Date : 9thApril 2020
Dear students,
Assalamu Alaikum. Hope all of you are doing fine. I have prepared some necessary notes/slides on Carbohydrates from chapter-03 for you as your holyday homework. Hope all of you will follow this.
Chapter-03
Cell Chemistry
Topic : Carbohydrate Contents
Definition
General Features
Classification
Reducing Sugar
Structure of Monosaccharide
Structure of Disaccharide
Structure of Polysaccharide
Importance of Carbohydrate
Concept map
Summary of Carbohydrate
What is Carbohydrate ?
The complex organic compound composed of Carbon (C) , Hydrogen (H) and Oxygen (O) is carbohydrate.
The atomic formula of carbohydrate is ( CH2O)n. Here the proportionate number of these three elements ( C, H and O) is 1:2:1, though it is not applicable everywhere. This proportion is specially applicable for
monosaccharide.
Therefore, the carbohydrates are more appropriately referred to as polyhydroxyaldehydes or polyhydroxyketones and their derivatives or the substances which yield these on hydrolysis.
The physical properties of Carbohydrates
1. Monosaccharide:
These are crystalline compounds, soluble in water, sweet tasted and needs digestion in order to be absorbed into the bloodstream.
2. Disaccharide:
These are crystalline, water soluble, sweet to the taste, and must be digested to monosaccharaides before they can be absorbed and used for energy.
3. Polysaccharides:
These are not water soluble and are not crystalline. They form colloidal suspensions instead of solutions. They are not sweet and must be digested before being absorbed.
Classification of Carbohydrates
Carbohydrates are classified according to the number of subunits that make them up . Carbohydrates
Monosaccharides Disaccharides Oligosaccharides Ploysaccharides (e.g. Sucrose,
Maltose) Structural Polysaccharides
(e.g. Cellulose) Storage Polysaccharides
(e.g. Starch, Glycogen) Triose
(e.g. Glyceraldehyde) Tetrose
(e.g. Erythrose) Pentose
(e.g. Ribose) Hexose
(e.g. Glucose) Heptose
(e.g. Sedoheptulose)
Trisaccharides
(e.g. Raffinose) Tetrasaccharides
(e.g. Stachyose) Pentasaccharides
(e.g. Verbascose)
Why Monosaccharides are reducing sugar ?
Monosaccharides are the simple sugar and the simplest form of
carbohydrates. They cannot be further hydrolyzed to simpler chemical compounds. They possessing free aldehyde groups (-CHO) at their carbon 1 or free keto groups (>C=O) at their carbon 2 and posses
reducing properties. In Benedict’s and Fehling’s reagents , these( –CHO or >C==O ) groups reduce Cu(OH)2 ( Cupric hydroxide) into Cu2O
(cuprous oxide) which creates red coloured suspension. Hence all monosaccharides are called reducing sugar.
Structure of Glucose and Fructose
Glucose and Fructose are considered as simple and the most abundant monosaccharides in the world . Both have similar formula C6H12O6.
Both are considered as simple reducing sugars and are absorbed directly into the bloodstream during digestion. However glucose is an aldohexose and fructose is a ketohexose.
Fig: Open chain structure of D-glucose
a-D Glucose b-D Glucose
Fig. : Ring structure of glucose
Structure of Monosaccharides (Fructose)
Structure of Disaccharides
Disaccharides
• Composed of 2 monosaccharides
• Cells can make disaccharides by joining two monosaccharides by biosynthesis.
Glucose + fructose = sucrose
• Table sugar
• Found naturally in plants: sugar cane, sugar beets, honey, maple syrup
• Sucrose may be purified from plant sources into Brown, White and Powdered Sugars.
Structure of Disaccharides
Glucose + galactose = lactose
• The primary sugar in milk and milk products.
• Many people have problems digesting large amounts of lactose (lactose intolerance)
Structure of Disaccharides
Glucose + glucose = Maltose
• Produced when starch breaks down.
• Used naturally in fermentation reactions of alcohol and beer manufacturing.
