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What are Lipids? – Structure, Classification, Properties, Functions

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  • Last Updated : 28 Nov, 2022
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Lipids are one of the significant macromolecules present in our bodies. Lipids are not polymers they aren’t made out of monomers. Lipids play different parts in many key biological capabilities, for example, they act as structural components of cell membranes, act as energy storage sources, and partake in signaling pathways. Edible lipids comprise roughly 25-28% of the eating regimen and they act as a beginning material for the creation of numerous significant items like cleanser items. The job of lipids in the diet routine has gotten a lot of consideration in light of the obvious association between saturated fats and blood cholesterol with arterial disease problems. Lipids are the main energy stockpiling com­pounds in the set of all animals. Plants store the greater part of their energy as carbs, basically as starch. Furthermore, lipids give protection to the crucial organs, shielding them from mecha­nical shock and keeping up with ideal internal heat levels. Lipids are necessary parts of cell layer structure and are related to transportation across cell films.

Lipid

The term lipid is defined as a family group of heterogeneous organic compounds which are soluble in non-polar solvents. Lipids naturally occur in most plants, animals, and microorganisms and are used as cell membrane components, energy storage molecules, insulation, and hormones. These chemical features are present in a broad range of molecules such as fatty acids, phospholipids, sterols, sphingolipids, terpenes, and others. Structurally, they are esters or amides of fatty acids. These molecules can be soluble in non-polar solvents but can’t be soluble in water.

Structure

Lipids are made up of two molecules, glycerol, and fatty acids. Glycerol molecule consists of three carbon atoms with a hydroxyl group attached to it and Fatty acids are the long chains of hydrocarbons with a carboxylic acid group at the end.

Structure of Lipid

 

Function

  • They act as energy storage.
  • Lipids play a very important role in the building up of biological cell membranes.
  • It acts as insulation, a poor conductor of heat.
  • Protecting the plant leaves from direct heat, and drying.
  • They also act as hormones in the body.
  • It acts as the structural component of the body and also acts as the hydrophobic barrier.
  • A major source of energy in animals.
  • It provides color to many fruits and vegetables with the presence of carotenoid pigment.

Classification of Lipids

Classification Of lipids

 

Types of Lipids

Lipids are mainly classified into three types. They are simple, complex, and derived lipids.

  • Simple Lipids: Simple lipids are triglycerides, esters of fatty acids, and wax esters. The hydrolysis of these lipids gives glycerol and fatty acids.
  • Complex Lipids: Complex or compound lipids are the esters of fatty acids with groups along with alcohol and fatty acids. Examples are Phospholipids, Glycolipids.
  • Derived lipids: Derived lipids are the hydrolyzed compounds of simple and complex lipids. Examples are fatty acids, steroids, fatty aldehydes, ketone bodies, lipid-soluble vitamins, and hormones.

Simple Lipids

Simple lipids are triglycerides, esters of fatty acids, and wax esters. The hydrolysis of these lipids gives glycerol and fatty acids. Simple lipids are classified into Triglycerides and Waxes.

Triglycerides

Triglycerides are the lipid molecules that are esters formed from one glycerol molecule associated with three fatty acid molecules. They are the constituents of fats and oils. Lipids that is solid at room temperature are fats and lipids that are liquid at room temperature are oils.

Glycerol

It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in those lipids known as glycerides. It is a simple polyol compound.

Glycerol

 

Fatty Acids 

Fatty acids are carboxylic acids; they are long chains of hydrocarbons with a carboxylic group at the end. Fatty acids are an important component of lipids, they are the building blocks of fat in the body. There are two types of fatty acids, saturated fatty acids, and unsaturated fatty acids.

  • Saturated fatty acids

It consists of single C-C single bonds. These molecules fit closely together in a regular pattern and strong attractions between fatty acid chains. These fatty acids have high melting points, which makes them solid at room temperature. Examples of saturated fatty acids are palmitic acid and stearic acid.

Saturated Fatty acid

 

  • Unsaturated fatty acids

Unsaturated fatty acids are the fatty acids that consist of one or more C=C double bonds. An unsaturated fatty acid is divided into two types.

  1. Mono polyunsaturated fatty acids. Example: oleic acid.
  2. Polyunsaturated fatty acids. Example: linolic acid.
Unsaturated Fatty Acids

 

Role of Fats

Fats play an essential role in the body including:

  • Fats help our body by absorbing and transporting important fat-soluble vitamins. 
  • They are an important source of essential fatty acids.
  • They insulate and protect our vital body organs.
  • Fats produce energy in the form of carbohydrates.
  • Fats are the structural component of cells.
  • They help the body produce and regulate hormones.
  • Fats support cell growth.
  • They maintain your core temperature.
  • Maintains blood pressure and cholesterol under control.

Waxes

Waxes are usually saturated with long chain monohydric alcohols. They are the simple esters of fatty acids. Here are some of the examples:

  • Beeswax: Beeswax includes fatty acids and some free alcohol.
  • Carnauba wax: It is a hard wax used on cars and boats.
  • Spermaceti: it consists of cetyl palmitate. Used for pharmaceuticals.

Complex Lipids 

Complex or compound lipids are the esters of fatty acids with groups along with alcohol and fatty acids. Examples are Phospholipids, Glycolipids.

Phospholipids

Phospholipids are constituents of cellular membranes. An ester is formed when a hydroxyl reacts with a carboxylic acid and losses H2O. Phospholipids are also known as phosphatides, are classes of lipids whose molecule has a hydrophilic head and two hydrophobic tails. A head containing a phosphate group and tails derived from fatty acids joined by a glycerol molecule. They serve as emulsifiers.

There are two types of phospholipids:

  • Glycerophospholipids 

Glycerophospholipids are the class of phospholipids containing glycerol as alcohol, two fatty acids, and phosphate. It is the most abundant lipid in the cell membrane.

  • Sphingophospholipids

Sphingophospholipids are the class of phospholipids containing sphingosine as alcohol. It produces ceramide by an amide linkage to a fatty acid. Ceramide is an important component of skin. It acts as a second messenger to regulate programmed cell death.

Glycolipid

It is a structural lipid, an essential part of the cell membrane. They are lipids with a carbohydrate, attached by a glycosidic bond. They act as receptors at the surface of the red blood cell. It helps in the determination of an individual blood group. It has an important role in maintaining of stability of the cell membrane. It kills the pathogens to help the immune system of the body. Cerebrosides and Gangliosides are the two types of Glycolipids.

Derived Lipids

Derived lipids are the hydrolyzed compounds of simple and complex lipids. Examples are fatty acids, steroids, fatty aldehydes, ketone bodies, lipid-soluble vitamins, and hormones.

Steroids 

Steroids are found in the cell membrane and have fused ring structures. Many steroids have -OH functional groups, they are also hydrophobic and insoluble in water. All the steroids have 4 linked carbon rings and most of them have a short tail. Steroids also act as hormones in the body.

Sterols 

Sterols are the solid steroid alcohols that are widely present in plants and animals such as cholesterol and ergosterol. They are the subgroup of steroids, which naturally occur in most eukaryotes. They are found in animal products. They are used to make bile for digestion in the body. Sterols can have greater than half of the membrane lipid content in cells and they are known to alter membrane structure and fluidity.

Carotenoids

Carotenoids are lipid-soluble compounds. They are pigments that are mainly responsible for many of the yellow and red colors of plant and animal products. Carotenoids consist of carotenes and xanthophylls. A class of hydrocarbons is carotenes and its oxygenated derivatives are xanthophylls. They give the color to many fruits and vegetables. They have antioxidant and anti-inflammatory properties for humans. Carotenoids are important in the health of the human eye.

Physical Properties

  • Lipids are insoluble in water.
  • At room temperature, lipids either present liquid condition or non-crystalline solids condition.
  • They act as energy storage molecules.
  • They are soluble in organic solvents like alcohol, chloroform, benzene, etc.
  • Fats consist of high proportions of saturated fatty acids.
  • Fats and Oils of pure form are colorless, odorless, and tasteless.
  • They even act as insulation.
  • Oils consist of high proportions of unsaturated fatty acids.

Chemical Properties

  • Halogenation: Halogenation is the reaction in which the free or combined unsaturated fatty acids gain double bonds on reacting with halogens. This cause halogen solutions to decolorize.
  • Saponification: It is the process in which hydrolyzing triglycerides with an enzyme called lipase or hydrolysis with an alkaline forms two products.
  • Hydrogenation: it is the process used for turning oils into fats. The hydrogenation process is used in the industries to produce fat products. Butter is one example of the hydrogenation process. It involves in breaking of double bonds of unsaturated fatty acids with hydrogen and turning them into hydrogenated (saturated) fatty acids.
  • Rancidity: Rancidity is the undesirable state that occurs in oils, fats, and their products. Due to oxidation of unsaturated fatty acids or hydrolysis of fats and oils, it produces an undesirable odor. In food industries, rancidity is one of the major concerns.
  • Hydrolysis of triglycerides: Carboxylic acid and alcohol are produced by hydrolysis of triglycerides with water.

Conceptual Question

Question 1: What are essential and non-essential fatty acids?

Answer: 

Based on the requirement of the human body, lipids are categorized into essential and non-essential fatty acids:

  • Essential Fatty Acids: Fatty acids that cannot be produced or synthesized in our bodies are called essential fatty acids. These fatty acids need to be taken through a diet to fulfil the body’s requirement for different metabolic functions. It includes linoleic acid, linolenic acid, and arachidonic acid.
  • Non-essential Fatty Acids: Non-essential fatty acids include those lipids that are synthesized by our body. They are not needed to be taken through any outside food source. It includes palmitic acid, oleic acid, and butyric acid.

Question 2: What are good fat and bad fat?

Answer: 

  • Bad fats are not good for the body they increase the risk of diseases. Bad fats are saturated fat, which increases the level of bad cholesterol i.e., Low-density lipoprotein. LDL or Low-density lipoprotein clogs the arteries and might increase the risk of heart disease, high cholesterol, and some cancers including colons.
  • Good fats are essential for the human body they lower the disease risk. Good fats are unsaturated fats it increases the levels of good cholesterol i.e., High-density lipoprotein. HDL or high-density lipoprotein grabs LDL by limiting it in the body and escorts it to the liver. Where LDL is broken down and eventually removed from the body.

Question 3: What methods are used for the lipid analysis?

Answer: 

Lipid analysis is done for the extraction of lipids and also for the quality analysis in the laboratories. The three types of methods are solvent extraction methods, nonsolvent extraction methods, and instrumental methods.

  • The methods used in the solvent extraction are Sample preparation, Sample selection, Goldfish method, Soxhlet method, Mojonnier method, Chloroform- Methanol procedure, and Total fat by gas chromatography.
  • The methods based on nonsolvent wet extraction are the Babcock method, the Gerber method.
  • The instrumental methods used for lipid analysis are the Infrared method, Specific gravity, and NMR method.

Question 4: What is the functions of phospholipids:

Answer: 

The functions of phospholipids are:

  1. They form the structural component of membranes.
  2. Essential in the synthesis of many different lipoproteins.
  3. It acts as a surfactant.
  4. It participates in the transport of lipids.
  5. Lipotropic factors, prevent the accumulation of fats in the liver.
  6. It helps in the transport of cholesterol, and removal from the body.

Question 5: What are the types of lipids?

Answer:

Lipids are categorized into two types; one is lipids with fatty acids and the other one is lipids without fatty acids:
Lipids with fatty acids are:

  • Waxes
  • Fats and oils
  • Phospholipids
  • Sphingolipids

Lipids without fatty acids are Steroids.

Question 6: What are triglycerides and their types?

Answer

Triglycerides are the lipid molecules that are esters formed from one glycerol molecule associated with three fatty acid molecules. Natural fats are mixtures of mixed triglycerides with a small number of simple triglycerides. There are two types:

  1. Simple: Simple triglycerides are type triglycerides if the three fatty acids are connected to glycerol of the same type of triglyceride. e.g., tripalmitin.
  2. Mixed: Mixed triglycerides are type triglyceride if they are of different types. e.g., stearo-diolein and palmito-oleo-stearin.

Question 7: Why omega 3 and 6 fatty acids are essential?

Answer: 

Omega 3 fatty acids(ω3) and Omega 6 fatty acids(ω6) are essential fatty acids (EFAs). They are unsaturated and need to add to the diet of a person. Because the human body’s metabolism cannot create from other fatty acids. Some examples of omega3 fatty acids are alpha-linolenic acid, Eicosapentaenoic acid (EPA), Docosahexaenoic acid (DHA), and some examples of omega6 fatty acids are linoleic acid, Arachidonic acid (AA).


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