BIO1010 Module 5: Macromolecules 2 - Lipids

Lipids

• Definition: Lipid

  • Lipids are a diverse group of hydrophobic biological molecules that are soluble in organic solvents but not in water. They include fats, oils, waxes, and sterols.

• Definition: Amphipathic

  • Molecules that have both hydrophobic (water-repelling) and hydrophilic (water-attracting) properties. This characteristic is crucial for the formation of cellular membranes.

• Definition: Ester linkage

  • A bond formed between a hydroxyl group of a fatty acid and a carboxyl group of glycerol, linking them together to form triglycerides and phospholipids.

Types of Lipids

• Triglycerides

  • Composed of three fatty acid molecules joined by ester linkages to a glycerol molecule. They serve as energy storage and insulation in organisms.

• Unsaturated Fatty Acids

  • Fatty acids that contain one or more double bonds between carbon atoms. This results in kinks within the hydrocarbon chain, preventing tight packing which keeps them liquid at room temperature (e.g., olive oil).

• Saturated Fatty Acids

  • Fatty acids with no double bonds between carbon atoms. They have the maximum number of hydrogen atoms, allowing them to pack closely together, typically resulting in a solid form at room temperature (e.g., butter).

• Phospholipids

  • Composed of two fatty acids and a phosphate group attached to a glycerol. They are key components of cell membranes, forming bilayers that separate the interior of the cell from the external environment.

• Cholesterol

  • A type of steroid that is an essential component of cell membranes, providing stability and fluidity. It serves as a precursor for steroid hormones.

• Steroids

  • A category of lipids distinguished by a four fused carbon ring structure. They play various roles, including acting as hormones (e.g., testosterone, estrogen).

Phospholipid Bilayer Formation

• Reason for Bilayer Formation:
  • When placed in water, phospholipids align themselves in a bilayer arrangement due to their amphipathic nature. The hydrophilic heads face outward, towards the water, while the hydrophobic tails face inward, away from the water, creating a stable barrier that forms the fundamental structure of cell membranes.