Carbohydrate Structure & Function

Question 1

Classification Strategies for Carbs

Answer 1

1. Nomenclature

2. StereoChemistry

Question 2

Nomenclature

pg. 109 (Memorize Structures)

Answer 2

1. Triose, Tetrose, Pentose, Hexose [Carbs w/ 3,4,5,6 C]

2. Aldehydes vs. Ketones

Question 3

Stereochemistry Terminology

Answer 3

Stereoisomers/Optical isomers
1. Enantiomers–non-super-imposable, mirror images
2. Diasteriomers–non-super-imposable, non-mirror
images
3. Epimers–diasteriomers with opposition at only 1 c

Properties of Stereoisomers

1. Absolute Configuration [R&S or D&L]
2. Optical Rotation [+ or -]—determined experimentally

Stereoisomer Depiction Method:
1. Fischer Projection [HA lines-wedges-out of the page;
VA lines-dashes-into the page]

Question 4

Optical/Stereoisomers

Answer 4

Carbohydrates that possess identical formulas but differ in spatial arrangement of their groups

Question 5

Absolute Configuration

Answer 5

Stereoisomer property that determines spatial arrangement of molecules around CCs

Question 6

Cyclic Sugars Terminology

Answer 6

Types of cyclic sugars:

1. Hemiacetals --- Aldehyde sugars    2. Hemiketals  ---- Ketal sugars

Most Stable Cyclic Sugars:

1. Pyranose—6 C
2. Furanose –5 C

Stereoisomer Depiction Method:

1. Haworths Projection
2. Chair Configuration–either Alpha or Beta anomers

Types of Stereoisomers:
1. Alpha Anomer–Trans/axial anomeric OH to -
CH2OH
2. Beta Anomer –Cis/equatorial anomeric OH to -
CH2OH

Question 7

Mutarotation

Answer 7

Rapid Transition of cyclic sugars b/w the alpha and beta anomeric configurations in solution

***[Beta Configuration] > [Alpha Configuration] in a solution at equilibrium b/c it exerts lesssteric hindeerance due to its equatorial anomeric OH position

Question 8

Rxns Monosaccharides Undergo

Answer 8

1. Oxidation-Reduction
2. Nucleophilic-Attack/Glycoside-Formation
3. Esterification

Question 9

Oxidation Reduction Rxns of Monosaccharides Terminology

Answer 9

Oxidation Nomenclature of open-chain sugars

1. Aldoses--->Aldonic Acids    2. Ketoses--->Ketonic Acids

Oxidation Nomenclature of cyclic sugars
1. Hemiacetals & hemiketals—>Lactones

Oxidizing Agents Used for Detecting Reducing Sugars in a Solution:
1. Tollen’s Reagent—Uses Ag((NH3)2)+—Ag+
becomes metallic silver in
presence of reducing sugars
2. Benedict’s Reagent—Cu2O precipitate forms in
presence of reducing sugars

Before being oxidized to carboxylic acids, ketones first undergo tautomerization to form an aldose/enol

Reduction Nomenclature of sugars

1. Aldose—>Alditol
2. Ketose—>Ketol

Question 10

Deoxy-Sugar

Answer 10

Sugar that replaces a aldetol’s OH group with H alone

Ex: Sugar group of DNA

Question 11

Esterification of Saccharides

Answer 11

Rxn Elements:
1. COOH + Monosaccharides —> ROR/esters

Rxn of OH groups of Monosaccharides and carboxylic acids/CA derivatives to form esters [….O…]

Ex:
1. Phosphorylation of glucose catalyzed by hexokinase or glucokinase in the liver

Question 12

Glycosidic Rxns of Monosaccharides

Answer 12

Rxn Elements
-H2O
1. ROH + Hemiacetals—> alpha or beta
Acetals [aka Glycosides]

Rxn Type: Dehydration Rxn

Potential Types of Glycosides:

1. Pyranosides
2. Furanosides

Type of Bond Formed
1. Glycosidic Bond [alpha or beta anomeric #, #]

Allow formation of di/polysaccharides*

Question 13

Complex Carbohydrates

Answer 13

Carbohydrates with 2+ sugar moieties

Complex Carbohydrates created by Glycosidic Bonds:

1. Disaccharides
2. Oligosaccharides
3. Polysaccharides

Question 14

Glycosidic Bonds in Complex Carbohydrates

Answer 14

Notation:
[Type of sugar-alpha or beta anomeric-#, #-type of
sugar]

In formation of glycosidic bonds, an alpha or beta anomeric OH of one sugar moiety forms a bond with any OH group of the other sugar moiety*

Ex: [glucose-alpha-1, 6-fructose] meaning the alpha anomeric OH of one sugar moiety bonded to the OH on C-6 of the second sugar moiety!

Question 15

Important Disaccharides Produced in the Body

Answer 15

1. Maltose
2. Lactose
3. Sucrose

pg 120

Question 16

Polysaccharides

Answer 16

Types of Polysaccharides
1. Homo vs. Heteropolysaccharides
2. Linear Vs. Branched—[Constituent monosaccharide
contains 2+ glycosidic bonds]

Biologically Important Polysaccharides:

1. Cellulose   ]    2. Glycogen   ]    ****All are composed of D-glucose    3. Starch        ]

Question 17

Cellulose

Answer 17

1. Homopolysaccharide chain of B-1,4-D-glucose held together by H-bonds
2. Main constituent of plants that serves as a source of fibers in humans given that it can’t be digested due to lack of cellulase enzyme

Question 18

Starch

Answer 18

Chemical Structure
1. Homopolysaccharide with a-1,4-D-glucose links
2. Types:
A. Amylose—
I. linear with a-1,4-D-glucose links
II. degraded with a- or b- amylase
B. Amylopectin—
I. branched with a-1,6-D-glucose links
II. degraded with branching enzymes

Real-life Implication

1. Main energy reservoir in plants
2. Digestable in humans

Presence of starch in a solution can be tested with an Iodine Reagent

Question 19

Glycogen

Answer 19

Chemical Structure
1. Chemical Nature
I. highly branched homopolysaccharide with a-
1,4-D-glucose & a-1,6-D-glucose glycosidic links
**similar to but more branched than
amylopectin*
2. Digestion
I. cleaved by Glycogen Phosphorylase at the non-
reducing end of branches

Real-Life Implication
1. Primary reservoir of energy in animals