COURSE:
BIOLOGY
CODE:
BIO101.
PROGRAMME:
MBChB.
LECTURER:
MRS MUSONDA
STUDENT NAME:
JOSHUA SIMUZINGILI
ID NUMBER:
210100941
ASSIGNMENT 2
1.Explain with examples the meaning of
a) reducing sugar and non-reducing sugar.
b) Compare reducing and non- reducing sugars.
2. Illustrate reducing sugars and non-reducing sugars using structural formulae
INTRODUCTION
Sugars (also called saccharides) are members of macro biomolecules called carbohydrates.
The name carbohydrate was introduced because many of the compounds had the general
formula Cx(H2O)y , thus appeared to be hydrates of carbon. The terminology is now
commonly used in a much broader sense to denote polyhydroxy aldehydes and ketones.
Carbohydrates are divided into four main groups namely monosaccharaides, disaccharides,
oligosaccharides and polysaccharides. These organic compounds can undergo oxidation or
reduction, the oxidation of a sugar’s anomeric carbon by copper(II) defines a reducing sugar
and those sugars that are not oxidized are called non-reducing sugars. This property will be
used as a basis for the analysis of reducing sugars and non-reducing sugars.
REDUCING SUGARS
A reducing sugar is one that serves as a reducing agent due to its free aldehyde or ketone
functional groups in its molecular structure. Reducing sugars include all common dietary
monosaccharaides (such as galactose, glucose and fructose) and some disaccharides (such as
lactose, maltose and cellobiose).
Monosaccharaides can be divided into two groups: aldoses, which have an aldehyde group,
and ketoses, which have a ketone group. Ketoses must first tautomerize to aldoses before
they can act as reducing sugars. Reducing sugars are so called because they can carry
out a type of chemical reaction known as reduction in the process they are oxidised. This is
made use of in the Benedict’s test using Benedict’s reagent. Benedict’s reagent is copper(II)
sulfate in an alkaline solution and has a distinctive blue colour. Reducing sugars reduce
soluble blue copper sulfate, containing copper(II) ions, to insoluble brick-red copper oxide,
containing copper(I). The copper oxide is seen as a brick-red precipitate.
Reducing sugar + Cu2+(blue) → oxidised sugar + Cu+( red-brown)
In other words, a reducing sugar, when chemically altered, can donate electrons to another
molecule, which will change the colour and also change the taste of food.
NON-REDUCING SUGARS
Non-reducing sugars are any type of carbohydrate which are unable to be oxidized by a
weak oxidizing agent and do not reduce other substances. Non-reducing sugars cannot act as
reducing agents due to the absence of free aldehyde groups or free ketone groups. They
include most disaccharides (such as maltose, Sucrose and lactose), Non-reducing
disaccharides have glycosidic bonds between their anomeric carbons and thus cannot
convert to an open-chain form with an aldehyde group; they are stuck in the cyclic form.
Polysaccharides are non-reducing (such as cellulose and chitin.) glycogen on the other end is
an exception despite being a polymer because it has one reducing end. When Benedict’s
solution is added to a non-reducing sugar there is no change in colour because non-reducing
sugars cannot be oxidized. Trehalose, Stachyose andVerbascose are some of examples of
non-reducing sugars.
A sugar without a hemiacetal is non-reducing because it does not behave as a reducing agent
toward oxidizing metal salts.
(Source: https://www.masterorganicchemistry.com/2017/09/12/reducing-sugars/)
A brief comparison of reducing sugars to non-reducing sugars can be summarized in the table below
REDUCING SUGARS
NON-REDUCING SUGARS
carbohydrates with free aldehyde and the
Have glycosidic bonds between
ketone group
their anomeric carbons cannot convert to
an open-chain form with an aldehyde group;
they are stuck in the cyclic form
acetal or the ketal form
hemiketal or the hemiacetal
All monosaccharides and some
Includes all polysaccharides(except for
dissaccharides
glycogen) and some dissacharides
Positive reaction towards Ferling’s test
Negative reaction towards Ferling’s test
reduce soluble blue copper sulfate
Cannot reduce Cu2+
containing copper(II) ions, to insoluble
brickred copper oxide, containing copper(I).
Cu2+ to Cu+
CONCLUSION
Several qualitative tests are used to detect the presence of reducing sugars. Two of them use
solutions of copper(II) ions: Benedict's reagent (Cu2+ in aqueous sodium citrate)
and Fehling's solution (Cu2+ in aqueous sodium tartrate). This property is the basis of
Fehling’s reaction, a qualitative test for the presence of reducing sugars. By measuring the
amount of oxidizing agent reduced by a solution of a sugar, it is also possible to estimate the
concentration of that sugar moreover, after the calculation of the exact amount of glucose
present, it becomes easier to prescribe the amount of insulin that must be taken by the
patients. For many years in medicine this test was used to detect and measure elevated
glucose levels in blood and urine in the diagnosis of diabetes mellitus. Secondly in food
chemistry the level of reducing sugars in wine, juice, and sugarcane are indicative of the
quality of these food products, monitoring the levels of reducing sugars during food
production has improved market quality .
REFERENCES
1. Pratt, Charlotte W.; Cornely, Kathleen (2013). Essential Biochemistry (Third ed.). Wiley.
p. 626. ISBN 978-1118083505.
2. Nelson, David L.; Cox, Michael M. (2008). Lehnniger: Principles of Biochemistry
(Fifth ed.). W.H. Freeman and Company. p. 241. ISBN 978-0716771081.
3. Jones, M., Fosbery, R., Gregory, J. and Taylor, D., n.d. Cambridge International AS and
A level biology. (4th ed). p.32. ISBN 978-1-107-63682-8
4. Klein, David. (2012). Organic Chemistry (First ed.). John Wiley & Sons. p. 11621165.ISBN 978-0471756149.
5. Cummings, John H. (2001). The Effect of Dietary Fiber on Fecal Weight and
Composition (3rd ed.). Boca Raton, Florida: CRC Press. p. 184. ISBN 978-08493-2387-