Chemical basis 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

  • Carbon
  • Hydrogen
  • Oxygen
  • Nitrogen
• Other essential elements for the survival of organisms

  • Sulphur
  • Phosphorous
  • Sodium
  • Potassium
  • Calcium
  • Magnesium
  • Iron
  • Chlorine
• Compounds which contain Carbon are known as organic compounds and compounds which do not contain Carbon are known as inorganic compounds.
• Four types of biological molecules

  • Carbohydrates
  • Proteins
  • Lipids
  • Nucleic acids
• Water, minerals and gasses are some of the inorganic molecules that are essential for the maintenance of life.
• Elements and their percentage in the human body

  • Oxygen (65%)
  • Carbon (18%)
  • Hydrogen (10%)
  • Nitrogen (3%)
  • Calcium (1.5%)
  • Phosphorous (1.0%)
  • Potassium (0.35%)
  • Sulphur (0.25%)
  • Sodium (0.15%)
  • Magnesium (0.05%)
  • Chlorine (Micro elements)
  • Iron (Micro elements)
  • Iodine (Micro elements)
• Carbohydrates


  The most abundant organic compound on earth, produced during photosynthesis of green plants
• Types of monosaccharides


  • Location they are present
  • Other facts
• Disaccharides


  Two monosaccharides join to form a disaccharide, releasing a water molecule
• Types of disaccharides


  • Maltose
  • Sucrose
  • Lactose
• Characters of disaccharides


  • Maltose: Union of two glucose molecules, intermediate product of starch hydrolysis
  • Sucrose: Union of glucose and fructose, present in white/brown sugar, sugarcane, beet, some fruits, phloem sap
  • Lactose: Union of glucose and galactose, only sugar absent in plants, not as sweet as sucrose, 4-6% in cow's milk, 6-7% in human milk
• Polysaccharides


  Polymerisation of a large number of monosaccharides, insoluble in normal water, not crystals
• Types of polysaccharides


  • Cellulose
  • Starch
  • Glycogen
• Characters of polysaccharides


  • Cellulose: No nutritional value, helps avoid constipation

  Starch: Carbohydrate that stores in plants

  Glycogen: Carbohydrate that stores in animal body
• Significance of carbohydrates


  • As an energy source

  As storage compound

  As a structural component in organism

  As a constituent of nucleic acid
• Tests to identify carbohydrates

  Starch test: Add iodine solution, observe purplish blue colour

  Monosaccharides & some disaccharides: Add Benedict solution, heat, observe colour change

  Disaccharides (sucrose): Add Benedict solution, heat, no colour change, then add dilute sulfuric acid and heat, observe colour change
• Protein is an essential constituent in all living cells, composed of C, H, O, N, and sometimes S.
• 17% of the mature human body is composed of proteins.
• Amino acid


  Polymerized amino acid molecules make up proteins, 20 different amino acids present
• Significance of proteins


  • As an energy source

  To make structural components

  As enzymes

  As hormones

  As antibodies
• Biuret test to identify proteins


  Grind dhal or egg yolk, add NaOH and CuSO4, observe pinkish purple or dark purple colour
• Enzymes


  Special proteins that catalyze biochemical reactions
• Activity of amylase on starch

  Add starch solution and amylase, test with iodine at intervals, observe gradual reduction in blue colour
• Lipids


  Fats and oils, contain C, H, O but with higher H:O ratio than carbohydrates, insoluble in polar solvents
• Significance of lipids


  • As an energy source

  To form different structural components

  For conservation of water

  To maintain body temperature

  To protect internal organs

  To synthesize some hormones
• Sudan III test to identify lipids


  Add oil and Sudan III reagent, observe red fat globules
• Types of fatty acids

  • Saturated fatty acids

  Unsaturated fatty acids
• Nucleic acids


  Linear polymers made up of nucleotides, contain C, H, O, N, P, important for storage and transfer of genetic information
• Types of nucleic acids

  • DNA (deoxyribonucleic acid)

  RNA (ribonucleic acid)
• Significance of nucleic acids

  • Important in storage of genetic information

  Important in transferring genetic information from generation to generation

  Important in protein synthesis
• Nucleic acid


  The most important molecule out of the main biological molecules in living matter in genetical aspect
• Nucleic acid


  A linear polymer made up of a large number of nucleotides
• Components of a nucleotide

  • Nitrogenous base
  • Pentose sugar group
  • Phosphate group
• DNA


  Deoxy ribo Nucleic Acid, transfers genetic characteristics from generation to generation
• RNA


  Ribo Nucleic Acid, involved in protein synthesis
• Significance of nucleic acids

  • Important in storage of genetic information
  • Important in transferring genetic information
  • Important in protein synthesis
  • Important in controlling cellular activities
  • RNA important in storing genetic information of some viruses
  • Variations in DNA due to mutations are important in evolution
• Activity 02 - Identification of water as a constituent in food

  1. Grind/crush meat, egg shell, and leaves

  2. Put them into crucible & heat them

  3. Hold a glass sheet above the crucible

  4. Use cobalt chloride to identify water
• Blue coloured Anhydrous cobalt chloride turns to pink, confirming water is formed