Condensation of two -amino acids to form a dipeptide. 1

N-Serine-Glycine-Tyrosine-Alanine-Leucine-CN-Ser-Gly-Tyr-Ala-Leu-C

N-SGYAL-C

2

Sugars and PolysaccharidesCarbohydrates: carbon hydrates

(CH2O)n or CnOnH2n

Monosaccharides : n≥3, polyhydroxy aldehydes and polyhydroxy ketones (single unit). Essential components of

all living organisms.

-Aldose: aldehydic carbonyl or potential aldehydic carbonyl group-Ketose: ketonic carbonyl or potential ketonic carbonyl group

Saccharides are also important components of nucleic acids, glycoproteins proteins and complex lipids.

3

Glyceraldehyde contains one chiral center* at C-2.

In general n carbon aldoses contain 2n-2 stereoisomers.

Dihydroxyacetone the simplest ketose, does not contain an chiral center

Erythrulose, the second sugar in the ketose series, contains one chiral center at C-3.

In general n carbon ketoses contain 2n-3 stereoisomers

1

2

3

1

2

3

1

2

3

4

C

C

CH2OH

H OH

OH

C

C

CH2OH

H OH

OH

H

C CH2OH

O

OHH

C O

CH2OH

CH2OH

C O

CH2OH

C

CH2OH

H OH

4

Nomenclature : - Fischer convention : D sugars have the same absolute configuration at the stereogenic center farthest removed from their carbonyl group as does D-glyceraldehyde.

- The L version of the sugars are the mirror image of their D counterparts

C

C

CH2OH

H OH

OH

C

OHH

HHO

OHH

OHH

CH2OH

OH

CH2OH

O

HHO

OHH

OHH

CH2OH

C

OHH

HHO

OHH

CH2OH

OH

C

OHH

OHH

CH2OH

OH

C

OHH

HHO

OHH

OHH

CH2OH

OH

C

HHO

OHH

HHO

HHO

CH2OH

OH

5

6

D-Arabinose D-Xylose

7

8

D-Erythrulose9

10

•L sugars are biologicaly much less abundant than D sugars. Know the structures of the sugars whose names are boxed.

•Aldoses to remember are:D-glyceraldehyde, D-erythrose, D-ribose, D-mannose, D-galactose, D-glucose

•Ketoses to remember are:Dihydroxyacetone, D-ribulose, D-xylulose, D-fructose

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Epimers

12

13

The reactions of alcohols with (a) aldehydes to form hemiacetals and (b) ketones to form hemiketals.

Configurations and conformations

Sugars can exist in several cyclic conformations, this is a consequence of the intrinsic chemical reactivity of the functional groups in the corresponding sugar

Intramolecular reactions

C

OHH

HHO

OHH

OHH

CH2OH

OH

CH2OH

O

HHO

OHH

OHH

CH2OH

14

15

16

-The ring closure process renders the former carbonyl group asymetric: !!!! New chiral center !!!!

-The newly generated pair of diastereomers are call anomers and the hemiacetal/ketal carbon is call anomeric carbon

anomer : OH substituent at the anomericcarbon is in the opposite side of the sugarring from the CH2OH group at the chiral center that designates the D or L configuration

anomer : OH substituent at the anomericcarbon is in the same side of the sugar ring from the CH2OH group at the chiral centerthat designates the D or L configuration

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18

After dissolution in water:

D-Glucose: Exclusively pyranoseD-fructose: 67% pyranose, 33% furanoseD-ribose: 75% pyranose, 25% furanose

However, in polymers:Glucose: pyranoseFructose: furanoseRibose: furanose

All the interconversions between furanose and pyranose form proceed through the linear form of the molecule.

D-glucose is 33% and 66% 19

Sugars are conformationally variable

20

2 forms of glucose 21

O

H

HO

H

HO

H

OH

OHHH

OH

O

H

HO

H

HO

H

H

OHHOH

OH

glucose glucose

D-glucose is 33% and 66%

22

Monosaccharides are modified

23

Monosaccharides are modified

24

Aldonic Acid

C

C

C

C

C

CH2OH

O H

OH

OHH

H

OHH

HHO

C

C

C

C

C

CH2OH

O OH

OH

OHH

H

OHH

HHO

C

C

C

C

C

C

O H

OH

OHH

H

OHH

HHO

OOH

Aldose Uronic Acid

Glucose Gluconic Acid Glucuronic Acid

Oxidation reduction reactions :

The aldehyde moiety in aldoses can be oxidize to yield a carboxylic acid, the resulting compounds are known as aldonic acids.

25

Monosaccharides are modified

26

C

C

C

C

C

H

O H

OH

OHH

H

OHH

OHH

C

C

C

C

C

H

OH

OHH

H

OHH

OHH

OHH

H

RiboseRibitol

- The reduction of the carbonyl group in aldoses and ketoses yields polyols known as alditols

27

CH2OH

CH2OH

OHH

Glycerol

H

OH

OH

H

H

OHH

OH

OHOH

H H

Inositol

28

Gulose GulonicAcid

Gulono--lactone

C

OHH

OHH

HHO

OHH

CH2OH

OOH

δ

Glucose

CHO

OHH

OHH

HHO

OHH

CH2OH

CHO

OHH

HHO

OHH

OHH

CH2OH

C

OHH

HHO

OHH

OHH

CH2OH

OOH

δ

GluconicAcid

C

OH

OO

OHH

CH2OH

OH

H

H

C

OH

OO

OHH

CH2OH

OH

H

Ascorbic acid29

Dehydroscorbicacid

Ascorbic acid

+ 2e-

C

OH

OO

OHH

CH2OH

OH

H

C

O

OO

OHH

CH2OH

O

H

30

31

Sugar derivatives:

The chemistry of sugars is largely that of their hydroxy and carbonyl groups.

Glycosidic bonds: are analogous to the peptide bond in proteins, polysaccharides; are held together by glycosidic bonds between neigboring monosaccharides units

32

33

1

234

5

6

1

23

4

5

6

-glucose

-glucose

OH

OH H

H

OHH

OH

CH2OH

H

OH

O

H

OH

H

OHH

OH

CH2OH

H

-glucose-(1,4)--glucose

glucose-()-glucose

34

-glucose-(1,4)--glucose

glucose-()-glucose 35

-glucose-(1,4)--glucose

glucose-()-glucose 36

-glucose-(1,6)--glucose

glucose-()-glucose 37

Trehalose

O

OH

OH

OH

CH2OH

OO OH

OH

OH

HO2HC

-glucose-(1,1)--glucose

glucose-()-glucose 38

-galactose-(1,4)--glucose

Galactose-()-glucose 39

glucose-(1,4)--fructose

glucose-()-fructose 40

Polysaccharides

41

Rigid - used for osmotic protectionLoad bearing function

Cellulose

Polysaccharides

42

43

Degrading cellulose

1015 kg of cellulose synthesized and degraded

annually

Disaccharide product of

breakdown is cellobiose

Only microbes can do this!

44

Exoskeltons for invertebrates

Chitin

1014 kg of chitin synthesized and degraded annually

(1,4)-N-acetylglucosamine

45

Storage Polysaccharides

StarchesAmylose

Amylopectin

Glycogen

46

(1 - 4)

AmylopectinBranched every 24 to 30 sugars

47

Amylose Amylopectin

48

Structure of glycogen.

More extensively branched (every 8-12 sugars)

Disaccharide breakdown products of starch are maltose and isomaltose

49

Cell Walls and Connective Tissue

50

Cell Walls and Connective Tissue

51

Lubricant for joints, “jelly” in the eye 52

Tensile strength in joints, heart53

Horns, hair, hoofs, nails, claws 54

Anticoagulant 55

56

Model of oligosaccharide dynamics in bovine pancreatic ribonuclease B (RNase B).57