Chemistry Chapter on Covalent Bonds

Chemical Bonds

• Covalent Bond: Involves electron sharing between atoms, e.g., hydrogen atoms (H – H).
• Polar Covalent Bond: Electrons are shared unequally due to differences in electronegativity; water (H2O) is a key example with oxygen being more electronegative.
• Ionic Bond: Attraction between cations and anions; example includes sodium (Na+) losing an electron and chlorine (Cl-) gaining an electron to form NaCl.
• Hydrogen Bond: Weak attraction between a hydrogen atom (partially positive) and an electronegative atom (like O or N); crucial in molecules like water and ammonia.
• Hydrophobic Interaction: Non-polar molecules interact in a polar solvent, e.g., fats in water.
• Van der Waals Interaction: Weak forces due to fluctuating charges occurring when atoms are close together.

Amino Acids

• Monomer Structure: Each amino acid contains an alpha-carbon, carboxyl group, amino group, hydrogen atom, and varying side chain (R group).
• 20 Common Amino Acids: Classified based on their R group's properties: polar, nonpolar, acidic, or basic.
• Zwitterions: Formed when amino acids dissolve in water; they have both basic (NH3+) and acidic (COO-) groups, allowing them to act as buffers.

Protein Structure

• Peptide Bonds: Link amino acids together to form polypeptides.
• Levels of Protein Organization:
  • Primary Structure: Linear sequence of amino acids determined by genetic code.
  • Secondary Structure: Formed by hydrogen bonds, leading to alpha-helix and beta-pleated sheet formations.
  • Tertiary Structure: Overall 3D shape resulting from interactions among side chains.
  • Quaternary Structure: Assembly of multiple polypeptide chains.

Denaturation of Proteins

• Denaturation: Loss of protein structure due to changes in pH, temperature, or salt concentration.
• Reversible Denaturation: Some proteins can return to functional shape if conditions normalize.

Carbohydrates

• Types of Carbohydrates:
  • Monosaccharides: Simplest sugars (e.g., glucose, C6H12O6), classified by carbonyl group location and carbon count.
  • Disaccharides: Formed from two monosaccharides via glycosidic linkage.
  • Oligosaccharides: Chains of 3-14 monosaccharides.
  • Polysaccharides: Larger polymers of sugar units.

Polysaccharides

• Glycogen: Storage polysaccharide in animals, highly branched for solubility.
• Cellulose: Major component of plant cell walls, consists of β-glucose with β glycosidic linkages.
• Chitin: Structural polysaccharide in arthropod exoskeletons and fungal cell walls.
• Murein (Peptidoglycan): Component of bacterial cell walls, cross-linked with amino acids.

Lipids

• Characteristics: Large biological molecules that are hydrophobic and do not form polymers; mainly composed of hydrocarbons.
• Types:
  • Fats (Triglycerides): Energy storage molecules.
  • Phospholipids: Major components of cell membranes.
  • Steroids: Diverse functions in cellular processes.

Nucleic Acids

• Types:
  • DNA: Double-stranded, contains deoxyribose, and encodes genetic information; pairs adenine with thymine, and guanine with cytosine.
  • RNA: Single-stranded, contains ribose, substitutes uracil for thymine, involved in protein synthesis.
• DNA Structure: Composed of two antiparallel strands forming a double helix with complementary base pairing.

Differences Between RNA and DNA

• RNA is shorter, single-stranded, and consists of ribose sugar; DNA is longer, double-stranded, and consists of deoxyribose sugar.
• RNA contains uracil; DNA contains thymine.
• RNA has multiple types (mRNA, tRNA, rRNA); DNA has one form.

This quiz covers the concepts of covalent bonds, including polar and non-polar molecules, with a focus on the water molecule. Understand how electronegativity affects electron sharing and bond polarity through illustrative examples. Test your knowledge of these essential chemistry principles.