ORGANIC MOLECULES
1.1 INORGANIC vs ORGANIC CHEMISTRY
JONS JACOB BERZELIUS - stated in 1810 that living things work by some mysterious “vital force,” a
hypothesis called vitalism. Related to this, he proposed that compounds could be distinguished by whether
they required any organisms in their manufacture (organic compounds) or whether these did not (inorganic
compounds).
VITALISM - organic molecules can’t be produced from inorganic molecules, but instead can only be
produced from a living organism or some part of a living organism.
ORGANIC
INORGANIC
C, H, O, N, P, S
Halogens (F, Cl, Br, I)
All elements
Usually covalent bond
Usually ionic bond
Unstable to heat
Stable to heat
Seldom forms electrolyte
Forms ions
Not commonly ionized
Low boiling and melting point
Usually high boiling and melting point
Soluble in nonpolar solvents
Soluble in polar solvents
Flammable or usually combusts to C, CO, and
CO2
Non-flammable or don’t combust easily
NOTE: In terms of polarity, alcohol (organic) is an exemption.
EXAMPLES:
● Organic - DNA, Sugar, Methane, and Ethanol
● Inorganic - Salt, Diamond, Co2, Silver, and Water
EXAMPLES for SOLUBILITY and POLARITY:
● Kerosene and Naphthalene
● H2O and Alcohol
EXAMPLES for COMBUSTION:
● Sawdust turns to black (Carbon)
➔ Complete combustion causes residue.
ORGANIC CHEMISTRY - is the study of carbons more specifically the study of hydrocarbons and its
derivatives.
NOTE: Protoplasm, the living substance of organisms, is composed of organic and inorganic compounds.
The inorganic compounds include water and mineral salts. The principal organic compounds (compounds
containing chains or rings of carbon atoms) are carbohydrates, proteins, lipids, and nucleic acids.
1.2 FUNCTIONAL GROUPS
1.3 ORGANIC MOLECULES
Organisms are composed mostly of water and organic molecules, chemical compounds that contain both
carbon and hydrogen. Life uses a tremendous variety of organic compounds. Organic molecules consisting
almost entirely of carbon and hydrogen are called hydrocarbons; methane (CH4) is the simplest. Because
a carbon atom forms four covalent bonds, however, this element can assemble into much more complex
molecules, including long chains, intricate branches, and rings. Many organic compounds also include other
essential elements, such as oxygen, nitrogen, phosphorus, or sulfur.
All organisms, from bacteria to plants to people, consist largely of the same four types of organic molecules:
Carbohydrates, Proteins, Nucleic Acids (DNA and RNA), and Lipids. Life’s chemistry is powerful
evidence that all species inherited the same basic chemical structures.
1.4 LARGE ORGANIC MOLECULES ARE COMPOSED OF SMALLER SUBUNITS
Proteins, nucleic acids, and some carbohydrates all share a property in common with one another: they are
polymers, which are chains of small molecular subunits called monomers. A polymer is made of
monomers that are linked together, just as a train is made of individual railcars.
MONOMERS:
❖ Monosaccharide
❖ Amino Acid
❖ Nucleotide
POLYMERS:
❖ Disaccharide
❖ Polysaccharide
❖ Protein
❖ Nucleic Acid
NOTE: Lipids aren't polymers because they are made up of smaller units of different kinds (like glycerol
and fatty acids) rather than monomers that repeat themselves. In short, they aren’t repeating units.
DEHYDRATION SYNTHESIS or CONDENSATION REACTION - Cells use a chemical reaction called
dehydration synthesis (or condensation reaction) to link monomers together into polymers. In this
reaction, a protein called an enzyme removes an -OH (hydroxyl group) from one molecule and a hydrogen
atom from another, forming H2O and a new covalent bond between the two smaller components. (The term
dehydration means water is lost). In repeating this reaction many times, cells can build extremely large
polymers consisting of thousands of monomers.
HYDROLYSIS - The reverse reaction, called hydrolysis, breaks down the covalent bonds that link
monomers. In hydrolysis, enzymes use atoms from water to add a hydroxyl group to one molecule and a
hydrogen atom to another (hydrolysis means “breaking with water”). Hydrolysis happens in your body when
digestive enzymes in your stomach and intestines break down the proteins and other polymers in food.
1.5 CARBOHYDRATES
CARBOHYDRATES - are used as fuel molecules to provide energy for cells (for cellular activities). These
are organic molecules that consist of carbon, hydrogen, and oxygen, often in the proportion 1:2:1.
- forms a glycosidic bonding or linkage
- (CH2O)n, where n is the number of carbons in the molecule
- ends with -ose (e.g. fructose, glucose, and maltose)
- carbohydrates are the simplest of the four main types of organic compounds, mostly because just a few
monomers account for the most common types in cells.
- carbohydrates are not actually hydrates of carbon. They are polyhydroxy aldehyde and ketones. The
term polyhydroxy means that the compounds contain many hydroxyl (-OH) groups.
- monosaccharides which contain a single saccharide group can polymerize to form much more complex
carbohydrates.
- the two main groups of carbohydrates are simple sugars and complex carbohydrates.
- no chemical test works for all carbohydrates.
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Carbohydrates are products of photosynthesis in plants.
They serve as the major component in the structure of plants and are a major source of energy for
most animals.
Referred to as saccharides (e.g. monosaccharide, disaccharide, oligosaccharide, and
polysaccharide) which comes from the Greek word for Sugar.
Carbohydrates attached to cell surface proteins (in the cell membrane) serve as “name tags” that
help the body’s immune system recognize its own cells.
At the center of a nucleic acid is a five-carbon sugar—ribose in RNA (ribonucleic acid) and
deoxyribose in DNA (deoxyribonucleic acid).
REMEMBER: An aldose is a polyhydroxy aldehyde, ie, an aldehyde that has a hydroxyl group
(OH) on every carbon atom except the carbonyl carbon atom (C=O).
1.6 PHYSICAL PROPERTIES OF CARBOHYDRATES
A. Physical Properties
1. Form
➔ Simple ones are generally crystalline
➔ Higher ones are generally powdery or fibrous
- e.g. Cellulose
2. Solubility
➔ Lower members are soluble in all proportion of water
- insoluble with 95% ethyl alcohol
➔ Some higher members are also insoluble in cold water
- e.g. Glycogen and Insulin
➔ Some higher members are also insoluble in cold water but are soluble in boiling
water
3. Taste
- the term sugar is given to anything that is sweet tasting
- most of the lower carbs are called sugar
Cause of sweet taste:
1. Glucophore - potential sweet tasting component
2. Auxogluc - a sweet taste is produced
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Fructose - 100% sweet taste
Invert Sugar – 75
Sucrose - 58
Glucose - 43
Maltose - 19
Galactose – 9.2
Lactose - least sweet
Honey
1.7 CHEMICAL PROPERTIES
The chemical properties of carbs is due to 2 major components.
1. Potentially free CHO and C=O (carbonyl) groups
2. (OH) hydroxyl group
a. Due to potentially free CHO or C=O groups
- Reaction with strong Alkali in Moore’s test
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Principles involved:
● Liberation of the (CHO) aldehyde group
● Polymerization of CHO’s group into a resinous substance
➔ to caramel
b. Reducing property
- Sugars are capable of reducing solution of metallic salts, especially if slightly alkaline
e.g. slightly alkaline:
1. Trommer’s Test - copper sulfate
2. Fehling’s Test - copper sulfate
3. Benedict’s Test - copper sulfate
4. Barfoed’s Test - copper sulfate
- Slightly acidic
- Use to different monosaccharides
OTHER REDUCTIN TEST
1. Nylander’s Test - Bi(OH)3
➔ Black ppt (precipitate) due to Bismuth
2. Picric Test - picric acid
➔ Mahogany red picramic acid
3. Phenyl hydrazine
➔ A specific test for Arabinose, Lactose, and Maltose
- sugar + phenyl hydrazine—osazone crystals
- Three stages to complete the reaction:
1. Glucose + Phenyl hydrazine—>Phenyl hydrazine
2. Phenyl hydrazine + Phenyl hydrazine conversion to second Carbon; C atom into
C=O group.
3. C=O group reacts with a third molecule of Phenyl hydrazine to form the insoluble
osazone crystal.
4. Oxidation of sugar - when sugars are boiled a strong acid will undergo various stages of oxidation.
e.g. using Glucose
4.1. Oxidation of CHO (C-1) group will form on aldonic acid
● Glucose - Gulonic acid
● Mannose - Mannoic acid
● Galactose - Galactonic acid
4.2. Oxidation of Primary Alcohol (C-6)
Aldonic acid - dicarboxylic acid + saccharic acid
Glucose - Glucaric acid
Mannose - Mannoric acid
Galactose - Galaric acid or Mucic acid
❖ Mucic Acid Test - is a specific test for Galactose
❖ Mucic Acid - is insoluble only in sugar acid.
4.3. If the (CHO) aldehyde group is protected and oxidation occurs only the primary alcohol groups
(C-6)
❖ Glucose - Glucoronic Acid
❖ Mannose - Mannuronic Acid
❖ Galactose - Galactoronic Acid
Glucoronic Acid
is an important physiological compound, because
1. it’s used to detoxify liver
2. important compound of cartilage and bone formation
Another example:
● Fructose - 3 Glucose and 3 manose
➔ since fructose is a ketene, it will not be oxidized directly
➔ it has to be broken down into glucose and mannose; then it will undergo oxidation
➔ during oxidation, fructose will be oxidized into:
REDUCTION OF SUGARS
- will determine the presence of (OH) hydroxyl group in sugar
- (CHO) aldehyde group can undergo reduction by ________, it is an alcohol group (C2OH)
Forming the following:
1. Glucose - Sorbitol
2. Mannose - Mannitol
3. Galactose - Dulcitol
4. Fructose - cannot be directly reduced
- converted into:
● Glucose
● Mannose
- then reduced to compound alcohol
Phosphoric Acid
● a common reagent used to react with (OH) hydroxyl groups
● which is found relevant during carbohydrate metabolism where the formation of phosphoric
acid ester play an important role in glucose metabolism
Phosphoric Acid Ester formed are:
1. Glucose - 1-PO4 or Cori Ester
2. Glucose - 6-PO4 or Robinson Ester
3. Fructose - 6-PO4 or Neuberg Ester
4. Fructose - 1.6-di PO4 or Harden Young Ester
REDUCTION WITH STRONG ACIDS
- Strong acids will act on CHOs dehydratiry them into:
1. Furanal (if pentanose)
2. Hydroxymethylfurfural (hexose or higher CHO)
➔ this dehydration product will then react with corresponding reagent to form colored
products of unknown nature.
➔ the color products will sometimes serve as a specific test for some CHO’s
e.g.
2.1. Molisch Test - a Naphtol and conc. HCl = violet ring
➔ a general test for CHO because all will give a positive result (+) with it
2.2. Seliwanoff Test - Resorchinol and conc. H2SO4
➔ must be performed in 30 sec. because if △ is continued beyond 30 sec.
➔ even glucose and other monosaccharide will give a (+) result
➔ (+) color is red with pt.
➔ specific test for ketose e.g. Fructose
➔ ketose wil form hydroxymethyl furfural within 30 sec, so it must be done
properly
2.3 Tollen’s Test - Phloroglucinol and conc. HCl
➔ specific only for galactose
➔ Lactose + Glucose may also give some degree of (+) result
2.4 Anthrone Test - Anthrone and conc. H2SO4 = green color
➔ specific for Glucose - but not proven conclusively
1.8 FERMENTATION
FERMENTATION - decomposition of an organic compound
- preferably a carbohydrate
- produced by a living organism or by its enzyme and form ethyl alcohol with CO2 evolution
I.
Yeast Fermentation
- caused by enzyme; enzyme present in yeast
Readily fermented by yeast:
➢ Glucose
➢ Mannose
➢ Fructose
Hydrolysis - will undergo fermentation:
➢ Maltose
➢ Sucrose
Are not fermented by yeast:
➢ Lactose
➢ Galactose
II.
Bacterial Fermentation
- fermented by bacteria - esp intestinal bacteria:
➢ Lactose
➢ Galactose
➔ Lactic Acid - cause some gastro intestinal disturbance especially in
infants
1.9 ENZYMES
a. Melibiase - enzymes that act only on galactose-glucose linkage
b. Sucrase - can act only on glucose and fructose linkage
1.10 SOURCES
1. Plants
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2. Animal
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Fruit
Vegetable
Bean
Rice
Peas
Milk
Milk product
1.11 BIOLOGICAL IMPORTANCE
1. Body Fuel
- Vital source of energy
- Optimal performance
- Carbohydrates (55-65% energy)
1.12 CARBOHYDRATE STRUCTURE
Saccharides with four or more carbon atoms can fold back on themselves to assume a ring form. Folding
into a ring occurs through a reaction between two functional groups in the same monosaccharide, as occurs
in Glucose. The ring form of most five- and six- carbon sugars at the position of the ring is asymmetric
because its four bonds link to different groups of atoms. This asymmetry allows monosaccharides such as
Glucose to exist as two different stereoisomers. The Glucose stereoisomer with an -OH group pointing
below the plane of the ring is known as alpha-glucose, or α-glucose; the stereoisomer with an -OH group
pointing above the plane of the ring is known as beta-glucose, or β-glucose.
I.
FISCHER PROJECTION (Linear): D and L
II.
HAWORTH PROJECTION (Cyclic/Ring): Alpha and Beta
Alpha (α) - is when the (OH) hydroxyl group of C1 is pointing at the opposite direction to the CH2OH. The
(OH) hydroxyl group of C1 is at the bottom.
Beta (β) - is when the (OH) hydroxyl group of C1 is pointing at the same direction to the CH2OH. The (OH)
hydroxyl group of C1 is at the top.
NOTE: Any —OH group at a chiral center that is to the right in a Fischer projection formula points down in
the Haworth projection formula and any —OH group to the left in a Fischer projection formula points up in
the Haworth projection formula.
: The α- and β- rings of monosaccharides can give the polysaccharides assembled from them vastly
different chemical properties. For example, Starches, which are assembled from α-glucose units, are
biologically reactive polysaccharides easily digested by animals; Cellulose, which is assembled from βglucose units, is relatively unreactive and, for most animals, completely indigestible.
I.
SIMPLE CARBOHYDRATES/SUGARS - provide quick energy
1) MONOSACCHARIDE - are the smallest carbohydrates, the most common contain five or six
carbon atoms.
- three to seven carbon atoms
- can’t be degraded into simpler products by hydrolysis reaction
- contain a single polyhydroxy aldehyde or polyhydroxy ketone unit
- PROPERTIES: pure monosaccharides are water-soluble, white, crystalline solids
● All monosaccharides can occur in linear form. Monosaccharides with four or more carbons can fold
back on themselves to assume a ring form. Folding into a ring occurs through a reaction between
two functional groups in the same monosaccharide, as occurs in Glucose.
● Short chains of monosaccharides on cell surfaces are important in immunity. For example, a
person’s blood type—A, B, AB, or O—refers to the combination of carbohydrates attached to the
surface of his or her blood cells. A transfusion of the “wrong” blood type can trigger a harmful
immune reaction.
● Monosaccharides may be in the form of Aldoses or Ketoses. Aldoses contain an aldehyde
functional group whereas ketoses have a ketone functional group.
● They are also referred to as “reducing sugars” because of these free functional groups being
able to be oxidized through chemical tests.
e.g. Benedict’s Test
BENEDICT’S TEST
❖ This test is demonstrated by adding Benedict’s solution. The benedict’s test works for
most monosaccharides and disaccharides. It specifically tests for free aldehyde groups (HC = 0) in sugars. This group reacts with copper sulfate in Benedict’s solution to form a
brick-red precipitate, Cu2O (Cuprous oxide) that is green to reddish orange. A green
solution indicates a small amount of reducing sugars. Non-reducing sugars produce no
change in color. (e.g., the solution remains blue).
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Glucose + Benedict’s slon —> positive for Benedict’s Test
Fructose + Benedict’s slon —> positive for Benedict’s Test
Sucrose + Benedict’s slon —> negative for Benedict’s Test
Starch + Benedict’s slon —> negative for Benedict’s Test
CLASSIFICATION OF MONOSACCHARIDES ACCORDING TO NUMBER OF CARBONS:
a. Trioses (C3H6O3):
● D(+) - glyceraldehyde
➢ Aldotriose
● Dihydroxyacetone
➢ Ketotriose
b. Tetrose (C4H8O4):
● Erythrose
➢ Aldotetrose
● Erythrulose
➢ Ketotetrose
c.
Pentose (C5H10O5):
● Xylose
➢ Aldopentose
● D-(-)-lyxose
➢ Aldopentose
a constituent of the heart muscle.
● D-(-)-ribose
➢ Aldopentose
- ribose and 2-deoxyribose - present as intermediates in metabolic
pathways and are important building blocks of RNA and DNA.
● Xylulose
➢ Ketopentose
● D-ribulose
➢ Ketopentose
● D-xylulose
➢ Ketopentose
● Ribose
● Deoxyribose
● Arabinose
d. Hexoses (C6H12O6):
● Glucose
➢ Aldohexose
● Mannose
➢ Aldohexose
● Galactose
➢ Aldohexose
● D-(+)-mannose
➢ Aldohexose
● D-(+)-glucose
➢ Aldohexose
- a 5% (m’v) glucose solution is often used in hospitals as intravenous
source of nourishment for patients who cannot take food by mouth.
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D-(+)-galactose
➢ Aldohexose
Fructose
➢ Ketohexose
D-(-)-fructose
➢ Ketohexose
D-mannose
➢ Ketohexose
- found in certain bacteria, fungi, and plants.
- converted to usable glucose in the body, but has no real physiological
significance
e. Heptose (C7H14O7):
● Sedoheptulose
● Sedoheptulose
BIOCHEMICALLY IMPORTANT MONOSACCHARIDES:
a. Glucose (Dextrose)
➢ Aldohexose (aldehyde)
➔ most abundant in nature
➔ nutritionally most important
➔ six membered cyclic form (Pyran)
b. Fructose
➢ Ketohexose (ketone)
➔ sweetest of all sugars; the fruit sugar
➔ found in many fruits and honey
➔ good dietary sugar—due to higher sweetness
➔ five membered cyclic form (Furan)
COMMON: Glucose and Fructose (hexose)
c. Galactose (Brain Sugar)
➢ Aldohexose (aldehyde)
➔ a component of milk sugar
➔ synthesized in humans
➔ also called brain sugar—part of the brain and nerve tissue
➔ Galactosemia — a genetic deficiency in the infant - the gene responsible for the
enzyme that converts D-galactose to D-glucose, such infant cannot metabolize
galactose and it builds up in the blood and tissue.
➔ used to differentiate between blood types
➔ six membered cyclic form
d. Ribose
➢ Aldopentose (aldehyde)
➔ part of DNA
part of RNA
➔ part of ATP
➔ five membered cyclic form (Furan)
COMMON: Galactose and Ribose (aldose)
FIVE IMPORTANT REACTIONS OF MONOSACCHARIDES:
a. Oxidation - to acidic sugars
b. Reduction - to sugar alcohols
c. Phosphate ester formation
d. Amino sugar formation
e. Glycoside formation
➔ These reactions will be considered with respect to Glucose; other aldoses, as well as
ketoses, undergo similar reactions.
2) DISACCHARIDE (C12H22O11) - two monosaccharides covalently bonded and joined by
dehydration synthesis (or acetal formation)
- one monosaccharide acts as a hemiacetal and other as an alcohol and the resulting ether bond is
glycosidic linkage.
➔ condensation of the (OH) hydroxyl function of the hemiacetal group of one monosaccharide
with the (OH) hydroxyl group of another monosaccharide forms the bond, called a
glycosidic bond, joining the two saccharides.
- Glycosidic bonds are formed when two monosaccharides are joined together. It is written in
chemical shorthand as a e.g. 1->4 linkage; 1->2, 1->3, and 1->6 linkages are also common in
carbohydrate chains. The linkages are designed as alpha (α) or beta (β) depending on the
orientation of the -OH group at the 1 carbon that forms the bond.
- upon hydrolysis they produce monosaccharides
- PROPERTIES: crystalline and water soluble
● Their function in cells is to provide a ready source of energy, which is released when their bonds
are broken
a. Maltose (Malt Sugar) *Reducing Sugar*
➢ Glucose and Glucose
➔ malt sugar, found in corn syrup and malt
➔ is present in germinating seeds and is a major sugar used in the brewing industry.
Beer brewers use it to promote fermentation.
➔ it provides energy in sprouting seeds.
➔ Consists of two molecules of Glucose joined by α- 1, 4-glycosidic bond
α- 1, 4-glycosidic bond means that the first sugar is in α-configuration and
its C-1 is linked to C4 of the second sugar component. The second sugar
may either be an alpha or a beta anomer.
b. Sucrose (Table Sugar) *Nonreducing Sugar*
➢ Glucose and Fructose
➔ is transported to and from different parts of leafy plants.
➔ it is probably the most plentiful sugar in nature.
➔ table sugar is made by extracting and crystallizing sucrose from plants, such as
sugar cane and sugar beets. The sucrose found in sugarcane sap and beet roots
is used by plants to fuel growth. Are produced commercially from the juice of sugar
cane and sugar beets.
➔ the α-anomeric carbon 1 of Glucose joins the β-anomeric carbon 2 of Fructose (α1, 2-glycosidic bond)
c. Lactose (Milk Sugar) *Reducing Sugar*
➢ Glucose and Galactose
➔ the primary sugar of milk
Human’s milk - (7-8%) lactose
Cow’s milk - (4-5%) lactose
➔ Lactose Intolerance — a condition in which people lack the enzyme lactase
needed to hydrolyze Lactose to Glucose and Galactose
Lactose intolerance is unpleasant, but its effects can be avoided by a diet
that rigorously excluded milk and milk products
➔ Consists of β-galactose with a β-1, 4-glycosidic linkage to β-glucose (or α-glucose)
d. Trehalose
➢ Glucose and Glucose
e. Cellobiose *Reducing Sugar*
➢ Glucose and Glucose
➔ produced in the hydrolysis of Cellulose
➔ one of the major fragments isolated after extensive hydrolysis of Cellulose
➔ Maltose is digested easily by humans because we have enzymes that can break
a α-(1->4) linkages but not β-(1->4) linkages of cellobiose
➔ The two Glucose units are joined by a β- 1, 4-glycosidic linkage
f.
Melibiose
➢ Glucose and Galactose
➔ formed through the action of sucrase on Raffinose
II. COMPLEX CARBOHYDRATES - support cells and organisms (Cellulose, Chitin) and store energy
(Starch, Glycogen)
1) OLIGOSACCHARIDES - contains 2-10 monosaccharide units - covalently bonded
- disaccharides are the most common type
- trisaccharide (Raffinose)
- tetrasaccharide (Stachyose)
● usually found associated with proteins and lipids in complex molecules that serve structural and
regulatory functions
● commonly found in onions, cabbage, broccoli, and wheat
● in humans, intestinal bacteria action on the indigestible Raffinose and Stachyose present in beans
produce gaseous products that can cause discomfort and flatulence.
a. Solanin
➔ a potato toxin, is an oligosaccharide found in association with an alkaloid
➔ bitter taste of potatoes is due to relatively higher levels of Solanin
TRISACCHARIDE (C18H34O17)
a. Raffinose
A condensation of:
➢ Glucose, Galactose, and Fructose
➔ it shows the linkage specificity of enzymes
TETRASACCHARIDE
a. Stachyose
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2) POLYSACCHARIDE (C6H10O5) - are formed either through polymerization or condensation
of monosaccharide monomers.
alternate name is Glycan
polysaccharides may be linear, unbranched molecules, or they may contain one or more branches
in which side chains of sugar units attach to main chain.
are huge molecules consisting of hundreds or thousands of monosaccharide monomers.
PROPERTIES: limited water solubility
Not sweet and don’t show positive tests with Tollen’s and Benedict’s solutions
Classified into:
❖ Homopolysaccharides - polymers of a single monosaccharide (Glycogen, Cellulose,
Starch)
❖ Heteropolysaccharides - contain more than one kind of monosaccharide (hyaluronic acid,
heparin, chondroitin sulfate)
They are further divided into two main groups:
a.) Animal origin:
E.g. mucoploysaccharide group which includes hyaluronic acid, heparin, chondroitin
sulfate, blood group, and serum mucoids.
b.) Plant origin:
The most common example is the mucilage group which includes agar, vegetable
gums and dectins. In plant cell walls, cellulose occurs in densely packed fibrils called
hemicelluloses.
storage polysaccharides:
● Starch
● Glycogen
structural polysaccharides:
● Cellulose
● Chitin
● Carrageenan
acidic polysaccharides:
● Heparin
● Hyaluronic acid
homopolysaccharides: (one saccharide)
● Starch (glucose)
● Glycogen (glucose)
● Cellulose (glucose)
● Chitin (glucose)
● Carrageenan (glucose)
● Inulin (fructose)
heteropolysaccharides: (more than one saccharide)
● Hyaluronic acid
● Heparin
● Chondroitin sulfate
● Alginic acid
a. Pentosans
Polymerization products of pentoses:
➢ e.g. Xylans, Ribans, Deoxyribans, and Arabans
➔ are not physiologically important to human organisms.
b. Hexosans
Polymerization products of hexoses
They are important nutritional requirements in the human body
e.g.:
I.
Glucans - derived from glucose
❖ storage polysaccharides:
a. Glycogen (animal starch)
- a more highly branched polysaccharide than Amylopectin, can be
assembled or disassembled readily to take up or release Glucose; it is
stored in large quantities in the liver and muscle tissue of many animals.
➔ more highly branched structure
➔ its branches are shorter
➔ like Amylopectin, is a nonlinear polymer of Glucose units joined by α-1, 4and α-1, 6-glycosidic bonds but has a lower molecular weight
➔ gives red-brown color with I2
➔ is non-reducing + gives red color with iodine
b. Starch (reserved carbohydrates for plants)
- potatoes, rice, wheat are all starchy, high-energy staples in the human
diet.
- The chief caloric distributor in the diet
- a polysaccharide composed of repeating units of Glucose
- most common storage product of plant photosynthesis.
➔ is a glucosan or glycan
➔ insoluble in H2O
➔ gives a blue color with iodine solution
e.g. IKI Test:
Starch soln + IKI soln
➔ blue or blue black
● saliva contains an enzyme, salivary amylase, which begins the process
of starch digestion by hydrolyzing some of the bonds between the Glucose
units that make up Starch. Maltose, is the end product of Starch digestion.
Two components of Starch granule:
❖ Amylopectin (80-85%)
- branched chain polymer
- each chain is composed of 24-30 glucose residue
- 80-85% of the starch
- Water-insoluble fraction
- Composed of 300-6000 Glucose units joined primarily by
α-1, 4-glucosidic bonds and occasionally by α-1, 6glucosidic bonds
➔ α-1, 6 bonds are responsible for branching which
occurs about once every 25-30 units
- purple color with iodine sol’n
❖ Amylose (15-20%)
- non branching, helical structure
- straight chain polymer
- experimental evidence indicates that the molecule is
actually coiled like a spring and is not a straight chain of
glucose units.
- when coiled in this fashion the molecule has just enough
room in its core to accomodate an iodine molecule.
-
15-20% of the starch
Water-soluble fraction
composed of about 60-300 Glucose molecule joined by α1, 4-glycosidic bonds
- the helical structure is responsible for the blue color with
iodine sol’n
➔ the characteristic blue color that starch gives when treated with iodine is due to the
formation of the amylose-I2 complex.
Starch and Glycogen have similar structures and functions. Both act as storage
molecules that readily breakdown into their Glucose monomers when cells need a
burst of energy.
c. Dextrin
➔ is an intermediate between starch and maltose
➔ is a product of starch hydrolysis which is acted by amylase
➔ chief constituent of plant framework
❖ structural polysaccharides:
d. Cellulose (forms plant cell walls)
- probably the most abundant carbohydrate on Earth, is an unbranched
polysaccharide assembled from Glucose monomers bound together by βlinkages.
- the primary structural fiber of plant cell walls; in this role, cellulose has
been linked to steel rods in reinforced concrete.
- it’s tough fibers enable the cell walls of plants to withstand enormous
weight and stress.
- fabrics such as cotton and linen are made from cellulose fibers extracted
from plant cell walls. Cotton (95% Cellulose) and Wood (50% Cellulose).
- animals such as mollusks, crustaceans, and insects synthesize an
enzyme that digests the cellulose they eat.
- in ruminant mammals, such as cows, microorganisms in the digestive tract
produce cellulase that breaks down cellulose.
- cellulose passes unchanged through the human tract as indigestible
fibrous matter.
- although humans can’t digest it because they lack in enzyme cellulase
that hydrolyze β-1, 4-glycosidic linkage, many nutritionists maintain that
the bulk provided by cellulose fibers help maintain healthy digestive
function. A high-fiber diet reduced risk of colon cancer.
➢ no one knows exactly why fiber has this effect. One possible
explanation for this is that fiber eases the movement of food
through the digestive tract, so it may shorten the length of time
that harmful chemicals linger within the intestines
- it serves as a dietary fiber in food—readily absorbs in water and results in
softer stools
- 20 - 35 g of dietary fiber is desired everyday
➔ source of feces
➔ not soluble in ordinary solvent
➔ yields D-glucose upon hydrolysis
➔ a linear polymer of Glucose units joined by β-1, 4-glycosidic bonds
linear nature of chains allows close packing into fibers, making it
difficult for solvent molecules to pull the chains apart, thus
cellulose is inert towards most solvent
➔ no color with iodine
Chitin
➔ assembled from glucose units modified by addition of nitrogen-containing groups.
➔ similar to the subunits of Cellulose in both function and structure, the modified Glucose monomers
of chitin are held by β-linkages.
➔ is the main structural fiber in the external skeleton or exoskeleton and other hard body parts of
arthropods such as insects, crabs, and spiders.
➔ is also a structural material in the cell walls of fungi such as mushrooms, bread molds, and yeasts.
➔ Itself is inert and practically insoluble in most solvents. Its derivative, chitosan, can be prepared
by simple alkali-catalyzed deacylation. Chitosan derivatives are commercially used as films, fibers,
surface coatings and ultrafiltration membranes.
➔ unlike cellulose, chitin is digested by enzymes that are widespread among microorganisms, plants,
and many animals. In plants and animals, including humans and other mammals, chitin-digesting
enzymes occur primarily as part of defense against fungal infections. However, humans cannot
digest chitin as a food source.
➔ polymer of N-acytyl-D-glucosamine bound by β-1, 4-glycosidic linkages (has a linear extended
structure like Cellulose)
Carrageenan
➔ occurs as hydrocolloid extracted from selected species of red algae
➔ widely used in the food industry
➔ its gelling property is used in enhancing the texture of various diary products and in preventing
oiling off in caramel and toffee during hot weather
➔ also serve as coating to retard moisture loss from foods and fresh produce like fruits and vegetables
➔ locally obtained from Eucheuma striatum, Eucheuma spinosum and Acanthapora
➔ sulphated polysaccharides, consisting of polymers of sulphated D-galactopyranose bonded
through alternating α-1->3 and β-1->4 glycosidic linkages
II.
Fructants - from fructose
a. Inulin
➔ is a starch found in tubes and roots of dahlia and dandelion, onion and
garlic
➔ easily hydrolyzed to fructose
➔ determined the rates of glomerular filtration
➔ no color change with iodine, soluble in warm H2O
c. Pentohexosans
➢ e.g. Pectin - Galactose
- Arabinose
OTHER MIXED POLYSACCHARIDE:
I.
Proteoglycan - amino sugar
➔ uronic sugar
❖ acidic polysaccharides:
a. Chondroitin (Chondroitin sulfate) - galactosamine
➔ glucuronic acid
➔ structural role in cartilage, bone, and cornea of the eye
➔ Consists of repeating units of D-glucuronic acid-D-glucosamine
sulfate
b. Heparin - stored in granules of mast cells
➔ produced in the liver
➔ acts as anticoagulant in blood that inhibits blood clot formation
➔ the strongest organic acid in the body
➔ used in open-heart surgery
➔ consists of repeating units of D-glucuronic acid and Dglucosamine
c. Hyaluronic acid - found in the synovial fluid
➔ vitreous body of the eye and LCT
➔ highly viscous - serve as lubricant in the fluid of joints and part of
vitreous humor of the eye
➔ when some insects sting, they inject an enzyme called
hyaluronidase, which breaks hyaluronic acid linkages and
facilitate the spread of the venom.
➔ repeating unit is a disaccharide composed of β-D-glucuronic acid
and N-acetyl-D-glucosamine in a β-(1->3)-linkage
➔ each disaccharide is attached to the next by β-(1->4)-linkage
➔ alternating β-(1->3) and β-(1->4)-linkage
Alginic Acid
➔ locally extracted from Sargassum seaweeds
➔ serves as base coating in meats and fish which reduces moisture loss and fat absorption
➔ consist of repeating units of β-1->4 bonded mannuronic and α-1->4 bonded L-guluronic acid, cell
wall material.
1.13 GLYCOLIPIDS AND GLYCOPROTEINS: CELL RECOGNITION
➢ Glycolipid - is a lipid molecule that has one or more carbohydrate (or carbohydrate derivative)
units covalently bonded to it.
➢ Glycoprotein - is a protein molecule that has one or more carbohydrate (or carbohydrate
derivative) units covalently bonded to it.
➢ such carbohydrate complexes are very important in cellular functions such as cell-cell recognition,
cell adhesion and cellular communication.
1.14 REDUCING SUGARS
Chemical Types of Carbohydrates:
 Sugars can be divided into two groups:
i.
Reducing Sugars:
Reducing sugars are those which has an aldehyde and ketone group in their structure. In other
words, these sugars have a free anomeric carbon atom (the carbon atom that contains the carbonyl
group, CHO for aldoses and CO for ketoses) ; by vitue of this, they have the ability to give an H +
atom to other substabnces e.g. they have the ability to reduce other substances and they
themselves get oxidized. All monosaccharides e.g. glucose, fructose, and galactose are reducing
sugars because they have a free carbon atom. Disaccharides as maltose and lactose are also
reducing sugars.
ii.
Non-reducing Sugars:
Their anomeric carbon atoms are engaged in making bonds with each other; therefore, they don’t
have a free aldehyde or ketone group in their structure, and thereby cannot reduce other
substances. Some disaccharides like sucrose and all polysaccharides are non-reducing sugars.
However, on hydrolysis (the breaking of bonds with water) with an acid, base, and an enzyme, they
yield smaller units which have a reducing capacity.