How to Analyse Chemical Composition?

Protoplasm is a complex mixture of both organic and inorganic compounds.

Molecules found in the protoplasm of cells are called biomolecules.

A Comparison of Elements Present in Non-living and Living matter

The collection of various types of molecules in a cell is called the cellular pool.

The cellular pool consists of various types of biomolecules such as : (a) water (b) inorganic materials (c) organic compounds.

The small molecules of low molecular weight, simple molecular conformations and higher solubilities are called micromolecules.

These include minerals, water, amino acids, simple sugars and nucleotides.

The various minerals found in cells have many uses.

Mitochondria are rich in manganese.

Molybdenum is necessary for fixation of nitrogen catalysed by the enzyme nitrogenase.

Copper occurs in cytochrome oxidase.

Magnesium is essential for a large number of enzymes, particularly those utilising ATP.

Ca and Mg decrease the excitability of nerves and muscles.

(i) Sodium and potassium are responsible for the maintenance of extracellular and intracellular fluids through the osmotic effects of their concentration. These two ions are also responsible for the maintenance of membrane potential and transmission of electrical impulses in the nerve cells. Both in cells and in extracellular fluids, diabasic phosphate (HPO₄^2–) and monobasic phosphate (H₂PO₄^2–) act as acidbase buffers to maintain the H⁺ ion concentration.

(ii) The most abundant element in cell/living matter is oxygen. O > C > N > H

(iii) Fe⁺⁺ and Cu⁺⁺ are found in cytochromes.

(iv) The concentration of the cations inside the cell is K > Na > Ca.

How To Analyse Chemical Composition?

In order to study the various biomolecules found in living tissues (a vegetable or a piece of liver etc.), the tissue is ground in trichloroacetic acid (Cl₃CCOOH) using pestle and mortar.

The resultant slurry is strained through cheese cloth or cotton and we obtain two fractions.

The filtrate is called acid soluble pool while the retentate is called acid insoluble fraction.

The acid soluble pool represents roughly the cytoplasmic composition.

The macro molecules from cytoplasm and organelles become the acid-insoluble fraction.

Chemicals present in both the fractions are further separated by various analytical techniques and identified.

Average Composition of Cells

Note : Protein > Nucleic acid > Carbohydrates > Lipids

The acid soluble pool contains chemicals called biomicromolecules as they have small molecular mass of 18-800 daltons approximately.

The acid insoluble fraction contains chemicals with large molecular mass of more than 800 daltons, they are biomacromolecules.

Biomacromolcules are large size, high molecular weight, complex molecules that are formed by condensation of biomicromolecules.

Their molecular mass is in the range of ten thousand daltons and above.

Biomacromolecules are of three types-proteins, nucleic acids and polysaccharides.

Note : Though lipids have a molecular mass similar to that of micromolecules i.e. less than 800 Da, but they do not appear in the acid Soluble pool due to their non-polar nature.

All biomacromolecules are polymers except lipids.

Polymers are formed by process of union of repeating subunits, each subunit being called monomer.

Monomers are simple small sized low molecular weight molecules which cannot be hydrolysed further into smaller subunits.

Polymers occur in the form of threads.

They are folded variously to form three-dimensional shapes required for their functioning.

 

A list of Representative Inorganic Constituents of Living Tissues

Depending upon the molecular weight and solubility, biomolecules are divided into two categories.

(a) Micromolecules are small sized, have low molecular weight, simple molecular structure and high solubility in the intracellular fluid matrix. These include water, mineralrs, gases, carbohydrates, lipids, amino acids and nucleotides.

(b) Macromolecules are large sized, have larger molecular weight, complex conformation and low solubility in the intracellular fluid matrix. They are generally formed by polymerisation of micromolecules. These include polysaccharides, proteins and nucleic acids.

Analytical techniques, when applied to the compound give us an idea of the molecular formula and the probable structure of the compound.

All the carbon compounds that we get from living tissue can be called "Biomolecules".

However, living organisms also have inorganic elements and compounds.

When the tissue is fully burnt all carbon compounds are oxidised to gaseous form (CO₂, water vapour) and are removed.

What is remaining is called "Ash".

This ash contains inorganic elements (like calcium, magnesium etc.).

Inorganic compounds like sulphate, phosphate etc. are also seen in the acid soluble fraction.

Therefore, elemental analysis gives elemental composition of living tissues in the form of H, O, Cl, C etc. while analysis of compounds gives an idea of the kind of organic and inorganic constituents present in living tissues.

From a chemistry point of view, one can identify functional groups like aldehydes, ketones, aromatic compounds etc.

But from a biological point of view, we shall classify them into aminoacids, nucleotide bases, fatty acids etc.