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Glycolipids are lipids with a glycosidic (covalent) bond to a carbohydrate.
- Their role is to keep the cell membrane stable and also to facilitate cellular recognition.
- It is important in the immune response and also in the connections that allow cells to connect to form tissues.
- Glycolipids are present on the surface of all the eukaryotic cell membranes, extending out from the phospholipid bilayer into the extracellular environment.
- Glycolipids contain a monosaccharide or oligosaccharide attached to a lipid moiety.
| Table of Content |
Key Terms: Lipids, Tissues, Cell Membrane, Polar Head, Glycerol, Enzymes, Glycolipids, Fatty acids, Cerebrosides, Gangliosides, Metabolism, Plasma membranes
What are Glycolipids?
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Glycolipids are lipids that include carbohydrates, fatty acids, sphingolipids, and even a glycerol group.
- A glycolipid is a substance that has one or more monosaccharide residues connected by a glycosidic bond.
- These substances can be found in high quantities in tissue, the brain, and nerve cells.
- Glycolipids are widely distributed throughout all cells and are often, but not only found in the plasma membrane.
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Structure of Glycolipid
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The structure of a glycolipid is composed of one or two fatty acids bonded to mono- or oligosaccharide groups attached to a sphingolipid or even a glycerol group (which may be acetylated or alkylated).
- Glycosphingolipids and glycoglycerolipids are different types of lipids.
- The hydrophobic feature of the lipid tail, which binds it to the plasma membrane's surface, enables glycolipids to connect and link to the lipid bilayer.
Glycolipid
Types of Glycolipids
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Glycolipids are structural lipids that are often present on the extracellular face of eukaryotic cell membranes. There are several forms of glycolipids, including:
Cerebrosides
These glycolipids, also known as glycosphingolipids, are most commonly found in the brain and peripheral nerve tissue. It works as an insulator and is primarily responsible for giving a protective coating to nerve cells.
Gangliosides
These types of glycolipids or glycosphingolipids are neutral compounds composed of residues of sialic acid. They are the primary components of the animal cell membrane and are abundant in the plasma membranes of neurons.
Metabolism of Glycolipids
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The glycolipid metabolism is discussed below
Glycosyltransferases
Glycosyltransferases are enzymes that not only bind the saccharide to the lipid molecule but also help to create the correct oligosaccharide, allowing the appropriate receptor on the cell surface to be activated in response to the presence of the glycolipid.
- The glycolipid is synthesized in the Golgi apparatus and embedded on the surface of a vesicle before being transported to the cell membrane.
- The vesicle connects to the cell membrane, allowing the glycolipid to be visible on the cell's outer membrane.
Glycoside hydrolases
Glycoside hydrolases catalyze the breakdown of glycosidic bonds. They are used to change the oligosaccharide structure of the glycan after it has been attached to the lipid. They can also remove glycans from glycolipids and convert them back into unmodified lipids.
Functions of Glycolipids
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The following are the functions of Glycolipids
Cell – Cell Interaction
Glycolipid's primary function in the body is to act as a recognition sequence for cell-cell interactions.
- The glycolipid saccharide will bind to a complementary carbohydrate or a lectin (carbohydrate-binding protein) of a neighboring cell.
- The interaction of such cell surface markers serves as the foundation for cell recognition and initiates cellular functions that make a contribution to events such as regulation, growth, and apoptosis.
Immune Response
The interaction among both leukocytes and endothelial cells throughout inflammation is an example of how glycolipids function within the body.
- To initiate the immune response, selectins, a type of lectin located on the surface of leukocytes as well as endothelial cells, bind to carbohydrates attached to glycolipids.
- Because of this binding, leukocytes leave circulation as well as congregate near the location of the inflammation.
- This is the first binding mechanism, followed either by the expression of integrins, which establish stronger bonds but also allow leukocytes to relocate to the inflammatory sites.
- Glycolipids are also involved in other responses, such as virus recognition of host cells.
Blood Types
Blood types are examples of how the glycolipids on the cell membranes mediate cell-environment interactions.
- The oligosaccharide connected to a particular glycolipid on the surface of the red blood cells, which behaves as an antigen, determines the four major human blood types (A, B, AB, and O).
- The unmodified antigen, known as the H antigen, is unique to type O and is found on red blood cells of any blood type.
- Blood type A has N-acetyl galactosamine as the primary determining structure, blood type B has galactose, and blood type AB has all three antigens.
- Antigens that are not present in a person's blood cause antibodies to also be produced, which bind to foreign glycolipids.
Types of Blood
Cell Proliferation
Glycolipids have been shown to regulate cell growth through connections with the growth factor receptors.
- Intracellular ceramide stimulates DNA synthesis throughout endothelial smooth muscle cells and platelet-derived growth factor-induced mitogenesis.
- Lactosylceramide activates NADPH oxidase, which modulates the expression of intracellular adhesion molecule-1 on human umbilical vein endothelial cells and induces the proliferation and migration of aortic smooth muscle cells.
Calcium Signalling
Gangliosides have been linked to calcium ions, which are thought to play a role in neuronal function.
- Ganglioside micelles have a high affinity for calcium ions and may play an important role in synaptic transmission.
- Sphingosine and ceramide have been shown to mediate calcium release from intracellular stores.
- Gangliosides could also help with calcium homeostasis and signaling.
- These glycolipids alter cellular calcium by modulating calcium influx streams, calcium transfer proteins, and calcium-dependent enzymes that have been altered by the association of the gangliosides.
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Things to Remember
- Glycolipids are lipids that include carbohydrates, fatty acids, sphingolipids, and even a glycerol group.
- Their role is to keep the cell membrane stable and also to facilitate cellular recognition.
- Glycolipids contain a monosaccharide or oligosaccharide attached to a lipid moiety.
- The structure of a glycolipid is composed of one or two fatty acids bonded to mono- or oligosaccharide groups attached to a sphingolipid.
- Glycosphingolipids and glycoglycerolipids are different types of lipids.
- Several forms of glycolipids are Cerebrosides and Gangliosides.
Sample Questions
Ques. What exactly are macromolecules? Give some examples. (2 Marks)
Ans. Macromolecules are biomolecules formed by the polymerization of a large number of higher molecular weight macromolecules. Because macromolecules are insoluble, they are found colloidally in intercellular fluid. A macromolecule is protein.
Ques. What is meant by protein tertiary structure? (2 Marks)
Ans. It is a structure formed when secondary coiled polypeptides fold to form a hollow, wanton ball-like structure. It is folded in such a way that the functional side groups are on the outside and the inactive side groups are on the inside.
Ques. From your understanding of proteins, could indeed you characterise what happens when milk is transformed into curd or yoghurt? (2 Marks)
Ans. Milk protein, such as casein, is denatured during fermentation, transforming globular protein molecules into fibrous proteins. This transformation is in charge of the production of yoghurt or curd.
Ques. Draw the structure of amino acid alanine’s. (1 Mark)
Ans. Structure of amino acid alanine’s is
Ques. Explain a glycosidic, peptide, and phosphodiester bond. (3 Marks)
Ans. Glycosidic bond: A glycosidic linkage is the bond between both the individual monosaccharides. This bond is formed between two adjacent monosaccharide units' carbon atoms.
Peptide bond: A peptide bond is a type of covalent bond. Protein amino acids are connected to one another via peptide bonds. When condensed, it is formed whenever the carboxyl group (-COOH) from one amino acid comes into contact with the amino group (-NH2) of the adjacent amino acid.
Phospho-Diester bond: A phospho-diester bond is a type of bond that connects consecutive sugar molecules inside a polynucleotide. It is formed by a strong covalent bond between two neighbouring sugar groups as well as phosphate. These are all the bonds that make up the nucleic acid's sugar-phosphate backbone.
Ques. Proteins have a basic structure. Can you relate protein purity or homogeneity to a method for determining that what amino acid is from either of the two termini (ends) of a protein? (3 Marks)
Ans. The structure of a protein refers to its positional information. The first amino acid in a protein is referred to as the N-terminal amino acid, while the last amino acid in a protein is referred to as the C-terminal amino acid.
Yes, we can use this data to determine the pureness or homogeneity of a protein. Amino acids can be acidic, basic, or neutral based on their carboxyl and amino groups. Proteins can be acidic, basic, or neutral in nature.
Ques. Determine how much cellulose is produced by all crops in the biosphere as well as compare it to how much paper is produced by man, and thus what is man's annual consumption of plant material. (3 Marks)
Ans. Out of 170 billion metric tons of total organic matter, the biosphere produces approximately 100 billion metric tons of cellulose. Paper production uses approximately 0.5 billion metric tons of wood. Trees are also used for other purposes such as food, medicine, timber, spices, and so on. It is estimated that 1.5 billion metric tons are required. 2 billion metric tons of wood are required for various purposes. As a result, estimating man's yearly vegetable intake material is difficult. As a result, use of cellulose resulted in a significant loss of vegetation.
Ques. Determine and compile a list of proteins used as therapeutic agents. Look for additional protein applications (e.g., Cosmetics etc.) (3 Marks)
Ans. The set of proteins for use as therapeutic agents is as follows:
Insulin, oxytocin, immunoglobin, ADH, thrombin, fibrinogen, renin, and streptokinase are all hormones.
Other applications include:
- As artificial sweeteners, they are used. Thaumatin is a calorie-free sweetener.
- Proteins are being used as nutritional supplements to help people stay healthy.
- They can be found in creams and shampoos.
Ques. Explain the vital properties of enzymes. (5 Marks)
Ans. Almost every enzyme is a protein. The following are important enzyme properties:
- They are complex macromolecules with a higher molecular weight.
- They catalyse biochemical reactions in the cell, assisting in the breakdown of complex molecules in to the simpler molecules or the joining of two separate molecules to form a larger one.
- Enzymes don't really initiate but rather speed up a reaction.
- They influence the rate of the biochemical reaction but not the guidance of the reaction.
- They are action-oriented.
- Increased enzyme turnover improves the effectiveness of a reaction. The majority of enzymes have a high turnover rate.
- Temperature has an effect on enzymes. Enzymatic activity decreases as temperature rises. Maximum activity is noticed at temperatures ranging from 30 to 40 degrees Celsius.
- Maximum activity is noticed at pH levels of 6-8.
- The enzymatic velocity increases with increasing substrate concentration, reaching maximum velocity.
Ques. Why glycolipids is called cerebroside? (1 Mark)
Ans: Glycolipids are called cerebrosides because of their presence in the brain.
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