Biomolecules One Shot
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BIOMOLECULES
INTRODUCTION
All living organisms are made up of the same elements and compounds. If we perform an analysis of a plant
tissue, animal tissue or a microbial paste, carbon, hydrogen, oxygen and several other elements are obtained.
The same analysis made on a non-living matter like a piece of earth's crust, gives a list of similar chemicals. A
close examination reveals that the relative abundance of carbon and Hydrogen with respect to other elements
is higher in living beings than in earth's crust.
HOW TO ANALYSE CHEMICAL COMPOSITION
l Various biomolecules present in a living tissue (like a vegetable or a piece of liver) can be studied by their
chemical analysis.
l Take a living tissue and grind it in trichloroacetic acid (Cl3CCOOH) using a mortar and pestle. We obtain a
thick slurry.
l When we strain this slurry through cheese cloth or cotton, it gives two fractions.
l One is called filtrate or acid soluble pool having thousands of organic compounds.
l Other fraction is called retentate or acid insoluble pool containing proteins, nucleic acid, polysaccharides etc.
l The acid soluble pool contains chemicals with small molecular mass of 18–800 daltons approximately. They
are called micromolecules or biomicromolecules. They include amino acids, sugars, nucleotides etc.
l The acid-insoluble fraction contains organic compounds that have molecular weights in the range of ten thousand
daltons and above. They are known as macromolecules or biomacromolecules. They include
polysaccharides, proteins, nucleic acids.
l *Lipids are not strictly macromolecules. their molecular weight do not exceed 800 Da, but they come under the
macromolecular fraction because when we grind a tissue, cell membrane and other membrances are broken
into pieces and form vesicles which are not water soluble (lipids are also present in structures like cell membrane
and other membranes).
l The acid-soluble fraction represents roughly the cytoplasmic composition (without organelles), while the acid-
insoluble fraction represents the macromolecules of the cytoplasm and cell organelles. The two fractions together
represent the entire chemical composition of living tissues or organisms.
Biomolecule- All the carbon compound that present in living tissue
All carbon compounds that we get from living tissue can be called - Biomolecules.
l Inorganic elements and compounds are also present in the living organisms which can be known with the help
of 'ash' analysis technique.
l A small amount of a living tissue (e.g. Leaf or liver and this is called wet weight) is weighed and dried. All the
water evaporates.
l When the tissue is fully burnt, the carbon compounds are oxidised to gaseous form like CO2, water vapour are
removed and the remnant is called 'ash'. This ash contains many inorganic elements like calcium, magnesium
etc.
l In the acid-soluble fraction - inorganic compounds like sulphates, phosphates etc are also present.
l Elemental analysis gives composition of living tissue in the form of O, C, H, N etc.
l Analysis of compounds gives an idea of the kind of organic and inorganic constituents as mentained in the table
From a biological point of view we can classify the biomolecules into micromolecules and macromolecules. Water is the most abundant chemical in living organisms.
PRIMARY AND SECONDARY METABOLITES
Living organisms produce thousands of organic compounds (biomolecules) including amino acids, sugars,
chlorophylls, haems etc. these are required for their basic or primary metabolic processes like photosynthesis,
respiration, protein and lipid metabolism etc. these are called primary metabolites.
Many plants, fungi and microbes of certain genera and families synthesize a number of organic compounds
(biomolecules) which are not involved in primary metabolism and seem to have no direct function in growth
and development of organisms. Such compounds are called secondary metabolites.
Thus, primary metabolites have identifiable functions and play known roles in normal physiological processes.
The functions or role of secondary metabolites in host organisms are not understood. However many of them
are useful to human welfare (e.g., rubber, drugs, spices, scents and pigments)
carbohydrates
Main source of energy.
First respiratory substrate – carbohydrate
Compounds of Carbon, Hydrogen and Oxygen with ratio of H and O is 2:1, so they are also called as hy-
drates of carbon.
Generalised formula of carbohydrates is Cx (H2O) y.
Chemically all carbohydrates are polyhydroxy aldehyde or ketones.
Simple carbohydrates which are soluble in water and sweet in taste are called "Sugar".
Carbohydrates are main source of energy in body. In a normal man 55-65% of energy is available to him is in
the form of carbohydrates present in his diet.
On the basis of number of saccharide units obtained upon hydrolysis, Carbohydrates are classified as Monosac-
charides, Oligo saccharides and Polysaccharides
A. MONOSACCHARIDES
1. They are simplest sugars which can not be further hydrolysed.
2. In their generalised formula x is mostly equal to y i.e. number of Carbon and Oxygen atoms same.
3. First step of oxidation – Phosphorylation
4. All monosaccharides occur in d and l form, except the Dihydroxy acetone
5. The structure of saccharides is either ring or straight chain.
6. A six membered ring is known as pyranose and five membered ring is furanose.
Pyranose and furanose names were given by "Haworth."
7. Anomer – In aqueous solution, Glucose occurs in cyclic structure. In anomers of glucose, position of –
H and –OH groups are changed on C1 carbon atom.
Epimer : Isomer formed as a result of interchange of the –OH and –H groups on carbon atom 2, 3 and 4 of
glucose, are known as epimer.
Monosaccharides with free aldehyde group are termed as Aldoses (PGAL, Erythrose, Ribose, Arabinose,
Deoxyribose, Glucose, Galactose, Mannose).
While monosaccharides with free ketone group are called ketoses (DHAP, Erythrulose, Ribulose, Xylulose,
Fructose, Sedoheptulose
All monosaccharides are "reducing sugars" as their free aldehyde or ketone groups are capable of reducing
Cu++ to Cu+.
This property is the basis of Benedict's test or fehling's test used to detect the presence of glucose in urine.
Classification of monosaccharides on the basis of number of carbons :
1. Trioses : Number of carbons = 3 (Simplest monosaccharide) Common formula = C3H6O3
e.g. DHAP , PGAL
2. Tetroses : Number of carbons = 4
* Common formula = C4H8O4
e.g. Erythrose , Erythrulose
3. Pentose : Number of carbons = 5
Common formula = C5H10O5
e.g. Xylose
Xylulose
Deoxyribose
Arabinose
Ribose
Ribulose
Hexoses : Number of carbons = 6
Common formula = C6H12O6
e.g. Glucose
Fructose
Galactose
Glucose : It is abundant in grapes so known as grape sugar.
* It is abundant in blood also so known as blood sugar.
* Main respiratory substance.
* It rotates PPL in right (clockwise) direction so it is dextrorotatory and also known as dextrose
Fructose :
* Sweetest carbohydrate
* More abundant in honey and sweet fruits so also known as fruit sugar.
* Rotates PPL in left (anti-clockwise) direction so it is laevorotatory and also known as 'Laevulose'.
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