18-1 Chemistry 121, Winter 2011, LA Tech Introduction to Organic Chemistry and Biochemistry...

18-1Chemistry 121, Winter 2011, LA Tech

Introduction to Organic Chemistry and Biochemistry

Instructor Dr. Upali Siriwardane (Ph.D. Ohio State)

E-mail: [email protected]

Office: 311 Carson Taylor Hall ; Phone: 318-257-4941;

Office Hours: MWF 8:00 am - 10:00 am;

TT 9:00 – 10:00 am & 1:00-2:00 pm.

December 17, 2010 Test 1 (Chapters 12-13)

January 19, 2011 Test 2 (Chapters 14,15 & 16)

February 7, 2011 Test 3(Chapters 17, 18 & 19)

February 23, 2011 Test 4 (Chapters 20, 21 & 22)

February 24, 2011 Comprehensive Make Up Exam:

Chemistry 121(01) Winter 2010-11


Chapter 18:Carbohydrates


Chapter 18: Carbohydrates18.1 Biochemistry--An Overview18.2 Occurrence and Functions of Carbohydrates18.3 Classification of Carbohydrates18.4 Chirality: Handedness in Molecules18.5 Stereoisomerism: Enantiomers and Diastereomers18.6 Designating Handedness Using Fischer Projections18.7 Properties of Enantiomers18.8 Classification of Monosaccharides18.9 Biochemically Important Monosaccharides18.10 Cyclic Forms of Monosaccharides18.11 Haworth Projection Formulas18.12 Reactions of Monosaccharides18.13 Disaccharides18.14 General Characteristics of Polysaccharides18.15 Storage Polysaccharides18.16 Structural Polysaccharides18.17 Acidic Polysaccharides18.18 Glycolipids and Glycoproteins18.19 Dietary Considerations and Carbohydrates


BiochemistryBiochemistry is the study of the chemical processes in

living organisms. It deals with the structure and function of cellular components, such as proteins, carbohydrates, lipids, nucleic acids, and other biomolecules.• Carbohydrates • Lipids • Proteins • Nucleic Acids • Use of carbohydrates as an energy source


The Study of Living ThingsBiochemistry is the study of the chemical

substances found in living organisms and the chemical interactions of these substances with each other.

A biochemical substance is a chemical substance found within a living organism.

Two types of biochemical substances: bioinorganic substances and bioorganic substances.• Bioinorganic substances : water and inorganic salts. • Bioorganic substances : carbohydrates, lipids,

proteins, and nucleic acids


Occurrence and Functions of Carbohydrates

“hydrates of carbon”: Cn (H2O)2

OccurrenceDifferent objects such as sheets of paper, insect skeletons,

fruits, cotton fabrics and ropes have one common feature: they all contain carbohydrates.

FunctionsThe chemical structure of carbohydrates, with their many

hydroxyl groups and the ability to assume

various spatial configurations, makes it possible for them to form nearly unlimited combinations

with other carbohydrate molecules, as well as with proteins and lipids. The resulting structures

perform important biological functions.


Classification of Carbohydrates MonosaccharidesThey consist of one sugar containing 3,4,5,6 and 7 carbon atoms and are

usually colorless, water-soluble, crystalline solids. Some monosaccharides have a sweet taste. Examples of monosaccharides include glucose (dextrose), fructose (levulose), galactose, xylose and ribose.

Disaccharides a sugar (a carbohydrate) composed of two monosaccharides.

Oligosaccharide An oligosaccharide is a saccharide polymer containing a small number

(typically 3-10 monosaccharides

PolysacharidesAre relatively complex carbohydrates. They are polymers made up of

many monosaccharides joined together by glycosidic bonds. They are insoluble in water, and have no sweet taste.


Classification of Sugars

Number of carbon atoms

Triose sugar: three carbon atoms

Tetroses sugar: four carbon atoms

Pentoses sugar five carbon atoms

Hexoses sugar: six carbon atoms

Number fo units (Saccharide-sugar units)

Monosaccharide (one sugar unit);

Disaccharide (two sugar units);

Oligosaccharide (2 to 10 sugar units);

Polysaccharide (over 10 sugar units).


Chirality: Handedness in Molecules

A "chiral" molecule is one that is not superimposable with its mirror image. Like left and right hands that have a

thumb, fingers in the same order, but are mirror images and not the same, chiral molecules have the same

things attached in the same order, but are mirror images and not the same.


MonosaccharidesGlyceraldehyde contains a stereocenter and exists

as a pair of enantiomers

CHO

CH OH

CH2OH

CHO

C

CH2OH

HHO

(S)-Glycer-aldehyde

(R)-Glycer-aldehyde


Fischer Projection FormulasFischer projection: a two dimensional

representation for showing the configuration of a tetrahedral stereocenter• horizontal lines represent bonds projecting forward • vertical lines represent bonds projecting to the rear• the first and last carbons in the chain are written in full;

others are indicated by the crossing of bonds

CHO

CH OH

CH2OH

CHO

H OH

CH2OH

(R)-Glyceraldehyde

convert to a Fischerprojection

(R)-Glyceraldehyde


Stereoisomerism: Enantiomers and Diastereomers

A Fischer projection is the most useful projection for discovering enantiomers. Compare the Glyceraldehyde enantiomer structures in this diagram.

D- and L-MonosaccharidesCHO

H OH

CH2OH

CHO

CH2OH

HHO

D D

L-GlyceraldehydeD-Glyceraldehyde

[]25 = +13.5° []25 = -13.5°

D-monosaccharide: a monosaccharide that, when written as a Fischer

projection, has the -OH on its penultimate carbon on the right

L-monosaccharide: a monosaccharide that, when written as a Fischer

projection, has the -OH on its penultimate carbon on the left


Properties of Enantiomers

Enantiomers have, when present in a symmetric environment, identical chemical and physical

properties except for their ability to rotate plane-polarized light by equal amounts but in opposite

directions.

A mixture of equal parts of an optically active isomer and its enantiomer is termed racemic and has

a net rotation of plane-polarized light of zero.

Enantiomers of each other often do have different chemical properties related to other substances

that are also enantiomers. Since many molecules in the bodies of living beings are enantiomers

themselves, there is often a marked difference in the effects of two symmetrical enantiomers on

living beings, including human beings.

http://en.wikipedia.org/wiki/Plane_(mathematics)

http://en.wikipedia.org/wiki/Polarized_light

http://en.wikipedia.org/wiki/Racemic

http://en.wikipedia.org/wiki/Polarized_light


DiastereomersHave more than one chiral centers

Diastereomers (or diastereoisomers) are stereoisomers that are not enantiomers (non-superposable mirror images of each other). Diastereomers can have different physical properties and different reactivity. In another definition diastereomers are pairs of isomers that have opposite configurations at one or more of the chiral centers but are not mirror images of each other.

http://en.wikipedia.org/wiki/Stereoisomer

http://en.wikipedia.org/wiki/Enantiomer

http://en.wikipedia.org/wiki/Superpose

http://en.wikipedia.org/wiki/Superpose


Diastereomers of Tartaric acidTartaric acid contains two asymmetric centers, but two of the "isomers"

are equivalent and together are called a meso compound. This configuration is not optically active, while the remaining two isomers are D- and L- mirror images, i.e., enantiomers. The meso form is a diastereomer of the other forms.

http://en.wikipedia.org/wiki/Tartaric_acid

http://en.wikipedia.org/wiki/Meso_compound

http://en.wikipedia.org/wiki/Meso_compound

http://en.wikipedia.org/wiki/Optical_activity


What is Plane Polarized Light?


Optically active of enantiomers

CHO

H OH

CH2OH

CHO

CH2OH

HHO

D D


[]25 = +13.5° []25 = -13.5°


D- and L-MonosaccharidesIn 1891, Emil Fischer made the arbitrary

assignments of D- and L- to the enantiomers of glyceraldehyde

CHO

H OH

CH2OH

CHO

CH2OH

HHO

D D


[]25 = +13.5° []25 = -13.5°


Aldoses:

Monosaccarides with aldehyde functional group. E.g. D-glucose

Ketoses:

Monosaccarides with keto functional group. E.g. D-fructose

Functional Groups


Aldoses


Aldoses

Hexoses


Cyclization of D-glucose

-D - glucose

- D - glucose

H

OH

O H

OH

H

OHH

OH

CH 2

OH

H

C

C

C

C

C

CH 2

OH

OH

OH

H

OHH

HO

H

H

OH

OH

OH

OH

H

H

H

OH

CH 2

OH

H

OH


Fischer & Haworth ProjectionIn solutions less than 1% of a sugar will be in the

linear form shown as Fischer projection

The normal form of most sugars is in a cyclic hemiacetal form shown as Haworth projection


Converting Fischer to Haworth Projection


a-Cyclic form of Gulose


Aldopentoses


Two monsaccharides connected by a bridging O atom called a glycosidic

bond as in sucrose.


D- and L-MonosaccharidesAccording to the conventions proposed by Fischer

• D-monosaccharide: a monosaccharide that, when written as a Fischer projection, has the -OH on its penultimate carbon on the right

• L-monosaccharide: a monosaccharide that, when written as a Fischer projection, has the -OH on its penultimate carbon on the left


D- and L-MonosaccharidesFollowing are

• the two most common D-aldotetroses and • the two most common D-aldopentoses

D-Erythrose D-Threose D-Ribose 2-Deoxy-D-ribose

CH2OH

CHO

OH

OHH

H

CH2OH

CHO

OH

HHO

H

CH2OH

CHO

OH

OHH

H

CH2OH

CHO

OH

HH

H

OHH OHH


D- and L-Monosaccharides• and the three common D-aldohexoses

CHO

H

OHH

HO

OHH

D-GlucosamineD-Glucose D-Galactose

CH2OH

OHH

CHO

H

OHH

HO

HHO

CH2OH

OHH

CHO

H

NH2H

HO

OHH

CH2OH

OHH


D- and L-MonosaccharidesAmino sugars

• N-acetyl-D-glucosamine is a component of many polysaccharides, including connective tissue such as cartilage; it is also a component of chitin, the hard shell-like exoskeleton of lobsters, crabs, and shrimp

CHO

OH

OH

H

NH2

H

H

HO

H

CH2OH

CHO

OH

OH

H

H

H

H

HO

H2N

CH2OH

CHO

OH

OH

H

NHCCH3

H

H

HO

H

CH2OH

OCHO

OH

H

H

NH2

H

HO

HO

H

CH2OH

4

2

D-Mannosamine(C-2 stereoisomer of D-glucosamine)

D-Glucosamine D-Galactosamine(C-4 stereoisomer of D-glucosamine)

N-Acetyl-D-glucosamine


Classification of MonosaccharidesMonosaccharides have the general formula CnH2nOn

the most common have from 3 to 9 carbons

Triose (3) , tetrose(4), pentose(5), hexose(6)

• aldose: a monosaccharide containing an aldehyde group: E.g. D-glucose

• ketose: a monosaccharide containing a ketone group: E.g. D-Fructose


Carbohydrates: MonosaccharidesCarbohydrate: a polyhydroxy aldehyde, a polyhydroxy

ketone, or a polymeric substance that gives these compounds on hydrolysis

Monosaccharide: a carbohydrate that cannot be hydrolyzed to a simpler carbohydrate

• monosaccharides have the general formula CnH2nOn

• the most common have from 3 to 9 carbons• aldose: a monosaccharide containing an aldehyde

group: E.g. D-glucose • ketose: a monosaccharide containing a ketone group:

E.g. D-Fructose


Monosaccharides• monosaccharides are classified by their number of

carbon atoms

hexose

heptoseoctose

triosetetrosepentose

FormulaNameC3H6O3C4H8O4

C5H10 O5

C6H12 O6

C7H14 O7C8H16 O8


Aldoses: Trioses, Tetroses and Pentoses


Aldoses: Hexoses


Important ketoses:

pentoses hexose heptoses


Monosaccharides• there are only two trioses

• often aldo- and keto- are omitted and these compounds are referred to simply as trioses

• although this designation does not tell the nature of the carbonyl group, it at least tells the number of carbons

CHO

CHOH

CH2OH

CH2OH

C=O

CH2OH

Dihydroxyacetone (a ketotriose)

Glyceraldehyde (an aldotriose)


Biochemically Important Monosaccharides

• Glucose is the most common monosaccharide consumed and is the circulating sugar of the bloodstream.

-Insulin and glucagon regulate blood levels of glucose.

• Galactose, a component of lactose (milk sugar) is also found in some plant gums and pectins.

-Galactosemia results from inability to metabolize galactose.

-If treated, galactosemia can be managed medically. Untreated galactosemia may result in mental retardation, liver damage, or death.

• Fructose is slightly sweeter than glucose. It is an intermediary in metabolism and is found in many fruits.

• Ribose and deoxyribose are aldopentose components of DNA and RNA.


Cyclic Forms of Monosaccharides

Intramolecular cyclization of simple sugars tend to exist primarily in cyclic form through hemiacetal or

hemiketal formation. It is the most stable arrangement.

C

C

C

CH2OH

C

C

OH

O

HC

C

C

CH2OH

C

C

O

OH

aldehyde hemiacetal


- and - anomers

The -OH group that forms can be above or below the ring resulting in two

forms - anomers

and are used to identify the two forms.

- OH group is down compared to CH2OH (trans).

- OH group is up compared to CH2OH (cis).


- and forms of D-glucose

-D - glucose

- D - glucose

H

OH

O H

OH

H

OHH

OH

CH 2 OH

H

C

C

C

C

C

CH 2 OH

OH

OH

H

OHH

HO

H

H

OH

OH

OH

OH

H

H

H

OH

CH 2 OH

H

OH


Haworth Projection Formulas• the anomers of D-glucopyranose

CHO

OH

H

OH

H

HO

H

H OH

CH2OH

HH OH

HHO

HOH

OH

H

CH2OHO

C

OH

HHO

HOH

H

CH2OHOH

O

H

OHH OH

HHO

HH

OH

H

CH2OHO

D-Glucose

-D-Glucopyranose (-D-Glucose)

()

()

-D-Glucopyranose (-D-Glucose)

anomeric carbon

+

anomericcarbon

5

5

1

1

redraw to show the -OH on carbon-5 close to thealdehyde on carbon-1

H


Converting Fischer to Haworth Projection


Haworth Projections• 5- and 6-membered hemiacetals are represented as

planar pentagons or hexagons viewed through the edge

• most commonly written with the anomeric carbon on the right and the hemiacetal oxygen to the back right

• - means that -OH on the anomeric carbon is cis to the terminal -CH2OH; - means it is trans

• a 6-membered hemiacetal is shown by the infix -pyran- • a 5-membered hemiacetal is shown by the infix -furan-

OOPyranFuran


Cyclic Structures in Haworth Projections

Aldopentoses also form cyclic hemiacetals• the most prevalent forms of D-ribose and other

pentoses in the biological world are furanoses

• the prefix deoxy- means “without oxygen”

OH ()

H

HOH OH

H HOHOCH2

H

OH ()

HOH H

H HOHOCH2

-D-Ribofuranose(-D-Ribose)

-2-Deoxy-D-ribofuranose(-2-Deoxy-D-ribose)


Cyclic StructuresD-Fructose, a 2-ketohexose, also forms a cyclic

hemiacetal

O

HO

HOCH2H

HHO

CH2OH

OHH

OH

HO

HOCH2H

HHO

H

HHO

HOHOHOCH2

CH2OH

O

HCH2OH

OH5

5

1

2

2

()

-D-Fructofuranose(-D-Fructose)

-D-Fructofuranose(-D-Fructose)

()

1

anomericcarbon

5

1

2


Fischer & Haworth ProjectionIn solutions less than 1% of a sugar will be in the

linear form shown as Fischer projection

The normal form of most sugars is in a cyclic hemiacetal form shown as Haworth projection


a-Cyclic form of Gulose


Aldopentoses


Aldoxeoses


Reactions of Monosaccharides

Reduction: The carbonyl group of a monosaccharide can be reduced to an hydroxyl group by a variety of reducing agents, including NaBH4

Oxidation: The -CHO group can be oxidized to –COOH

Reducing sugar: any carbohydrate that reacts with an oxidizing agent to form an aldonic acid

Oxidation: OH to –COOH

Enzyme-catalyzed oxidation of the 1° alcohol at carbon-6 of a hexose gives a uronic acid

Glucose Assay: The analytical procedure most often performed in the clinical chemistry laboratory is the determination of glucose in blood, urine, or other biological fluid


Reduction to AlditolsThe carbonyl group of a monosaccharide can be

reduced to an hydroxyl group by a variety of reducing agents, including NaBH4


Reduction to Alditols• name alditols by replacing the -ose of the name of the

monosaccharide by -itol• sorbitol is found in the plant world in many berries and

in cherries, plums, pears, apples, and seaweed; it is about 60% as sweet as sugar

• other common alditols include

CH2OH

CH2OH

OHHOHH

CH2OH

CH2OH

OHHHHOOHH

CH2OHHHOHHOOHH

CH2OHOHH

D-Mannitol XylitolErythritol


Oxidation to Aldonic AcidsThe -CHO group can be oxidized to -COOH

• reducing sugar: any carbohydrate that reacts with an oxidizing agent to form an aldonic acid


Oxidation to Uronic AcidsEnzyme-catalyzed oxidation of the 1° alcohol at

carbon-6 of a hexose gives a uronic acid


Oxidation to Uronic Acids• the body uses glucuronic acid to detoxify foreign

alcohols and phenols• these compounds are converted in the liver to

glycosides of glucuronic acid and then excreted in the urine

• the intravenous anesthetic propofol is converted to the following water-soluble glucuronide and excreted

O

OHOHO

OH

COO-

HO

Propofol A urine-soluble glucuronide


Glucose AssayThe analytical procedure most often performed in

the clinical chemistry laboratory is the determination of glucose in blood, urine, or other biological fluid• this need arises because of the high incidence of

diabetes in the population


Glucose AssayThe glucose oxidase method is completely specific

for D-glucose

+

+

glucoseoxidase

D-Gluconic acid

Hydrogen peroxide

-D-Glucopyranose

OHOH

HOHO

CH2 OHO

H2 O2

O2 + H2O

CO2H

CH2OH

OHHHHOOHHOHH


Glucose Assay• O2 is reduced to hydrogen peroxide, H2O2

• the concentration of H2O2 is proportional to the concentration of glucose in the sample

• in one procedure, hydrogen peroxide is used to oxidize o-toluidine to a colored product, whose concentration is determined spectrophotometrically

NH2

CH3

H2O2peroxidase colored product+

2-Methylaniline(o-Toluidine)


Ascorbic Acid (Vitamin C)L-Ascorbic acid (vitamin C) is synthesized both

biochemically and industrially from D-glucoseCHO

CH2OH

OHHHHOOHHOHH

CH2OH

OHH

HHO

O

OH

O

D-Glucose

both biochemialand industrial

syntheses

L-Ascorbic acid (Vitamin C)


Ascorbic Acid (Vitamin C)• L-ascorbic acid is very easily oxidized to L-

dehydroascorbic acid • both compounds are physiologically active and are

found in most body fluids

CH2OH

OHH

HHO

O

OH

O

CH2OH

OHH

HO

O

O

O

L-Ascorbic acid (Vitamin C)

L-Dehydroascorbic acid

oxidation

reduction


Disaccharides

A disaccharide forms by reaction of the -OH group on the anomeric carbon of one monosaccharide with an –OH group of a second monosaccharide.

• The linkage between monosaccharides in a disaccharide is referred to as a glycosidic linkage and is named according to the number of the carbon at which the linkage begins and the carbon on the second monosaccharide at which the linkage ends.

-The glycosidic linkage is also designated a or β, depending upon whether the conformation at the anomeric carbon is up or down.


Two monsaccharides connected by a bridging O atom called a glycosidic bond as in

sucrose.

Disaccharides


SucroseTable sugar, obtained from the juice of sugar cane

and sugar beet


LactoseThe principle sugar present in milk

• about 5 - 8% in human milk, 4 - 5% in cow’s milk


MaltoseFrom malt, the juice of sprouted barley and other

cereal grains


Uses for polysaccharides

•Storage polysaccharides

Energy storage - starch and glycogen

•Structural polysaccharides

Used to provide protective walls or lubricative coating to cells - cellulose and

mucopolysaccharides.

•Structural peptidoglycans

•Bacterial cell walls

Polysaccharides


StarchStarch is used for energy storage in plants

• it can be separated into two fractions; amylose and amylopectin

• amylose is composed of unbranched chains of up to 4000 D-glucose units joined by -1,4-glycosidic bonds

• amylopectin is a highly branched polymer of D-glucose; chains consist of 24-30 units of D-glucose joined by -1,4-glycosidic bonds and branches created by -1,6-glycosidic bonds


Starch• at the cellular level, the biochemical basis for this

classification is a group of relatively small membrane-bound carbohydrates


•Straight chain that forms coils (1 4) linkage.

O

O

H

HOH

OH

CH2OH

OOH

OHH

HO

HOH2C

O OH

OH

H

HO

HOH2C

O

O

HOH

HHO

HOH2C

O

O

H

HO

H

OH

CH2OH

O

OH

OHH

OH

CH2OH

O

O

HHO

HOH

CH2OH

Amylose starch


•Energy storage of animals.

•Stored in liver and muscles as granules.

•Similar to amylopectin but more highly branched.

O

O

O

O

O

O

O

O

O

O

O

O

O

O

c

(1 6) linkage

at crosslink

c

Glycogen


GlycogenThe reserve carbohydrate for animals

• a nonlinear polymer of D-glucose units joined by -1,4- and -1,6-glycosidic bonds

• the total amount of glycogen in the body of a well-nourished adult is about 350 g (about 3/4 of a pound) divided almost equally between liver and muscle


• Most abundant polysaccharide.

• (1 4) glycosidic linkages.

• Result in long fibers - for plant structure.

O O

H

OHH

OH

CH2OH

O OCH2OH

OHH

HO HO O

H

OHH

OH

CH2OH

O OCH2OH

OHH

HO HO O

H

OHH

OH

CH2OH

OCH2OH

OHH

HO H

Structural Polysaccharides: Cellulose


CelluloseCellulose is a linear polymer of D-glucose units

joined by -1,4-glycosidic bonds• it has an average molecular weight of 400,000,

corresponding to approximately 2800 D-glucose units per molecule

• both rayon and acetate rayon are made from chemically modified cellulose


H OO

HH

OHH

COO-

HO

H O

OH

O

HH

NH

CH2OH

H

C OCH3

H OO

HH

OHH

COO-

HO

H O

OH HH

NH

CH2OH

H

C OCH3

H OO

HH

OHH

COO-

HO

H O

OH

O

HH

NH

CH2OH

H

C OCH3O

•These materials provide a thin, viscous, jelly-like coating to cells.

•The most abundant form is hyaluronic acid.

•

(1 3)

(1 4)

Mucopolysaccharides: lubricative coatings

Alternating units of N-acetylglucosamine

and D-glucuronic acid.


Glycolipids and Glycoproteins

Glycolipids: are carbohydrate-attached lipids. Their role is to provide energy and also serve as markers for cellular recognition.

Glycoproteins: are the proteins covalently attached to carbohydrates such as glucose, galactose, lactose, fucose, sialic acid, N-acetylglucosamine, N-acetylgalactosamine, etc.

The antigens which determine blood types belong to glycoproteins and glycolipids (more info later).

http://www.web-books.com/MoBio/Free/Ch1B5.htm


Cyclic StructureMonosaccharides have hydroxyl and carbonyl

groups in the same molecule and exist almost entirely as five- and six-membered cyclic hemiacetals• anomeric carbon: the hemiacetal carbon of a cyclic

form of a monosaccharide• anomers: monosaccharides that differ in configuration

only at their anomeric carbons


GlycosidesGlycoside: a carbohydrate in which the -OH on its

anomeric carbon is replaced by -OR

HH OH

HHO

HOH

OH

H

CH2OHO

CH3OH H+

-H2O

OCH2OH

H

OH

OCH3H

HOH

OHH

H

OCH2OH

H

OH

HH

HOH

OHH

OCH3

(-D-Glucose)-D-Glucopyranose

Methyl -D-glucopyranoside(Methyl -D-glucoside)

anomeric carbon

+

+

Methyl -D-glucopyranoside(Methyl -D-glucoside)

glycosidicbond glycosidic

bond


GlycosidesGlycosidic bond: the bond from the anomeric

carbon of the glycoside to an -OR group

To name a glycoside, name the alkyl or aryl group bonded to oxygen followed by the name of the carbohydrate; replace the ending -e by -ide• methyl -D-glucopyranoside• methyl -D-ribofuranoside


N-Glycosides• the anomeric carbon of a cyclic hemiacetal also reacts

with an N-H of an amine to form an N-glycoside• especially important in the biological world are the N-

glycosides of D-Ribose and 2-deoxy-D-ribose with the following heterocyclic aromatic amines

HN

NH

O

O

Uracil

N

NH

O

NH2

Cytosine

HN

NH

O

O

Thymine

CH3N

N N

N

H

NH2

HN

N N

N

H

O

H2N

Adenine Guanine

Pyrimidine bases Purine bases


N-Glycosides• following is the b-N-glycoside formed between D-

ribofuranose and cytosine

H

H

H

H

OHOCH2

HO OH

NH2

O

N

N

anomericcarbon

a -N-glycosidicbond


Blood Group SubstancesMembranes of animal plasma cells have large

numbers of relatively small carbohydrates• these membrane-bound carbohydrates are part of the

mechanism by which cell types recognize each other; they act as antigenic determinants

• among the first discovered of these antigenic determinants are the blood group substances

In the ABO system, individuals are classified according to four blood types: A, B, AB, and O


Blood Group Substances• one of these membrane-bound monosaccharides is L-

fucose

HHO

OHH

CH3

CHO

OHH

HHO

An L-monosaccharide;this -OH is on the left inthe Fischer projection

L-Fucose

Carbon 6 is -CH3 ratherrather than -CH2OH


Blood Group SubstancesA, B, AB, and O blood types

N-Acetyl-D-galactosamine

D-Galactose N-Acetyl-D-glucosamine

D-Galactose N-Acetyl-D-glucosamine

Redblood cell

Type A

Type B

D-GalactoseType O N-Acetyl-D-glucosamine

Redblood cell

Redblood cell

D-galactose

(-1,4)

(-1,4)

(-1,3)

(-1,3)

(-1,3)

L-Fucose

(-1,2)

L-Fucose

(-1,2)

L-Fucose

(-1,2)


Polysaccharides

•These are biopolymers composed of hundreds to thousands of

simple sugar units (monosaccharides).

•The most common monosaccharide used

in polysaccharides is glucose.

C

C

C

C

C

CH 2

OH

OH

OH

H

OHH

HO

H

H

OH


Polysaccharides

•Uses for polysaccharides

•Storage polysaccharides

•Energy storage - starch and glycogen

•Structural polysaccharides

•Used to provide protective walls or lubricative

coating to cells - cellulose and mucopolysaccharides.

•Structural peptidoglycans

•Bacterial cell walls


Starch

•Energy storage used by plants

•Long repeating chain of -D-glucose

•Chains up to 4000 units

•Amylose straight chain

•Amylopectin branched structure

•Starch is a mixture of about 75% amylopectin and 25% amylose.


Amylose starch

•Straight chain that forms coils (1 4) linkage.

O

O

H

HOH

OH

CH2OH

OOH

OHH

HO

HOH2C

O OH

OH

H

HO

HOH2C

O

O

HOH

HHO

HOH2C

O

O

H

HO

H

OH

CH2OH

O

OH

OHH

OH

CH2OH

O

O

HHO

HOH

CH2OH


Amylose starch

Example showing coiled structure

- 12 glucose units

- hydrogens and side chains are omitted.


Amylopectin starch

•Amylopectin differs from amylose only in that it has side chains. These are formed from

• a (1 6) links

•Side chains occur every 24-30 units.

•Starch is stored as starch grains. They cannot diffuse from the cell and have little effect on

the osmotic pressure of the cell.


Glycogen

•Energy storage of animals.

•Stored in liver and muscles as granules.

•Similar to amylopectin but more highly branched.

O

O

O

O

O

O

O

O

O

O

O

O

O

O

c

(1 6) linkage

at crosslinkc


Cellulose

• Most abundant polysaccharide.

• (1 4) glycosidic linkages.

• Result in long fibers - for plant structure.

O O

H

OHH

OH

CH2OH

O OCH2OH

OHH

HO HO O

H

OHH

OH

CH2OH

O OCH2OH

OHH

HO HO O

H

OHH

OH

CH2OH

OCH2OH

OHH

HO H


H OO

HH

OHH

COO-

HO

H O

OH

O

HH

NH

CH2OH

H

C OCH3

H OO

HH

OHH

COO-

HO

H O

OH HH

NH

CH2OH

H

C OCH3

H OO

HH

OHH

COO-

HO

H O

OH

O

HH

NH

CH2OH

H

C OCH3O

Mucopolysaccharides•

These materials provide a thin, viscous, jelly-like coating to cells.

•The most abundant form is hyaluronic acid.

•

•Alternating units of

• N-acetylglucosamine

• and D-glucuronic acid.

(1 4)

(1 3)


Reducing and Nonreducing sugar.

Monosaccharides both aldoses and ketoses Disaccharides with free hemiacetal or hemiketal ends:maltose and lactose

Aldoses Aldehyde sugars should show positive test for the

Benedict's test

Ketoses give a positive test for Benedict's test because of

the ability of ketoses to get converted to aldoses (aldehydes) via enediol.


Enediol Intermediate


Galactosemia and Lactose Intolerance.

Galactosemia

Lack of enzymes necessary for the conversion of galactose to phosphorylated glucose which is used in the cellular metabolism or glycolysis

Lactose Intolerance.

Lack of diagestive enzyme, lactase to break down lactose to glucose and galactose


Practice Exercise

Answers:

a. Not a chiral center

b. Not a chiral center

c. Chiral center

d. Not a chiral center



Interactions Between Chiral Compounds

Our body responds differently to different enantiomers:

One may give higher rate or one may be inactive• Example: Body response to D form of hormone

epinephrine is 20 times greater than its L isomer



Exercise


Dominant form of monosaccharides with 5 or more C atoms is cyclic - cyclic forms are in equilibrium with open chain form

Cyclic forms are formed by the reaction of carbonyl group (C=O) with hydroxyl (-OH) group on carbon 5

Cyclic Hemiacetal Forms of D-Glucose


Practice Exercise

Which of the monosaccharides glucose, fructose, galactose, and ribose has each of the following structural characteristics? (There may be more than one correct answer for a given characteristic)

a. It is a pentose.

b. It is a ketose.

c. Its cyclic form has a 6-membered ring.

d. Its cyclic form has two carbon atoms outside the ring.

Answers:

a. Ribose

b. Fructose

c. Glucose, galactose

d. Fructose



Five important reactions of monosaccharides:• Oxidation to acidic sugars • Reduction to sugar alcohols • Glycoside formation• Phosphate ester formation • Amino sugar formation

These reactions will be considered with respect to glucose.

Other aldoses, as well as ketoses, undergo similar reactions.


OxidationOxidation to acidic functional groups present in

sugars: The redox chemistry of monosaccharides is closely linked to the alcohol and aldehyde

Oxidation can yield three different types of acidic sugars depending on the type of oxidizing agent used:• Weak oxidizing agents such as Tollens and

Benedict’s solutions oxidize the aldehyde end to give an aldonic acid.

• A reducing sugar is a carbohydrate that gives a positive test with Tollens and Benedict’s solutions.



Oxidizing Agents

Strong oxidizing agents can oxidize both ends of a monosaccharide at the same time (the carbonyl group and the terminal primary alcohol group) to produce a dicarboxylic acid: • Such polyhydroxy dicarboxylic acids are known

as aldaric acids.


Oxidization

In biochemical systems enzymes can oxidize the primary alcohol end of an aldose such as glucose, without oxidation of the aldehyde group, to produce an alduronic acid.


Amino Sugar Formation

Amino sugar formation: An amino sugar - one of the hydroxyl groups of a monosaccharide is replaced with an amino group

In naturally occurring amino sugars the carbon 2 hydroxyl group is replaced by an amino group

Amino sugars and their N-acetyl derivatives are important building blocks of polysaccharides such as chitin


Cellobiose

Cellobiose is produced as an intermediate in the hydrolysis of the polysaccharide cellulose:• Cellobiose contains two b - D-glucose

monosaccharide units linked through a b (1—4) glycosidic linkage.

O OH

OH

OH

CH2OH

HO

OHOH

OH

CH2OH

O

Cellobiose

(1-4)


Chitin• Similar to cellulose in both function and structure• Linear polymer with all b (14) glycosidic linkages - it has a

N-acetyl amino derivative of glucose• Function is to give rigidity to the exoskeleton s of crabs,

lobsters, shrimp, insects, and other arthropods

N-Acetyl

b-D-Glucoseamine

O

HN

OH

O

OH

O

OHO

HO O

OH

HO O

OHO

HO

O

O

O

HN

O

HN

O

HN

O


Acidic polysaccharides - polysaccharides with a repeating disaccharide unit containing an amino sugar and a sugar with a negative charge due to a sulfate or a carboxyl group.

Structural polysaccharide present in connective tissue associated with joints, cartilage, synovial fluids in animals and humans • Primary function is lubrication necessary for joint

movement• These are heteropolysaccharides - have more than one

type of monosaccharide monomers is present.

Examples:• Hyaluronic acid• Heparin


Hyaluronic Acid and HeparinHyaluronic acid:

• Alternating residues of N-acetyl-b-D-glucosamine and D-glucuronic acid.

• Highly viscous - serve as lubricants in the fluid of joints and part vitreous humor of the eye.

Heparin:• An anticoagulant-

prevents blood clots. • Polysaccharide with 15–

90 disaccharide residues per chain.


A glycolipid is a lipid molecule that has one or more carbohydrate (or carbohydrate derivative) units covalently bonded to it.

A glycoprotein is a protein molecule that has one or more carbohydrate (or carbohydrate derivative) units covalently bonded to it.


Nutrition

Foods high in carbs content constitute over 50% of the diet of most people of the world -- a balanced dietary food should contain about 60% of carbohydrate:• Corn in South America• Rice in Asia• Starchy root vegetables in parts of Africa• Potato and wheat in North America

Nutritionist divide dietary carbs into two classes:• Simple carb: dietary monosaccharides or disaccharides -

sweet to taste commonly referred to as sugars - 20 % of the energy in the US die

• Complex carbs: Dietary polysaccharides -- starch and cellulose - normally not sweet to taste


Glycemic Foods

A developing concern about intake of carbohydrates involves how fast the given dietary carbs are broken down to glucose within the human body

Glycemic effect refers to:• how quickly carbs are digested • how high blood glucose rise• how quickly blood glucose levels return to

normal

Glycemic index (GI) has been developed for rating foods

18-1 Chemistry 121, Winter 2011, LA Tech Introduction to Organic Chemistry and Biochemistry...

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