BASIC SCIENCE II: Chemicals of Life

The bodies of all organisms are composed of 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 & Nitrogen. Other than above Sulphur, Phosphorous, Sodium, Potassium, Calcium, Magnesium, Iron and Chlorine are essential for the survival of organisms.

The below diagram 1.1 shows the percentages of main elements in the human body.

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. Those organic compounds that build up the living body or living matter are known as biological molecules. There are four types of biological molecules. They are:

• Carbohydrates
• Proteins
• Lipids
• Nucleic acids

Water, minerals and gasses are some of the inorganic molecules that are essential for the maintenance of life.

1. 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 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.

The carbohydrates can be classified into three groups as seen below according to the way they are formed.

• 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.

Maltose, Sucrose and Lactose are examples for disaccharides. The characters of disaccharides are discussed in the table below.

Table 1.2 Characters of different types of disaccharides

• 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.

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 during oxidation.
  As storage compound
• As a structural component in organism
• As a constituent of Nucleic acid

Tests to identify Carbohydrates

The below mentioned tests can be conducted to test Starch, Monosaccharides & Disaccharides which are some of the identified Carbohydrates.
Starch test

• Obtain small amount of food & grind well with water.
• Add a drop of Iodine solution to the above solution.
  Observation: Purplish blue colour appears

Test for Monosaccharides & some Disaccharides

• Obtain a solution of Gluscose, into a test tube.
• Add few drops of Benedict solution to the above solution.
• Immerse the above solution in a water bath and heat.
• Can observe colour change as below.

Disaccharides (Sucrose)

• Obtain a sucrose solution into a test tube.
• Add few drops of Benedict solution to it.
• Immerse the test tube in a water bath & heat it.
• No colour change.
• Then add few drops of diluted Sulphuric acid (H2SO4) & heat.

2. Proteins

Protein is an essential constituent in all living cells. Carbon(C) Hydrogen (H), Oxygen (O) & 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.

• Amino acids

Below is the structure of a typical amino acid molecule.

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.

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.

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. Other than that collagen protein is a component of connective tissues in animals. Hairs & 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 & coordination of organisms. Eg : Insulin, Growth hormone
• As antibodies: The antibodies that are produced in the body to protect the body against microorganisms that enter into the body are proteins.

Test to identify proteins

• Biurette test
• Obtain a solution made by grinding dhal or an egg yolk into a test tube.
• Add an extra amount of Sodium hydroxide (NaOH) and then add few drops of Copper Sulphate (CuSO4)

Observation – Solution turn to pinkish purple or dark purple colour

Enzymes

The special proteins (organic catalysts) that are produced within the organism to increase the rate of bio- chemical reactions are known as enzymes.

For example to convert sucrose into Glucose, sucrose has to be heated with a dilute acid. But the enzymes present in the digestive system do the same reaction at a low temperature. Therefore the activity of enzyme is to catalyze the bio- chemical reactions.

Activity of Amylase on starch

Method

• Put 2ml of starch solution into a test tube.
• Add 2ml of amylase into it and mix well.
• Get a drop from the solution after 2 minutes and place it on a white porcelain tile and add a drop of iodine onto the drop of mixture.
• Continue same procedure for about 20 minutes in 2 minute intervals.

Observation

The blue colour of the drop obtained from the mixture gradually reduces with time and finally obtains the colour of Iodine (yellow /brown colour)

That is due to Moltose produced in starch hydrolysis with Amylase enzyme.

Starch gives black blue colour with iodine but it does not give colour change with iodine after 20 minutes as there is no starch there.That is because starch is changed into another compound by Amylase.

3. Lipids

Fats & oils belong to this group. (Lipids which are solid at room temperature are called fats and liquids are called oils.)

Similar to carbohydrates, fats also contain Carbon, Hydrogen & Oxygen as constituent elements. But the ratio of hydrogen to oxygen in fats are very much higher than carbohydrates. Lipids are insoluble in polar solvents including water.

They are soluble in organic solvents.

Ground nut, coconut, gingelly, butter and margarine are examples for foods which contain lipids.

Fatty acids & glycerol react to form Lipids.

Significance of Lipids

• As an energy source: Lipids act as an energy source as carbohydrates & proteins. More energy is produced during burning of lipids.
• To form different structural components: Lipid is one of the most important compounds in cell membrane. (Specially phospho lipids & cholesterol)
• For conservation of water: The wax known as cutin present on the surface of the plant body conserve water. Most animals’ body covering also contains wax which helps to avoid desiccation as it is impermeable to water.
• To maintain the body temperature: Warm blooded animals such as birds and mammals possess a hypodermal
  fat layer which acts as a thermal insulator. It helps to maintain their body temperature.
• To protect internal body organs: The fat layer surrounds the organs & structures in the body and absorbs external shocks. Thereby provides protection.
• To synthesize some hormones: Some Hormones of vertebrates (Oestrogen, testosterone, Cortisol) are lipid compounds.

Test to identify lipids

Sudan III test

• Put some amount of gingelly oil or coconut oil into a test tube.
• Add sudan III reagent into it.

Observation – Appearance of red fat globules

Conclusion – Lipid present in that food

Fatty acids can be divided into two groups as follows.

Saturated fatty acids: fatty acids where the Carbon atom contains the maximum number of Hydrogen atoms are called saturated fatty acids. Saturated fatty acids exist in room temperature as solids or semi-solids.

Unsaturated fatty acids: fatty acids where the Carbon atom does not contain the maximum number of Hydrogen atoms are called unsaturated fatty acids. Unsaturated fatty acids exist in room temperature as liquids.

4. Nucleic Acids

Nucleic acid is the most important molecule out of the main biological molecules in living matter in genetical aspect. It is a linear polymer made up of large number of nucleotides. It contains Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N) and Phosphorous (P).

Each nucleotide is made up of 3 components. They are;

1. Nitrogenous base
2. Pentose sugar group
3. Phosphate group

Nucleic acids are mainly of two types.

• DNA – Deoxy ribo Nucleic Acid
• RNA – Ribo Nucleic Acid

DNA

The structural unit of DNA is Deoxyribo Nucleotide. DNA transfers genetic characteristics from generation to generation

RNA

Except DNA, the other nucleic acid present in organisms is RNA. The structural unit of RNA is Ribonucleotide. Protein synthesis is the function of RNA.

Significance of Nucleic acid

• Important in storage of genetic information of organisms.
• Important in transferring genetic information from generation to generation.
• Important in protein synthesis process.
• Important in controlling all cellular activities in a cell. The information to control cellular activities is present in DNA.
• RNA is important in storing genetic information of some viruses.
• The variations occur in DNA due to mutations are important in evolution.

The above biological molecules contain mainly Carbon (C), Hydrogen (H), Oxygen (O) & Nitrogen (N). We will conduct below mentioned activities to confirm the presence of those elements.

Identification of water as a constituent in food

Materials required

Meat, Egg shell, Plant leaves, Crucible

Method

• Grind /crush meat, egg shell, and leaves separately.
• Put them into crucible & heat them separately till they burn.
• During burning, hold a glass sheet above the crucible.
• Use cobalt chloride to identify whether the liquid drops on the glass is water.

Observation: Blue coloured Anhydrous cobalt chloride turn to pink

Can confirm that water is formed on the glass sheet. Therefore the food that is used for the experiment contains water as a constituent.

Identification of presence of Carbon(C) in bio-molecules

Materials required

Several crucibles, plant leaves, piece of fish, rice.

Method.

• Make pulps by crushing all above materials separately.
• Put them separately into crucibles and heat well.
• The final residue obtained should be rubbed against a white paper.

Observation: Get lines drawn due to coal

Can confirm the food that is used for the experiment contains Carbon (C).

Identification of presence of Nitrogen(N) in bio-molecules

Materials Required

Two test tubes, solution of sodium hydroxide, solution of copper sulphate, egg white, piece of fish.

Method

• Crush fish thoroughly, add water and mix well. Filter the solution.
• Put 2ml of the fish extraction and egg white in to separate test tubes.
• Add equal volume of sodium hydroxide.
• Add few drops of copper sulphate to it.

Observation: Purple colour appears in the solution

The above observation confirms the presence of protein in food. As Nitrogen is a constituent of proteins,it is confirmed that the above tissues contain Nitrogen.

5. Water

The highest proportion of the body mass of living organisms is composed of water which is an inorganic compound. 2/3 rd of the body weight of most of oranisms is by water. water is an essential medium for the maintenance of living matter. The table below, shows the specific properties of water and contribution of them to the maintenance of life.

6. Minerals

Minerals are important as a nutrient constituent to maintain the life processes of organisms. They are absorbed as trace or macro elements into the body. The elements needed in higher amounts are known as macro elements and the elements needed in small amounts are known as trace elements.

7% of the body weight is by minerals. ¾th of the above amount is by Calcium and Phosphorous. Other than that Potassium, Iron, Magnesium, Copper & Chlorine are also included. The elements are required in small amounts. But when they are not present in correct amounts, plants and animals show deficiency symptoms.

Functions of minerals in plants & deficiency symptoms of them are mentioned in the following table.

7. Vitamins

They are organic compounds important in bio chemical reaction. Vitamins can be classified into 2 groups according to the solubility in water. Vitamin B & C are water soluble and A, D, E, & K are insoluble in water. But these are fat soluble.

The vitamins are needed for activities of human body, Their uses and deficiency symptoms are given in the table below.

Vitamin B is a complex vitamin. There are vitamins as B1″ B2, B6, B12 in that complex’ these are obtained through food and some vitamins are synthesized by bacteria living in human intestine.

Summary

• The main substances that form the living body are carbohydrates, proteins, lipids & nucleic acids. They are known as biological molecules belong to living matter.
• Beside organic compounds, inorganic compounds such as water, mineral salts also play an important role in living systems.
• Main elements found in biological molecules are C,H,O,N.
• The proteins that catalyze biochemical reactions are enzymes.
• Although Minerals & vitamins are needed in small amounts, when they are deficient in supply, organisms show deficiency symptoms.
• The specific properties of water are highly important in maintenance of life.

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