CLASS 2 SIMPLE

Class 2 Learning Outcomes

  • Describe chemical building blocks: atom, element, molecule.

  • Discuss unique properties of water and their causes.

  • Identify four organic molecules: carbohydrates, lipids, proteins, nucleic acids.

Chemical Building Blocks

  • Atom: Smallest chemical unit.

  • Element: Matter of one type of atom (e.g., C, N, O).

  • Molecule: Combination of two or more atoms; can be the same (e.g., N₂) or different (compound like CO₂).

Structure of Atoms

  • Nucleus: Contains protons (positive charge) and neutrons (neutral).

  • Electrons: Negatively charged, orbit the nucleus; stabilize it; arranged in shells corresponding to energy levels.

Chemical Bonds

  • Atoms seek stability by filling outer electron shells (1st: 2 e⁻, 2nd: 8 e⁻, 3rd: 8 e⁻).

Types of Chemical Bonds

  1. Ionic Bond: Attraction between oppositely charged ions (e.g., NaCl).

  2. Covalent Bond: Atoms share electrons (e.g., CH₄).

  3. Hydrogen Bond: Attraction between polar molecules (e.g., H₂O).

Properties of Water

  • Approximately 75% of cell weight.

  • Polar solvent allows dissolution of many ionic/polar substances.

  • Each water molecule can form up to four hydrogen bonds.

Characteristics of Water

  • High boiling point due to strong molecular attraction.

  • Unique structure makes ice float; hydrogen bonds affect density.

  • Provides surface tension; crucial for digestion; stabilizes temperature changes.

pH and Water

  • Water can split into H⁺ and OH⁻ ions; pH scale measures acidity.

  • pH 7 = neutral; below 7 = acidic; above 7 = basic.

Organic Molecules

  • Molecules containing carbon and hydrogen; categorized into:

    1. Carbohydrates: Sugars and starches (C:H:O ratio = 1:2:1); function mainly as energy sources.

    • Types: monosaccharides (e.g., glucose), disaccharides (e.g., sucrose), polysaccharides (e.g., cellulose).

    1. Lipids: Fats, phospholipids, and steroids; energy storage; non-polar (hydrophobic).

    2. Proteins: Composed of amino acids; function in structure and enzyme activity.

    3. Nucleic Acids: DNA & RNA, built from nucleotides; genetic information storage and communication.

DNA vs RNA

  • DNA: Double-stranded, contains A, T, C, G; stores genetic info.

  • RNA: Single-stranded, contains A, U, C, G; involved in protein synthesis.

Summary

  • Reviewed chemical building blocks, bonds, properties of water, and organic molecules.

  • Next class: Microscopy and Cell Structure (Chapter 3).