Detailed Notes on Lipids

Definition of Lipids: Lipids are a loosely defined group of macromolecules that are hydrophobic or amphiphilic in nature.
- Types of lipids include:
- Fats: Typically of animal origin.
- Oils: Usually derived from vegetable sources (e.g., olive, corn, coconut).
- Waxes: Such as beeswax and earwax.
- Vitamins: Some vitamins like A and E.
- Steroids: Include cholesterol, testosterone, and estrogen.
Common Characteristics:
- Insoluble in water due to high proportions of nonpolar C-H bonds, making them hydrophobic.
- Soluble in nonpolar organic solvents.
- Do not fold like proteins; structures expose hydrophilic groups to surrounding water.
- They spontaneously self-assemble in aqueous environments, which is crucial for cell membrane formation.

Structure:
- Composed of a glycerol backbone and three fatty acids.
- Formed via dehydration reaction, establishing ester linkages between the hydroxyl (-OH) group of glycerol and the carboxylic acid (-COOH) group of fatty acids.
- Amphiphilic nature: Hydrocarbon backbone is hydrophobic, while the carboxylic acid group is hydrophilic.
Function:
- Serve as excellent energy storage molecules.
- Yield 9 kcal/gram (compared to 4 kcal/gram for carbohydrates).
- Provide insulation in certain animals.
- Stored in adipose (fat) cells.
Fatty Acids:
- Saturated Fatty Acids:
- Structure: Internal carbon atoms bonded to two hydrogen atoms; linear structure.
- Higher melting point and solid at room temperature; usually of animal origin.
- Unsaturated Fatty Acids:
- Contain one (monounsaturated) or more (polyunsaturated) double bonds.
- Lower melting point due to kinks in the hydrocarbon chain, typically derived from plants (with some exceptions, like fish).

Defined by their configuration, where carbon chains on both sides of a double bond are in opposite orientations.
Turn liquid fats into solids; they melt at higher temperatures (30-40 °C).
Created through incomplete hydrogenation of unsaturated vegetable fats.
Associated with increased risk of coronary heart disease and linked to elevated LDL levels (bad cholesterol) relative to HDL (good cholesterol).

Basic Structure:
- Consist of a glycerol backbone, two fatty acids, and a phosphate group.
- The fatty acid tails are nonpolar (hydrophobic), while the phosphate group with an attached charged organic molecule (like choline) is polar (hydrophilic).
Function:
- Form cell membranes through the arrangement known as the phospholipid bilayer.
- In the bilayer, hydrophilic heads face outward towards the water, and hydrophobic tails face inward, away from water.

Includes hormones like progesterone, testosterone, estrogen, cortisol, and aldosterone.
Cholesterol is the precursor for steroid hormones, synthesized through enzyme-catalyzed reactions involving its four carbon ring structure.

Synthesized from arachidonic acid; have diverse structures.
Act locally on nearby cells and are involved in various functions including:
- Inducing inflammation (e.g., prostacyclin, leukotriene B4).
- Assisting in labor (prostaglandin E2).
- Blood clotting (thromboxane A2).
- Triggering asthma attacks (leukotriene B4).
Can be inhibited by drugs like aspirin, which inhibit the enzymes responsible for their production.