Molecules of Life
All chemicals / molecules functional in living organisms whether inorganic or organic, are known as biomolecules. About 5000 chemicals are found in cell and at any time about 1000 chemical reactions are being carried out.
- The sum total of all the organic and inorganic compounds, molecules and ions contained in the cells is collectively called cellular pool.
- Inorganic chemicals or substances include mineral salts (e.g., calcium phosphate), ions (e.g., Zn2+, K+), gases (O2 , CO2 ) and water.
- Organic substances or chemicals are carbohydrates, amino acids, proteins, enzymes, lipids, nucleotides, nucleic acids, hormones, vitamins etc.
| Element | % Weight of elements | |
|---|---|---|
| Earth’s crust | Human body | |
| Hydrogen (H) | 0.14 | 0.5 |
| Carbon (C) | 0.03 | 18.5 |
| Oxygen (O) | 46.6 | 65.0 |
| Nitrogen (N) | Very little | 3.3 |
| Sulphur (S) | 0.03 | 0.3 |
| Sodium (Na) | 2.8 | 0.2 |
| Calcium (Ca) | 3.6 | 1.5 |
| Magnesium (Mg) | 2.1 | 0.1 |
| Silicon (Si) | 27.7 | Negligible |
| * Adopted from CNR Rao. Understanding Chemistry Universities Press. Hyderabad. | ||
There is a wide diversity in living organisms in our biosphere. Now a question that arises in our minds is: Are all living organisms made of the same chemicals, i.e., elements and compounds? You have learnt in chemistry how elemental analysis is performed. If we perform such an analysis on a plant tissue, animal tissue or a microbial paste, we obtain a list of elements like carbon, hydrogen, oxygen and several others and their respective content per unit mass of a living tissue. If the same analysis is performed on a piece of earth’s crust as an example of non-living matter, we obtain a similar list. What are the differences between the two lists? In absolute terms, no such differences could be made out. All the elements present in a sample of earth’s crust are also present in a sample of living tissue. However, a closer examination reveals that the relative abundance of carbon and hydrogen with respect to other elements is higher in any living organism than in earth’s crust. List of certain other elements is given in table.
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