Introduction
Glycolipids are the component of the cell membrane. Only 5% of lipids in the cell membrane are glycolipids. Lipids are an important biochemical compound in plants and animals, consisting of carbon, hydrogen, and oxygen. The main function of lipids is to store energy and act as components of cell membrane formation.
According to the structure, there are three types of lipids, simple, compound, and derivative lipids. Glycolipid is a compound lipid. They play an important role in the photosynthesis process. All eukaryotic cells contain these molecules on the membrane surface.
The cell membrane is usually composed of phospholipid bilayers. Protein molecules are scattered in the phospholipid layer. On the outside of this phospholipid layer, there is often a tiny carbohydrate chain attached called glycolipids. It is a very important lipid of the cell membrane. Below is a description of its structure and how it works (3) & (6).
What is Glycolipid?
It is a compound lipid that is when carbohydrates are combined with simple lipids (fatty acids), forming a glycolipid. It contains nitrogen but no phosphoric acid. In this case, glucose or galactose is attached to lipids. When galactose is attached to a lipid, it is called a galactolipid. Chloroplast membranes of plant cells contain high levels of these lipid molecules.
It is found in unicellular organisms such as bacteria and yeast, as well as in complex organisms such as animals and plants. These molecules interact with each other, especially in animal cells, through hydrogen bonds between their carbohydrate chain and by Van der Wales forces within their fatty acid chains (4) & (7).
Types of Glycolipid
It contains fatty acids, amino alcohol sphingosine, and carbohydrate molecules. These lipid molecules are found in large amounts in the brain and myelin sheaths of nerves. Glycolipids are of two types.
1. Cerebrosides
They are composed of fatty acid, sphingosine, and galactose. Cerebrosides are found in large amounts in the brain. Phosphoric acid groups are not present in these types of glycolipids. It is known as galactolipids because it is composed of galactose. They are also found in the myelin sheath of the nervous system.
Function
Its primary function is to protect the nerve cells.
2. Gangliosides
It is found in ganglion cells of nervous tissue. Gangliosides are composed of sialic acid (sugar) and ceramide (fatty acid). The amount of sialic acid is very high in this type of glycolipid. Gangliosides are also found in red blood cells and parenchymatous tissues, like spleen tissue. It occurs in the brain. The Ganglioside is the primary component of an animal’s cell membrane.
Function
It acts as a receptor for bacterial protein toxins, such as cholera toxins and pituitary glycoprotein hormones (4) & (5).
Properties of Glycolipid
It is an important class of cell membrane lipids that are synthesized by both eukaryotic and prokaryotic organisms. There are some interesting features of this lipid molecule.
1. The lipid molecules are attached to the carbohydrates by the glycosidic bond.
2. This type of lipid forms an important organ of the glycocalyx, which is extremely important for many cellular processes.
3. Photosynthetic organs store more glycolipids than phospholipids.
4. The sugar residue of the glycolipid molecule is expanded from the phospholipid bilayer.
5. Its backbone is made with glycerol.
6. The glycosidic bond of this molecule is a covalent type bond.
7. These lipids combine glucose or galactose with the hydroxyl group of glycerol’s alpha position.
8. Their role is to maintain the stability of the cell membrane.
9. It is basically composed of a sphingosine skeleton in animal cells.
10. In plants, these lipids are combined with two common diglycerides and sulfonic acid derivatives.
11. These lipids have two ends. The head region is hydrophilic and the tail region is hydrophobic.
12. It is distributed in tissue, the brain, and also in nerve cells.
13. About two-thirds of the total glycolipids are distributed in Golgi bodies, lysosomes, and mitochondria (1) & (7).
Structure of glycolipid
The structure of glycolipid consists of monosaccharide or oligosaccharide groups attached to a glycerol group containing one or two fatty acids. They are glycoglycerolipids and glycosphingolipids. These two glycolipids are the largest amounts of lipids in the cell membrane. Both lipids have a glycerol backbone. Fatty acids are attached to this backbone.
It has two ends, a hydrophilic head, and a hydrophobic tail. The hydrophilic head is electrically charged and the hydrophobic tail is uncharged. The carbohydrate groups attached to the polar head part of the outer membrane of the cell are the components of these compound lipids. This lipid and carbohydrate group forms a conjugation through a covalent bond. The bond is known as a glycosidic bond.
This lipid is located in the outer membrane of the cell. The cell coat is made up of glycolipids. Bacteria’s glycolipids structure is the same as an animal’s glycolipids structure. However, SN-1, 2-diglyceride contains carbohydrate residues connected by glycosylation in the 3rd position. Among the bacterial glycolipids, the most common residues of saccharides are galactose and glucose (2) & (1).
Function of glycolipid
It is a component of eukaryotic cell membranes. So its functionality is very significant. It plays a role in controlling many important functions.
1. The main function of these lipids is to stabilize cell membranes by forming hydrogen bonds with the surrounding water molecules.
2. It plays a key role in cell attachment during tissue formation.
3. The carbohydrate molecule of a glycolipid is attached to a neighboring carbohydrate molecule. This integration results in increased cell response and cell recognition.
4. They help to determine the types of blood groups. Mainly carbohydrates of these lipids help in this process.
5. It is present on the surface of red blood cells in the form of an antigen.
6. They are attached to the leukocytes and produce an immune system. It also plays an important role in destroying pathogens.
7. These compound lipids participate in the formation of chloroplast membranes in the plant cell.
8. It plays a special role in the process of photosynthesis.
9. They provide energy to the cell.
10. These types of lipids also play an important role in the growth and development of cells.
11. It forms a bilayer in the outer cell membrane similar to that of phospholipids (4) & (5).
Q&A
1. What are glycolipids?
Glycolipid is a type of complex lipid. It is the component of the cell membrane. They are found in the outer part of the cell membrane. Glycolipids are formed when a carbohydrate group is combined with simple lipids or fatty acid groups. This group forms a glycosidic bond. Like phospholipid, it is also a primary component of the cell.
2. What do glycolipids do?
- The primary function of glycolipids is to stabilize cell membranes by forming hydrogen bonds with the surrounding water molecules.
- They play an essential role in the growth and development of cell and cellular interactions.
- It is an important component of the chloroplast cell membrane.
- The cell coat or glycocalyx is mainly made of glycolipids.
- Glycolysis helps in the formation of photosynthetic organs as well as the photosynthesis process.
- It helps in determining blood groups.
3. Where are glycolipids found?
Glycolipids are found in unicellular organisms such as bacteria, and yeast, as well as in complex organisms such as animals and plants. In eukaryotic cells, it is found in the outer membrane of the cell membrane. They are attached to the phospholipid bilayers. These lipids extend from the phospholipid bilayers into the extracellular part. They are also found in plant cells. It is densely located in the membrane of chloroplasts of plant cells.
4. How do glycolipids and glycoproteins help in cell-to-cell recognition?
Glycolipids and glycoproteins both are cell membrane components. They stabilize cell membranes by forming hydrogen bonds with the surrounding water molecules. However, glycoproteins and glycolipids are used as receptor molecules binding with hormones. Both components of the cell membrane also play as antibodies. They help to determine the types of blood groups, which are used in allowing cells to recognize each other.
5. What are glycoproteins and glycolipids?
Oligosaccharide chains attached to proteins are known as glycoproteins. When they are covalently attached to lipids, these are known as glycolipids respectively.
Glycoproteins
Glycoproteins are conjugated proteins. It is a protein molecule that binds to carbohydrates in a tiny chain. This protein molecule contains oligosaccharide chains. The oligosaccharide chains are attached to amino acids by covalent bonds. Glycoproteins are located on the surface of the lipid bilayer of the cell membrane. They have stabilized cell membranes by forming hydrogen bonds with the surrounding water molecules. Its main function is to serve as antigens. There are three types of glycoprotein in the cell or plasma membrane. These are-
- Structural protein
- Carrier protein
- Enzymatic protein
Glycolipids
Glycolipid is a compound lipid. It is a lipid molecule that binds to carbohydrates. These lipid molecules are the components of the cell membrane. They are located in the extracellular part of the phospholipid layer of the cell or plasma membrane. The backbone of glycolipids is made with glycerol. It binds to carbohydrates by glycosidic bonds.
Reference
1. Chandrasekhar Chakrabarti. Modern approach to a textbook of core Zoology, General & Honours. Nirmala Library, A Publishing House under the Prestigious International Standard Book Number (ISBN) System. Kolkata, (India). Part – II, chapter- cell and cellular organelles. Page: 2nd -10- 2 to 2nd – 10- 4.
