ASSIGNMENT 1
1a. Explain why glucose is a reducing sugar and fructose is not.
Glucose is classified as a reducing sugar because it has a free aldehyde or ketone group that
can donate electrons to other compounds. In the case of glucose, the aldehyde group is located
on the first carbon atom of the sugar molecule. This aldehyde group can undergo a chemical
reaction known as a redox reaction, where it donates electrons to another compound, thereby
reducing it. This property of glucose makes it an important component in various biological
processes, such as glycolysis, where it serves as a source of energy for cells.
Fructose, on the other hand, is not classified as a reducing sugar because it lacks a free aldehyde
or ketone group. Instead, fructose has a ketone group on the second carbon atom of the sugar
molecule. This ketone group is not reactive in the same way as an aldehyde group, and therefore
fructose cannot donate electrons to other compounds in the same manner as glucose. As a result,
fructose is not able to undergo the same redox reactions as glucose and is therefore not
considered a reducing sugar.
b. Describe the composition of starch highlighting the differences in Amylose and
Amylopectin (7)
Amylose is a linear polymer of glucose units linked together by alpha-1,4 glycosidic bonds. It
is a long, straight chain molecule that is soluble in hot water and forms a gel-like substance
when it is cooled. Amylose contributes to the thickness and creaminess of various food
products, such as puddings and sauces. It is also responsible for the formation of the blue-black
colour when iodine is added to a starch solution. Amylose typically makes up about 20-30% of
starch
Amylopectin is a branched polymer of glucose units linked together by alpha-1,4 and alpha1,6 glycosidic bonds. It has a highly branched structure, with multiple side chains branching
off from the main chain. Amylopectin is insoluble in water and does not form gels like amylose.
Instead, it contributes to the sticky and cohesive properties of starch, making it ideal for use as
a
thickening
agent
in
various
food
products
The difference in structure between amylose and amylopectin is key to their different properties
and functionalities. While amylose is a long, linear chain that forms gels and contributes to the
creaminess of food products, amylopectin is a highly branched structure that provides viscosity
and texture to food products. Both components play important roles in the cooking and
processing of starch-based foods, as well as in the storage and release of energy in plants.
c. Describe the difference in structure and characteristics between cellulose and starch.
One of the main differences between cellulose and starch lies in their structural composition.
Cellulose is a polysaccharide made up of β-glucose monomers linked together by β-1,4glycosidic bonds. This results in a linear and rigid structure, with hydrogen bonding between
adjacent glucose molecules contributing to the formation of microfibrils. These microfibrils
are further arranged into larger microfibrils, creating a strong and resistant network that forms
the
main
component
of
plant
cell
Starch is also a polysaccharide composed of glucose units, but in this case, the glucose
molecules are linked by α-1,4-glycosidic bonds. Additionally, starch can contain branching
points where α-1,6-glycosidic bonds connect the glucose chains. This branching gives starch a
more flexible and helical structure, making it easily digestible by enzymes such as amylase
Another important difference between cellulose and starch is in their function and
characteristics. Cellulose is a structural component of plant cell walls, providing rigidity and
support to the plant cell. Due to its linear and rigid structure, cellulose is insoluble in water and
resistant to degradation by most enzymes, making it indigestible for many organisms, including
humans. However, cellulose serves as an important dietary fiber that aids in digestion and
promotes
gut
health
Starch serves as a storage form of energy in plants, storing glucose for later use. Starch is found
in various plant tissues such as seeds, tubers, and grains, where it can be readily broken down
into glucose by enzymes to produce energy. This makes starch a valuable source of nutrition
for humans and animals.
2. Illustrate the formation of a triglyceride molecule from glycerol and fatty acids
References:
1. Jane, J. L., & Robyt, J. F. (1984). Structure of amylose and amylopectin films.
Carbohydrate
Research,
128,
111-123.
2. Tester, R. F., & Karkalas, J. (2002). Starch composition, fine structure and
architecture.
Journal
of
Cereal
Science,
39(2),
151-165.
3. Lodish H, Berk A, Zipursky SL, et al. Molecular Cell Biology. 4th edition. New
York: W. H. Freeman; 2000. Section 14.5, Polysaccharides: The Peptidoglycan
of Bacterial Cell Walls and the Murein Sacculus of Yeast.