Carbohydrates PDF

# CARBOHYDRATES ## Other Names - Saccharides - The word saccharide comes from the ancient Greek word "Sugar" ## Definition - Carbohydrates are biological, complex, organic, neutral compounds consisting mainly of carbon (C), hydrogen (H), and oxygen (O). - Carbohydrates are aldehyde (CHO) or ket...

# CARBOHYDRATES ## Other Names - Saccharides - The word saccharide comes from the ancient Greek word "Sugar" ## Definition - Carbohydrates are biological, complex, organic, neutral compounds consisting mainly of carbon (C), hydrogen (H), and oxygen (O). - Carbohydrates are aldehyde (CHO) or ketone (C=O) derivatives of polyhydric alcohols (have more than one OH group). - Carbohydrates are Polyhydroxy aldehydes or Polyhydroxy ketons. - The ratio of Hydrogen to oxygen is the same as in water = 2:1, hence the name Carbo - Hydrates. - They have the general empirical formula $C_nH_{2n}O_n$ - e.g. Glucose formula is $C_6H_{12}O_6$ ## Properties of Carbohydrates - All types of carbohydrates contain one free active group (Carbonyl group) in its structure, which may be Aldehyde (CHO) or Ketone (C=O); and responsible for chemical activity of the sugar. - They are the most abundant class of organic compounds found in living organisms; because they are widely distributed in human, plants, and animals. - In plants, they are produced by photosynthesis from carbon dioxide ($CO_2$) and water ($H_2O$) with the help of light energy. ## Importance of Carbohydrates 1. **The Main Source of Energy**: for human and animals, carbohydrates can be hydrolyzed and oxidized during metabolism to release energy, e.g, glucose (the main source of energy production in our bodies). 2. Carbohydrates represent a big class of the three essential food stuffs (carbohydrates, lipids, proteins). 3. Carbohydrates store energy in the form of starch granules in plant cells and in the form of Glycogen in animal cells. 4. They enter in the composition of the recognition sites (receptors) on cell surfaces. 5. Carbohydrates are an essential component of the genetic material DNA (in the form of deoxyribose sugar) and RNA (in the form of ribose sugar). 6. Carbohydrates have an important role in detoxification in the body; for elimination and excretion of excess drugs and toxic waste products in the body. 7. They take part in many physiological reactions, as they form different biomolecules. - **Clotting Factors**: Have a role in blood clotting. - **Immunoglobulins** : Have a role in immunity. - **Oligosaccharides**: Have a role in fertilization. 8. They share in the composition of all the cellular organelles, such as the Cell Membrane, Mitochondria, Nucleus, and Endoplasmic Reticulum, to give structural integrity. 9. Carbohydrates, especially polysaccharides have structural and supportive functions (e.g., Cellulose in plants and Chitin in arthropods). 10. Structural polysaccharides are frequently found in combination with: - Proteins as (Glycoproteins or Mucoproteins). - Lipids (Lipopolysaccharides). ## Classification of Carbohydrates Carbohydrates are classified according to the number of its sugar units into the following groups: 1. **Monosaccharides**: Contain 1 sugar unit. 2. **Disaccharides**: Contain 2 sugar units. 3. **Oligosaccharides**: Contain 3-10 sugar units. 4. **Polysaccharides**: Contain more than 10 sugar units. **Note:** - Mono = one, Di = two, Oligo = few, Poly = many. - Tri = 3, Tetra = 4, Penta = 5, Hexa = 6, Hepta = 7 Monosaccharides and disaccharides are the smallest in size and have the lowest molecular weight than other carbohydrates. So, they are commonly named sugars. ## (A) Monosaccharides - They are the simplest form of sugars. - They cannot be hydrolyzed into simpler units. - They contain only one sugar unit. - They are the building units of the more complicated carbohydrates, such as Disaccharides and polysaccharides, e.g: (starch, dextrin, and glycogen). ## Subdividing Monosaccharides **1. Monosaccharides are subdivided according to type of free active (Carbonyl) group into:** - **1. Aldo-sugars (Aldoses)** - Contain aldehyde (CHO) group. - **2. Keto-sugars (Ketoses)** - Contain Ketone (C=O) group. **2. Monosaccharides are subdivided according to the number of carbon atoms into:** - **1. Trioses** - Contain 3 C atoms. - e.g. Glyceraldehyde and Di-Hydroxy-acetone. - **2. Tetroses** - Contain 4 C atoms. - e.g. Erythrose and Erythrulose. - **3. Pentoses** - Contain 5 C atoms. - e.g. Ribose, Xylose, Ribulose, Xylulose. - **4. Hexoses** - Contain 6 C atoms. - e.g. Glucose, Fructose, Galactose, Mannose ## Types of Mono Saccharides | Carbon Atom | Aldehyde | Examples | Ketone | Examples | | :---------- | :-------- | :-------- | :------ | :-------- | | n=3, $C_3(H_2O)_6$ triose | Aldo triose | Glycerose | Keto triose | Dihydroxyaceton | | n=4, $C_4(H_2O)_4$ tetrose | Aldo tetrose | Erythros | Keto tetrose | Erythrulose | | n=5, $C_5(H_2O)_5$ pentose | Aldo pentose | Ribose, Xylose | Keto pentose | Ribulose, Xylulose | | n=6, $C_6(H_2O)_6$ hexose | Aldo hexose | Glucose, Galactose, Mannose | Keto hexose | Fructose | | n=7, $C_7(H_2O)_7$ heptose | Aldo heptose | Galactoheptulose, Glucoheptulose | Keto heptose | Pseudoheptulose | ## **Importance of PENTOSES:** 1. Ribose and deoxyribose enter in the structure of Nucleic Acids: RNA, DNA. 2. Ribose enters in the structure of high energy phosphate compounds like ATP, GTP, ADP. 3. Ribose enters in the structure of coenzymes: NAD, NADP, FAD, FMN. ## **Importance of HEXOSES:** 1. **GLUCOSE:** - It is the main physiological sugar in blood and the only sugar used by the tissues. - It is one of the major sources of energy for different tissues of the body. - It is the only source of energy to the brain and nervous tissue. - It is a component of all disaccharides and most polysaccharides. - It can be stored in the body in the form of glycogen under control of the liver. - It can be converted to: - Ribose in Liver for the synthesis of RNA and DNA. - Galactose in mammary gland for milk synthesis. - Fructose in Seminal Vesicle for nutrition of sperms. 2. **GALACTOSE:** - It is synthesised in the mammary gland of the mother from glucose to synthesise the lactose of milk. - It is also obtained by digestion, hydrolysis of lactose (milk sugar) in the intestine of newborns. - After absorption, it will be converted to glucose in the liver. 3. **FRUCTOSE**: - It is present in fruit juice and honey. - It is the main sugar of semen for nutrition of sperms. - It can be converted to glucose in the liver. 4. **MANNOSE**: - It is not found in free form. - It is important for the formation of many glycoproteins and mucopolysaccharides. # General Properties of Monosaccharides 1. All monosaccharides are soluble in water. 2. They have a sweet taste. 3. They contain a symmetric carbon atom except Dihydroxy-acetone. 4. They contain free active group CHO or C=O. 5. All monosaccharides are Reducing sugars. 6. They are optically active compounds except Dihydroxy-acetone. 7. They show optical activity, specific rotation, and mutarotation. 8. They can be oxidized by mild and strong oxidizing agents. 9. They show Methylation, Esterification, and Dehydration reactions. 10. They can form osazone crystals with phenyl hydrazine. ## **In this practical chapter, we shall deal with the physical and chemical properties of:** 1. The aldo-hexose **Glucose**. 2. The keto-hexose **Fructose**. # Identification of Carbohydrate Solution Any type of carbohydrate solutions can be identified through: - Physical properties of the solution. - Chemical Properties (Tests). ## Physical Properties of Monosaccharide Solutions: (Mainly Glucose and Fructose) 1. **State**: Solution 2. **Color**: Colorless. 3. **Odor**: Odorless when fresh. 4. **Taste**: Sweet taste. 5. **Solubility**: Soluble in cold water. 6. **Reaction (pH)**: Neutral. 7. **Aspect**: Clear. 8. **Consistency**: Watery. **N.B:** - When sugar solution is left for a long period, especially in high temperature and high humidity, it suffers from alcoholic fermentation and becomes fermented by yeast and bacteria, to form alcohol and $CO_2$. - So, Non fresh sugar solutions have alcoholic odor. - The clear aspect of monosaccharides is due to: - Its low molecular weight and size. - Leading to complete dissolving and disappearance of the sugar in the inter-spaces of water. - So, the light beam can pass through this solution directly without scattering so called: True solution. ## Chemical Properties (Tests) of Monosaccharides: Most reactions and tests carried out depend mainly on the presence of the free active aldehyde group in glucose molecules and the free active ketone group in fructose molecules. ### 1. Molisch's Test **Definition**: - It is a general test used for identification of all carbohydrates. - It is a very sensitive, qualitative chemical test for the presence of carbohydrates in solutions. - It is named after the Austrian botanist "Hans Molisch" who discovered this test for the presence of carbohydrates in plants. - All carbohydrates give a positive result with Molisch test. - Monosaccharides give a rapid positive result, while Disaccharides and polysaccharides react slower. **Chemicals:** - Sugar solution. - Concentrated sulfuric acid ($H_2SO_4$). - α-Naphthol 10%. - Alcoholic α-Naphthol 1%. **Idea, Principle of the test:** - This test depends on the addition of a strong, concentrated acid, like Sulphuric acid ($H_2SO_4$) on carbohydrate solutions. - The acid will withdraw three water molecules from the sugar structure by dehydration reaction. - Turning it to a colorless ring structure called: - **Furfural ring** in the case of pentoses (as ribose) - **Hydroxyl-Methyl-Furfural** in the case of hexoses (as glucose and fructose). - Addition of the phenolic indicator (alcoholic α-Naphthol) to the colorless rings (hydroxyl-methyl-furfural or furfural), they combine together by a condensation reaction with loss of one water molecule. - It finally forms a **purple violet** ring of furfural, hydroxyl-methyl-furfural complex, which appears in the test tube (bottom). **Test Procedures:** 1. In a clean test tube, put 2 ml of glucose or fructose solution. 2. Add 5 drops of freshly prepared alcoholic 1% α-Naphthol. 3. Shake gently. 4. Add 2 ml of Conc. Sulfuric acid drop by drop slowly on the wall of the test tube while the tube is inclined. 5. Wait seconds and observe. **Observation:** - A purple violet ring appears between the two layers of solutions, (conc. $H_2SO_4$ is lower and sugar solution is above), and spread by shaking. **Results:** - It is a carbohydrate solution - **Positive Result** **N.B:** - Avoid quick addition and quick shaking of $H_2SO_4$ to the sugar solution to avoid charring of the sugar. - Alcoholic α-Naphthol is an indicator that does not share in any step of the reaction, but is only responsible for ring coloration. - Specific gravity of Sulphuric acid is higher (heavier) than the solution ➡ so, when the acid is added slowly on the wall of the test tube, it descends to the bottom and replaces the solution, and finally the acid represents the lower part and the solution represents the upper part of the test tube.