Carbohydrates Flashcards
Trioses
- simplest monosaccharide
- contain 3 Carbons
Tetroses
contain 4 Carbons
Pentoses
contain 5 Carbons
Hexoses
contain 6 Carbons
Aldoses
- carbs that contain an aldehyde group as their most oxidized functional group
- aldehyde carbon is C1 and can participate in glycosidic linkages
Ketoses
- carbs that contain a ketone as their most oxidized functional group
- “keto” glucose
- fructose is this type of carb
Stereoisomers
- optical isomers
- compounds with same chemical formula but differ in spatial arrangement of their component atoms
- include diastereomers and enantiomers
Enantiomers
- isomerism between stereoisomers that are non-identical
- non-superimposable mirror images of each other
- all chiral carbons are reversed
- Ex. D- and L- sugars
Absolute Configuration
- use of L- and D- assignment
- reference the C above the CH2OH group to determine L or D assignment
- L: -OH group on C points left
- D: -OH group on C points right
Relative Configuration
- use of R and S assignment
- optical activity
- if stereocenter of molecule is R then it is (+)
- if stereocenter of molecule is S then it is (-)
Diastereomers
- sugars that differ at one or more chiral carbons
- non-superimposable, not mirror images
Epimers
- diastereomer subtype (isomers are NOT mirror images)
- sugars differ at only one chiral carbon
- Ex. D-galactose is a C4 Epimer of glucose
- Ex. D-Mannose is a C2 Epimer of glucose
Anomers
- epimer subtype
- special class of C1 epimers
- anomeric carbon is the one that has -OH group pointing up in one epimer and -OH group pointing down in the other epimer
- labeled as alpha or beta
Alpha-Anomer
-OH on the anomeric carbon is trans to the free -CH2OH group (axial and down)
Beta-Anomer
-OH on the anomeric carbon is cis to the free -CH2OH group (equatorial and up)
How does the side groups change in a monosaccharide when you convert it from its straight chain Fischer projection to the Hawthorn Projection?
any group on the right in the Fischer Projection will point down in the Hawthorn Projection
Mutarotation
- spontaneous change of configuration between the alpha or beta anomer because of free rotation of the single bond between C1 and C2
- occurs more rapidly when rxn is catalyzed by an acid or base
Monosaccharides
- contain alcohols and either aldehydes or ketones
- single carbohydrate units
Reduction of Monosaccharides
- decreases the number of C-O bonds
- increases the number of C-H bonds
Oxidation of Monosaccharides
- increases the number of C-O bonds
- decreases the number of C-H bonds
What monosaccharide forms when the hydroxyl group on the anomeric carbon is oxidized?
Lactone
Reducing Sugars
- monosaccharides with a a hemiacetal ring
- must have the property of being able to be oxidized
- capable of transferring hydrogens (electrons) to other compounds
- the reducing end consists of a hemiacetal
- Ex. aldoses
What two reagents can be used to detect the presence of a reducing sugar?
- Tollen’s Reagent
- Benedict’s Reagent
Tollen’s Reagent
[Ag(NH3)2]+
-in the presence of a reducing sugar (aldehydes) the reagent is reduced and produces a silvery mirror
Benedict’s Reagent
Cu(OH)2
- identifies reducing sugars that have free hemiacetals
- in the presence of a reducing sugar, a red precipitate of Cu2O will form
Tautomerization
- rearrangement of bonds in a compound
- usually involves moving a H and forming a double bond
- occurs when a ketose (nonreducing sugar) is converted to an enol then aldose product (reducing sugar)
Enol
an organic compound that contains a hydroxyl group bonded to a carbon atom having a double bond and that is usually characterized by the grouping C=C(OH)
Deoxy Sugar
sugars with a -H group replacing an -OH group at the 2’ C
Esterification of Monosaccharides
reaction by which a hydroxyl group reacts with either a carboxylic acid or a carboxylic acid derivative to form an ester
Phosphorylation of Monosaccharides
- reaction in which a phosphate ester is formed by transferring a phosphate group from ATP onto a sugar
- example of esterification – hydroxyl group acts as nucleophile and attacks terminal phosphate group in ATP, producing a substitution reaction at C6 (now a glycosidic linkage between C6 and phosphate group
Acetals (Ketals)
formed by the reaction of hemiacetals (hemiketals) with alcohols under acidic conditions
Glycoside
- molecule that contains a bond between a functional group and a carbon in a sugar
- bond is termed glycosidic linkage
Glycosidic Linkages
- formed when an alcohol functional group attached to an anomeric carbon of a sugar reacts with another alcohol functional group
- linkages join monosaccharides together to create disaccharides or polysaccharides
What type of reaction occurs during glycoside formation?
dehydration reaction
Disaccharides
two monosaccharides linked via glycosidic bonds
Which direction do alpha-glycosidic linkages point?
down
Which direction do beta-glycosidic linkages point?
up
Lactose
Lauren Gets Gold
Lactose = Glucose + Galactose
- disaccharide
- formed in reaction between galactose and glucose with a beta-1,4 glycosidic linkage
- galactose-beta-1,4-glucose
Sucrose
Sarah Gets Fat
Sucrose = Glucose + Fructose
- disaccharide
- formed in a reaction between glucose and fructose with an alpha-1,2 glycosidic linkage
- glucose-alpha-1,2-fructose
Maltose
- disaccharide
- formed in a reaction between 2 glucose molecules with an alpha-1,4 glycosidic linkage
- glucose-alpha-1,4-glucose
Polysaccharides
long chains of monosaccharides linked together by glycosidic bonds
Cellulose
- polysaccharide
- main substance in plant cell walls
- chain of beta-D-glucose molecules linked by beta-1,4 glycosidic bonds
- H bonds hold the polymer chains together
Can humans digest cellulose?
No, we only have the enzyme necessary to cleave alpha-glycosidic linkages
Starches
- polysaccharides
- digestible by humans
- linked alpha-D-glucose monomers
Amylose
- starch
- plant storage form of starch
- linear glucose polymer linked via alpha-1,4 glycosidic bonds
Amylopectin
- starch
- contains alpha-1,4 glycosidic linkages between glucose monomers and every 20-30 glucoses there is branching due to alpha-1,6 glycosidic linkages
- easier to digest than amylose b/c of branched structure
What reagent can test for the presence of starch?
iodine
Amylase
- digestive enzyme (secreted by the salivary glands, and by the pancreas –> goes to small intestine)
- cleaves alpha-1,4 glycosidic bonds
Beta-Amylase
cleaves amylose at the non-reducing end of the polymer to yield maltose
Alpha-Amylase
- hydrolyses alpha bonds of large, alpha-linked polysaccharides, such as starch and glycogen, yielding glucose and maltose
- major form of amylase found in humans and other mammals
Glycogen
- polysaccharide
- carbohydrate storage unit in animals
- made up of alpha-1,4 linked glucose molecules with apha-1,6 linkage occurring every 10 glucose monomers making it highly branched
- more soluble in solution and easy to digest due to highly branched nature
Glycogen Phosphorylase
- cleaves glucose from the non-reducing end of a glycogen branch and phosphorylates it
- produces glucose 1-phosphate
What kind of sugar is sucrose?
NON-REDUCING SUGAR!
