Biomolecules ncert chemical analysis
Channel: ISHTA’s BIO ACADEMY
Date: 29/06/2021

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 (Table 9.1).
9.1 HOW TO ANALYSE CHEMICAL COMPOSITION?
We can continue asking in the same way, what type of organic compounds
are found in living organisms? How does one go about finding the answer?
To get an answer, one has to perform a chemical analysis. We can take any
living tissue (a vegetable or a piece of liver, etc.) and grind it in trichloroacetic
acid (Cl 3
CCOOH) using a mortar and a pestle. We obtain a thick slurry. If
we were to strain this through a cheesecloth or cotton we would obtain two
fractions. One is called the filtrate or more technically, the acid-soluble
pool, and the second, the retentate or the acid-insoluble fraction. Scientists
have found thousands of organic compounds in the acid-soluble pool.
BIOMOLECULES
CHAPTER 9
9.1 How to Analyse
Chemical
Composition?
9.2 Primary and
Secondary
Metabolites
9.3 Biomacromolecules
9.4 Proteins
9.5 Polysaccharides
9.6 Nucleic Acids
9.7 Structure of
Proteins
9.8 Nature of Bond
Linking Monomers
in a Polymer
9.9 Dynamic State of
Body Constituents
- Concept of
Metabolism
9.10 Metabolic Basis for
Living
9.11 The Living State
9.12 Enzymes
2015-16(19/01/2015)
BIOMOLECULES 143
In higher classes you will learn about how
to analyse a living tissue sample and identify a
particular organic compound. It will suffice to
say here that one extracts the compounds, then
subjects the extract to various separation
techniques till one has separated a compound
from all other compounds. In other words, one
isolates and purifies a compound. 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
tissues can be called ‘biomolecules’. However,
living organisms have also got inorganic
elements and compounds in them. How do we
know this? A slightly different but destructive
experiment has to be done. One weighs a small
amount of a living tissue (say a leaf or liver and
this is called wet weight) and dry it. All the water,
evaporates. The remaining material gives dry
weight. Now if the tissue is fully burnt, all the
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 hydrogen, oxygen, chlorine, carbon etc.
while analysis for compounds gives an idea of
Element % Weight of
 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