Lipids

Fats and oils store energy: Efficient energy storage molecules in living organisms.

Phospholipids—structural role in cell membranes: Crucial components in cell membrane structure.

Steroids and modified fatty acids — cholesterol; hormones and vitamins: Essential in metabolic pathways, hormone and vitamin production.

Carotenoids and chlorophylls—capture light energy in plants: Pigments responsible for capturing light during photosynthesis.

Lipids are nonpolar hydrocarbons: Organic molecules primarily composed of nonpolar hydrocarbons.

Not polymers in the strict sense, because they are not covalently bonded: Not typical polymers due to the absence of repeating monomer units.

Weak but additive van der Waals forces hold them together when sufficiently close: Held together by cumulative weak van der Waals forces.

Lipid coating around nerves provides electrical insulation: Forms an insulating coating around nerves.

Unsaturated fatty acids: some double bonds in carbon chain: Contain double bonds, resulting in kinks in their structure.

Animal fats tend to be saturated: packed together tightly (straight); solid at room temperature: Predominantly saturated and solid at room temperature.

Plant oils tend to be unsaturated: the “kinks” prevent packing; liquid at room temperature: Predominantly unsaturated, resulting in a liquid state at room temperature.

Amphiphatic: they have opposing chemical properties (fatty acids): Possess both hydrophobic and hydrophilic regions.

Phospholipids: fatty acids bound to glycerol; a phosphate group replaces one fatty acid: Consist of fatty acids bound to glycerol with one fatty acid replaced by a phosphate group.

Phosphate group is hydrophilic—the “head”: Hydrophilic part of phospholipids.

“Tails” are fatty acid chains—hydrophobic: Hydrophobic part of phospholipids.

amphipathic: Possess both hydrophobic and hydrophilic regions.

In water, phospholipids line up with the hydrophobic “tails” together and the phosphate “heads” facing outward, to form a bilayer: Arrangement of phospholipids in water to form a bilayer.

Biological membranes have this kind of phospholipid bilayer structure: Structure found in biological membranes.

Steroids: multiple rings share carbons: Steroids consist of multiple rings sharing carbon atoms.

Cholesterol reduces permeability of lipid membranes; Cholesterol is the central component in several metabolic pathways; it plays a role in membrane fluidity but its most important function is in reducing the permeability of the cell membrane. Cholesterol helps to restrict the passage of molecules by increasing the packing of phospholipids: Cholesterol's functions in reducing membrane permeability and affecting membrane fluidity.

Carotenoids and chlorophylls—capture light energy in plants: Pigments responsible for capturing light energy in plants.

Two broad classifications of carotenoids: carotenes and xanthophylls. The difference between the two groups is chemical: xanthophylls contain oxygen, while carotenes are hydrocarbons and do not contain oxygen: Classification of carotenoids based on chemical composition.

Also, the two absorb different wavelengths of light during a plant’s photosynthesis process, so xanthophylls are more yellow while carotenes are orange: Differential light absorption by carotenoid groups in photosynthesis.