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