Biomolecules Survey Part 1:CarbohydratesLecture Supplement page 81

Sucrose

O

O O

CH2OH

HOHO

HO

OH

OH

CH2OH

CH2OH

Why Should I Study This?

•All organisms utilize carbohydrates important biomolecules

•Nutrition: “Carbos” are more than just starch and sugar

•Application of previous concepts:

Functional groupsStereochemistry

Other structural features} control biological properties

Why is this topic important?

Origin of “Carbohydrate”

Monosaccharide: Cannot be hydrolyzed into simpler sugars

Glucose C6H12O6

Fructose C6H12O6 no changeH2O, H3O+

no changeH2O, H3O+

Hydrolysis: “Water breaking;” reaction with water, often in the presence of acid or base

Sucrose C12H22O11H2O, H3O+

glucose + fructose

Cellulose CnH2nOn

H2O, H3O+

many glucose

Disaccharide: Saccharide composed of two simpler sugars

Polysaccharide: Composed of many monosaccharides

Starch CnH2nOnH2O, H3O+

many glucose

Origin of “Carbohydrate”

Sugar general formula = CnH2nOn

Confirmationsucrose + H2SO4 C + H2O (steam)

dehydrating agent

= Cn(H2O)n

= carbohydrate

= “carbon hydrate”

sucrose

H2SO4steam

carbon

Movie file: sucrose_dehydration.mov

an aldohexoseC3 = trioseC4 = tetroseC5 = pentoseC6 = hexose

Monosaccharide Molecular Structure

•Chain of three to six carbons

•One aldehyde or ketone

C

C

C

C

C

CH2OH

OHH

HHO

OHH

OHH

H O

-ose = saccharide

Example: Glucose, a C6 aldehyde

All common/ important monosaccharides have...

aldehyde = aldoseketone = ketoseAldoses more common than ketoses

•All other carbons are alcohols H-C-OH or CH2OH

The (D)-Aldose FamilyThe (D)-Aldotrioses

C

C

CH2OH

HO H

H O

C

C

CH2OH

H OH

H O

One stereocenter two enantiomers

(L)-(-)-glyceraldehyde (D)-(+)-glyceraldehyde

Stereochemical configuration•D = OH above CH2OH on the right

•Configuration of most natural aldoses•L-aldoses generally unimportant•No correlation of D/L with +/- or with R/S

C

C

CH2OH

H OH

H O

C

C

CH2OH

H OH

H O

The (D)-Aldose FamilyFischer Projections

Emil Fischer

•Determined relative structure of (D)-aldoses

•Guessed (D)-glyceraldehyde = R configuration (confirmed by x-ray crystallography; 1950)

•Nobel Prize in Chemistry 1902

(D)-(+)-glyceraldehyde

C

C

CH2OH

H OH

H O

Vertical lines= broken wedges

Horizontal lines= solid wedges

Fischer projection

CHO

H OH

CH2OH

The (D)-Aldose FamilyThe (D)-Aldotetroses

Two stereocenters four stereoisomers Two (D) and two (L)

(D)-(-)-erythrose (D)-(-)-threoseNot found in nature

C

C

CH2OH

H OH

COH

H OH C

C

CH2OH

H OH

COH

HO H

The (D)-Aldose FamilyThe (D)-Aldopentoses

Three stereocenters eight stereoisomers Four (D) and four (L)

(D)-(-)-ribosein RNA (ribonucleic acid)

in DNA (deoxyribonucleic acid)

(D)-(-)-arabinose (D)-(-)-lyxoseRare in nature

(D)-(+)-xyloseC

C

CH2OH

H OH

H OH

CH

C

OH

OH

C

C

CH2OH

H OH

H OH

CHO

C

H

OH

C

C

CH2OH

H OH

HO H

CH

C

OH

OH

C

C

CH2OH

H OH

HO H

CHO

C

H

OH

The (D)-Aldose FamilyThe (D)-Aldohexoses

Four stereocenters 16 stereoisomers eight (D) and eight (L)

(D)-(+)-allosenot found in nature

C

C

CH2OH

H OH

H OH

CH OH

CH OH

COH

(D)-(+)-altrose

C

C

CH2OH

H OH

H OH

CH OH

CHO H

COH

(D)-(+)-glucosemost abundant

monosaccharide

C

C

CH2OH

H OH

H OH

CHO H

CH OH

COH

(D)-(+)-mannose

C

C

CH2OH

H OH

H OH

CHO H

CHO H

COH

The (D)-Aldose FamilyThe (D)-Aldohexoses

Four stereocenters 16 stereoisomers eight (D) and eight (L)

(D)-(-)-gulosenot found in nature

C

C

CH2OH

H OH

HO H

CH OH

CH OH

COH

(D)-(-)-idose

C

C

CH2OH

H OH

HO H

CH OH

CHO H

COH

(D)-(+)-galactosefairly common

C

C

CH2OH

H OH

HO H

CHO H

CH OH

COH

(D)-(+)-talose

C

C

CH2OH

H OH

HO H

CHO H

CHO H

COH

Must I memorize all of these structures?•Most important aldoses: Glucose, ribose, galactose•Learn by doing problems

Midterm 1• 1 hour exam (in class on Friday, May 4)• Will cover:

– Intro & Review up through Carbohydrates (Mass Spectrometry and IR will not be on exam)

• Last name A-K in CS50• Last name L-Z in Franz 1260• Tools

– Pen and/or pencil– Eraser– Model kit– No calculators or cell phone

How should I study?• Review past “Exam 1”s on Hardinger’s website

http://www.chem.ucla.edu/harding/index.html(on left frame, click “Ch14C” then in middle frame click “Current and Past Exam and Keys”)

Midterm Review Session (Problem Solving Session)

• Tues, 5/1 YH3069 from 7-9pm (Ray)

• Will go over past midterms, Thinkbook problems, Vollhardt problems, Klein problems, etc. (at Ray’s discretion)

Cyclic Monosaccharides

Many acyclic monosaccharides in equilibrium with more stable cyclic isomers

(D)-(+)-glucose

OH

CH2OH

HO

HOHO

O

H

O

CH2OH

HO

HOHO

OH

H

O

CH2OH

HO

HOHO

H

OH

-D-glucopyranose

-D-glucopyranose

O

PyranOH axial

Less stable configuration

OH equatorialMore stable configuration

•Example: Glucose

Cyclic Monosaccharides and : Anomeric Carbon Stereochemistry

O

CH2OH

HO

HOHO

OH

H

-D-glucopyranose

O

CH2OH

HO

HOHO

H

OH

-D-glucopyranose

•Was carbon of carbonyl in acyclic form•Point of attachment to other monosaccharides•If anomeric group = OH, stereochemistry shifts •If anomeric group = OR, stereochemistry fixed as or

OHO

Anomeric carbon

= trans CH2OH, anomeric OH = cis CH2OH, anomeric OH

cistrans

Cyclic MonosaccharidesHaworth Projections

-D-glucopyranose

O OH

OH

OH

HO

CH2OH

O

OH

OH

HO

CH2OH

OH

O

CH2OH

HO

HOHO

OH

-D-glucopyranoseO

CH2OH

HO

HOHO OH

Cyclic MonosaccharidesFuranoses

Which ribose OH becomes ribofuranose ether?

X = OH: -D-ribofuranose (RNA)X = H: -D-2-deoxyribofuranose (DNA)

O

HO

HO X

OH

anomeric carbon

X = OH: D-riboseX = H: D-2-deoxyribose

O

furan furanose

C

C

C

CH2OH

H OH

H X

H OH

COH

1

2

3

4

5

1

234

5

Cyclic MonosaccharidesFuranoses in DNA

A short segment of theDNA double helix

or ?

OOP

O

O

O

O

O

OP

O

O

O

N

NN

N

NH2

N

NH

O

O

H3C

OOP

O

O

O

N

NN

N NH2

H

O

Disaccharides

•Disaccharide: A carbohydrate composed of two monosaccharides

An acetalC-O-C-O-C

A hemiacetalC-O-C-O-H

•Useful vocabulary:

Two carbohydrates linked by an acetal functional group

Other anomeric carbon = hemiacetal functional group

O

OOHO

HOHO

CH2OH

HO

HO

CH2OH

OH

Fixed or

/ mixture

O

O

O

OOHO

HOHO

CH2OH

HO

HO

CH2OH

OH

DisaccharidesCarbohydrate Ring Numbering

•Anomeric carbon receives lowest number:

Carbon 1 in aldoses

Carbon 2 (rarely 3) in ketoses

•All other carbons numbered in order

Cyclic form (and anomers)

Acyclic form

HO

OH

1

23

45

6

OH

O

OH

HO

H

HO

O

1

23

45

6

OH

OH

OH

HO

H

Glucose(a aldohexose)

Fructose(a ketohexose)

HO

2

3

45

6

OH

OH

OH

O

1

OH

Cyclic form(and anomers)

Acyclic form

HO

2

3

45

6

O

OH

OH

OH

1

OH

12

OHH3

HHO4

OHH5

OHH

CH2OH6

OH CH2OH1

2O

3HHO

4OHH

5OHH

CH2OH6

DisaccharidesMaltose

1,4’--D-glucopyranosyl-D-glucopyranose

OO

O

CH2OH

HO

HOHO

HOHO

CH2OH

OH

/ mixture

H3O+/H2O

hydrolysisStarch

H3O+/H2O

hydrolysis

2O

OH

CH2OH

HOHO

HO

Glucopyranose

•Product of partial hydrolysis of starch

•Anomeric carbon has -linkage; easily digested by mammals (we have enzymes

that can split linkages)

DisaccharidesLactose

1,4’--D-galactopyranosyl-D-glucopyranose

•Present in mammalian milk (up to 8 % by weight; varies with species)

•Readily digested by infant mammals; requires enzyme lactase

•Adults often less tolerant due to low levels of lactase

•Lactaid milk is pre-treated with lactase enzyme

Lactose

OO

O

CH2OHHO

HO

OH

HO

CH2OH

OHHOH3O+/H2O

hydrolysis

+O

OH

CH2OH

HOHO

HO

GlucopyranoseGalactopyranose

OCH2OH

HO

HO

HO OH

DisaccharidesSucrose

2,1’--D-fructofuranosyl--D-glucopyranoside

•Unusual structure: Anomeric carbon-O-anomeric carbon

•Easily digested by mammals: -linkage at anomeric carbon

•Most common disaccharide in nature

•Produced only by plants such as sugar cane, sugar beets

•World production 2008: 158.8 x 109 kg (~5 x 1013 sugar packets)

Sucrose

O

O O

CH2OH

HOHO

HO

OH

OH

CH2OH

CH2OH

H3O+/H2O

hydrolysis

O

OH

CH2OH

HOHO

HO

Glucopyranose FructofuranoseA ketose

+ O

OH

OH

CH2OHHO

CH2OH

Polysaccharides

•Polysaccharide: Hydrolysis yields many monosaccharide molecules

•Most important are glucose polymers: Cellulose and starch

PolysaccharidesCellulose

•Linear 1,4'--D-glucopyranose polymer

•~5,000 - 10,000 glucopyranose molecules per cellulose molecule – high molecular weight

Repeating subunit:Glucopyranose

OO

OO

OOO

HO

CH2OH

OHHO

CH2OH

OH

CH2OH

HOOH

•Most abundant organic substance in nature

•Main function: Structural

H3O+/H2O

hydrolysis

O

OH

CH2OH

HOHO

HO

Many glucopyranose

•Not easily digested by mammals

Wood is ~50% cellulose by weight

Strength due to intermolecular hydrogen bonding

Cellulose chains lie by side in bundles and twist together to form fibers

PolysaccharidesChitin

•Linear 1,4'--D-glucopyranose polymer

•Found in shells of crustaceans (crab, shrimp, lobster) and also insects

Repeating subunit:N-Acetyl Glucosamine

•Major component: Glucosamine, which is used to treat symptoms of arthritis

OO

OH

ONH

HO

O CH3

OO

OH

NH

HO

O CH3

OO

OH

NH

HO

O CH3

OO

OH

NH

HO

O CH3

H3O+/H2O

hydrolysis

Many N-Acetyl Glucosamine units

O

OH

HONH

HO

O CH3

OH

PolysaccharidesOO

HO

CH2OH

HO OOHO

CH2OH

HO O

O

OHO

CH2OH

HOAmylose

STARCH•Two forms: Amylose, amylopectin

Amylose•30% of starch•Linear polymer containing 300 to 3,000 glucopyranose

OOHO

CH2OH

HO OOHO

HO O

O

OHO

CH2OH

HO

O

O

OHO

CH2OH

HO

Amylopectin

Amylopectin•70% of starch•Branched polymer with a branch every 20-25 glucose units•Containing 2,000 to 200,000 glucopyranose

•1,4’--D-glucopyranose polymer•Main function: Energy storage•Hydrolysis yields glucopyranose•Easily digested by mammals•Helical shape (as opposed to cellulose tightly packed, linear structure)•Water can penetrate into the helical coils (starch is water-soluble, while cellulose is not)

GLYCOGEN•Storage polysaccharide in animals•Branching every 10 glucose units

Napoloen’s Buttons p. 82

Amylose, amylopectin, and glycogen all feature linkages (which are readily digestible by mammals), but they differ in the extent of branching. Remember: glycolytic (sugar-cleaving) enzymes can clip off sugars only at the ends of chains. More branched chains are therefore metabolized at a faster rate than less branched chains, which is especially advantageous for animals, which need sudden spurts of energy.