List of the symbols and abbreviations
1.3 Carbohydrates
Carbohydrates are a common class of simple organic compounds. Carbohydrate is an aldehyde or a ketone that has additional hydroxyl groups. The simplest carbohydrates are called monosaccharide. Monosaccharide link together to form oligosaccharides (disaccharides, trisaccharides, tetrasaccharides) and polysaccharides. Two monosaccharides together to form a disaccharide. Carbohydrates consisting of two to ten simple sugars are called oligosaccharides, and those with a larger number are called polysaccharides [3].
Carbohydrates constitute a major class of naturally occurring organic compounds. They are essential to the maintenance of life in both plants and animals [4]. Carbohydrates are the ultimate source of most of our food. We eat starch-containing grain or feed it to animals to be converted into meat and fat which we then eat. We make clothes with cellulose in the form of cotton and linen, rayon and cellulose acetate. We build houses and furniture from cellulose in the form of wood. Thus carbohydrates quite literally provide us with the 7.
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Introduction Chapter I necessities of life: food, clothing and shelter. The study of carbohydrates is also one of the most exciting fields of organic chemistry [5].
Functions of Carbohydrates: Carbohydrates have live majors' functions within the body.
These are as follows:
Carbohydrates catabolism and Glucose: Carbohydrates supply energy for the brain in the form of glucose.
Amino acid catabolism: They give energy by avoiding the breakdown of amino acids.
Cellular and protein recognition: Its remove glycoprotein, hormones by the liver from the bloodstream.
Dietary fiber: It is used as dietary fiber in the human body.
Biochemical functions of carbohydrates: Carbohydrates serve several biochemical functions which are:
They act as a fuel of cellular metabolism.
It's used in several biosynthesis reactions.
Its source of polysaccharide like glycogen and starch which supply energy to the plant and animal cells.
It is used for function of organism's fertilization, development and immune system [6].
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Classification of Carbohydrates:
The Carbohydrates are divided into three major classes depending upon whether or not they undergo hydrolysis and if they do in the number of products formed.
I. Monosaccharides: The monosaccharides are polyhydroxy aldehydes or polyhydroxy ketones which can not be decomposed by hydrolysis to give simpler carbohydrates. Examples are glucose and fructose.
C61-11206 + H2 0 -> no Reaction Glucose or fructose
Introduction Chapter I 2. Oligosaccharides : The oligosaccharides are carbohydrates which yield a definite
number (2 -9) of mono saccharide molecules on hydrolysis. They include,
Disaccharides, which yield two monosaccharide molecules on hydrolysis. Examples are sucrose and maltose, both of which have molecluar formula, C121-122011
C121-122011+H2 0 - C61-11206 + C6H1206
Sucrose Glucose Fructose
121-122011 H2 0 -* C6H1206 + C6171120 6 Maltose Glucose Glucose
Trisaccharides, which yield three monosaccharides on hydrolysis. Example is raffinese which has molecular formula, C181-132016.
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3. Polysaccharides: The polysaccharides are carbohydrates of high molecular weight which yield many monosaccharide molecules on hydrolysis. Examples, starch, cellulose etc.
(C6H1005)+ n H2 0 -* n C61-11206 starch or cellulose, glucose.
In general the monosaccharide and oligosaccharides are crystalline solids, soluble in water and sweet to taste. They are collectively known as sugars. The polysaccharides are insoluble in water and tasteless.
- The Carbohydrates may also be classified as either reducing or non reducing sugars. All those carbohydrates which have the ability to reduce Fehling's solution and tollents reagent are referred to as reducing sugars. All monosaccharide and the disaccharides other than sucrose are reducing sugars. The monosaccharides are the basis of carbohydrate chemistry since all carbohydrates are either monosaccharide or are converted into monosaccharide on hydrolysis. The monosaccharides are polyhydroxy aldhehydes or polyhydroxy ketons. They are divided into two categories, such as:
Introduction Chapter I 0
the Aldoses, which contain an aldehyde group, —J—H 0 the Ketoses , which contain a ketone group,
—C—
Glucose and fructose are specific examples of an aldose and a ketose.
The aldoses and ketoses may be represented by the following general formula.
H CH2OH
I I
c=O c=O
I I (CHOH)
I
(CHOH) I
CH20H CH20H
Aldoses Ketoses
Glucose and fructose are specific example of an aldose and a ketose [4].
Glucose (C61-11206):
The most common carbohydrate is glucose. Glucose is a monosaccharide an aldohexose and a reducing sugar [6]. Glucose occurs naturally both in a combined and free state. In the free state, it is present in most sweet fruits and in honey. Small quantities of glucose are also present in human blood and urine, but urine of sufferers from diabetes may contain as much as 8 to 10 percent of glucose. In the combined state, it forms a major component of many disaccharides eg .sucrose, maltose etc. [4].
Disaccharides are carbohydrates which is made of two monosaccharide units. On hydrohysis a molecule of disaccharide yields two molecules of monosaccharide [5]. When a hydroxyl group of one monosaccharide molecule acts as the alcohol to form a glycosidic linkage with the hemiacetal group of a second monosaccharide, the resulting glycoside is called a disaccharide. They are therefore acetals, formed from two monosaccharide by the water in the presence of an acid or by enzymes yields two monosaccharides [4].
C6 H12 06 +C6 H1206 -* C12H22011 +H20 monosaccharide disaccharide
Introduction Chapter I
F Sucrose:
Sucrose is called saccharose which is ordinary table sugar refined from sugarcane or sugar beets [3]. Sucrose has the molecular formula C121-122011 . It does not reduce Tollen's and fehling's reagent. It is a non reducing sugar and in this respect it differs from the other disaccharides [5].
Maltose:
Maltose consists of two a -D- glucose molecules where carbon 1 of one molecule attached to the oxygen at carbon 4 of the second molecule. This is called a I a 4 glycosidic linkage [3]. Maltose has the molecular formula C12H22011 . It reduces tollen's and fehling's reagent and hence is a reducing sugar [5]. Maltose exists in a and O forms, each of which exhibits mutarotation [4]. It is a colorless, crystalline solid. It is soluble in water but insoluble in alcohol or ether. An aqueous solution of maltose is dextrorotatory and exhibits mutarotation [4]
The studied carbohydrates (glucose, sucrose and maltose) cyclic structures are shown in below:
CH2OH HO
HO-. OH
H
Glucose
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Introduction Chapter 1