1. Disaccharides
A disaccharide is a sugar (a carbohydrate)
composed of two monosaccharide's
It is formed when two sugars are joined together
and a molecule of water is removed
They have the general formula C12H22O11.
C6H12O6 + C6H12O6 = C12H22O11 + H2O
Glucose + Glucose = Maltose + Water
2. Important Disaccharides are:-
• sucrose (glucose and fructose)
• lactose (glucose and galactose)
• maltose (2 molecules of glucose)
3.
4. Maltose
Maltose does not have a specific function in the
body
Maltose or malt sugar, is a disaccharide formed
from two units of glucose.
It is formed by O-glycosidic linkage between one
molecule of α-D- glucose with another molecule of
α-D- glucose
Maltose is the disaccharide produced
when amylase breaks down starch.
Maltose can be broken down into two glucose
molecules by hydrolysis.
5. In living organisms, the enzyme maltase can
achieve this very rapidly.
Formed in vivo by the action of salivary amylase
on starch and in vitro by the partial hydrolysis of
starch by acids.
Produced commercially by hydrolysis of starch.
Malt sugar,present in germinating seeds.
Used as fementive reagent.
6. Lactose
Commercially known as milk sugar.
Lactose is a disaccharide derived from
the condensation of galactose and glucose.
Contains O-glycosidic linkage between one
molecule of galactose with another molecule of
glucose.
Lactose is milk sugar and found in appreciable
quantities in milk to the extent of about 5%.
Specific enzyme which hydolyses is lactase
present in intestinal juice.
7. Lactase in mucosal cells hydrolyzes lactose to its
constituent monosaccharides.
Milk sugar,cows milk contains 5% lactose,human
milk contains 7%.
Bacteria cause fermentation of lactose forming
lactic acid. When these reaction occur ,it changes
the taste to a sour
The nutritional source of energy for infants during
nursing
Lactose makes milk tastes sweet and is an
ingredient in many processed foods that contain
dairy
8. Manufacturers add whey, a byproduct of dairy
production that contains lactose, to certain food
products, such as breads, cookies, cakes,
doughnuts, breakfast bars and ice cream
Many people are lactose intolerant and do not
produce sufficient amounts of lactase to digest
lactose, causing such symptoms as nausea,
diarrhea, gas
You can take a lactase supplement to help you
digest lactose and ameliorate the symptoms.
9. Sucrose
Sucrose is the disaccharide present most in the
human diet
Sucrose is commonly known as table sugar
Is a sugar used at home
The molecule is a disaccharide derived
from glucose and fructose with the molecular
formula C12H22O11.
On hydrolysis yields one molecule each of D-
glucose and D- fructose.
10. It is very soluble and very sweet.
The specific enzyme which hydrolyses sucrose is
sucrase present in intestinal juice.
Sucrose is dextrorotatory,because glucose and
fructose(furanose form) are dextrorotatory.
This 50:50 mixture of glucose and fructose is
called invert sugar because it reverses the
rotation of polarized light
Invert sugar is more sweeter than sucrose due to
the presence of free fructose.
Honey is rich in invert sugar
Jams and jellies also contain invert sugar
11. Source of sucrose is sugar beets and sugar cane.
Caramel is solid residue produced by heating
sucrose.
Used in pharmaceutically to make syrups.
12. Reducing properties
In maltose
The aldehyde groups are at carbon 1 in each of
the original glucose molecules. Since the linkage
is 1.4, one free aldehyde group remains. Therefore,
maltose acts as a reducing sugar.
In sucrose
The glucose part had the aldehyde at carbon 1,
and the fructose part had the ketone group at
carbon 2. since the linkage is 1,2, neither group is
free. Therefore, sucrose is not a reducing sugar.
In lactose
Which has a 1,4-linkage, acts as a reducing sugar
because both of the original aldehyde group wre
on carbon 1, and one of them is free to react.
13. Fermentation
Sucrose and maltose will ferment when yeast is
added because yeast contains the enzyme
sucrase and maltase.
Lactose will not ferment because yeast does not
contain lactase.
14. Testing for disaccharides
The chemical reactions of these sugars can be
used to distinguish them in the laboratory.
If you have 2 test tubes containing a
disaccharide,C12H22O11.To determine if it is
sucrose lactose or maltose.
We can use the alkaline Cu complex reaction of
glucose and the principle of fermentation.
15. In terms of Solubility
Sucrose – very soluble in water
Maltose – fairly soluble
Lactose – only slightly soluble
The disaccharides, just like monosaccharide are
white crystalline, sweet solids.
The disaccharides are also optically active; they
rotate the plane of polarized light.
However, even though they are soluble in water,
they are too large to pass through cell membranes.
16. Polysaccharides
• Are polymers of monosaccharides.
• Hydrolysis produces many molecules of monosaccharide.
• Can be formed from pentoses or the 5 carbon sugars or the
hexoses or six carbon sugars.
• Those from pentoses are called pentosans
• Those from hexoses are hexosans or sometimes called the
glucosans.
• The hexosans are most common in terms of physiology.
• The hexosans have the general formula ( C6H10O5 )x
Where x is a large number.
Some of the common hexosans are starch, cellulose and
dextrin.
18. STARCH
Starch is a polymer consisting of D-glucose units.
Starches (and other glucose polymers) are usually insoluble in
water because of the high molecular weight, but they can
form thick colloidal suspensions with water.
Main sources of starch are rice, corn, wheat, potatoes.
A storage polysaccharide in plants.
It contains two polysaccharide units,amylose and amylopectin.
19. STARCH –AMYLOSE
Amylose consists of long unbranched chains of Alpha D-
glucose(50-5000 glucose units) connected by ᾳ(1→4) glycosidic
linkages.
10%-20% of the starch in plants is in this form.
Water soluble.
Amylose forms helices (coils) which can trap molecules of
iodine, forming a characteristic deep blue-purple color(Iodine is
often used as a test for the presence of starch).
20. STARCH — AMYLOPECTIN
Amylopectin consists of long chains of glucose up
to 1 million glucose units connected by ᾳ(1→4)
glycosidic linkages, with ᾳ(1→6) branches every 24
to 30 glucose units along the chain.
80-90% of starch is in this form in plants.
21. ACTION OF ENZYMES ON STARCH
The enzymes hydrolyzing starch are called amylases.
Saliva contains salivary amylase and pancreatic
juice contains pancreatic amylase.
These amylases are α amylases and hydrolyze starch
into maltose,isomaltose and α dextrins.
22. DEXTRINS
These are immediate products of hydrolysis of starch by
acids or by the enzyme amylase.
Consists of complex mixture of molecules of different sizes
and structures.
Present in the leaves of all starch producing plants.
Sweet in taste.
α- dextrins have eight α -D-glucose residues showing mostly
glycosidic linkages in addition to an α(1 →4) linkage at α(1
→6) each of branching site.
It is occasionally used to replace lost blood in emergency
situations, when replacement blood is not available.
It is used in some eye drops as a lubricant.
Also used as molecular sieves to separate proteins and other
large molecules (gel filtration chromatography)
23. GLYCOGEN
Also known as animal starch.
Stored in muscle and liver (mostly).
Present in cells as granules (high MW).
Contains both a(1,4) links and a(1,6) branches at every 12-
14glucose unit (more frequent than in starch).
Forms a colloidal solution in water and gives a red color with
iodine.
Glycogen is formed in the body cells from molecules of glucose.
In a process called glycogenesis.
When glycogen is hydrolyzed to glucose, the process is called
glycogenolysis.
24. CELLULOSE
A polymer consisting of long,unbranched chains of
D-glucose connected by
glycosidic linkages,may contain from
15000 glucose units in one molecule.
25.
26. INULIN
b-(1,2) linked fructofuranoses
linear only; no branching
Lower molecular weight than starch
Hydrolysis yields fructose
Sources include onions, garlic etc.
Used as diagnostic agent for the evaluation of
glomerular filtration rate (renal function test)
27. CHITIN
chitin is the second most abundant carbohydrate
polymer
Like cellulose, chitin is a structural polymer
present in the cell wall of fungi and in the
exoskeletons of crustaceans, insects and spiders
Consists of N-acetyl-D-glucosamine units joined by
29. Hyaluronic acid
Hyaluronan is a polymer of disaccharides, themselves
composed of D-glucuronic acid and D-N-acetylglucosamine,
linked via alternating β-1,4 and β-1,3 glycosidic bonds.
Hyaluronan can be 25,000 disaccharide repeats in length
Hyaluronan is also a major component of skin, where it is
involved in tissue repair
Hyaluronan is a common ingredient in skin-care products.
Distribution in connective tissue, skin etc.
