Disaccharides are carbohydrates that break down into two monosaccharides upon hydrolysis. There are two types - reducing disaccharides that can act as reducing sugars, like lactose, maltose, and cellobiose, and non-reducing disaccharides that cannot, like sucrose and trehalose. Disaccharides are formed through a condensation reaction that bonds two monosaccharides, removing a water molecule. Common examples include sucrose (glucose + fructose), maltose (two glucose molecules), and lactose (glucose + galactose). Disaccharides serve as an energy source, as our bodies break them down into absorbable monosaccharides like glucose and fructose.

1. DISACCHARIDES
AND
THERE FUNCTIONS

2. Disaccharides are those carbohydrates that on hydrolysis with acids or
enzymes give two molecules of monosaccharides which can either be the
same or different.
The oxide linkage is formed after the loss of the water molecule and then the
two monosaccharides are formed by that linkage. When two monosaccharide
units are joined via the oxygen atom then that linkage is called a glycosidic
linkage.
What are Disaccharides?

3. There are two functionally different classes of disaccharides:
Reducing disaccharides, in which one monosaccharide, the reducing sugar of the pair,
still has a free hemiacetal unit that can perform as a
reducing aldehyde group; lactose, maltose and cellobiose are examples of reducing
disaccharides, each with one hemiacetal unit, the other occupied by the glycosidic
bond, which prevents it from acting as a reducing agent. They can easily be detected
by the Woehlk test or Fearon's test on methylamine.
Non-reducing disaccharides, in which the component monosaccharides bond through
an acetal linkage between their anomeric centers. This results in neither
monosaccharide being left with a hemiacetal unit that is free to act as a reducing
agent. Sucrose and trehalose are examples of non-reducing disaccharides because
their glycosidic bond is between their respective hemiacetal carbon atoms. The
reduced chemical reactivity of the non-reducing sugars in comparison to reducing
sugars, may be an advantage where stability in storage is important.
Classification

4. Formation
The formation of a disaccharide molecule from two monosaccharide molecules
proceeds by displacing a hydroxy group from one molecule and a hydrogen
nucleus (a proton) from the other, so that the now vacant bonds on the
monosaccharides join the two monomers together. Because of the removal of the
water molecule from the product, the term of convenience for such a process is
"dehydration reaction" (also "condensation reaction" or "dehydration synthesis"). For
example, milk sugar (lactose) is a disaccharide made by condensation of one
molecule of each of the monosaccharides glucose and galactose, whereas the
disaccharide sucrose in sugar cane and sugar beet, is a condensation product of
glucose and fructose. Maltose, another common disaccharide, is condensed from
two glucose molecules.
The dehydration reaction that bonds monosaccharides into disaccharides (and also
bonds monosaccharides into more complex polysaccharides) forms what are called
glycosidic bonds

5. Structure of Disaccharides (Sucrose)
The most common disaccharide is
sucrose which gives D -(+)- glucose
and D-(-)- fructose on hydrolysis.
Both the monosaccharides i.e. glucose
and fructose are connected through
the glycosidic linkage between alpha
glucose and second carbon
beta fructose. Sucrose is a non-
reducing sugar as both the reducing
groups of glucose and fructose are
involved in the glycosidic bond
formation.

6. Examples of Disaccharides
1. Sucrose
Sucrose being dextrorotatory in nature gives dextrorotatory
glucose as well as laevorotatory fructose on hydrolysis. The
overall mixture is laevorotatory and this is because the
laevorotation of fructose (-92.4) is more than the dextrorotation
of glucose (+52.5).

7. 2. Maltose
Maltose is also one of the disaccharides which have two α -D-glucose units which
are connected by the first carbon of the glucose and also linked to the fourth
carbon of another glucose unit. In the solution, a free aldehyde can be produced at
the first carbon of the second glucose of the solution and it is a reducing sugar as it
shows reducing properties.

8. 3. Lactose
Commonly it is called milk sugar as this disaccharide is found in milk. It is
made up of Beta-D-galactose and β-D-glucose. The bond is between the
first carbon of galactose and the fourth carbon of glucose. This is also a
reducing sugar.

9. Some More Types of Disaccharides
There few more types which are not that popular, such as:
Trehalose
It is made up of 2 molecules of glucose which are linked differently. This can be found in
fungi, plants, and insects.
Lactulose
It is formed from galactose and fructose. It is helpful for the treatment of constipation
and liver diseases.
Cellobiose
It is also made up of two glucose molecules which are also arranged differently. These
can be seen bacteriology which is a form of chemical analysis.
Chitobiose
It comprises two glucosamine molecules which are linked. It is seen in some bacteria,
exoskeletons of insects and is also found in fish, octopus, and squid.

10. What function
do
disaccharides
serve in the
body?

11. Disaccharides act as an energy source for the
body, just like any other carbohydrate. When we
eat foods that contain disaccharides, our bodies
break them down into simple sugars
(monosaccharides) for absorption in the small
intestine

12. THANKS!