Detailed Notes Chapter-9- Biomolecules

Introduction

1. Diversity of Living Organisms:

   • Living organisms exhibit wide diversity in the biosphere.
   • Raises the question: Are all living organisms composed of the same chemicals?

2. Chemical Analysis:

   • Elemental analysis is used to determine the chemical composition of substances.
   • Plant tissue, animal tissue, and microbial paste undergo such analysis.

3. Comparison of Results:

   • Results from living organisms’ analysis compared to non-living matter (earth’s crust).

4. Similarity in Composition:

   • Both living and non-living samples yield similar lists of elements.
   • All elements found in the earth’s crust are also present in living tissues.

5. Relative Abundance Difference:

   • While the elements are the same, their relative abundances differ.
   • Notably, carbon and hydrogen are more abundant in living organisms than in the earth’s crust.

6. Conclusion:

   • Living organisms have higher concentrations of carbon and hydrogen relative to other elements compared to non-living matter.

9.1 HOW TO ANALYSE CHEMICAL COMPOSITION

1. Sample Preparation:

   • Take a living tissue sample, such as a vegetable or a piece of liver.
   • Grind the sample in trichloroacetic acid (Cl3CCOOH) using a mortar and pestle to obtain a thick slurry.

2. Fractionation:

   • Strain the slurry through cheesecloth or cotton to obtain two fractions:
     • Filtrate (acid-soluble pool): Contains organic compounds dissolved in the acid.
     • Retentate (acid-insoluble fraction): Contains organic compounds that are not soluble in the acid.

3. Analysis of Acid-Soluble Pool:

   • Thousands of organic compounds have been found in the acid-soluble pool.
   • Further analysis involves extraction, separation, and purification of individual compounds using various techniques.
   • Analytical techniques provide information about the molecular formula and probable structure of each compound.

4. Identification of Biomolecules:

   • Organic compounds obtained from living tissues are collectively referred to as “biomolecules.”
   • These biomolecules include amino acids, nucleotide bases, fatty acids, etc.

5. Analysis of Inorganic Constituents:

   • Destructive experiment: Weigh a small amount of tissue (wet weight), dry it to obtain dry weight, then fully burn it to remove carbon compounds.
   • Remaining ash contains inorganic elements (e.g., calcium, magnesium) and compounds (e.g., sulphate, phosphate).

6. Elemental and Compound Analysis:

   • Elemental analysis provides the elemental composition of living tissues (e.g., hydrogen, oxygen, carbon).
   • Compound analysis reveals the types of organic and inorganic constituents present.

7. Functional Group Identification:

   • From a chemical perspective, functional groups like aldehydes, ketones, and aromatic compounds are identified.
   • From a biological perspective, compounds are classified into amino acids, nucleotide bases, fatty acids, etc.

8. Characteristics of Amino Acids:

   • Amino acids are organic compounds containing an amino group and an acidic group on the same carbon (α-carbon).
   • The structure includes hydrogen, carboxyl group, amino group, and a variable R group.
   • Twenty types of amino acids occur in proteins, differing based on the R group.

9. Properties of Amino Acids:

   • Chemical and physical properties depend on the amino, carboxyl, and R functional groups.
   • Amino acids can be acidic, basic, neutral, or aromatic, based on their functional groups.
   • Amino acids exhibit ionizable nature, affecting their structure in solutions of different pH levels.

   • Lipids Overview:

     • Lipids are generally water-insoluble compounds.
     • They can be simple fatty acids or more complex molecules.

   • Structure of Fatty Acids:

     • Fatty acids consist of a carboxyl group attached to an R group.
     • The R group can vary, such as methyl (–CH3), ethyl (–C2H5), or a higher number of –CH2 groups (1 to 19 carbons).
     • Examples include palmitic acid (16 carbons) and arachidonic acid (20 carbons).

   • Saturated vs. Unsaturated Fatty Acids:

     • Fatty acids can be saturated (without double bonds) or unsaturated (with one or more C=C double bonds).

   • Glycerol and Lipids:

     • Glycerol is a simple lipid composed of trihydroxy propane.
     • Many lipids contain both glycerol and fatty acids, forming monoglycerides, diglycerides, and triglycerides (fats and oils).

   • Melting Points and Classification:

     • Fats and oils are classified based on their melting points.
     • Oils have lower melting points and remain liquid at room temperature, like gingelly oil.

   • Phospholipids:

     • Some lipids contain phosphorus and phosphorylated organic compounds.
     • Phospholipids, like lecithin, are found in cell membranes.

   • Complex Lipids in Neural Tissues:

     • Some tissues, especially neural tissues, have lipids with more complex structures.

   • Carbon Compounds with Heterocyclic Rings:

     • Living organisms contain carbon compounds with heterocyclic rings.
     • Nitrogen bases like adenine, guanine, cytosine, uracil, and thymine are examples.

   • Nucleosides and Nucleotides:

     • When nitrogen bases are attached to a sugar, they form nucleosides.
     • Nucleosides with a phosphate group esterified to the sugar are called nucleotides.
     • Examples include adenosine, guanosine, thymidine, uridine, cytidine (nucleosides), and adenylic acid, thymidylic acid, guanylic acid, uridylic acid, cytidylic acid (nucleotides).

   • Role of Nucleic Acids:

     • Nucleic acids like DNA and RNA consist of nucleotides and function as genetic material.

9.2 PRIMARY AND SECONDARY METABOLITES

1. Biomolecules as Metabolites:

   • Biomolecules encompass thousands of organic compounds found in living organisms, including amino acids, sugars, etc.
   • These compounds are referred to as metabolites.

2. Primary Metabolites:

   • In animal tissues, primary metabolites such as amino acids and sugars are commonly found.
   • These compounds play essential roles in normal physiological processes.

3. Secondary Metabolites:

   • In plant, fungal, and microbial cells, thousands of compounds beyond primary metabolites are observed.
   • Examples include alkaloids, flavonoids, rubber, essential oils, antibiotics, colored pigments, scents, gums, and spices.
   • These compounds are termed secondary metabolites.

4. Characteristics of Secondary Metabolites:

   • While primary metabolites have identifiable functions and known roles in physiological processes, the functions of many secondary metabolites in host organisms are not fully understood.
   • Secondary metabolites often serve purposes beneficial to human welfare, such as in the production of rubber, drugs, spices, scents, and pigments.
   • Some secondary metabolites also hold ecological significance.

9.3 BIOMACROMOLECULES

1. Classification based on Molecular Weight:

   • Compounds found in the acid-soluble pool have molecular weights ranging from 18 to approximately 800 daltons (Da).
   • The acid-insoluble fraction contains proteins, nucleic acids, polysaccharides, and lipids, with molecular weights typically exceeding ten thousand daltons.

2. Types of Biomolecules:

   • Biomolecules are classified into micromolecules (or simply biomolecules) and macromolecules.
   • Micromolecules have molecular weights less than one thousand daltons, while macromolecules are found in the acid-insoluble fraction and typically have higher molecular weights.

3. Lipids in the Acid-Insoluble Fraction:

   • Despite their small molecular weights (not exceeding 800 Da), lipids are included in the acid-insoluble fraction.
   • Lipids form structures like cell membranes, which are disrupted when tissues are ground. The resulting membrane fragments, such as vesicles, are not water-soluble and are thus separated along with the acid-insoluble pool.

4. Representation of Cellular Composition:

   • The acid-soluble pool represents the cytoplasmic composition, while macromolecules from cytoplasm and organelles constitute the acid-insoluble fraction.
   • Together, they represent the entire chemical composition of living tissues or organisms.

5. Abundance of Water:

   • Water is the most abundant chemical in living organisms, based on its abundance in their chemical composition.