(a) Disaccharide : contains two monosaccharides e.g. lactose, maltose, sucrose

Maltose ® Glucose + Glucose

Sucrose ® Glucose + Fructose

Lactose ® Glucose + Galactose

(b) trisaccharide: containing 3 monosaccharides. e.g. raffinose

(c) tetrasaccharide: containing 4 monosaccharide e.g stachyose

3) Polysaccharides

General formula n (C₆H₁₀O₅). These complex carbohydrates are formed by chains of at least ten monosaccharides.

They are of two types:

(a) Homoglycans: containing only one type of monosaccharide (e.g. glycogen, starch, cellulose, contain only glucose molecules). Starch is a very important polysaccharide because it is formed through a chain of hundreds or thousands of glucose units. Carbohydrates in plants are stored in the form of starches. Starch contained in energy rich food like rice, corn, and potatoes form part of the staple diet of most people.

Starch
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A second important polysaccharide is glycogen. Glycogen also contains thousands of glucose chains; the difference from starch though is in its branching pattern. Glucose is stored in the human liver in the form of glycogen.

Another important polysaccharide is cellulose. Cellulose is used primarily as a structural carbohydrate. It is also composed of glucose units, linked in a different orientation but the units cannot be released from one another except by a few species of organisms. Wood is formed from cellulose. Even the cell wall of all plants is made up of cellulose. Cotton and paper are also cellulose products.

(b) Heteroglucans: contain more than one type of monosaccharide linked together (e.g. mucilage, gum etc.)

4) Proteins and its derivatives

Proteins are the fundamental chemical compounds of the protoplasm indispensable for vital life processes. They are complex, large molecules each containing thousands of atoms. proteins contain nitrogen in addition to carbon, hydrogen and oxygen; they usually also contain phosphorus and sulfur. These compounds are polymers of unit structures called amino acids, represented chemically as:

-NH₂ is an amino group, - COOH is the carboxyl group, ,and R represents the variable chain forming different amino acids. There are 20 diferent of amino acids. The amino acids differ depending on the nature of the R group. Examples of. amino acids are valine, alanine, glutamic acid, tyrosine and histidine.

Two molecules of amino acids are joined by the carboxyl group of one ammino acid with the amino group of the other by loss of one molecule of water. This process is called dehydration synthesis and the bond thus formed between two molecules is referred to as the peptide or peptide bond.

There are 3 types of proteins namely :

(1) Simple proteins: like albumins and globulins formed by group of amino acids only.

(2) Derived proteins: like proteose and peptones which are hydrolytic cleavage products of complex proteins.

(3) Conjugated proteins: like nucleo proteins (Proteins + nucleic acid), lipoproteins (protein + lipid), or glycoproteins (protein + carbohydrates) which are formed by the combination of proteins with some non-protein molecule. This non-protein portion is called Prosthetic group.

All living things require protein for survival. In fact an organism is constructed by means of proteins. All living things then, in any form - liquid, solid, or plasma - contain proteins. Protein is also seen as a supporting tissue with main tissue. Bone, tendons, muscle, cartilage, ligaments are all formed of protein.

Enzymes are a specified class of proteins. Enzymes act as catalysts in chemical reactions of the body. They are not used up by the reaction, rather they remain chemically unchanged and available to catalyze succeeding reactions.

Table of Contents

2.0 - Introduction
2.1 Structural Organization and Chemical Basis Of Life
2.2 Organic Compounds
2.3 Nucleotides and Nucleic Acid
2.4 Lipids

Chapter 3