Biological Molecules Summary

Chemical Elements in Biological Molecules

  • Carbohydrates: Carbon, Hydrogen, Oxygen
  • Fats: Carbon, Hydrogen, Oxygen
  • Proteins: Carbon, Hydrogen, Oxygen, Nitrogen, Sulfur (sometimes)

Key Concepts

  • Elements: Substances that cannot be chemically broken down.
  • Atoms: Basic unit of an element, made of protons, neutrons, and electrons.
  • Molecules: Group of atoms bonded together.

Nutrients

  • Nutrients provide energy for cellular processes.
  • Essential nutrients for humans: Water, Carbohydrates, Fats, Proteins, Vitamins, Minerals, Fibre

Organic Substances

  • Contain Carbon and Hydrogen.
  • Include carbohydrates, proteins, and fats.

Carbohydrates

  • Contain Carbon, Hydrogen, and Oxygen.
  • Include sugars and starches.
  • Glucose is a simple sugar (monosaccharide) with 6 Carbon atoms.
  • Complex sugars: Disaccharides (2 saccharides), Polysaccharides (many saccharides).
  • Starch and Glycogen are made from glucose molecules.
    • Excess glucose stored as starch in plants.
    • Excess glucose stored as glycogen and fat in humans/animals.
  • Simple sugars (mono- and di-saccharides) are soluble and taste sweet.
  • Complex carbohydrates (polysaccharides) are insoluble and do not taste sweet.

Proteins

  • Contain Carbon, Hydrogen, Oxygen, Nitrogen (may contain Sulfur).
  • Made of amino acids.
  • 20 different amino acids (essential and nonessential).
  • Amino acids are joined by peptide bonds.
  • Soluble proteins: haemoglobin, enzymes, antibodies, hormones.
  • Insoluble proteins: Keratin (in skin and hair).
  • Proteins are components of cell membranes.
  • Enzymes are biological catalysts that speed up reactions. They bind with substrates.
  • Antibodies are part of the immune system and fight antigens.

Fats (Lipids)

  • Contain Carbon, Hydrogen, Oxygen.
  • Each molecule consists of 1 glycerol and 3 fatty acids.
  • Used for energy storage and thermal insulation.

DNA

  • A nucleic acid made of nucleotide monomers.
  • Nucleotide monomers contain deoxyribose sugar.
  • DNA has two strands coiled in a double helix.
  • Phosphate group and deoxyribose sugar form the backbone.
  • Nitrogenous bases: Adenine (A), Guanine (G), Cytosine (C), Thymine (T).
    • A always bonds with T.
    • G always bonds with C.

Chemical Tests

  • Iodine solution: Tests for starch (positive: blue-black).
  • Benedict’s solution: Tests for reducing sugars (positive: red/orange).
  • Biuret test: Tests for proteins (positive: purple/violet/lilac).
  • Ethanol emulsion test: Tests for fats/oils (positive: cloudy/milky).
  • DCPIP test: Tests for Vitamin C (positive: loses colour).