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Carbohydrates Are the Largest Group of Biomolecules
Carbohydrates are polyhydroxy aldehydes and ketones and
compounds that can be hydrolyzed to them.
glucose(chain form)
fructose(chain form)
HOH
OOH
OH
OH
OH
HO
OHOH
OH
OH
O
O
HOOH
OH
OOHO
OH OH
OH
HO
lactose
aldose(aldehyde)
ketose(ketone)
glucose fructose
HOH
OOH
OH
OH
OH
HO
OHOH
OH
OH
O
For Your Information…
glucoseisomerase
Natural corn syrup contains mainly glucose – enzymatic isomerization produces fructose, which has a sweeter taste. Cheap source of sweetener.
Nucleotides (e.g ATP)
Carbohydrates Compose 50% of the Earth’s Biomass
CelluloseChitin
Lactose
Cell surface receptor molecules (ABO blood
types)
Carbohydrate Terminology
Monosaccharides: Simplest carbohydrates, 3-7 carbon atoms in chain with C=O at C1 or C2
D-glucose
CHO
OHH
HHO
OHH
OHH
CH2OH
CHO
OHH
CH2OH
CHO
OHH
OHH
CH2OH
CHO
OHH
OHH
OHH
CH2OH
D-riboseD-erythroseD-glyceraldehyde
Triose (3C) Tetrose (4C) Pentose (5C) Hexose (5C)
Drawing Carbohydrate Structures
Carbohydrates contain one or more stereocenters (except dihydroxyacetone) and
may be represented by Fischer projection formulas
CHO
OHH
HHO
OHH
OHH
CH2OH
CHO
OHH
HHO
OHH
OHH
CH2OH
Fischer projection formula ofD-glucose
equal to
Carbonyl carbons are placed at the top and the carbon skeleton runs along the vertical axis
Naturally Occurring Carbohydrates Are of the D-Configuration
D-Sugars have the OH group on the sterogenic center furthest from the carbonyl carbon on the right
L-Sugars have the OH group on the sterogenic center furthest from the carbonyl carbon on the left
CHO
OHH
HHO
OHH
OHH
CH2OH
D-glucose
D- and L-glucose are enantiomers
CHO
HO H
H OH
HO H
HO H
CH2OH
L-glucose
Physical Properties of Carbohydrates
Sweet tasting
Relative sweetness varies - fructose sweeter than glucose
Polar
Many carbohydrates water soluble
Many insoluble in organic solvents (diethyl ether)
High melting points
OHOHO
OHOH
OH
OAcOAcO
OAcOAc
OAc
Water soluble Organic soluble
Monosaccharide Structures
Monosaccharides can undergo intramolecular cyclization reactions to form hemiacetals
CHO
OHH
HHO
OHH
OHH
CH2OH
OH
H
H
OH
OH
H
OH
HHO H
O
rotate O
OH
OH
OH
HO
OHcyclize
Haworth projection
O
OH
OH
OH
HO
OH
-anomer
-anomer
OHOHO
OH
OH
OH
Chair form(more realistic)
OHOHO
OHOH
OH
-anomer
-anomer
D-glucose
Pyranose and Furanose Structures
Pyranose
Six-membered ring containing O
Anomeric carbon
OHOHO
OHOH
OH
Furanose
Five-membered ring containing O
O
pyran
furan
O
-D-glucopyranose
-D-ribofuranose
Anomeric carbon
O
OHOH
HO OH
Disaccharides and Polysaccharides
Polysaccharides: Polymers of monosaccharides linked via glycosidic bonds. “Complex carbohydrates”
Disaccharides: Two monosaccharides linked via glycosidic bond.
O
HOOH
OH
OOHO
OH OH
OH
HO
-glycosidic bond
LactoseGalactose (left) and glucose (right) monomers
AmyloseLinear polymer
Amylose and Amylopectin Are Glucose Polymers Found in Starch-Containing Foods
AmylopectinBranched polymer
-(1-4)-glycosidic bondsand
-(1-6)-glycosidic bonds
-(1-4)-glycosidic bonds
Humans digest starch – we have the enzymes to hydrolyze the glycosidic bonds
Cellulose
Cellulose is a Linear Polymer of Glucose Linked via-(1-4)-Glycosidic Bonds
-(1-4)-glycosidic bonds
Humans and other non-ruminant animals lack the enzymes to hydrolyze -(1-4)-glycosidic bonds in cellulose, so it is excreted
unchanged (fiber).
Glycogen Is a Highly Branched Polymer of Glucose
Glycogen and the enzyme glycogenin – a glycosyltransferase involved in glycogen
synthesis
Extensive branching allows cells to quickly access glucose
ABO Blood Types Due to Different Carbohydrates on Red Blood Cell Surface
www.wikipedia.org
Carbohydrates on RBCs Act as Antigens That May be Attacked by Antibodies
www.wikipedia.org
Nucleotides Are N-Glycosides
N
NN
N
NH2
OHO
OH OH
1'2'3'4'
5'
Adenosine(RNA, ATP)
N
NN
N
NH2
OHO
OH
1'2'3'4'
5'
2-Deoxyadenosine(DNA)
Polynucleotides Are Covalently Linked via 3’,5’-Phosphodiester Bonds
Adenine (A)
Guanine (G)
Thymine (T)
Cytosine (C)Phosphodiester
linkage