Biochemistry I, Spring Term
Lecture 24
Lecture 24: Carbohydrates 2
March 20, 2013
Assigned reading: Horton 8.5, 8.6, 8.7B, Nelson. Ch 7.1-7.2.
Key Terms:








chair and boat form
pyranose & furanose
glycosidic bond
reducing end
disaccharide nomenclature
Cellulose ( 1-4 glucose)

Amylose ( 1-4 glucose)
Amylopectin & Glycogen ( 1-4 &  1-6
glucose)
Bacterial Cell Wall Structure (NAG, NAG,
tetrapeptide, pentaglycine
Conformation of Ring Structures:
The most stable conformations are the "chair" forms. The "boat" form is less stable than either chair form. In
the case of glucose, the left chair form is more stable than the right chair form.
CH2OH
CH2OH H
OH
O
OH
CH2OH
HO
OH
O
OH
H
OH
O
O
H
HO
OH
OH
OH
OH
OH
OH
Disaccharides: Linkage of the anomeric carbon
of one monosaccharide to the OH of another
monosaccharide via a condensation reaction. The
bond is termed a glycosidic bond.
The end of the disaccharide that contains the free
anomeric carbon is referred to as the reducing
end because it is capable of reducing various
metal ions, such as Cu2+.
OH
OH
OH
H
O
H
CH2OH
OH
O
O
OH
HO
O
O
CH2OH
H
O
H
OH
O
CH2OH
CH2OH
O
OH
OH
O
OH
OH
OH
OH
HO
OH
O
H2O
Cu2+
O
2H+ + 2e
Cuo
Nomenclature: To describe disaccharides you need to
specify the following:
1. The names of the two monosaccharides.
2. Their cyclic form:
O
O
a) furanose for 5 membered rings
b) pyranose for 6 membered rings
Furan
3. How they are linked together (one
pyran
anomeric is always used)
4. The configuration of the anomeric carbon.
The six simple rules for naming disaccharides are as follows:
1. The non-reducing end defines the first sugar.
2. Configuration of the anomeric carbon of the 1st sugar (,β)
3. Name of 1st monosaccharide, root name followed by pyranosyl (6-ring) or furanosyl (5-ring)
4. Atoms which are linked together, 1st sugar then 2nd sugar.
5. Configuration of the anomeric carbon of the second sugar (,β) (often omitted if the anomeric carbon is
free since α & β forms are in equilibrium.)
6. Name of 2nd monosaccharide, root name followed by pyranose (6-ring) or furanose (5-ring)
(If both anomeric carbons are involved, then the name ends in ‘oside”, not ‘ose’)
1
Biochemistry I, Spring Term
Lecture 24
March 20, 2013
Lactose (milk sugar):
CH2OH
O
CH2OH
O
HO
CH2OH
OH
OH
O
CH2OH
O
OH
OH
OH
CH2OH
O
HO
O
OH
OH
OH
O
3
4
5
CH2OH
OH
OH
OH
CH2OH
O
O
OH
O
OH
CH2OH
O
HO
OH
OH
OH
CH2OH
CH2OH
O
HO
O
O
-galactopyranosyl-(1→4)- -glucopyranose
6
CH2OH
O
HO
OH
OH
(alternate drawing)
-galactopyranosyl-(1→4)--glucopyranose
Rule # 2
O
OH
OH
OH
CH2OH
O
HO
O
OH
OH
OH
In solution:
OH
OH
OH
OH
OH
OH
-galactopyranosyl-(1→4)-glucopyranose
Lactose is the major sugar in mammalian milk.
 Infants produce lactase to hydrolyze the disaccharide to monosaccharides.
 Some adults have low levels of lactase. This leads to lactose intolerance. The ingested lactose is not
absorbed in the small intestine, but instead is fermented by bacteria in the large intestine, producing
uncomfortable volumes of CO2.
Sucrose (table sugar): The anomeric carbon
of glucose forms a glycosidic bond to the
anomeric carbon of fructose.
6
Sucrose
CH2OH
5
CH2OH
O
OH
CH2OH
 
O
OH
glucose
4 OH
3
OH
OH
O
HO
OH
1
2
OH
6 CH2OH
O
CH2OH
(alternative
drawing)
O

O

5
glucose
fructose HO 2
fructose
4
3 CH2OH 1
-glucopyranosyl-(1-2) -fructofuranoside
OH
-fructofuranosyl-(2-1) -glucopyranoside
C. Polysaccharides: Many monosaccharides
linked by glycosidic bonds. Most polysaccharides are polymers of either glucose, or
modified glucose.
Short-hand nomenclature: In the case of homo-polymers, the short-hand notation is to simply describe the
linkage between the glucose units: both the conformation of the anomeric carbon and the carbons participating
in the glycosidic bond, i.e. (1-4) instead of β-glucopyranosyl (1-4) β glucopyranose.
Energy Storage Polysaccharides
CH OH
2
1. Starch [plants] (mixture of amylose and
O
amylopectin).
O
 amylose =  (1-4) glucose.
 Similar in structure to -helix in
proteins: forms a helix with extensive hydrogen
bonding.
CH2OH
O
CH2OH
CH2OH
O
O
O
O
O
OH
CH2OH
O
OH
2. Amylopectin [plants] = amylose plus  (1-6) branches.
3. Glycogen [animals] =
 more highly branched than amylopectin.
CH2OH
OH
CH2
O
O
OH
OH
O
OH
OH
2
Biochemistry I, Spring Term
Lecture 24
March 20, 2013
Release of glucose from glycogen:
 glucose units released from non-reducing end by the enzyme glycogen phosphorylase, producing
glucose-1-phosphate (G-1-P). G-1-P is used to generate energy.
CH2OH
O
CH2OH
O
O
HO
CH2OH
CH2
CH2OH
O
O
CH2OH
O
O
O
HO
Inorganic
phosphate
(Pi)
O
O
O
CH2OH
O
O
O
O
HO
CH2
CH2OH
O
HO
O
CH2OH
O
O
CH2OH
O
O
CH2OH
O
O
O P
O
O
O
O
Structural Polysaccharides
1. Cellulose: Structural polysaccharide of plants.
  1-4 glucose, can't be digested by mammalian enzymes.
 Similar in structure to -sheets in proteins: forms flat sheets with
multiple hydrogen bonds between strands.
 Digested by symbiotic microorganisms (such as those in termites)
CH2OH
O
CH2OH
O
(alternative drawings)
OH
O
OH
(1-4)
OH
O
O
OH
O
O
CH2OH
O
O
O
O
OH
O
CH2OH
CH2OH
CH2OH
CH2OH
OH
O
OH
OH
OH
O
OH
CH2OH
O
OH
OH
O
OH
O
(1-4)
OH
OH
OH
2. Bacterial Cell Walls:
 Polysaccharide chains of alternating N-acetylglucose amine
CH OH
(NAG) and N-acetylmuraminc acid (NAM)
O OH
OH
 Muramic acid on NAM linked to a small peptide (L-Ala DGln L-Lys D-Ala)- note unusual D-amino acids.
OH
NH
 NAM peptide chains are crosslinked with pentaglycine
bridges that extend off of terminal Ala and join to L-Lys
glucosamine
sidechain on adjacent chain, forming a tough crosslinked cell
wall.
 Synthesis of bacterial cell walls is inhibited by antibiotic penicillin.
 Lysozyme – bactericidal enzyme
o hydrolyzes β-(1-4) linkages between NAM & NAG
o Transition state is half-chair intermediate.
H3C CH2OH
CH2OH
2
O OH
O
O OH
O
OH
OH
OH
HN
OH
HN
CH3
CH3
2
O
O
N-acetyl glucosamine
(NAG)
N-acetylmuramic acid
(NAM)
NAM
OH
NAG
CH2OH
O
NH
O
R1
O
O
O
O
CH3
N H
O
H
O
NAM
O
O
HN
O
O
O
HN
O
O
OH
HN
HN
O
Lys
Ala
NH2
OH
CH2OH
O
R1 O
HN
O
O
CH3
O
O
N
O
H
O
CH3
H
N H
O
N
CH3
Lys
NH2
Ala
GLY
iso-peptide GLY
bond
GLY
GLY
Gln
Ala
NAG
Ala
O
Ala
Lys
O
OH
CH3
O
H3C
CH2OH
Gln
HN
N
Gln
HN
CH3
O
H3C
NAM
O
CH3
O
OH
O
N
Ala
CH2OH
O
CH3
O
H3C
O
O
O
O
O
CH2OH
O
CH2OH
CH3
O
NAG
O
H3C
CH2OH
O
OH
HN
O
O
CH2OH
CH3
O
CH2OH
O Lysozyme
N
H
H2N
CH2OH
CH3
H
O
H
N
O C
GLY
3
CH3