Biological Molecules

    What is biological molecules?

    Biomolecules are the most essential organic molecules, which are involved in the maintenance and metabolic processes of living organisms. A biomolecule or biological molecule is loosely defined as a molecule produced by a living organism and essential to one or more typically biological processes.

    • Biomolecules include large macromolecules such as proteins, carbohydrates, lipids, and nucleic acids, as well as small molecules such as vitamins and hormones4]

    The chemical elements that make up each of the listed biological macromolecules:

    (a) Carbohydrates:

    • Carbon (C)
    • Hydrogen (H)
    • Oxygen (O)

    (b) Lipids (fats and oils):

    • Carbon (C)
    • Hydrogen (H)
    • Oxygen (O)

    (c) Proteins:

    • Carbon (C)
    • Hydrogen (H)
    • Oxygen (O)
    • Nitrogen (N)
    • Sulfur (S) (often present in certain amino acids, though not always)

    (d) DNA:

    • Carbon (C)
    • Hydrogen (H)
    • Oxygen (O)
    • Nitrogen (N)
    • Phosphorus (P)

    Here’s a more detailed breakdown of how large molecules are formed from smaller molecules:

    1. Carbohydrates:
      • Starch, Cellulose, and Glycogen are polysaccharides made from glucose.
        • Starch is primarily used by plants to store energy. It is composed of long chains of glucose molecules linked together.
        • Cellulose is a structural component in plant cell walls. It consists of glucose units linked in a way that forms strong, rigid structures.
        • Glycogen serves as an energy reserve in animals and is similar to starch but more highly branched.
    1. Proteins:
      • Proteins are polymers of amino acids. Amino acids are small molecules that contain an amino group, a carboxyl group, and a unique side chain. Proteins are formed when amino acids are linked together by peptide bonds, creating long chains that fold into specific three-dimensional structures.
    1. Lipids:
      • Lipids are primarily composed of fatty acids and glycerol.
        • Fatty Acids are long hydrocarbon chains with a carboxyl group at one end.
        • Glycerol is a three-carbon molecule with hydroxyl groups.
        • When fatty acids and glycerol combine through ester bonds, they form triglycerides, which are a type of lipid used for energy storage.
    1. DNA:
      • DNA (Deoxyribonucleic Acid) is made up of nucleotides.
        • Each nucleotide consists of a phosphate group, a sugar molecule (deoxyribose), and a nitrogenous base (adenine, thymine, cytosine, or guanine).
        • Nucleotides link together through phosphodiester bonds to form a long, double-stranded helical structure known as DNA.

    In summary, large biological molecules like starch, proteins, lipids, and DNA are all synthesized from smaller, simpler molecules through various biochemical processes.

    Chemical Tests

    (a) Starch (Iodine Solution Test)

    Description:

    • Starch is a polysaccharide made up of glucose units. The iodine solution test detects starch because iodine interacts with the helical structure of starch, forming a blue-black complex.

    Test Procedure:

    1. Add iodine solution to the sample (a few drops are sufficient).
    2. Observe the color change.

    Result Interpretation:

    • Positive Test:

    The solution turns blue-black, indicating the presence of starch.

    • Negative Test:

    The solution remains yellow-brown, indicating no starch is present.

    (b) Glucose and Maltose (Benedict’s Solution Test)

    Description:

    • Benedict’s solution tests for reducing sugars like glucose and maltose. Reducing sugars have free aldehyde or ketone groups that react with Benedict’s reagent, which contains copper(II) ions, resulting in a color change.

    Test Procedure:

    1. Add Benedict’s solution to the sample.
    2. Heat the mixture in a boiling water bath for a few minutes.

    Result Interpretation:

    • Positive Test:

    A color change indicates the presence of reducing sugars. The colors range from green (low concentration) to yellow, orange, and red (high concentration).

    • Negative Test:

    The solution remains blue, indicating no reducing sugars are present.

    (c) Protein (Biuret Test)

    Description:

    • The Biuret test detects proteins based on the presence of peptide bonds. Biuret reagent contains copper sulfate, which reacts with peptide bonds to produce a violet or purple color.

    Test Procedure:

    1. Add Biuret reagent to the sample.
    2. Mix the solution

    Result Interpretation:

    • Positive Test:

    The solution turns violet or purple, indicating the presence of proteins.

    • Negative Test:

    The solution remains blue, indicating no proteins are present.

    (d) Lipids (Ethanol Emulsion Test)

    Description:

    • The ethanol emulsion test detects lipids based on their ability to form an emulsion with ethanol and water. Lipids are insoluble in water but soluble in ethanol.

    Test Procedure:

    1. Dissolve the sample in ethanol.
    2. Add water to the ethanol solution.
    3. Shake the mixture

    Result Interpretation:

    • Positive Test:

    A milky or cloudy emulsion forms, indicating the presence of lipids.

    • Negative Test:

    The solution remains clear, indicating no lipids are present.

    These tests are commonly used in laboratory settings to identify the presence of specific biomolecules in various samples.