Carbohydrates By Dr Ghulam Abbas Carbohydrate functions Energy

Carbohydrates By Dr. Ghulam Abbas

Carbohydrate functions Energy sources (glucose/glycogen) Structural element • cell wall (plants, bacteria) • connective tissues • adhesion between cells

Plant cell wall The Gram positive cell wall

Carbohydrates in Food • Chemical structures of carbohydrates contain many carbon atoms bonded to hydroxide group. They are also called sugars or saccharides. Carbohydrates can be small or very large molecules. • Sugars or saccharides: Scientists also use The word saccharides to describe sugars. If there is only one sugar molecule it is called monosaccharide, if there are two, it is called disaccharide. If there are three , it is a trisachharadie.

Sugars Monosaccharides • Glucose • Fructose • Galactose Disaccharides Sucrose - - Table sugar (Glucose and Fructose) Lactose - - Milk sugar (Glucose and Galactose) Maltose - - ----Corn sugar (Glucose and Glucose)

Monoosaccharide Aldose 6 C: glucose, mannose 5 C: ribose, xylose, 4 C: erythrose, threose 3 C: glyceraldehyde Ketose 6 C: fructose, sorbose

Monoosaccharide

Monoosaccharide Galactose Mannose Ribose Glucose

Sweetness of Sugars Sugar • • • Fructose Sucrose Glucose Galactose Maltose Lactose Sweetness 1. 3 1. 0 0. 56 0. 4 -0. 6 0. 3 -0. 5 0. 2 -0. 3

Carbohydrates • Carbohydrates act as the most important source of energy for our body and one of the main types of nutrients. In living systems carbohydrates mainly convert to glucose which is also called as blood sugar and uses this sugar as energy source. • The excess of glucose stores in the form of starch (in plants) and glycogen (in animal) for when it is needed. Depending on their chemical structures, carbohydrates can be simple or complex compounds.

• Types of carbohydrates: There are two types of carbohydrates; Simple and complex carbohydrates. Most of our carbohydrates come from complex carbohydrates. • Simple carbohydrates: A sugar called glucose is the most important monosaccharide on Earth. In plants glucose is synthesized by photosynthesis and use in cellular respiration. Sugar is actually disaccharide. The sugar used in our dinner table is made of glucose and another monosaccharide called fructose.

• Functional group isomers: • Monosaccharide like glucose, fructose, mannose and galactose can show different isomerism. For example, glucose and fructose are functional isomer of each other as glucose contains aldehyde group and fructose contains ketonic group in molecule.

Epimer Definition • They can also show stereoisomerism due to the presence of chiral carbon atoms. Those stereoisomers which are differing in its configuration at only one chiral carbon atom are called as Epimers. For example, glucose and galactose are Epimers of each other, as they differ in only in the position of hydroxyl group at C 4.

Epimer Definition

• Simple carbohydrates are composed of single unit sugars called monosaccharides and disaccharides. Glucose and fructose are examples of common monosaccharides. • Simple carbohydrates are easily digested and converted into sugars rapidly in blood stream. • Simple carbohydrates are also called sugars. They exist in either a natural or refined form. Natural sugars are found in fruits and vegetables.

What kinds of foods provide carbohydrates? Some are in milk; most are in plant foods, including fruits, vegetables, grain products, dry beans, nuts, and seeds.

Oligosaccharide Sugars which are formed by joining of 2 -10 monomers units. Examples: Maltose, sucrose, lactose, Reffinose.

Glycosidic linkage/acetal lingkage

• Dietary Fiber: Plant materials that are eaten but can’t be digested by human enzymes. • Dietary Fiber in plants are cellulose, pectin and lignin. Although its rigid bonds are resistant to digestive enzymes [β(1 -4 linked D-glucose)], and thus pass through our digestive system intact. Fiber is extremely important in maintaining good health. • Some of the benefits of fibers include:

Dietary Fiber • Regulation of blood sugar. Fibers slow down the digestion of other foods while it is eaten, and helps to prevent large changes in blood sugar. • Lowering the blood cholesterol: fiber binds with fatty acids and cholesterol into large clusters that our body can get rid easily. • Promotion of intestinal health: Fibers are helpful in digestion and prevent constipation and hemorrhoids by regulating bowel movement. • Adds to feeling of fullness when eating.

Dietary Fiber

How body uses carbohydrates • When we eat carbohydrates , the body breaks them down into simple sugars, which are absorb into the blood stream. As the sugar level rises in body, the pancreases release a hormone called insulin. Insulin is needed to move sugar from blood into the cells, where sugar can be used as a source of energy.

Carbohydrates

Sugars • Glucose: The central actor in this game is glucose, known also as blood sugar, grape sugar and dextrose (D-glucose is dextrorotatory). Glucose is “reducing sugar” that is it is oxidized by ferric (Fe+3) and cupric (Cu+2) ions yielding reduced metal ions. • Galactose: It is found in milk and milk products. It is also a reducing sugar and form 6 membered ring when dissolved. Galactose is almost identical to glucose only exception being the position of “OH” group on carbon 4.

Sugars • Fructose: It is third (3 rd) most common sugar found in our diet. As with glucose it also form ring structure when dissolved. • Because carbonyl group is on carbon 2, fructose form a “ 5 remembered ring” carbon 1 and 6 are attached to the central ring which effects both intestinal uptake and metabolism of carbohydrates. • Fructose is natural but limited component of our food, being found in limited amounts in many types of fruits and berries. • Fructose is one of the two sugars that are found in sucrose (table sugar). It is sweeter than table sugar. • It is thus suggested by many health experts that one can cut down on the calori intake by replacing sucrose with fructose. Since fructose is 30 -40% sweeter than sucrose, one should be able to eat 30 -40 % less sugar and get the same sweetening effect.

Ribose • Ribose is essential part of our metabolic system, being found in physphorylated form in ATP and others things. The diet supplement industry has presented ribose as a strength and energy giving stuff.

Disaccharides • Sucrose: The disaccharide sucrose is composed of glucose and fructose joined by an alpha 1 -2 bond. Sucrose is relatively “new comer” in our diet. It is actually not especially sweet, and we use large amount of it to get taste we desire in breakfast cereals, soft drinks, cakes and sweets. C 1, 2 glycosidic bond

Lactose • Lactose (milk sugar) is a disaccharide composed of glucose and galactose. • The enzyme responsible for synthesis of lactose is specific for the beta form of glucose and the result is beta 1 -4 glucosidic bond between the two monomers. • Lactose is the only substance with such bond which can be digested in human intestine. • This requires the presence of lactase, another enzyme involved in carbohydrate digestion that is produced and bound to the mucosal cell membrane.

Maltose • Maltose and isomaltose are not the major components of our diet but are formed from polysaccharides in the intestine through the action of amylase. • These disaccharides are glucose dimers and are digested by maltase and isomaltase that are produced and bound to the mucosal cell. The glucose formed is then readily absorbed.

Complex carbohydrates are often referred as starch and starchy foods. They are found in naturally in foods and also refined in processed foods. Complex carbohydrates as natural starches are found in; Banana, barley, beans, brow rice, chickpeas, lentils, nuts, oats, potatoes, root vegetables, sweet corn, wholegrain cereals, wholegrain pasta, yams.

Refined sugars • Biscuits, Cakes and pastries. • Chocolate • Honey and Jams, Jellies • Brown and white cane sugar • Pizzas, prepared food and sauces • Soft drinks, sweets and snack bar. Sugars; clockwise from top-left: White refined, unrefined, brown, unprocessed cane

Comples carbohydrates • Comples sugars (polysaccharides) are built from single-unit sugars joined in long chains. Two types of complex carbohydrates are particularly important in nutrition. • Starch: It is polysaccharide that plants use to store energy. It is the main constituent of comples carbohydrates in human diet. • Examples of starchy foods are potatoes, rice and pasta.

Starch Amylose

Glycogen

Cellulose Monomer: glucose Bonding: -1, 4 Carboxymethyl cellulose

BONDING IN SUCROSE C 1, 2 glycosidic bond

Polysaccharides • The minor difference results in entirely dissimilar 3 -dimentional structure. Beta 1 -4 linked glucosyl group from sheet that pack together to form the rigid structure called cellulose. This is the major polysaccharide of grass, leaves and trees and is said to include around 50% of all biological carbon found in our planet. The digestion of cellulose is entirely dependent upon intestinal flora in herbivores. • Starch in plant and glycogen in human has completely different structure.

C 1, 4 glycosidic bond Starch Cellulose

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