lipids Flashcards
(7 cards)
What are the roles of lipids?
- Energy: Provide twice as much energy than carbohydrates due to having more C-H bonds than C-O bonds.
- Waterproofing: Insoluble in water, useful for waterproofing; plants and insects have waxy, lipid cuticles that conserve water; mammals produce an oily secretion from sebaceous glands in the skin.
- Insulation: Slow conductors of heat, retain body heat when stored beneath the body surface, and act as electrical insulators in the myelin sheath around nerve cells.
- Protection: Fat stored around delicate organs, e.g., kidney.
What are triglycerides?
Triglycerides are formed from 3 fatty acids combined with glycerol. The OH- group from each fatty acid forms an ester bond with the OH- groups in glycerol in a condensation reaction. Variations in fatty acids (over 70 types, all containing -COOH) result in different properties of fats and oils.
What are the different types of triglycerides?
- Saturated: Contains NO C-C double bonds.
- Unsaturated: Contains at least one C-C double bond.
- Monounsaturated: Contains a single C-C double bond.
- Polyunsaturated: Contains multiple C-C double bonds.
How is the structure of triglycerides related to its function?
- High ratio of C-H bonds releases more energy than C-O bonds.
- Low mass-energy ratio makes it good for storage as more energy is stored in a low volume, allowing animals to carry less weight.
- Insoluble in water as they are large, non-polar molecules, so their storage doesn’t affect water potential in cells.
- Release water when oxidized, providing an important source of water, especially for organisms living in dry deserts.
What are phospholipids?
Phospholipids consist of two fatty acids and a phosphate molecule bonded with ester bonds to glycerol. The phosphate is polar, resulting in a hydrophilic head (phosphate molecule) and a hydrophobic tail (triglyceride). When placed in water, the hydrophilic head positions closer to water while the hydrophobic tail moves away.
How is the structure of phospholipids related to its function?
- Forms a bilayer in aqueous environments due to the hydrophobic tail and hydrophilic head, creating a cell-surface phospholipid bilayer with a hydrophobic barrier inside and outside the cell.
- Allows formation of glycolipids by combining with carbohydrates, which is important in cell recognition.
What is the test for lipids?
The emulsion test: The substance is shaken with ethanol and poured into water. A positive result is indicated by a milky emulsion on top.
