Biology Chapter on Elements and Macromolecules

Common Elements in Cells

• Major elements include carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur (CHONPS).
• These elements are essential for forming the structures and functions of biological molecules.

Classes of Macromolecules

• Four main classes: carbohydrates, lipids, proteins, and nucleic acids.
• Corresponding monomers:
  • Carbohydrates: monosaccharides (e.g., glucose)
  • Lipids: fatty acids and glycerol
  • Proteins: amino acids
  • Nucleic acids: nucleotides

Electronegativity and Bond Types

• Electronegativity refers to an atom’s ability to attract electrons in a chemical bond.
• Differences in electronegativity determine bond types:
  • Nonpolar covalent bonds: difference of 0 to 0.4 (e.g., H₂)
  • Polar covalent bonds: difference of 0.5 to 1.7 (e.g., H₂O)
  • Ionic bonds: difference greater than 1.7 (e.g., NaCl)

Behavior of Molecules in Water

• Nonpolar covalent molecules (e.g., oils) do not mix with water; they are hydrophobic, meaning they repel water.
• Polar covalent molecules (e.g., sugars and salts) dissolve in water due to interaction with water molecules, classified as hydrophilic.

Hydrophobic vs. Hydrophilic Molecules

• Hydrophobic molecules are typically nonpolar and do not interact well with water, avoiding it.
• Hydrophilic molecules are polar or ionic, allowing them to form hydrogen bonds with water.

Water Molecule Structure

• Water (H₂O) consists of two hydrogen atoms and one oxygen atom connected by covalent bonds.
• Hydrogen bonds occur between water molecules, resulting in unique properties like cohesion and surface tension.

Contrast of Bond Types

• Covalent bonds: electrons are shared between atoms; strong and stable.
• Ionic bonds: transfer of electrons between atoms leads to electrostatic attraction; usually form between metals and nonmetals.
• Hydrogen bonds: weak attraction between a hydrogen atom bonded to an electronegative atom and another electronegative atom; important in biological structures.