond). Non-reducting sugar.

Lactose

glucose + galactose via a glacatose-b-1,4- glucose. Requires lactase enzyme in humans to break beta linkage.

maltose

A complex carbohydrate that contains only a-1,4-glycosidic linkages

Disaccharides

A double sugar, consisting of two monosaccharides joined by dehydration synthesis. The reducing end of a disaccharide is the monosaccharide with a free anomeric carbon that is not involved in a glycosidic bond and is thus capable of converting to the open-chain form.

Fisher projection

A method of drawing organic molecules in which horizontal lines are coming out of the page (wedges) and vertical lines are going into the page (dashes

Homopolysaccharide

A polysaccharide composed entirely of one type of monosaccharide

Phosphorylation

A similar reaction in which the -OH on carbohydrate undergoes nucleophilic attack and results in the transfer of a phosphate group.

Epimers

A special type of diastereogmer where the configuration of two compounds only differs around one carbon.

Enantiomers

A special type of stereoisomer that exist between two molecules that are nonidentical, non superimposable, mirror images. Can only be between two molecules

Haworth projection

A useful method for describing the three dimensional arrangement of cyclic structures. When converting Fisher to Haworth: 1) -OH to right = down 2) -OH to left = up

Benedict's reagent

Aldehyde group of an aldose is readily oxidized, indicated by a red precipitate of Cu2O

hemiacetal

Aldose monosaccharides that undergo intramolecular reactions. Monosaccharides have an OH group (nucleophile) and carbonyl (common electrophile).

Important polysaccharides

Cellulose, starch, and glycogen polysaccharides of D glucose Differ in configuration about the anomeric C and the position of the glycosidic bond can be linear or branched

Stereoisomers (optical isomers)

Compounds with the same chemical formula but differ in terms of spatial arrangement of their component atoms.

Deoxy sugar

Contains a H that replaces an OH group on the sugar DNA

What rings are allowed?

Due to ring strain, the only cyclic molecules that are stable in solution are pyranose and furanose.

Starches (amylose and amylopectin)

Function as the main energy source for plants. Amylose = a-1,4-glucose linkages Amylopectin = a-1,6-glucose branching every 25-30 yet normal 1,4 too polysaccharide of D glucose can digest because alpha

Glycogen

Functions as the main energy storage for humans. Long and highly branched chains of a-1,4-glucose and a-1,6- glysodic linkages (more than amylopectin. 1/10 while amylopectin 1/25) branching optimizes energy efficiency of glycogen, allows more to be stored. Allows enzymes to work at multiple sites simultaneously polysaccharide of d glucose

Furanosides

Glycosides derived from furanose rings

Pyranosides

Glycosides formed from pyranose rings

D and L

In Fisher projections, all D sugars have the hydroxide of their highest numbered chiral center on the right, and all L-sugars have that hydroxide on the left.

Tollen's test

In a positive Tollen's test, aldehydes reduce Ag+ to metallic silver

Which anomer is less favored

In solution, the alpha anomer is less favored bc the hydroxyl group of the anomeric carbon is axial, adding to the steric strain of the molecule

Hemiketal

Ketose monosaccharides that undergo intramolecular reactions.

Basic structural unit of carbohydrate

Monosaccharide; the simplest monosaccharides contain three C atoms and are called trioses Aldotriose aldo= aldehyde Triose- 3 Cs in backbone The basic structure of a monosaccharide is illustrated by the simple sugar glyceraldehyde (an aldose). Chiral molecule Think of alds as a little more reactive

Reactions of carbohydrates

Monosaccharides contain alcohols and either alds or ketones, & these functional groups undergo the same reactions that they do when present in other compounds. 1)oxidation reduction 2)esterification 3)nucleophilic attack (creating glycosides)

Number of stereoisomers a compound can have?

Number of stereoisomers with common backbone = 2^n n= chiral carbons

Carbohydrate Nomenclature

Numbering of C atoms in a monosaccharide follow normal rules- carbonyl C is most oxidized so it is number 1

Aldonic acids

Oxidized aldoses

Dilute nitric acid

Powerful oxidizing agent, will oxidize both the aldehyde and primary alcohol (on c6) to C acids.

Glycoside formation

The basis for building complex carbohydrates and requires the anomeric carbon to link another sugar. dehydration rxn opposite is hydrolysis

Anomeric Carbon

The carbonyl carbon becomes chiral during the intramolecular process

Naming complex carbohydrate

The linkages are named for the configuration of the anomeric C and e numbers of the hydroxyl contain Cs involved in the bond. alpha 1-6 etc

Mutarotation

The rapid interconversion btwn different anomers of a sugar; The conversion the -OH group from alpha to beta around the anomeric carbon. Exposing hemiacetal rings to water will cause them to spontaneously cycle btwn open and closed form. Bond btwn C1 and C2 rotates freely, so either anomer can form. Mutarotation occurs more rapidly when the rxn is catalyzed with an acid or base. Mutarotation results in mixure of both anomers in equilibrium concentrations

Tautomerization

The rearrangement of bonds within a compound, usually by moving a hydrogen and forming a double bond ketoses can tautomerize to form enol

Reducing end

The reducing end of a disaccharide is the monosaccharide with a free anomeric carbon that is not involved in a glycosidic bond and is thus capable of converting to the open-chain form.

Dihydroxyacetone

The simplest ketone sugar Like most ketoses, the carbonyl C is C2 Not chiral Ketotriose 3 C, ketone instead of aldehyde Ketoses can have glycosidid bond at this carbon

Diastereomers

Two sugars that are in the same family (both are either ketoses or hexoses, and have the same # of carbons) that are not identical and not mirror images of each other.

Glucose oxidase

Used to test for glucose; enzyme which does not react with other reducing sugars.

Alditol

When the aldehyde gorup of an aldose is reduced to an alcohol.

Are ketoses also reducing sugars?

Yes; give positive Tollen's test and Benedict's test. Cant be oxidized directly to C acids, but they tautomerize under basic conditions via keto-enol shifts --> aldose form which can react in these tests to make C acids.

Hemiacetals react with alcohols to form

acetals The anomeric hydroxyl group is transformed into an alkoxy group, yielding a mixture of alpha and Beta acetals. water is LG The resulting C-O bond is glycosidic bonds, and acetals formed are glycosides **disaccharides and poly form as a result of glycosidic bonds btwn monosaccharides.

Esterification

bc carbs have OH groups, they are able to participate in rxns with C acids and C acid derivatives to form esters In body, esterification is v similar to phosphorylation of glucose-- phosphate ester is formed

Glycogen phosphorylase

cleaves glucose at the nonreducing end of glycogen and phosphorylates it, producing glucose 1 phosphate

Glyceraldehyde and Dihydroxyacetone are

isomers

Aldoses are considered a...

reducing agent bc they can be oxidized (a substance that tends to bring about reduction by being oxidized and losing electrons) So any monosaccharide with a hemiacetal ring is considered a reducing sugar