Chapter 8 Carbohydrates

1
Chapter 8 Carbohydrates

• POINTS TO KNOW
• Structures of 8 common sugars
• Units making up common disaccharides and
  polysaccharides
• Nomenclature rules
• Characteristic Functional Groups of complex
  carbohydrates

2
Chapter 8 Carbohydrates

• Contain only C, H, and O
• Most abundant biomolecules
• Classified by location of their carbonyl group
  (ketose or aldose) and the number of C atoms (3
  and above) aldotriose, ketotetrose, -pentose,
  -hexose, -heptose, etc.)

3
Carbohydrates

• Fisher convention Horizontal lines project
  toward the readers vertical lines project away.

CHO
CHO
HO
OH
H
H
CH2OH
CH2OH
L-Glyceraldehyde
D-Glyceraldehyde
4
Carbohydrates

• Fisher convention Horizontal lines project
  toward the readers vertical lines project away.

CHO
CHO
H
HO
OH
H
CH2OH
CH2OH
L-Glyceraldehyde
D-Glyceraldehyde
5
Carbohydrates
HC O
CH2OH
OH
H
O
C
C
CH2OH
CH2OH

• Monosaccharides single carbonyl derivatives of
  polyhydroxy alcohols
• Ketoses - Carbonyl ketone (dihydroxyacetone)
• Aldoses - Carbonyl aldehyde (D-glyceraldehyde)

6
Carbohydrates

• Epimer Series
• Vary by configuration about one anomeric carbon
• Each Aldoses have 2 n-2 epimers Hexoses have 2
  n-3 epimers based on the of non-carbonyl
  chiral carbons
• D- versus L- determined by penultimate carbon
  (counting from carbonyl group)
• Aldotriose (D-Glyceraldehyde) ? Aldohexoses
  (D-Glucose)
• Ketotrioses (Dihydroxyacetone) ? Ketohexoses
  (D-fructose)

7
Carbohydrates

• Epimers to Know
• D Glyceraldehyde Dihydroxyacetone
• Ribose, Ribulose
• Glucose, Galactose, Mannose, Fructose

(QUIZ WEDNESDAY)
8
Carbohydrates

• Fisher versus Haworth Projections
• D-Glucose

D-Glucose
?-D-Glucopyranose
9
Carbohydrates

• Haworth Projections Hemiacetal or Hemiketal
  Conformation

Hemiacetal
Alcohol Aldehyde
CH2OH
5
H
O
H
H
1
H
OH
HO
OH
5
OH
H
?-D-Glucopyranose (pyranose form)
D-Glucose
10

• Haworth Projections
• anomer 1 OH and 5 CH2OH opposite
• ? anomer 1 OH and 5 CH2OH same

36.4
63.6
CH2OH
CH2OH
H
H
O
O
H
OH
H
H
1
1
H
H
OH
OH
HO
HO
OH
H
OH
H
OH
H
?-D-Glucopyranose (pyranose form)
?-D-Glucopyranose (pyranose form)
11

• Haworth Projections
• anomer 1 OH and 5 CH2OH opposite
• ? anomer 1 OH and 5 CH2OH same

36.4
63.6
CH2OH
CH2OH
CH2OH
CH2OH
o
o
o
o
?-D-Glucopyranose (pyranose form)
?-D-Glucopyranose (pyranose form)
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Sugar Derivatives

• Aldonic Acids mild oxidation of aldehyde to a
  carboxylic acid (Gluconic Acid)
• Uronic Acids oxidation of primary alcohol to
  carboxylic acid (Glucuronic Acid)
• Glycerol, Ribitol, Inositol - reduction of
  carboxyl to form acyclic and cylic polyhydroxy
  alcohols (glycerol)

13
Sugar Derivatives

• Deoxy and Dideoxy Sugars (DNA)
• Amino Sugars OH replaced by NH3 glucosamine
  and galactosamine
• GLYCOSIDES joins monomers by anomeric carbon of
  first monomer to any OH on next monomer

14
Carbohydrate Nomeclature

• Monosaccharide to Disaccharide
• Lactose

Reducing End Rx with mild Oxid. Agents
CH2OH
CH2OH
HO
OH
H
O
O
H
H
O
H
OH
H
OH
H
H
H
OH
H
OH
H
Galactose Glucose (? (1?4) glycosidic linkage)
O- ?-D-Galactopyranosyl- (1?4) D-glucopyranose
15
Carbohydrates

• Monosaccharide to Disaccharide
• Sucrose
• Most abundant disaccharideplant sugar transport

CH2OH
H
HOCH2
H
O
O
H
H
1
2
H
HO
H
OH
O
OH
CH2OH
OH
H
OH
H
Glucose Fructose (? (1?2) glycosidic linkage)
O- ? -D-glucopyranosyl- (1?2) ?-D-fructofuranosi
de
16
Carbohydrates

• Monomer to Polymers Glycans
• D-Glucose to ?-Amylose to Glycogen
  (Homopolysaccharides)

CH2OH
CH2OH
CH2OH
H
H
H
O
H
O
O
H
H
H
H
H
H
OH
H
H
OH
OH
O
HO
OH
OH
H
OH
H
OH
H
?-Amylose to Amylopectin or Glycogen (? (1?4)
glycosidic bond)
?-D-Glucose
17
Storage Carbohydrates

• Glucose Polymers

Amylose -- repeating ? (1?4) glycosidic bond.
Broken down during digestion by amylase and a
debranching enzyme. HE helical structure. Amyl
pectin (plant starch)-- repeating ? (1?4)
glycosidic bond repeating ? (1?6) glycosidic
bond every 24-30 residues up to 1,000,000
residues! Glycogen (animal sugar storage)--
repeating ? (1?4) glycosidic bond repeating ?
(1?6) glycosidic bond every 8-12 residues.
Mobilized from muscle with glycogen phosphorylase
from non-reducing end.
18
Storage Carbohydrates

• Glucose Polymers

• Cellulose -- repeating ? (1?4) glycosidic bond
  for up to 15,000 residues. Structural function
  in plant cell walls antiparallel chains of 40
  monomers in 3-D H-bonded lattice.
• Difficult to digest due to linkage and tightly
  H-bonded structure. Cellulases requiredfound
  only termites herbivore microorganisms

19
Structural Carbohydrates

• Cellulose

CH2OH
CH2OH
CH2OH
H
H
H
O
O
O
OH
H
H
H
O
H
OH
H
H
OH
OH
HO
H
H
H
OH
H
OH
H
OH
H
? (1?4) glycosidic bond
?-D-Glucose
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Structural Carbohydrates

• Chitin
• Insect Skeletons

CH2OH
CH2OH
CH2OH
CH2OH
CH2OH
H
H
H
H
O
H
O
O
O
O
OH
H
H
H
H
H
O
O
H
H
OH
OH
H
H
OH
OH
H
OH
HO
HO
H
H
H
H
H
NHCOCH3
H
NHCOCH3
H
H
H
H
H
NHCOCH3
NHCOCH3
NHCOCH3
? (1?4) glycosidic bond
N-Acetylglucosamine
21
Structural Carbohydrates

• Glycoaminoglycans

• Alternating uronic acids and hexosamines, often
  sulfated
• Extracellular
• Viscoelastic and lubricating Cartilage, tendon,
  skin, vessels
• Examples Hyaluronate, Chondroitin-4-sulfate,
  Heparin, Keratan sulfate

COO-
CH2OH
H
H
O
O
H
H
H
OH
H
H
HO
H
O
OH
H
H
NHCOCH3
22
Glycoproteins

• Proteoglycans bottlebrush structure
  consisting of core protein with bristles of
  glycosaminoglycans.
• N-linked oligosaccharides via Asn
• O-linked via Ser, Thr
• Highly negatively charged and hydrated for
  cushioning effect

23
Glycoproteins

• Peptidoglycan N-acetylglucoamine
  N-acetylmuramic acid with tetrapeptide
  crosslinked by pentaglycine bridges
• Bacterial cell walls
• Thick layer in Gram bacteria (Staph, Strep)
• Thin layer in Gram bacteria (E. coli)
• Natural occurrence of a D-amino acid
• Site of penicillin activities. Penicillin mimics
  the crosslink structure and inhibits cells wall
  synthesis hence, selective for bacteria

24
Glycoproteins

• Glycosylated Proteins
• Common to secreted and membrane-associated
  proteins
• Fewer glycosylation sites than proteogylcans
• More varied functions
• Often rigidly positioned at membrane surface
  loops of proteins
• OFTEN HIGHLY IMMUNOGENIC A/B/O blood groups

25
Glycoproteins

• Glycosylated Proteins
• Responsible for receptor-mediated cellular
  binding/communication/recognition events
• Antibody recognition and binding sites
• Egg recognition and binding by sperm
• Parasite, Bacteria and Virus attachment sites
  during infections
• Cellular contact inhibition (cancer)
• Protein tagging for transport receptor
  recognition

26
Glycoproteins

• N-linked to Asn at Asn-X-Ser or Asn-X-Thr
• Co-translational process in the Golgi
• High in Mannose with N-Acetylglucosamine,
  Galactose, Glucose, Sialic Acid, and Fucose
• O-linked to Ser or Thr