Lipids definition

• Lipids, a heterogeneous family of organic compounds, are soluble in nonpolar chemical solvents but insoluble in water.
• They are utilised for insulation, hormones, energy storage molecules, and cell membrane components in the majority of plants, animals, and microbes where they naturally exist.

Properties of Lipids

• Lipids may exist as either liquids or non-crystalline solids at normal temperatures.
• Purified fats and oils are tasteless, odourless, and colourless.
• Lipids are organic substances with an abundance of power.
• Water-soluble yet not
• soluble in organic solvents such as benzene, acetone, chloroform, alcohol, and so on.
• without ionic charges.
• Saturated fatty acids make up a large component of solid triglycerides (fats).
• Unsaturated fatty acids make up a large component of liquid triglycerides (oils).

1. Hydrolysis of triglycerols

Triglycerols, such as numerous esters, undergo hydrolysis when they react with water to form carboxylic acid as well as alcohol.

2. Saponification:

Triacylglycerols may be hydrolyzed in many ways, with alkali or lipase enzymes being the most common. Because soap, typically sodium or potassium salts of fatty acids, is one of the by-products of alkaline hydrolysis, this process is called saponification.

3. Hydrogenation

Carbon-carbon double bonds in unsaturated fatty acids may be converted into saturated fatty acids by interaction with hydrogen.

4. Halocarbonation

Unsaturated fatty acids interact with halogens through addition along the double bond, regardless of whether they are liberated or incorporated in fats and oils as esters (s). As a result of the reaction, the halogen solution turns colourless.

5. Rancidity:

Any fat or oil that has an unpleasant odour is said to be rancid. Rancidity is a result of oxidation and hydrolysis processes. Triacylglycerols possessing unsaturated fatty acids become rancid as a result of oxidation.

Structure of Lipids

• Despite the fact that lipids are mostly made of carbon, hydrogen, as well as oxygen, lipids comprise much less water than other molecules, such as carbohydrates.
• Unlike polysaccharides and proteins, lipids lack a recurring monomeric unit, preventing them from becoming polymers.
• Glycerol as well as fatty acids are the two constituent compounds.
• A glycerol molecule consists of three carbon atoms, each of which is connected to a hydroxyl group, and two hydrogen atoms.
• Fatty acids are molecules containing an acid group at one end and an R-shaped hydrocarbon chain at the other.
• They may or may not be saturated.
• If no C=C bonds can be formed and every conceivable bond can be formed using a hydrogen atom, the fatty acid is said to be saturated.
• On the other hand, unsaturated fatty acids do possess C=C linkages.
• Unlike monounsaturated fatty acids, polyunsaturated fatty acids have several C=C linkages.

Structure of Triglycerides

• Triglycerides are lipids made up of three fatty acid molecules linked to one glycerol molecule.
• Ester bonds are covalent connections that connect the molecules.
• They develop as a result of a condensation process.
• Since the charges on the molecule are equally distributed, no hydrogen bonds can form with the water molecules, making the molecule water-insoluble.

Classification (Types) of Lipids

Lipids may be categorised based on similarities in their molecular structures and the products of their hydrolysis. There are three main subclasses established:

1. Simple lipids

(a) While fats and oils are hydrolyzed, fatty acids as well as glycerol are produced.

(b) Wax, which upon hydrolysis produces long-chain alcohols and fatty acids.

Fats and Oils

• Triacylglycerols are the names given to these classes of compounds because they consist of three fatty acids bound to glycerol, a trihydroxy alcohol, to form esters.
• Their respective physical states at ambient temperatures explain the difference. A lipid is often called a fat whether it is hard at 25 °C, as well as an oil whether it is liquid.
• The above changes in melting points correlate to variations in the degree of unsaturation of the constituent fatty acids.

Waxes

• Wax is an ester comprising a fatty acid and a long-chain alcohol (often mono-hydroxy).
• Wax often contains acids and alcohols with chains of between 12 and 34 carbon atoms.

2. Compound lipids

(a) Phospholipids: Phospholipids that, following hydrolysis, provide fatty acids, glycerol, the amino alcohol sphingosine, phosphoric acid, as well as a nitrogen-containing alcohol.

They may be sphingophospholipids or glycerophospholipids, based on the alcohol group present (glycerol or sphingosine).

(b) Glycolipids: Glycolipids the breakdown of which yields fatty acids, sphingosine or glycerol, and a carbohydrate.

Based on the present alcohol group, they might be glyceroglycolipids or sphingoglycolipids (glycerol or sphingosine).

3. Derived lipids:

• The by-products of the hydrolysis of simple as well as complex lipids are derived lipids. They consist of derivatives of fatty acids, glycerol, sphingosine, and steroids.
• Different from lipids made primarily of fatty acids are phenanthrene molecules called steroid derivatives.

Functions

It is well known that lipids are very crucial to a cell’s ability to operate normally. Lipids have a crucial function in the formation of organellar and cell membranes, in addition to acting as extremely reduced energy storage forms. Lipids serve a variety of purposes, including:

1. Energy Reserves
2. Biological Membrane Production
3. Insulation
4. Providing protection, such as preventing the withering of plant leaves,
5. Bouyancy
6. hormonal influences
7. They serve as a structural component of the body and provide the hydrophobic barrier required to separate the watery constituents of cells from subcellular structures.
8. High-lipid-content animals and crops depend largely on lipids as an energy source.
9. Micelles containing phosphatidylcholine are required for the activation of numerous enzyme activators, including glucose-6-phosphatase, stearyl CoA desaturase,-monooxygenase, and hydroxybutyric dehydrogenase (a mitochondrial enzyme).

References

http://www.phys.sinica.edu.tw/TIGPNANO/Course/2006_Spring/classnotes/Nanobio%20031006.pdf

https://alevelnotes.com/Lipids/58

Smith, C. M., Marks, A. D., Lieberman, M. A., Marks, D. B., & Marks, D. B. (2005). Marks’ basic medical biochemistry: A clinical approach. Philadelphia: Lippincott Williams & Wilkins.