Biological Macromolecules: Quick Review

Nucleic Acids

  • Monomer: nucleotide (phosphate group, 5‑carbon sugar, nitrogenous base)
  • Backbone: phosphate–sugar–phosphate–sugar; bases project outward
  • Bases: DNA = Cytosine (C), Guanine (G), Adenine (A), Thymine (T); RNA = Cytosine (C), Guanine (G), Adenine (A), Uracil (U)
  • Structure: DNA = double helix; RNA = usually single strand; directionality on each strand with ends labeled 3^{\prime} and 5^{\prime}; DNA is anti‑parallel
  • Function: genetic material; passes from generation to generation
  • Key note: nucleic acids carry genetic information; monomer = nucleotide; polymer = nucleic acid

Proteins

  • Monomer: amino acids; 20 different amino acids in proteins
  • Core structure: central carbon (the \"alpha\" carbon) with a hydrogen, a carboxyl group, an amino group, and an R (side) chain
  • R group: determines chemical properties (polar, nonpolar, charged; hydrophilic vs hydrophobic)
  • Directionality: amino end (N‑terminus) and carboxyl end (C‑terminus)
  • Bonding: amino acids join via dehydration synthesis to form peptide bonds; hydrolysis adds water to break them
  • Function: build most cellular structures and enzymes; dietary proteins are broken down to amino acids for reuse

Lipids

  • Monomer concept: not a simple monomer; class of molecules often nonpolar; energy storage and membranes
  • Structure: hydrocarbon tails (nonpolar); phospholipids are amphipathic with a polar head
  • Energy and membranes: high energy per tail; membranes require phospholipid bilayers
  • Saturation: unsaturated (double bonds cause bends) vs saturated (no double bonds; straight)
  • Trans fats: hydrogenation can create trans fats; health concerns
  • Examples: cholesterol, triglycerides, phospholipids

Carbohydrates

  • Monomer: sugars; building block = glucose
  • Functions: energy source; some provide structure (cellulose in plants, chitin in insects)
  • Polysaccharides: amylose (linear starch), glycogen (highly branched), cellulose (linear), chitin
  • Directionality and bonds: glycosidic bonds determine structure; orientation affects whether the polymer is linear or branched
  • Forms: simple sugars (glucose) can exist in alpha or beta forms; dehydration synthesis links monosaccharides

Common concepts across macromolecules

  • Dehydration synthesis: monomers join; water is released; forms covalent bonds (e.g., peptide, glycosidic, phosphodiester bonds)
  • Hydrolysis: water added; bonds broken; releases monomers (dietary digestion provides monomers for reuse)