Index
They are organic compounds found in the tissues of plants and animals.
Function
Lipids serve as energy storage molecules, function as solvents for water-insoluble vitamins , provide insulation against loss of body heat, act as a protective cushion for vital organs, and are structural components of cell membranes.
Lipids are a heterogeneous group of compounds, including fats, oils, steroids, waxes, and other compounds, that are more closely related by their physical properties than by their chemical properties.
Lipids are important in biological systems because they form the cell membrane , a mechanical barrier that divides a cell from the external environment.
Lipids also provide energy for life and several essential vitamins are lipids.
lipid metabolism
Starch and sucrose are not the only by-products available for energy production in plants.
Fats and oils are important forms of reduced carbon storage in many seeds, including those of important agricultural species such as soybeans, sunflowers, and cotton.
Oils often serve an important storage function in non-domesticated plants that produce small seeds. Some fruits, like avocado, also store fats and oils.
In biology, the term lipid can refer to almost any molecule that is hydrophobic enough to split into an organic solvent from an aqueous solution.
Lipids can be considered to be biological molecules that are soluble in organic solvents, such as chloroform and methanol, and are poorly soluble in aqueous solutions.
There are two main classes of lipids: saponifiable and unsaponifiable, based on their reactivity with strong bases.
Non-saponifiable classes include “fat soluble” vitamins (A, E) and cholesterol.
Saponifiable lipids contain long-chain carboxylic acids, or fatty acids, esterified to a “main” molecule, which is glycerol or spingosin.
Saponifiable lipids
A saponifiable lipid contains one or more ester groups that allow it to be hydrolyzed in the presence of an acid, base, or enzymes.
Triglycerides are three fatty acids attached to a glycerol molecule (glycerin).
Fatty acids are long carbon chains with hydrogen attached to carbon but not oxygen (as seen in sugars).
They do not form rings. Triglycerides are stored for energy and metabolic water (as in the camel’s hump).
Other fatty acids attached to more elegant molecules than glycerol (those with a positive and / or negative charged group) have a polar (hydrophilic) end and a non-polar (hydrophobic) tail where the fatty acids meet.
These lipids form a lipid bilayer and are an integral part of all cell membranes.
The outer charged part of the molecules in the bilayer can interact with the extracellular fluid on one side and with the intracellular fluid on the other side of the membrane, while the inner discharged part of the molecule seals the intracellular and extracellular fluid areas and it cannot be easily mixed.
Types of saponifiable lipids
Simple
Simple lipids only contain carbon, hydrogen and oxygen. And they are divided into:
Acylglycerides
Its function is as an energy reserve and as a thermal insulator. Neutral fats, triglycerides or triacylglycerols are esters of glycerol and three fatty acids
Neutral fats, which are often deposited in cells as potential sources of chemical energy, represent the main type of stored lipid; They appear as droplets in the cytoplasm and most of the lipids that are recovered in the soluble phase or the cytosol of the altered cells take this form.
Cerides (waxes)
Its function is protective. Cerides are esters composed of long chain fatty acids and monohydric alcohols.
The ends of the ceride molecules are insoluble in water (hydrophobic).
Complex
They are lipids that, in addition to containing carbon, hydrogen and oxygen in their molecule, also contain other elements such as nitrogen, phosphorus, sulfur or another biomolecule such as a carbohydrate.
Complex lipids are also called membrane lipids because they are the main molecules that make up cell membranes. These are:
Phospholipids
Phospholipids are made up of an alcohol molecule (glycerol or sphingosine) to which two fatty acids and a phosphate group are attached. Phospholipids are divided into:
- Phosphoglycerides: in these compounds the alcohol is a glycerol. Phosphatidic acid and its derivatives are present in plasma membranes, where they play an active role in membrane function in addition to serving as major structural components.
- Eosphosphingolipids: in these compounds the alcohol is a sphingosine. The myelin sheath surrounding the axons of neurons is particularly rich in sphingolipid sphingomyelin.
Glycolipids (cerebrosides and gangliosides)
The outer surface of the plasma membrane of most cells is covered with short chains of sugars.
These sugars are parts of glycoproteins or are attached to membrane lipids, forming glycolipids.
Glycolipids in the plasma membrane play vital roles in immunity, blood group specificity, and cell recognition.
The carbohydrates found in glycolipids range from individual monosaccharides such as glucose and galactose to short, branched or unbranched oligosaccharides.
