SCH4U Carbohydrates
2.5 Starch and Cellulose
Assignment: Page 128 # 1-6
Simple and Complex Carbohydrates
Carbo (Cn) Hydrates (H2O)n
P Simple carbohydrates (monosaccharides)
are often called simple sugars
P Simple sugars are aldoses or ketoses
P Complex carbohydrates (polysaccharides)
are made of simple carbohydrates linked
together
Sugars
• Monosaccharides have molecular formulas that
are usually multiples of CH 2O
• Glucose is the most common monosaccharide
• Monosaccharides are classified by location of the
carbonyl group and by number of carbons in the
carbon skeleton
Triose sugars
(C 3H 6O 3)
Pentose sugars
(C 5H 10O 5)
Hexose sugars
(C 5H 12O 6)
Glyceraldehyde
Ribose
Galactose
Glucose
Dihydroxyacetone
Ribulose
Fructose
Some basic vocabulary
OH
monosaccharide
O
HO
HO
OH
OH
glucose – metabolic sugar
HO
OH
disaccharide
OH
O
HO
OH
O
O
HO
OH
Lactose – milk sugar
oligosaccharide or polysaccharide
OH
O
OH
OH
O
HO
OH
O
HO
O
OH
O
OH
HO
Cellulose – plant cells walls
OH
O
OH
O
HO
O
OH
Features of oligosaccharides
P They can be branched
P Combine simple sugars as different isomers
(alpha and beta)
b
OH
Gal
HO
GlcNAc
OH
O
OH
O
4
O
3
O
H 3C
OH
OH
O
O
OH 1
Fuc
OH
NHAc
a
b
Starch
á 1,4 - polyglucose
O
HO
OH
O
HO
O
HO
OH
O
HO
O
HO
OH
O
HO
Glycogen (starch):
a storage form of glucose
O
HO
OH
O
HO
O
n
Starch
25% Amylose, 75% Amylopectin
P Amylose - á 1,4-linear (branches every 200
units)
P Amylopectin - á 1,4-linear with á -1,6 (branch
OH
every 20 units)
HO
HO
O
OH
HO
O
O
HO
HO
OR
Amylose Structure
Amylopectin Structure
Digesting Starch
Amylase in saliva “fits” amylose (starch)
P Digestion of starch begins in our mouths
P Amylase is an enzyme that helps to break
starch into simple sugars for absorption
Substrate
(sucrose)
Glucose
Enzyme
(sucrose)
Fructose
Chemistry of Digestion: Carbohydrates
Figure 21-6: Carbohydrate digestion
Amaranth starch
(Bar: 1 µm)
Arrowroot starch
(Bar: 20 µm)
Buckwheat starch
(Bar: 5 µm)
Cassava starch
(Bar: 10 µm)
Corn starch
(Bar: 10 µm)
Oat starch
(Bar: 5 µm)
Potato starch
(Bar: 50 µm)
Rice starch
(Bar: 2 µm)
Kidney bean starch
(Bar: 20 µm)
Cellulose Structure
b-1,4 polyglucose
• Very large molecule
• Crystalline (hydrogen-bonded) and noncrystalline regions
Cellulose structure
â 1,4-polyglucose
P Polymers with alpha glucose are helical
P Polymers with beta glucose are straight
P Hydrogen bonds between cellulose make
parallel fibres very strong for plant structures
Gluacose
Glu
bcose
ag
anblducosriensgtructures
Star1
cli4
–
h:
nkg
aa
g
louefcos
meonomers.
Cellul1
oli4
–se:
nka
gb
g
luefcos
o
meonomers.
Cellulose microfibrils
in a plant cell wall
Cell walls
Microfibril
0.5 µm
Plant cells
Cellulose
molecules
b Glucose
monomer
Digesting Cellulose
We do not have an enzyme that “fits”
P Digestion of cellulose does not occur in
human digestion
P We do not have an enzyme that “fits” the 3D
shape of cellulose
• Enzymes that digest starch by hydrolyzing alpha
linkages can't hydrolyze beta linkages in cellulose
• Cellulose in human food passes through the
digestive tract as insoluble fiber
• Some microbes use enzymes to digest cellulose
• Many herbivores, from cows to termites, have
symbiotic relationships with these microbes
Examples of carbohydrate-based drugs
OSO 3–
O
HO
HO
–O 3SHN
–O 2C
O
HO
O
–O 3SO
O
–O 3SHN
OH
O
O
HO
O
HO
–O 3SHN
OCH 3
O
CO 2–
OSO 3–
O
OSO 3–
Heparin pentasaccharide – anti-coagulant
OH
HO
HO
H 2N
H 3C
OH
HN
HO
NH 2+
O
OH
OH
O
HO
H 2N
O
Acarbose – diabetes
NH
HO
NH
OH
OH
O
OHC
O
OH
OH
O
HO
O
OH
OH
H 3C
HO
O
NHCH 3
O
OH
OH
CO 2–
O
HO
AcHN
HN
H 2N
OH
OH
CH 3
Streptomycin – antibiotic
Relenza – anti-flu drug
NH 2+
NH 2+
Examples of glycosylated natural products
O
O
OH
O
OH
HO
H3C
OH
CH3 O
O
CH3
H3 C
O
OH O
O
HO
O
H3 C
O
OH
OH
CH3
OH
O
O
Doxorubicin – anti-cancer drug
HO
HO
H3 C
O
O
HO
H3C
O
O
HO
CH3
OH
CH3
Erythromycin A – antibiotic
HO CH
3
H3 C
N(CH3 )2
OH
CH3
NH3 +
CH 3
O
H3 C
O
OH
O
Digoxin – cardiovascular
O
O
Monosaccharide building blocks used in
mammalian glycoconjugates
OH
HO
O
HO
HO
OH
OH
OH
HO
Galactose (Gal)
HO
HO
O
OH
NHAc
N-Acetylglucosamine
(GlcNAc)
OH
CO 2–
OH
HO
AcHN
O
HO
OH
Glucose (Glc)
HO
HO
OH
O
Sialic acid (Sia)
OH
OH
Glucuronic acid
(GlcUA)
OH
HO
O
HO
HO
O
OH
OH
HO OH
Fucose (Fuc)
OH
Mannose (Man)
OH
O
H 3C
HO
HO
OH
O
HO
OH
O
OH
NHAc
N-Acetylgalactosamine
(GalNAc)
HO
HO
O
OH
OH
Xylose (Xyl)
Pectin
Used as thickeners (jelly)
Polysaccharides are synthesized inside cells
Extracellular milieu
Carbohydratespecific receptor
Monosaccharides
Cell surface
glycoconjugates
Metabolic
interconversions
ER/Golgi
Monosaccharide
"building blocks"
Cytosol
Glycoconjugate assembly
in the secretory compartments
Oligosaccharides are major components
of the cell surface
Glycoprotein
Glycolipid
Oligosaccharides