•Dr. Hewida Fadel
•Dr. Tarek El Sewedy
Intended Learning Outcomes
By the end of this lecture, students will learn:
1.
The basic structure and classes of carbohydrates.
2.
Biological function of carbohydrates
Lecture content
 What are carbohydrates?
 Classification of carbohydrates.
 Classification of monosaccharides.
 Reducing & non reducing sugars.
 Classification of polysaccharides.
 Biological function of carbohydrates
Biomolecules of life
1.
Carbohydrates
2. Proteins.
3. Lipids
4. Nucleic acids
What are carbohydrates?
 In biochemistry, carbohydrates is a synonymous of saccharide.
 The word saccharide comes from the Greek word sákkharon, meaning “sugar".
 The term carbohydrate often means any food that is particularly rich in the comples
carbohydrate starch (such as cereals, bread, and pasta) or simple carbohydrates, such
as sugar (found in candy, jams, and desserts).
 Carbo-hydrate is composed of carbon and water (C.H2O)n. For every carbon there is
1 water molecule or 2 hydrogen atoms and 1 oxygen atom (with some exceptions).
Classification of carbohydrates
There are a variety of classification schemes.
 The most common classification scheme divides the
carbohydrates into groups according to the number of
individual simple sugar units.
 Monosaccharides contain a single unit
 disaccharides contain two sugar units (2 monosaccharides)
 polysaccharides contain many sugar units as in polymers
Monosaccharides can be further classified by the
number of carbons present.
 Six carbons = Hexose (ex. Glucose, Galactose,fructose)
 Five carbons = Pentose (ex. Ribose)
 Four = Tetrose (Erythose )
 Three = Triose (Glyceraldehyde)
Modified monosaccharides
 phosphorylated sugars are one example of modified monosaccharides.
 An important phosphorylated sugar is glucose 6-phosphate.
 glucose 6-phosphate provides energy in certain metabolic pathways, and
it can be converted and stored as glycogen when blood glucose levels are
high. If blood glucose levels are low, glucose 6-phosphate can be
converted back into glucose to enter the bloodstream again.
 glucose 6-phosphate possesses a negative charge. This prevents the
molecule from leaving the lipid-bilayer membranes. This allows the cell
to easily uses the modified sugar to provide energy, or convert it to
glycogen as storage.
Classification according to
Functional Groups
• Aldoses: Are sugars containing an aldehyde functional group on carbon #1
(anomeric carbon)- Monosaccharides in this group are glucose, galactose, ribose,
and glyceraldehyde.
• Ketoses: Sugars containing the ketone group on carbon # 2 (anomeric carbon)The major sugar in this group is fructose.
Classification according to reducing capability
Reducing capability is defined by the presence of free aldehyde or ketone group.
A. Reducing: Contain free groups (contain one free anomeric carbon atom),
glucose, maltose, lactose and fructose.
• All Monosaccharides are reducing sugars. Two of three disaccharides maltose
and lactose, have the free groups needed to act as reducing agents.
B. Non-reducing: Contain no free groups.
Sucrose and polysaccharides are non reducing.
(sucrose's anomeric carbon is not "free" since this carbon is used to link fructose
and glucose together.
Reducing Disaccharides
Lactose
Maltose
Non reducing disaccharide
Classification of polysaccharides

Homo-polysaccharides (all the same type)

Hetero-polysaccharides (mixtures of monomer
types)

Complex carbohydrates (joined to non-carbohydrate
molecules)
fructose
glucose
galactosea
monosaccharaides…
joined together to
make disaccharides.
sucrose
(fructose-glucose)
maltose
(glucose-glucose)
Disaccharides
lactose
(glucosegalactose)
Glucose
Starch
(unbranched)
Starch
(branched)
Glycogen
Polysaccharides
Cellulose
Carbohydrate Function
• Sources of Immediate energy (ATP) as produced by
glucose catabolism(Glycolysis and Krebs cycle).
• Source of stored energy (Glycogen stored in liver).
• Intermediates in the biosynthesis of other basic
biomolecules (fats and proteins).
• Associated with other molecules such as vitamins
and antibiotics.
Cont, Carbohydrate function
• Structural function: ex. Ribose, deoxyribose and
cellulose and starch in plants.
• Involved in many cell functions such cell-cell
recognition and protein folding.
Digestion of carbohydrates
a) α-amylase (in saliva) randomly hydrolyzes all the
glycosidic bonds of starch.
•
By the time the chewed food reaches the stomach,
where acidity deactivates the amylase, the average
chain length of starch has gone from several
thousand to fewer than 8 glucose units.
b) Digestion continues in the small intestines with
pancreatic amylase. This degrades the starch to
maltose .
c) Further digestion occurs down the digestive tract in
the small intestine. The resulting monosaccharides
are absorbed by the small intestine and transported
into the blood stream
• In living organisms, most carbohydrates are found bound
to other compounds rather than as simple sugars

Glycoproteins (hormones, antibodies)

Glycolipids

Nucleic acid.
Monosaccharaides
• Monosaccharaides are also known as “simple
sugars”
• They are classified by:
1. Number of carbons.
2. Whether they are aldoses or ketoses.
• D-glyceraldehyde is the simplest of the aldoses.
• Glucose is the most widely known
Glucose
 Glucose is a monosaccharide with formula C6H12O6
 It is absorbed directly into the bloodstream during digestion.
 Bread, rice, pasta are rich in glucose.
 Glucose is a common medical analyte measured in blood samples. The insulin
reaction, regulate the concentration of glucose in the blood. A high
fasting blood sugar level is an indication of diabetic conditions
 Glucose is used as an energy source in most organisms aerobic or anaerobic
respiration. The first step of this is the phosphorylation of glucose
by hexokinase to prepare it for breakdown to provide energy. The major reason
for the immediate phosphorylation of glucose by a hexokinase is to prevent
diffusion out of the cell.
 Organisms use glucose as a precursor for the synthesis of several important
substances. Starch, cellulose, and glycogen ("animal starch").
 Some of these polymers like starch or glycogen serve as energy stores while
others like cellulose have structural roles.
 In plants, glucose is a product of photosynthesis. In animals, glucose results
from the breakdown of glycogen, a process known as Glycogenolysis.
 In animals, glucose is synthesized in the liver and kidneys from non-
carbohydrate intermediates, such as pyruvate and glycerol, by a process known
as Gluconeogenesis.
 Glucose is produced commercially via the enzymatic hydrolysis of starch. Many
crops can be used as the source of starch. Maize, rice, wheat
 Glucose is classified as a monosaccharide, an aldose, a
hexose, and is a reducing sugar.
 Glucose is synthesized by chlorophyll in plants using
carbon dioxide from the air and sunlight as an energy
source. Glucose is further converted to starch for storage.
Fructose
Fructose
 Fructose is found naturally in fruits and
vegetables.
 Fructose is metabolized differently than
glucose and other sugars, doesn’t stimulate
insulin and is characteristically low
glycemic. For these reasons, it’s often used
in low-glycemic food applications
 15 to 80% sweeter than sucrose, and tastes
particularly sweet when cold or in solution
Disaccharides
Disaccharides
 Disaccharides are formed when two monosaccharaides are
joined together and a molecule of water is removed.
 Milk sugar (lactose) is made from glucose and galactose
 sugar cane sugar (sucrose) is made from glucose and fructose.
 Maltose is made up of two glucose molecules.
 The two monosaccharides are bonded via a glycosidic bond
 Can be degraded to monosaccharides by hydrolysis
producing water.
Sucrose
Sucrose
• Formed of Glucose and fructose monomers joined together.
• known as table sugar
• Commercially obtained from sugar cane or sugar beet
• Used pharmaceutically to make syrups
Lactose
• Lactose is a famous disaccharide, resulting from a galactose
joining to glucose.
• Milk is the most famous source of Lactose.
• Used in infant formulations, and as a diluent in
pharmaceuticals
Maltose
 Made up of two glucose molecules.
 Produced when amylase breaks down starch.
 Obtained from malt sugar and when glucose is
caramelized.
Polysaccharides
Starch
 Starch or amylum is a carbohydrate consisting of a
large number of glucose units joined together by
glycosidic bonds.
 produced by all green plants as an energy store
 It is the most common carbohydrate in the human
diet like potatoes, wheat, maize (corn), rice.
Cont, Starch
• consists of two types of molecules: the linear and helical
amylose and the branched amylopectin.
• Glycogen, the glucose store of animals, is a more branched
version of amylopectin.
 Used as an additive for food processing, typically used as
thickeners and stabilizers in foods such as puddings, custards,
soups, and salad dressings, and to make noodles and pastas.
 Depending on the plant, starch generally contains 20 to 25%
amylose and 75 to 80% amylopectin by weight.
Another view of amylose and amylopectin, the two forms of starch. Amylopectin
is a highly branched structure, with branches occurring every 12 to 30 residues
Glycogen
• Glycogen is also known as “animal starch”.
• It is stored in muscle and liver tissue
• Complete hydrolysis yields glucose
• Glycogen is the glucose storage polymer in animals, is
similar in structure to amylopectin, but glycogen has
more branches
• The highly branched structure permits rapid release of
glucose from glycogen stores, i.e. in muscle during
exercise. The ability to rapidly mobilize glucose is more
essential to animals than to plants
ASSIGNMENTS
Students selected in the previous slide are requested to prepare
slides about any of the following topics and delivered before next
lecture:
1. Importance of carbohydrates in human life.
2. Carbohydrates and cell membrane.
3.
Carbohydrates in plants.
4. Importance of glycogen.
5. Disease related to high glucose level.
6. Disease related to low glucose level.
7. Polysaccharides.
8. Functions of glycoprotein.
9. Carbohydrate and energy.
10. Carbohydrate digestion.
‫‪Students selected for assignment‬‬
‫ابانوب اسحاق عبد المسيح سيحه‬
‫ابراهيم صداق ابراهيم مؤنس‬
‫ابراهيم ماجد عبد الغني ابو زيد‬
‫ابراهيم محمد احمد قاسم‬
‫احمد السيد احمد الريس‬
‫احمد جمال احمد يوسف الدراجينى‬
‫احمد جمال الدين عبد الجواد ابو المجد‬
‫احمد حسن احمد عبد المقصود‬
‫احمد حسن علي ابراهيم حميدة‬
‫احمد حسين احمد رسالن‬
Study Questions:
 Mention the 4 major biomolecules of life.
 Mention one classification of carbohydrates giving
examples.
 Explain why sucrose is a non reducing while maltose is
a reducing sugar
Suggested readings:
• Harper’s Biochemistry 26th edition