CHAPTER 3 - CARBOHYDRATES/GLYCANS
A: Mono- and Disaccharides
Learning Goals/Objectives for Chapter 3A: After class and
this reading, students will be able to
- define a sugar
- apply knowledge about reactions at carbonyl carbons of
aldehyde and ketones in the formation of hemiacetals/hemiketals
and acetals/ketals from organic chemistry to draw mechanics
showing cyclization of aldoses and ketoses and (hemiacetal/hemiketal
formation) and of polymerization of aldoses and ketones to form
dissacharide and polysaccharide (acetal/ketals).
- draw open chain, Haworth (planar), and puckered (nonplanar)
representations of 6 member cyclic sugars
- know the names of common trioses, ribose (5C) and hexoses
and draw open chain, Haworth, and puckered representations of
- differentiate between enantiomers, diastereomers and anomers
of the hexoses
- explain the difference between reducing and nonreducing
- draw the structure and name common sugar derivatives of the
The link below is an extraordinary and free resource on glycobiology.
It defines the word "glycan" as a "generic term for any
sugar or assembly of sugars, in free form or attached to another
molecule" and "is used interchangeably ... with
A3. Monosaccharide Derivatives
Many derivatives of monosaccharides are found in nature. These include
- oxidized forms in which the aldehyde and/or alcohol functional
groups are oxidized to carboxylic acids
- phosporylated forms in which phosphate is added by ATP to form
- amine derivatives such as glucosamine or galactosamine
- acetylated amine derivatives such as N-Acetyl-GlcNAc (GlcNAc) or
- lactone forms (intramolecular esters) in which an OH group attacks a
carbony C that was previously oxidized to a carboxylic acid
- condensation products of sugar derivatives
with lactate (CH3CHOHCO2-) and pyruvate, (CH3COCO2- ), both from the
glycolytic pathway, to form muramic acid and neuraminic acids, (also
called sialic acids), respectively.
Figure: Sugar Derivatives
In the above figure, N-acetylmuramic acid, found in bacterial cell walls,
consists of GlcNAc in ether link at C3 with lactate, while N-acetylneuraminic
acid results from an intramolecular cyclization of a condensation product of
ManNAc and pyruvate.
Figure: Is sialic acid the big difference between humans and
What happens when non-vegan humans eat animal products (meat, milk) with
N-glycoyl neuraminic acids (Neu5Gc)? Varki et al found that some gets
incorporated into human membrane glycans (see next Chapter).
Sialic acids on surface proteins can serve as "receptors" that allowing
binding of self-cells as well as foreign cells or proteins that have evolved
to bind them. Byres et al discovered that a toxin, SubAB, secreted by
E. Coli 0157, can bind Neu5Gc. Hence eating meat products can make us
more susceptible to bacteria that recognize Neu5Gc.
Chapter 3A: Monosaccharide Sections
Biochemistry Online Table of Contents
Archived version of full Chapter 3A:
Mono- and Disaccharides
Biochemistry Online by Henry Jakubowski is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.