Chemistry 501 Handout 7 Carbohydrates and Glycobiology Chapter 7

1
Chemistry 501 Handout 7Carbohydrates and
GlycobiologyChapter 7
Lehninger. Principles of Biochemistry. by Nelson
and Cox, 5th Edition W.H. Freeman and Company
2
The two families of monosaccharides are aldoses
and ketoses
Representative monosaccharides
3
Monosaccharides have asymmetric centers
Three ways to represent the two stereoisomers of
glyceraldehyde
4
(No Transcript)
5
(No Transcript)
6
(No Transcript)
7
(No Transcript)
8
(No Transcript)
9
Epimers (two sugars that differ only in the
configuration around one carbon atom)
10
Formation of hemiacetals and hemiketals
11
Formation of the two cyclic forms of D-glucose
Isomeric forms of monosaccharides that
differ only in the configuration about the
hemiacetal or hemiketal carbon atom are called
anomers.
The a and b anomes of D-glucose interconvert in
aqueous solution by a process called mutarotation.
12
Pyranoses and furanoses
13
Conformational formulas of pyranoses
14
Some hexose derivatives important in biology
15
Sugars as reducing agents
Glucose and other sugars capable of reducing
Cu2 are called reducing sugars
16
Disaccharides contain a glycosidic bond
anomeric carbon
Formation of maltose
The glycosidic bond protects the anomeric carbon
from oxidation.
Glu(a1?4)Glu
17
Some common disaccharides
reducing sugar
non reducing sugar
non reducing sugar
Non reducing sugars are named as glycosides.
Glc(a1?2b)Fru
configuration of the anomeric Carbon
carbons joined by The glycosidic bond
18
Polysaccharides (also called Glycans)
Most carbohydrates found in nature occur as
polysaccharides.
19
Some homopolysaccharides are stored forms of fuel
Electron micrographs of starch and glycogen
granules
Other homopolysaccharides (e.g. cellulose and
chitin) serve as structural elements in plant
cell walls and animal exoskeletons.
20
Amylose and amylopectin, the polysaccharides of
starch
occurs every 24 to 30 residues
Strands of amylopectin form double
helical structures with each other or with
amylose strands
amylopectin
21
Some homopolysaccharides serve structural roles
The structure of cellulose (linear, unbranched
homopolysaccharide)
Cellulose breakdown by wood fungi
Most animals cannot use cellulose as a fuel
source, because they lack an enzyme to hydrolyze
the b1?4 linkage.
22
A short segment of chitin (linear
homopolysaccharide composed of N-acetylglucosamine
residues in b linkage)
June beetle (exoskeleton of chitin)
23
Bacterial and algal cell walls contain structural
heteropolysaccharides
Peptidoglycan (alternating b1?4-linked
GlcNac-Mur2Ac crosslinked by short peptides)
exact structure depends on the bacterial species
Lysozyme kills bacteria by hydrolyzing the b1?4
bond.
The structure of agarose
24
Repeating units of some common glycosaminoglycans
of extracellular matrix
linear polymers composed of repeating
disaccharide units
Glucoronic acid
N-Acetylglucosamine
25
(No Transcript)
26
Proteoglycans are glycosaminoglycan-containing
macromolecules of the cell surface and
extracellular matrix
Proteoglycan structure
27
Two families of membrane proteoglycans
Mammalian cells have at least 30 types of
proteoglycans. Basic unit a core protein with
covalently attached glycosaminoglycan(s).
Heparan sulfate bind a variety of extracellular
ligands and thereby modulate the ligands
interaction with specific receptors of the cell
surface
28
Four types of protein interactions with NS
domains of heparan sulfate
29
Some proteoglycans can form proteoglycan
aggregates
Aggrecan interacts strongly with collagen in the
extracellular matrix of cartilage,
contributing to the development and
tensile strength of this connective tissue
Proteoglycan aggregate of the extracellular matrix
30
Interactions between cells and the extracellular
matrix
Cross-linked meshwork that gives the
whole extracellular matrix strength and resilience
31
Glycoproteins have covalently attached
oligosaccharides
oligosaccharide linkages in glycoproteins
32
Bacterial lipopolysaccharides
Principal determinant of the serotype
(immunological reactivity) of the bacterium
Lipopolysaccharide of the outer membrane of
Salmonella typhimurium
33
Role of lectin-ligand interactions in lymphocyte
movement to the site of an infection or injury
34
An ulcer in the making
Helicobacter pylori cells adhering to
the gastric surface
This bacterium causes ulcers by interactions
between a bacterial surface lectin and the Leb
oligosaccharide of the gastric epithelium.
35
Lectin-carbohydrate interactions are highly
specific and often polyvalent
Details of a lectin-carbohydrate interaction
36
Roles of oligosaccharides in recognition and
adhesion at the cell surface
37
Hydrophobic interactions in sugar residues
Galactose