Biochemistry 1 (MLBC-201)

•Dr. Hewida Fadel

•Dr. Tarek El Sewedy

Biochemistry 1(MLBC-201)

Lecture 3

Carbohydrates Structure And classification

By the end of this lecture, students will learn:

1. The basic structure and classes of carbohydrates.

Intended Learning Outcomes

Lecture content

What are carbohydrates?

Classification of carbohydrates.

Classification of monosaccharides.

Reducing & non reducing sugars.

Classification of polysaccharides.

Biomolecules of life1. 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 carbohydratesThere 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 monosaccharidesphosphorylated 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 capabilityReducing 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 polysaccharidesHomo-polysaccharides (all the same type)Hetero-polysaccharides (mixtures of

monomer types)Complex carbohydrates (joined to non-

carbohydrate molecules)

3. Polysaccharides

1-MONOSACCHARIDES (CH20)N

2-DISACCHARIDES

Disaccharides

fructose glucose galactosea

sucrose maltose lactose

(fructose-glucose) (glucose-glucose) (glucose-galactose)

monosaccharaides…

joined together to make disaccharides.

Polysaccharides

Glucose

Starch (unbranche

d)

Starch (branched)

Glycogen Cellulose

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 assignmentفرحات علي إسراء

أسكندراني أسعد أميرة

الموجود عبد إنجي

وجدي محمد هالة

محمد خالد باسم

الحناوي سامي ريهام

السالم عبد مح&مد مروة

يوسف محمدي أيمان

درويش محمد رضوى

أحمد محمود ندى

سيحه المسيح عبد اسحاق ابانوب

مؤنس ابراهيم صداق ابراهيم

زيد ابو الغني عبد ماجد ابراهيم

قا&سم احمد محمد ابراهيم

الريس احمد السيد احمد

الدراجينى يوسف احمد جمال احمد

المجد ابو الجواد عبد الدين جمال احمد

المقصود عبد احمد حسن احمد

حميدة اب&راهيم علي حسن احمد

رسالن احمد حسين احمد

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

• Harper’s Biochemistry 26th edition

Suggested readings: