Chapter 11 (Carbohydrates)

Galactosemia

• Genetic metabolic disorder where the body cannot metabolize galactose (not lactose intolerant → lactase)

• Serious/life threatening

Hemiacetal vs Acetal

Term	How it Forms	Groups on Carbon	Reactivity
Hemiacetal	Aldehyde + 1 alcohol	–OH + –OR	Reducing sugar, reactive
Acetal	Hemiacetal + 1 more alcohol	2 × –OR	Non-reducing, stable

Hemiacetal

• Form from aldehyde and 1 alcohol

• Contain groups OH, OR, H, R

• Reducing sugar, reactive/unstable

• Cyclic are much more stable than the open-chain

Hemiketal

• Form from ketone and 1 alcohol

• Contain groups OH, OR, R, R

Acetal

• Hemiacetal reacts with another alcohol group

• Contain group OR, OR, R, H

Chiral Column Chromatography

• Separation of enantiomers due to differences in affinity for stationary phase that stemmed from the asymmetry of both entities. (One enantiomer will elude faster than the other)

• A chiral adsorbent (chiral material that can selectively bind one enantiomer over the other from a mixture) is used in chiral chromatography

Resolving Agent

Should be enantiomerically pure

Haworth to Fisher Projections

• CH₂OH up → D classification

• CH₂OH down → L classification

Carbohydrates Function

• Provide energy through oxidation

• Supply carbon for cell components synthesis

• Serve as chemical energy storage

• Form structural elements of cells and tissues

Monosaccharide

Simple carbohydrate consisting of 3-6 carbon atoms

• Glucose

• Galactose

• Fructose

• Ribose

• Deoxyribose

Oligosaccharide

Carbohydrate formed by combination of 3-10 monosaccharide units

Enantiomers

• Non-superimposable (non-identical), mirror image of each other

• Have similar chemical and physical properties in achiral environment

• Display different physiological effects in a chiral environment, when they interact with another chiral object)

Chiral

• A term for compounds or objects that cannot be superimposed on their mirror image

• Ex: hands, gloves, shoes are chiral objects

Meso Compound

A molecule with at least two chiral centers with a plane of symmetry

Common Stereoisomers

Polycyclic (compound w/ 2 or more linked hydrocarbon rings) & steroids that are common in nature

Hexoses

Monosaccharides that contains the same formula C₆H₁₂O₆ such as glucose, fructose, and galactose

Resolution

A process of separating racemic mixture and is very expensive

• One method involves converting mixture of enantiomers into diastereomers (more distinct physical/chemical properties). More easily separable then goes through chemical transformation that regenerates original pair of enantiomers

Thalidomide

Morning sickness drug now known to cause birth defects due to levorotatory(-) enantiomer

Drugs Target Biomolecules

• Design to target enzymes due to them controlling the manner and speed which chemical reactions in the human body take place

• Another target is the biological receptors, whose function is to modulate a signal that leads to physiological response

D/L Classifications

• Based on the OH attached to chiral carbon farthest from the carbonyl group

• D-compounds have OH projecting to the right

• L-compounds have OH projecting to the left

Epimers

Diastereomers that differ in only one chiral center

Carbonyl Group

• Carbon double-bonded to an oxygen

• Written as CHO in fisher projection

Optically Active Molecules

• All chiral molecules are active

• All achiral & racemic are inactive

• Dextrorotatory (+/d): rotates light clockwise

• Levorotatory (-/l): rotates light counter-clockwise

• Distinguish enantiomers in ordinary achiral environment

Pyranose Ring

A six-membered sugar ring containing an oxygen atom

Haworth Structure

Depiction of 3-D carbohydrate structures as flat rings with groups pointing up/down around the ring

Anomeric Carbon

• A carbonyl carbon in the open-ring form, become chiral by turning to acetal or hemiacetal after the ring closes.

• Gives rise to two stereoisomers (alpha/beta)

Anomers

Special type of stereoisomer found in cyclic sugars, differs only at the carbon of an acetal/hemiacetal (anomeric carbon).

Furanose Ring

A five-membered sugar ring containing an oxygen atom

Aldoses

• Monosaccharide that contains aldehyde group

• Prefix aldo-

• Form hemiacetals on cyclization

Ketoses

• Monosaccharide that contains ketone group

• Prefix keto-

• Form hemiketals on cyclization

Monosaccharide Suffix

Name	Number of carbons
Triose	3
Tetrose	4
Pentose	5
Hexose	6
Heptose	7

Ribose

Monosaccharides that makes up the backbone of ribonucleic acid (RNA)

Deoxyribose

• Monosaccharide that makes up the backbone of deoxyribonucleic acid (DNA)

• Differs from ribose in carbon 2 such that OH is replaced by H

Disaccharides

• Lactose

• Sucrose

• Maltose

Polysaccharides

• Starch

• Cellulose

• Glycogen

Maltose

• Comprised of an alpha-D-glucose and a D-glucose molecule

• Alpha (1→4) glycosidic linkage

• Hydrolysis of starch

Lactose

• Comprise of beta-D-galactose and D-glucose molecule

• Beta (1→4) glycosidic linkage

• Constitutes 5% cow’s milk and 7% human milk, mammalian milk

Sucrose

• Comprise of alpha-D-glucose and beta-D-fructose molecule

• Alpha 1 → beta 2 glycosidic linkage

• Not a reducing sugar because the anomeric carbons of both sugars are forming an acetal

• Sweetener, sugarcane, preservative

Disaccharides Reducing-Sugar Identification

When only one anomeric carbon is involved in glycosidic linkage, it’s reducing sugar

Dextrose/Glucose

• Known as blood sugar since it’s transported by the blood to body tissues for energy requirements

• Other sugars are absorbed by the liver and converted to glucose

• Commonly used as sweetener, and baby foods

Galactose

Synthesize in the mammary glands and transform into lactose, the sugar found in milk. Also present in the nerve tissue

Fructose

• Most important ketohexose

• Known as levulose/fruit sugar due to being the sweetest monosaccharides and use as sweetener

Deoxy Sugars

One or more of the carbons missing OH

Amino Sugars

One more more carbons where the OH groups are replaced with NH₂

Reducing Sugar

• A sugar whose anomeric carbon contain OH group and are not tied up to glycosidic bond

• Oxidized by weak oxidizing agent such as Benedict’s reagent (Cu²⁺)

• A free hemiacetal/hemiketal or carbonyl in solution

Benedict’s Test

• Cannot detect specific sugar

• Both galactose & glucose will be positive

• * New glucose detection system uses test strips coated with glucose oxidase that only catalyzes oxidation of the aldehyde group glucose

Phosphate Esters

• Form by alcohols react with phosphoric acid

• The phosphodiester bonds connect the deoxyribose and phosphate group that make up the backbone of DNA

Raffinose, Stachylose, Verbascose

• Oligosaccharides composed of galactoses

• Contains galactosidic bonds which human lack galactosidase enzymes

• Cause bloating due to bacterial metabolism that produces gases

• In peas, beans

ABO Blood Group Antigens

• A-antigen has N-Acetyl-D-Galactosamine

• B-antigen has galactose

Polysaccharides

• High molecular weight

• Tasteless

• Insoluble

• Cannot pass through membrane

Starch

• Long chains of D-glucose, there are two major forms

• Amylose: long unbranched chains of D-glucose units connected by alpha(1-4)

• Amylopectin: branched polymers, the branches linked by alpha(1-6)

Glycogen

• Also called animal starch

• Homopolysaccharides that joins by glucose

• Storage carbohydrate for animals that is structurally similar to amylopectin except more highly branched

• Release D-glucose upon hydrolysis, helps mains normal blood sugar levels, provide energy for muscle for human

Cellulose

• Homopolysaccharides D-glucose linked by beta(1→4)

• Humans do not have enzyme to digest beta(1→4), therefore it serves as dietary fiber that pass through the human digestive tract largely unchanged because humans lack the enzymes to break them down.

• Adds bulk to stool and speeds intestinal transit

Hyaluronic Acid

• Heteropolysaccharides in connective tissue

• Composed alternating of N-acetyl-D-glucosamine and D-glucuronate

• Connect alternatively by beta(1→4) and beta(1→3) bonds

• The lubricating fluid that surrounds joints, in the vitreous humor present inside the eye, and is an important component of articular cartilage

Chondroitin-4-Sulfate

• Heteropolysaccharides in connective tissue

• Composed alternating of N-acetyl-D-galactosamine and D-glucuronate

• Connect alternatively by beta(1→4) and beta(1→3)

• Can be purchased without prescription to repair damaged cartilage

Heparin

• Repeating disaccharide made of D-glucuronate-2-sulfate and N-sulfo-D-glucosamine-6-sulfate with alpha (1→4)

• Used primarily as anticoagulant

Cis-Trans Isomer

Subtype of diastereomers

Racemic Mixture

Equal mass of two enantiomers

Glycosidic Bond

A hemiacetal/hemiketal on one sugar reacts with an alcohol on another form an acetal