Chapter 9: Biomolecules

Summary

• Living organisms are composed of similar elements and compounds as non-living matter, but with higher relative abundance of carbon and hydrogen.
• Chemical analysis of living tissues reveals organic compounds categorized as biomolecules.
• Types of Biomolecules:
  • Micromolecules: Small molecular weight compounds (<1000 Da) such as amino acids, sugars, fatty acids, glycerol, nucleotides.
  • Macromolecules: Larger compounds (≥10000 Da) including proteins, nucleic acids, polysaccharides, and lipids.
• Primary Metabolites: Essential compounds like amino acids and sugars found in animal tissues.
• Secondary Metabolites: Additional compounds found in plants, fungi, and microbes, such as alkaloids and flavonoids.
• Proteins are polymers of amino acids and perform various functions including enzymatic activity, transport, and structural roles.
• Nucleic acids (DNA and RNA) serve as genetic material.
• Polysaccharides are energy storage forms (e.g., starch, glycogen) and structural components (e.g., cellulose).
• Lipids include fats and oils, which are glycerides formed by the esterification of fatty acids to glycerol.

Chapter 9: Biomolecules

9.1 How to Analyse Chemical Composition?

• Living organisms are composed of various chemicals, including elements and compounds.
• Elemental analysis can be performed on plant, animal, or microbial tissues to obtain a list of elements such as carbon, hydrogen, and oxygen.
• The relative abundance of carbon and hydrogen is higher in living organisms compared to non-living matter.

9.2 Primary and Secondary Metabolites

• Primary Metabolites: Compounds essential for normal physiological processes (e.g., amino acids, sugars).
• Secondary Metabolites: Compounds found in plants, fungi, and microbes that do not have identifiable functions but are useful to humans (e.g., alkaloids, flavonoids).

Table 9.3: Some Secondary Metabolites

• Pigments: Carotenoids, Anthocyanins
• Alkaloids: Morphine, Codeine
• Terpenoids: Monoterpenes, Diterpenes
• Essential Oils: Lemon grass oil
• Toxins: Abrin, Ricin
• Drugs: Vinblastin, Curcumin

9.3 Biomacromolecules

• Biomolecules can be classified into micromolecules (molecular weight < 1000 Da) and macromolecules (molecular weight ≥ 10,000 Da).
• Macromolecules include proteins, nucleic acids, polysaccharides, and lipids.

9.4 Proteins

• Proteins are polypeptides formed by amino acids linked by peptide bonds.
• There are 20 types of amino acids, and proteins serve various functions, including:
  • Collagen: Intercellular ground substance
  • Trypsin: Enzyme
  • Insulin: Hormone
  • Antibodies: Fight infectious agents
  • Receptors: Sensory reception

Table 9.5: Some Proteins and their Functions

9.5 Polysaccharides

• Polysaccharides are long chains of sugars, such as cellulose (homopolymer of glucose) and glycogen (energy storage in animals).
• They can have reducing and non-reducing ends and may form helical structures.

9.6 Nucleic Acids

• Nucleic acids consist of nucleotides and serve as genetic material (DNA and RNA).

9.7 Structure of Proteins

• Proteins have a hierarchy of structures: primary, secondary, tertiary, and quaternary.

9.8 Enzymes

• Enzymes are proteins that catalyze biochemical reactions, requiring optimal conditions for activity.
• They lower the activation energy of reactions and exhibit substrate specificity.

Common Mistakes and Exam Tips

Common Pitfalls

• Misunderstanding Biomolecules: Students often confuse the definitions and classifications of biomolecules, such as distinguishing between primary and secondary metabolites.
• Elemental Analysis Confusion: Many students fail to recognize that while the elemental composition of living and non-living matter may be similar, the relative abundance of elements like carbon and hydrogen is significantly higher in living organisms.
• Ignoring Molecular Weights: Students may overlook the importance of molecular weights in categorizing biomolecules, particularly the distinction between micromolecules and macromolecules.
• Enzyme Function Misconceptions: There is often confusion about the role of cofactors and the concept of enzyme inhibition, particularly the difference between competitive and non-competitive inhibitors.

Exam Tips

• Focus on Definitions: Ensure you clearly understand the definitions of key terms such as metabolites, biomolecules, and macromolecules.
• Use Tables for Comparison: When studying, create tables comparing the elemental composition of living and non-living matter to visualize differences.
• Memorize Key Examples: Familiarize yourself with examples of primary and secondary metabolites, as well as common enzymes and their classifications.
• Practice Diagrams: Be prepared to draw and label diagrams of biomolecules, including their structures and functional groups, as visual representation can aid in retention.
• Review Enzyme Mechanisms: Understand the mechanisms of enzyme action and the role of cofactors, as well as the significance of enzyme inhibition in biochemical reactions.