Chemical Basis of Life- PDF

# Chemical Basis of Life The bodies of all organisms are composed of a variety of chemical compounds. These chemical compounds are formed by the bonding of naturally existing elements in different ways. There are only about 25 elements in the living body out of the 92 elements present in nature. T...

# Chemical Basis of Life The bodies of all organisms are composed of a variety of chemical compounds. These chemical compounds are formed by the bonding of naturally existing elements in different ways. There are only about 25 elements in the living body out of the 92 elements present in nature. They are present at different locations in the body in different forms. The most common 4 elements in the living body are Carbon, Hydrogen, Oxygen and Nitrogen. Other than above Sulfur, Phosphorus, Sodium, Potassium, Calcium, Magnesium, Iron and Chlorine are essential for the survival of organisms. Figure 1.1 shows the percentages of main elements in the human body. | Element | Percentage | |---|---| | Oxygen | 65% | | Carbon | 18% | | Hydrogen | 10% | | Nitrogen | 3% | | Others | 4% | ## Chemical Compounds Chemical compounds that build up living matter can be divided into two categories as organic compounds and inorganic compounds. Compounds which contain Carbon are known as organic compounds and compounds which do not contain Carbon are known as inorganic compounds. (Carbon dioxide, Carbon monoxide, Carbonates and Bicarbonates are some of the inorganic compounds which contain Carbon) Those organic compounds that build up the living body or living matter are known as bio molecules. They are: - Carbohydrates - Proteins - Lipids - Nucleic acids These are considered as the main types of bio molecules. Instead of these four types, Vitamins are also one of the organic compounds found in living matter. Water, minerals and gases are some of the inorganic molecules that are essential for the maintenance of life. ### Extra Knowledge | Element | Percentage based on mass% | Locations present in human body | |---|---|---| | O | 65 | All fluids, tissues, bones, proteins everywhere in the body | | C | 18 | All fluids, tissues, bones, proteins | | H | 10 | All fluids, tissues, bones, proteins | | N | 3 | Brain, lungs, kidneys, liver, heart, thyroid gland, muscles, bones | | Ca | 1.5 | Urine, bones | | P | 1.0 | Enzymes | | K | 0.35 | All fluids, tissues | | S | 0.25 | Proteins | | Na | 0.15 | Brain, lungs, kidneys, liver, heart, thyroid gland, muscles | | Mg | 0.05 | Skin cells | | Cl | 0.2 | Haemoglobin in blood | | Fe | 0.007 | Hormones in thyroid gland | | I | 0.0002 | | ## Carbohydrates This is the most abundant organic compound on earth. They are produced during the photosynthesis of green plants. Potato, sweet potato, grains, sugar, flour are some of the examples for foods which contain carbohydrates. The main elemental composition of carbohydrates is Carbon (C), Hydrogen (H) and Oxygen (O). Hydrogen and oxygen combine in 2:1 ratio in carbohydrates. **Common molecular formula** $C_n(H_2O)_n$ ### Carbohydrates Classification Carbohydrates can be classified into three groups as below according to the way they are formed. **Carbohydrates** - **Monosaccharides** ($C_6H_{12}O_6$) - Glucose - Fructose - Galactose - **Disaccharides** ($C_{12}H_{22}O_{11}$) - Maltose - Sucrose - Lactose - **Polysaccharides** ($C_6H_{10}O_5)_n$ - Starch - Cellulose - Glycogen **n = Number of monosaccharide molecules** #### Monosaccharides Monosaccharide is the structural unit of carbohydrates. They are commonly known as simple sugars. They are crystal shaped, generally sweet and water soluble molecules. Glucose, Fructose, and Galactose are examples for monosaccharides. The characters of monosaccharides are discussed in the table below. | Type of monosaccharide | Location it's present | Other facts | |---|---|---| | Glucose | Ripen fruits Bee honey | The end product during hydrolysis of all starchy food is glucose. These glucose is absorbed into blood Plants produce glucose during photosynthesis | | Fructose | Ripen fruits Beehoney Pumpkin carrots | Energy is released during breakdown of glucose in cellular respiration Known as "fruit sugar" Fructose is formed during ripening of fruits This is the sweetest sugar | | Galactose | Dairy products | The end product during hydrolysis of lactose No sweet taste | #### Disaccharides Two Monosaccharides join to form a Disaccharide. During this process a water molecule is released. In the same way relevant Monosaccharides can be obtained by hydrolyzing Disaccharides. Disaccharides are sweet, water soluble crystals. Monosaccharide + Monosaccharide → Disaccharide + Water molecule $2C_6H_{12}O_6$ → $C_{12}H_{22}O_{11}$ + $H_2O$ Maltose, Sucrose and Lactose are examples for disaccharides. The characters of disaccharides are discussed in the table below. | Type of disaccharide | Location it's Present | Other Facts | |---|---|---| | Maltose | Germinating seeds | Union of two glucose molecules forms a Maltose molecule Glucose + Glucose → Maltose + Water An intermediate product of starch hydrolysis | | Sucrose | White and brown Sugar Sugar cane and Beet Some fruits Phloem sap in trees | Union of a Glucose molecule with a Fructose molecule forms a Sucrose molecule Glucose + Fructose → Sucrose+Water | | Lactose | In dairy products | Union of a Glucose molecule with a Galactose molecule forms a Lactose molecule Galactose + Glucose → Lactose+Water The only sugar that is absent in plants Not sweet as Sucrose The percentage of Lactose in cows milk according to the composition is 4% - 6% The percentage of Lactose in human milk according to the composition is 6% - 7% | #### Polysaccharides Polymerisation of a large number of monosaccharides form a polysaccharide molecule. Hydrolysis of Polysaccharide results relevant monosaccharides. Insoluble in normal water. They are not crystals. Cellulose, Starch and Glycogen are examples for polysaccharides. The structural unit of Cellulose, Starch and Glycogen is Glucose, but their properties are different according to the number of Glucose molecules and how they are bound with each other. The characters of polysaccharides are discussed in the table below. | Type of polysaccharide | Location it's Present | Other Facts | |---|---|---| | Cellulose | Cell wall of plant cells In fibres | It is not digested in the human digestive system, but it helps to avoid constipation. | | Starch | Grains, Yams, Jak, Bread Fruit | The type of carbohydrate that stores in plants is starch. | | Glycogen | Animal liver and muscles | The type of carbohydrate that stores in animal body is Glycogen | ### Extra Knowledge A diagram of a glucose molecule: - H - C - OH - H - H - HO - C - H - OH - H - OH - OH - H - OH ## Significance of Carbohydrates - **As an energy Source** The main source to obtain energy for the activities of organisms is the carbohydrate. The Monosaccharides (Glucose) produced due to hydrolysis of those compounds release energy. - **As a storage compound** - **As a structural component in plant cell wall** - **As a constituent of Nucleic acid** ## Tests to identify Carbohydrates The below mentioned tests can be conducted to test Starch, Monosaccharides and Disaccharides which are some of the identified Carbohydrates in foods. ### Starch test - Small amount of food is obtained and grind well with water. - A drop of Iodine solution is added to the above solution. Purplish blue colour appears ### Test for Glucose - A solution of Glucose is obtained into a test tube. - Few drops of Benedict solution to the above solution is added. - The above solution is immersed in a water bath and heated. - Can observe colour changes as below. **Blue → Green → Green yellow → Orange → Brick red precipitate** ### Test for (Sucrose) - A sucrose solution is obtained into a test tube. - Few drops of Benedict solution is added to it. - The test tube is immersed in a water bath and heated. No colour change. - Few drops of diluted Sulphuric acid ($H_2SO_4$) is added to a freshly prepared sugar solution and heated. - Next few drops of Benedict solution is added to it. - Can observe colour changes as below. **Blue → Green → Green yellow → Orange → Brick red precipitate** ## Proteins Protein is an essential constituent in all living cells. Carbon(C) Hydrogen (H), Oxygen (O) and Nitrogen (N) are always present in proteins. Sometimes Sulphur can also be present. 17% of the mature human body is composed of proteins. Protein is a complex molecule made up of polymerized amino acid molecules. Meat, fish, egg white cereals are some of the foods rich with proteins. ### Extra Knowledge #### Amino acids Below is the structure of a typical amino acid molecule. - Amino group - $NH_2$ - C - COOH - Carboxyl group - H - R R- represents a group containing both Carbon (C) and Hydrogen (H). Due to the change in R group, 20 different amino acids are present. All proteins present in organisms from bacteria to human are made up of these 20 different amino acids combined in different sequences. The simplest Amino acid is Glycine. Here Hydrogen (H) is present as the R group. - H - H - C - $NH_2$ - COOH Some amino acids cannot be synthesized within the body. So they have to be taken from outside with food. Therefore they are known as essential amino acids. ### Extra Knowledge Different proteins present in plants and animals | Protein present in | Name | |---|---| | Muscles | Myosin, actin | | Bones | Osein | | Red blood cells | Haemoglobin | | Hairs | Keratin | | Leguminous food | Legumin | | Wheat | Gluten | | Egg white | Albumin | ## Significance of Proteins - **As an energy source** When energy supply from Lipids and Carbohydrates is not sufficient protein is used in energy generation. - **To make structural components** Proteins are important components in making cell membrane. Hairs and feathers also contain keratin protein. - **As enzymes** All the bio-chemical reactions take place in organisms are catalyzed by enzymes. The enzymes are proteins. - **As hormones** Some hormones are proteins which involve in homeostasis and coordination of organisms. - **As antibodies** The antibodies that are produced in the body to protect the body against microorganisms that enter into the body are proteins.