Macromolecules: Carbohydrates & Lipids

The Four Classes of Large Biomolecules

• All living things are made up of four classes: Carbohydrates, Lipids, Proteins, Nucleic Acids
• Macromolecules are large polymers; polymers are built from monomers
• Three of the four classes are polymers: Carbohydrates, Proteins, Nucleic Acids
• Polymerization occurs via dehydration synthesis (loss of water); polymers are broken down by hydrolysis

Macromolecules as Polymers and Monomers

• Macromolecules are polymers built from repeating monomers
• Dehydration synthesis forms covalent bonds with loss of a water molecule
• Hydrolysis breaks polymers into monomers by adding water
• Large variety arises from a small set of monomers

The Diversity of Polymers

• Cells have thousands of different macromolecules
• Variation: among cells, within species, between species
• Vast variety can be built from a small monomer set

Carbohydrates: Fuel & Building Material

• Monosaccharides: simplest sugars; general formula $\mathrm{CH<em>2O}$; glucose: $\mathrm{C</em>6H<em>{12}O</em>6}$
• Disaccharides: formed by dehydration; glycosidic linkage
• Polysaccharides: storage (starch in plants; glycogen in animals) and structural (cellulose, chitin)

Storage Polysaccharides

• Starch: plant storage; amylose is the simplest form
• Glycogen: animal storage; liver and muscle storage

Structural Polysaccharides

• Cellulose: major component of plant cell walls; glucose polymer with beta linkages
• Chitin: exoskeletons of arthropods; structural support in fungi

Lipids: Hydrophobic & Diverse

• Lipids are hydrophobic, do not form polymers; major types: fats, phospholipids, steroids
• Predominantly hydrocarbons; little affinity for water
• Fats: glycerol + three fatty acids; ester linkages; triglycerides
• Dehydration synthesis forms fatty acid esters with glycerol
• Ester linkage: C of fatty acid to O of glycerol hydroxyl
• Saturated fats: no double bonds; solid at room temperature; animal fats
• Unsaturated fats: one or more double bonds; liquid at room temperature; plant/fish fats
• Trans fats: hydrogenation creates trans double bonds; higher cardiovascular risk
• Essential fatty acids (omega-3): must be obtained in diet
• Functions of fats: energy storage; adipose tissue cushions and insulates

Phospholipids & Membranes

• Phospholipids form bilayers in water; hydrophobic tails inward; hydrophilic heads outward
• Major component of cell membranes

Steroids

• Steroids: four fused carbon rings
• Cholesterol: component of animal membranes; essential but high levels linked to cardiovascular disease