REFERENCES

1. Bah Hock Guan, Sri Naasariya, 2013, Matriculation Biology 1 Fourth Edition, Oriental Academic Publication.

2. Campbell, N.A. & Reece, J.B., Biology Eighth Edition, Pearson, The Benjamin Cummings Publishing Company, Inc., 2007.

3. https://en.wikipedia.org

CONCLUSIONS OF CARBOHYDRATES

Carbohydrates are simple organic compounds that are aldehydes or ketones with many hydroxyl groups added, usually one on each carbon atom that is not part of the aldehyde or ketone functional group. Their common reactions are through Carbohydrate metabolism. Carbohydrate metabolism denotes the various biochemical processes responsible for the formation, breakdown and interconversion of carbohydrates in living organisms.

POLYSACCHARIDES

DEFINITION:
Polysaccharides are long carbohydrate molecules of monosaccharide units joined together by glycosidic bond. They range in structure from linear to highly branched. Polysaccharides are often quite heterogeneous, containing slight modifications of the repeating unit. Depending on the structure, these macromolecules can have distinct 
properties from their monosaccharide building blocks. They may be amorphous or even insoluble in water.
Examples include storage polysaccharides such as starch and glycogen, and structural polysaccharides such as cellulose and chitin.

STORAGE POLYSACCHARIDES:

Starch

Starch are glucose polymers in which glucopyranose units are bonded by alpha-linkages. It is made up of a mixture of amylose (15–20%) and amylopectin (80–85%). Amylose consists of a linear chain of several hundred glucose molecules and Amylopectin is a branched molecule made of several thousand glucose units (every chain of 24–30 glucose units is one unit of Amylopectin). Starches are insoluble in water. They can be digested by hydrolysis, catalyzed by enzymes called amylases, which can break the alpha-linkages (glycosidic bonds). Humans and other animals have amylases, so they can digest starches. Potato, wheat, rice and maize are major sources of starch in the human diet. The formations of starches are the ways that plants store glucose.

Glycogen

Glycogen serves as the secondary long-term energy storage in animal and fungal cells, with the primary energy stores being held in adipose tissue. Glycogen is made primarily by the liver and the muscles, but can also be made byglycogenesis within the brain and stomach.

Glycogen is the analogue of starch, a glucose polymer in plants, and is sometimes referred to as animal starch, having a similar structure to amylopectin but more extensively branched and compact than starch. Glycogen is a polymer of α(1→4) glycosidic bonds linked, with α(1→6)-linked branches. Glycogen is found in the form of granules in the cytosol/cytoplasm in many cell types, and plays an important role in the glucose cycle. Glycogen forms an energy reserve that can be quickly mobilized to meet a sudden need for glucose, but one that is less compact than the less immediately available energy reserves of triglycerides (lipids).

In the liver hepatocytes, glycogen can compose up to eight percent (100–120 g in an adult) of the fresh weight soon after a meal. Only the glycogen stored in the liver can be made accessible to other organs. In the muscles, glycogen is found in a low concentration of one to two percent of the muscle mass. The amount of glycogen stored in the body—especially within the muscles, liver, and red blood cells—varies with physical activity,basal metabolic rate, and eating habits such as intermittent fasting. Small amounts of glycogen are found in the kidneys, and even smaller amounts in certain glialcells in the brain and white blood cells. The uterus also stores glycogen during pregnancy, to nourish the embryo.

Glycogen is composed of a branched chain of glucose residues. It is stored in liver and muscles.

• It is an energy reserve for animals.
• It is the chief form of carbohydrate stored in animal body.
• It is insoluble in water. It turns red when mixed with iodine.
• It also yields glucose on hydrolysis.

Cellulose

The structural component of plants are formed primarily from cellulose. Wood is largely cellulose and lignin, while paperand cotton are nearly pure cellulose. Cellulose is a polymer made with repeated glucose units bonded together by beta-linkages. Humans and many other animals lack an enzyme to break the beta-linkages, so they do not digest cellulose. Certain animals such as termites can digest cellulose, because bacteria possessing the enzyme are present in their gut. Cellulose is insoluble in water. It does not change color when mixed with iodine. On hydrolysis, it yields glucose. It is the most abundant carbohydrate in nature.

DISACCHARIDES

DEFINITION
A disaccharides is the carbohydrate formed when two monosaccharides undergo a condensation reaction which involves the elimination of a small molecule, such as water, from the functional groups only. Like monosaccharides, disaccharides form an aqueous solution when dissolved in water. Three common examples are sucrose, lactose and maltose.
'Disaccharide' is one of the four chemical groupings of carbohydrates (monosaccharides, disaccharides, and polysaccharides)


 CONTENTS
There are two different types of disaccharides: reducing disaccharides, in which one monosaccharide, the reducing sugar, still has a free hemiacetal unit; and non-reducing disaccharides, in which the components bond through an acetal linkage between their anomeric centers and neither monosaccharide has a free hemiacetal unit. Maltose is examples of reducing disaccharides. Sucrose is examples of non-reducing disaccharides.


CLASSIFICATION
There are two different types of disaccharides: reducing disaccharides, in which one monosaccharide, the reducing sugar, still has a free hemiacetal unit; and non-reducing disaccharides, in which the components bond through an acetal linkage between their anomeric centers and neither monosaccharide has a free hemiacetal unit. Maltose are examples of reducing disaccharides. Sucrose and are examples of non-reducing disaccharides.


FORMATION
Disaccharides are formed when two monosaccharides are joined together and a molecule of water is removed, a process known as dehydration reaction. For example; milk sugar (lactose) is made from glucose and galactose whereas the sugar from sugar cane and sugar beets (sucrose) is made from glusose and fructose. Maltose, another notable disaccharide, is made up of two glucose molecules.The two monosaccharides are bonded via a dehydration reaction (also called a condensation reaction or dehydration synthesis) that leads to the loss of a molecule of water and formation of a glycosidic bond.


PROPERTIES
The glycosidic bond can be formed between any hydroxyl group on the component monosaccharide. So, even if both component sugars are the same (e.g., glucose), different bond combinations (regiochemistry) and stereochemistry (alpha- or beta-) result in disaccharides that are different chemical and physical properties.

Depending on the monosaccharides constituents, disaccharides are sometimes crystalline, sometimes water-soluble, and sometimes sweet-tasting and sticky-feeling.

MALTOSE

Maltose also known as maltobiose or malt sugar, is a disaccharide formed from two units of glucose joined with an α(1→4) bond, formed from a condensation reaction. The isomer isomaltose has two glucose molecules linked through an α(1→6) bond. Maltose is the second member of an important biochemical series of glucose chains. Maltose is the disaccharide produced when amylase breaks down starch. It is found in germinating seeds such as barley as they break down their starch stores to use for food. It is also produced when glucose is caramelized.

Maltose can be broken down into two glucose molecules by hydrolysis. In living organisms, the enzyme maltase can achieve this very rapidly. In the laboratory, heating with a strong acid for several minutes will produce the same result. Isomaltose is broken by isomaltase

SUCROSE

Sucrose is the organic compound commonly known as table sugar and sometimes called saccharos. A white, odorless, crystalline powder with a sweet taste, it is best known for its role in food. The molecule is a disaccharide composed of the monosaccharides glucose and fructose with the molecular formula C₁₂H₂₂O₁₁. The word was formed in the mid-19th century from Latin sucrum = "sugar" and the chemical suffix -ose. The abbreviated term Suc is often used for sucrose in the literature.

LACTOSE

Lactose is a disaccharide sugar derived from galactose and glucose that is found in milk. Lactose makes up around 2~8% of milk (by weight), although the amount varies among species and individuals. It is extracted from sweet or sour whey. The name comes from lac or lactis, the Latin word for milk, plus the -ose ending used to name sugars. It has a formula of C₁₂H₂₂O₁₁.

MONOSACCHARIDES

DEFINITION

Monosaccharides are the most basic units of biologically important carbohydrates. They are the simplest form of sugar and are usually colourless,water-soluble,crystalline solids and sweet tasting.Examples of monosaccharidesare glucose , fructose, galactose,xylose and ribose. Monosaccharides are the building blocks of disaccharides (such as sucrose) and polysaccharides (such as cellulose and starch). Further, each carbon atom that supports hydroxyl group (except for the first and last) is chiral, giving rise to a number of isomeric forms all with the same chemical formula. For instance, galactose and glucose are both aldohexoses, but have different chemical and physical properties.Monosaccharides can be classified by the number x of carbon atoms they contain: diose (2) triose (3) tetrose (4), pentose (5), hexose (6), heptose (7), and so on.

Linear-chain monosaccharides

Simple monosaccharides have a linear and unbranched carbon skeleton with one carbonyl (C=O) functional group, and one hydroxyl (OH) group on each of the remaining carbon atoms. Therefore, the molecular structure of a simple monosaccharide can be written as H(CHOH)_n(C=O)(CHOH)_mH, where n+1+m = x; so that its elemental formula is C_xH_2xO_x.
By convention, the carbon atoms are numbered from 1 to x along the backbone, starting from the end that is closest to the C=O group.
If the carbonyl is at position 1 (that is, n or m is zero), the molecule begins with an formyl group H(C=O)-, and is technically an aldehyde. In that case, the compound is termed an aldose. Otherwise, the molecule has a   group, a carbonyl -(C=O)- between two carbons; then it is formally a ketone, and is termed a ketose.

GLUCOSE
Gucose is a simple monosaccharides found in plants. It is one of the three dietary monosaccharides, along with fructose and galactose, that are absorbed directly into the bloodstream during digestion. An important carbohydrate in biology cells use it as the primary source of energy and a metabolic intermediate. Glucose is one of the main products of photosynthesis and fuels for cellular respiration.

GALACTOSE
Galactose is a monosaccharides.When combined with glucose (monosaccharide), through a condensation reaction, the result is the disaccharide lactose. The hydrolysis of lactose to glucose and galactose is catalyzed by the enzyme lacatase and β-galactose.Galactose is found in dairy products sugar beets, other gums and mucilages. It is also synthesized by the body, where it forms part of glycolipids and glycoproteins in several tissues.

FRUCTOSE

Fructose, or fruit sugar, is a simple monosaccharides found in many plants, where it is often linked to glucose forming sucrose.It is one of the three dietary monosaccharides, along with glucose and galactose that are absorbed directly into the bloodstream during digestion. Fructose was discovered by French chemist Augustin-Pierre Dubrunfaut in 1847.Pure, dry fructose is a very sweet, white, odorless, crystalline solid and is the most water-soluble of all the sugars.From plant sources, fructose is found in honey, tree and vine fruits, flowers, berries, and most root vegetables. In plants, fructose may be present as the monosaccharide or as a molecular component of sucrose, which is a disaccharides.

CLASSIFICATION OF CARBOHYDRATES

MONOSACCHARIDES

Monosaccharides is a simple sugar. Monosaccharides consist of at least three carbon atoms, one of which is attached to an oxygen atom to form an aldehyde group (CHO) or a ketone, and the others of which are each attached to a hydroxyl group (OH). Monosaccharides can occur as chains or rings. Fructose, glucose, and galactose are the examples of simple sugar of monosaccharides.

DISACCHARIDES

Disaccharides is the carbohydrate formed when two monosaccharides undergo a condensation reaction which involves the elimination of a small molecule, such as water, from the functional group only. Like monosaccharides ,disaccharides form an aqueous solution when dissolved in water. Three common examples are sucrose, lactose, and maltose .'Disaccharide' is one of the four chemical groupings of carbohydrates (monosaccharide, disaccharide, and polysaccharide).

POLYSACCHARIDES

Polysaccharides are long carbohydrate molecules of monosaccharide units joined together by glycosidic bonds They range in structure from linear to highly branched. Polysaccharides are often quite heterogeneous, containing slight modifications of the repeating unit. Depending on the structure, these macromolecules can have distinct properties from their monosaccharide building blocks.Examples include storage polysaccharides such as starch and glycogen, and structural polysaccharides such as cellulose and chitin.

FUNCTION OF CARBOHYDRATES

Carbohydrates provide the body with a source of fuel and energy that is required to carry out daily activities and exercise. Any extra energy is stored in the body until it is needed.

Our bodies need a constant supply of energy to function properly and a lack of carbohydrates in the diet can cause tiredness or fatigue, poor mental function and lack of endurance and stamina.

Carbohydrates are also important for the correct working of our brain, heart and nervous, digestive and immune systems.

Fibre, which is also a form of carbohydrate, is essential for the elimination of waste materials and toxins from the body and helps to keep the intestines disease-free and clean.                                                        
     
 Carbohydrates are an essential part of a healthy diet and should make up 50% of our daily calorie intake. The majority should come from complex carbohydrates, preferably the wholemeal varieties, as well as a large intake of fruit and vegetables.

Simple carbohydrates of the refined kind, including refined sugar (sucrose) should be limited. They have no nutritional value and are generally high in sugars and fats.

To make it really simple:

"Good" carbohydrates are:

Bran, wheat germ, wholemeal bread, brown rice, potatoes, all forms of pasta but especially wholemeal pasta, barley, oats, lentils, chickpeas, beans, peas, corn, sweet potatoes, wholegrain cereals such as Weetabix, muesli, All bran, brown breads, root vegetables such as carrots, turnips, leeks and radishes.

"Bad" carbohydrates are:

Sweets, sugary breakfast cereals, cakes, pastries, syrup, table sugar (sucrose), fizzy drinks, biscuits, chocolate.