Biochemistry:%20A%20Short%20Course

1
Carbohydrates Structure and Function

• Sugar features
• 3 carbon minimum aldehyde or ketone present
  (C H2O)n
• Energy storage lubricant signaling

2
Carbohydrate Isomeric Forms
H
3
D-Aldose Sugar Configurations
Numbering begins at the carbonyl end of the
sugar Penultimate carbon (pink) sets L-
versus D-form
4
Isomer Classification
Constitutional Isomers? Enantiomers? Diastereome
rs? Epimers? Anomers? What is the Enantiomer
of D-Erythrose?
5
D-Ketose Sugar Configurations
Carbonyl carbon (blue) is the anomeric carbon
that generates two anomeric forms in the cyclic
structure Anomeric carbon switches between an
achiral and chiral form
6
Pyanose Formation by Intramolecular Linkage
7
Furanose Formation by Intramolecular Linkage
Numbering via anomeric-carbon identification?
8
Fructose Isomers
Anomeric Carbon Alpha hydroxyl down Beta
hydroxyl up Isomer Options Constitutional or
Stereo-isomers? Enantiomers or
diastereoisomers? Epimers or anomers?
9
Carbohydrate Isomeric Forms
H
10
Pictorial Representations of Glucose
Cyclic form Haworth project and chair
configuration Linear form Fisher
projection Most abundant natural form?
v
Why is only one configuration the most abundant
form?
11
Corn Syrup and Honey Rich in Fructose
Does this isomeric exactness really matter for
enjoying life?
?
Perceived as highly sweet
Perceived as mildly sweet
12
Reducing Sugars - Reactive Aldehydes
The protein modification referred to as advanced
glycosylation end products (AGE) is implicated in
aging, arteriosclerosis and diabetes Hemoglobin
glycosylation is a high blood- sugar marker
Benedicts reagent
Experiment Observation Inference
Test solution Benedict's reagent boil cool. Red ppt or green ppt or yellow ppt obtained Reducing sugar e.g. Glucose is present
Test solution Benedict's reagent boil cool. Solution remains clear Non-reducing sugar e.g. Sucrose is present
13
Disaccharide Biosynthesis via Glycosyltransferase
Reaction
14
Alpha and Beta Assignments for Anomeric Carbons
Only
Why is frucofuranosyl labeled in a beta
configuration?
15
Flipping a Box Upright On Its Legs
Legs up shift to down Leg left shifts to right
Left peg up stays up Legs in front stay front
16
Cellulose Straight Chains ß-1,4 Linkage
Plant fiber-forming structural polymer Most
abundant organic compound in nature Dietary
fiber not digested except by bacteria
17
Glycogen and Starch Bent Chain a-1,4-Linkage
Homopolymer for glucose storage Muscle/liver
glycogen rich 1,6 branched linkage (1 in
10) Plant tissuewith amylose (unbranched)
amylopectin (1 in 30 branching)
18
Glycoproteins Carbohydrates Attached to
Proteins
More protein than carbohydrate N-linked via Asn
or O-linked via Ser or Thr Chemical signature
for protein or whole cell surfaces
19
Glycosylation of Extracellular Proteins
Red blood cell stimulatory hormone
erythropoietin (EPO) Glycosylation enhances
stability Endurance athletes illegally use to
increase oxygen- carrying capacity EPO
spiking-detection based on glycosylation patterns
20
Modified Saccharides
N- O- C-glycosidic linkages Increase biochemical
versatility (e.g. chemical signaling)
21
Glycosaminoglycan Structural Units
Chitin N-acetylglucosamine homopolymer Present
in insect, crustacean, and arachnid exoskeleton
Second most abundant polysaccharide in
nature
22
Glycosaminoglycan Heteropolymers
Glucosamine/galactosamine amino sugar derivatives
Repeating disaccharide units with negatively
charged group
23
Proteoglycans Polysaccharides Proteins
Lubricants , structural components, and cell
adhesion Cartilage collagen (strength) and
agrecans (shock absorber) More polysaccharide
than protein
24
Chapter 11 Problems 1, 3, 5, 7, 9, 13, 15, 17,
19, 27
and 31