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In this article, we will discuss the structure and function of triglycerides in detail. Besides this, we will also compare triglycerides with phospholipids. So, let us get started.
Lipids
- Like carbohydrates, lipids are macromolecules that contain hydrogen, carbon, and oxygen atoms. However, lipids contain a lower proportion of oxygen atoms as compared to carbohydrates.
- Lipids are nonpolar and insoluble in water. It means that they are hydrophobic.
- Different types of lipids include phospholipids, fats and oils (made up of triglycerides) waxes, and steroids. Waxes and steroids are considered lipids because they are insoluble in water.
Now, in the next section, we will discuss triglycerides in detail.
Triglycerides
- Triglycerides refer to the non-polar, hydrophobic (water-insoluble molecules).
- Triglycerides are lipids that contain one glycerol molecule that is bonded with three fatty acids. It means that the monomers of triglycerides are fatty acids and glycerol. Glycerol is alcohol because it is an organic molecule that has a hydroxyl group that is bonded to a carbon atom)
- Fatty acids have a methyl group at one end of a hydrocarbon chain and a carboxyl group at the other end. Hydrocarbon chain refers to the chains of hydrogen-bonded to carbon atoms.
Saturated and Unsaturated fatty acids
Not all fatty acids are the same. The length of their hydrocarbon chain varies. They can also be saturated or unsaturated. The example of saturated fatty acid includes animal fat and examples of unsaturated fatty acids include vegetable oils.
Unsaturated fatty acids are further divided into the following two categories:
- Mono-unsaturated fatty acids
- Poly-unsaturated fatty acids
If hydrogen atoms are on the same side of the double bond, then they are referred to as cis-fatty acids. Enzymes can metabolize these fatty acids.
If hydrogen atoms are on the opposite sides of the double bond, then they are referred to as trans-fatty acids. These fatty acids cannot create enzyme-substrate complexes, hence, they cannot be metabolized by the enzymes. These fatty acids are associated with coronary heart disease.
Triglycerides Formation – Esterification
Triglycerides are created by the process of esterification. The bonds between the triglyceride molecules are covalent and are referred to as ester bonds. An ester bond is created when the hydroxyl group of the glycerol creates a bond with the carboxyl group of the fatty acid. A water molecule is released for every ester bond created. Hence, when one triglyceride is formed, then three water molecules are released. We can say that the ester bonds are created during a condensation reaction.
In the next section of the article, we will discuss the structure and function of triglycerides.
Functions of Triglycerides
Triglycerides play an important role in many living organisms. Some of the functions of triglycerides are explained below:
Energy Storage
Several carbon-hydrogen bonds are present in the long chains of hydrocarbon. The proportion of oxygen is less in these chains which means that the triglycerides are greatly reduced. Hence, during cellular respiration, when triglycerides are reduced, the bonds break to release energy. This energy is then used to produce ATP. Due to this reason, triglycerides store more energy per gram as compared to other macromolecules carbohydrates, and proteins.
Because triglycerides are water-insoluble, hence they do not cause osmotic water uptake in cells, so they can be stored. Different organisms store triglycerides in different ways. For example:
- Triglycerides in plants are stored in the form of oils in their fruits and seeds. If the triglycerides from plants are extracted from the fruits and seeds, they are liquid at room temperature. The reason behind them being liquid at room temperature is the presence of double bonds.
- Unlike plants, triglycerides in mammals are stored in the form of oil droplets in adipose tissue. These stored triglycerides assist them to survive when no food is available. The example of mammals that benefit from the stored glycerides is hibernating bears.
When carbon-hydrogen bonds are oxidized, a huge number of water molecules are released during cellular respiration. This process also helps certain animals in their survival. For instance, desert animals retain this water in the absence of liquid water. Similarly, birds and embryos of reptiles also used this water.
Insulation
One of the elements of the myelin sheath is triglycerides that surround nerve fibres. This provides insulation which enhances the transmission speed of the nerve impulses. Triglycerides also form a part of the adipose tissue layer that is present beneath the skin. This layer also provides insulation against heat loss.
Protection
Stored triglycerides are present in the adipose tissue of mammals. This tissue protects organs from possible damage.
Buoyancy
Since fat tissue has low density, hence it enhances the ability of animals to float.
So far, in this article, we have discussed triglycerides in detail. Now, we will discuss phospholipids which are another important type of lipids.
Phospholipids
Phospholipids are created from monomers of fatty acids and glycerol; hence they are categorized as lipids. In phospholipids, two fatty acids are bonded with a glycerol molecule because one is replaced by a phosphate ion. The phosphate ion is soluble in water because it is polar. The tails of fatty acids are non-polar, hence they are insoluble in water, i.e., they are hydrophobic. Both phospholipids and triglycerides release three water molecules upon formation. The fatty acid tails in phospholipids are hydrophobic, whereas the phosphate head is hydrophilic. It means that the orientation of the phosphate group will be towards the water, but away from the remaining molecule. Due to this, phospholipids have special properties which enable them to be utilized in the formation of membranes.
Phospholipids are amphipathic which means that they contain both hydrophobic and hydrophilic components. Because they contain both hydrophobic and hydrophilic components, therefore the molecules of phospholipids create monolayers or bilayers in water. Phospholipids can have saturated and unsaturated fatty acids. This enables the control of the fluidity of membranes which helps in maintaining the fluidity of the membrane at low temperatures.
In the next section, we will discuss the differences between phospholipids and triglycerides.
Differences Between Phospholipids and Triglycerides
- Phospholipids contain two fatty acid tails, whereas triglycerides have three fatty acids
- As the name implies, phosphate ion is present in the phospholipids, whereas it is absent in triglycerides.
- Phospholipids have a polar phosphate head, whereas triglycerides are non-polar
- Phospholipids are the important component of the cell membrane, whereas triglycerides play a crucial role in energy storage
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