The comparisons and contrast of glycolipids and phospholipids, And its significant role in the cell

Abstract
Phospholipids and Glycolipids are made of fats. They are amphipathic compounds which are important in forming cell membrane Taylor (1997). The Phospholipids provides the basic structure of cell membrane, whereas glycolipids act as cell-cell recognition and receptor sites for chemical signals Taylor (1997). The roles of these molecules are to ensure the structure and stability of membranes Taylor (1997).

Introduction
In the early twentieth century scientists have come to believe that cells are surrounded by thin oil-like layer Loeb (1904). Hugo Fricke also determined that the Lipid Bilayer of the cell membrane was 3.3 nm thick Fricke (1925). However, later analysis shows that this assumption was incorrect, to mean that the cell membrane is a single molecular layer Dooren LJ, (1986). Gorter and Grendel drew correct conclusions that cell membrane is a lipid bi-layer Philip (1993). This theory was confirmed through the use of electron microscope in the late 1950’s.
Fats are formed by condensation reaction between fatty acid and alcohol Taylor (1997). A basic similarity of Phospholipids and Glycolypids is that they both lie in the cell membranes Taylor (1997). They are amphipathic compounds, where the phosphate group is pointing toward intra and extracellular water environment Lodish (2000). The hydrophobic fatty acid tails with the molecules interacts with water, and the other end does not Lodish (2000); as seen below.

      This is an important characteristic in the formation of membranes. Although they are amphipathic, what makes them different is the group attached to them and how their structure is suited to their function in the cell membranes.

Phospholipids make up membranes. Glycolipids are normally found on the outer surface of the cell membrane Buehler (2011). The following diagram shows the structure of a membrane.

 Glycolipids are also abundant in the plasma membrane of eukaryotic cells and are also found in exoplasmic leaflet of membranes H. Lodish (2000).

They are both derivations of fats and elite certain immune reaction. They consist of two long non-polar hydrocarbon tails linked to a hydrophilic head group Lodish (2000).

Fats and oil are made up from fatty acid and glycerol Taylor (1997). Glycerol contains three hydroxyl groups (-OH) Taylor (1997). When glycerol condenses it forms three hydrocarbon fatty acid tails Taylor (1997). The compound formed is called a triglyceride Taylor (1997).  The formation of a phospholipid is formed in a similar way. Phospholipid has a general formula R.COOH, where R represents a medium or long chain of carbon atoms Lodish (2000). In this case, R is a phosphate group Lodish (2000). One of the hydroxyl groups is replaced by a phosphate group, where the other two forms fatty acid tails Taylor (1997).

All phospholipids contains one or more acyl chains derived form fatty acids, which consists of  hydrocarbon chain attached to  a carboxylic group (–COOH)  Lodish (2000). So as a result phospholipids are considered amphipathic Taylor (1997). The phosphate head carries an electrical charge which makes it polar, (hydrophilic) whereas the fatty acid tails are non-polar and are therefore hydrophobic Taylor (1997).

     If phospholipid was spread out on the surface of water, the polar hydrophilic head will project towards the inside and outside of the cell to the aqueous environment; whereas the non-polar end (the fatty acid tails) will project into the air, to form a layer only one cell thick Taylor (1997).

     Let’s say more of this phospholipid was added on the surface of water, or shaken, what would be the arrangement then? Particles known as micelles are formed Taylor (1997). The hydrophobic part of the phospholipid minimizes contact with water by aligning themselves tightly together in the centre of the bi-layer, forming a hydrophobic core Lodish (2000). All phospholipids can pack together into the characteristic bi-layer structure Lodish (2000)

     The close packing of these hydrocarbons is stabilized by Van der Waals interactions Lodish (2000). The hydrophilic part of the phospholipid faces the aqueous environment. Ionic and hydrogen bonds will stable the interactions of the polar head group in the water Lodish (2000).This arrangement forms what we called a phospholipid bi-layer, in which two layers of phospholipidmolecules occur, Taylor (1997). This layer is the formation of cell membranes. Refer to the following picture.

       Glycolipids are formed by the association of lipids with carbohydrates Taylor (1997). They contain a hydrophobic ceramide anchor and a hydrophilic head group made up of saccharides Beuhler (2011).

A major difference between glycolipids and phospholipids lies in the extensive hydrogen bonding capacity of the glycolipids, their phase behavior is dominated by this hydrogen bonding capacity Gabius (2002). In the cell membranes, Glycolypids help to determine the blood type of an individual Del Mar (1972). In the body they play an important role in embryonic development in which the blood type of babies in mother’s womb is shared with the mother’s blood type.

     Glycolipids contain glycoprotein which is protein bonded to sugar molecule Dr. James (1998). Glycolipids work along with this protein bonded-sugar molecules to identify foreign cells Lodish (2000). The receptor site (of the glycolipid) binds to a molecule and recognizes that it is an invader Taylor (1997). They act like cell markers (as in antigen) Taylor (1997). Glycoprotein acts as location in the cell Taylor (1997). They tell your white blood cells that foreign organisms are present in the cell and needs to be destroyed Taylor (1997).

     Receptors present at the surface of the red blood cells classify our blood type (they mark our blood cells). This is why if a patient was suppose to give blood, the recipients immune system will detect and treat the donated blood from the donor as foreign. Foreign antigens are attack by the recipients’ immune system and are destroyed Del Mar (1972).

     Parts of these molecules coat the outer surface of the cell forming chemical configurations that make the surface of the cell unique, different from one type of cell to another, different from one specie to another, and even different from one individual organism to another Del Mar (1972).

     Several glycolipids and phospholipids derived from bacteria, protozoa and other plant species in recent studies found out to be as antigens for NKT cells Tsuji (2006). By a number of studies, Natural Killer T cells are known to play a protective role against cancers and other infectious diseases Tsuji (2006).

     Glycolipids differ from phospolipids because it contains no phosphate group. Glycolipids stand out as a class of its own because of the fact that the fat is connected to a sugar molecule. Dr. James (1998). Therefore, glycolipids are simply fats that are bonded to sugars. Dr. James (1998). 

Reference

·         D.J Taylor et al, (1997) Biological science 1: organisms, energy and environment, United Kingdom, Cambridge

·         Lukas K. Beuhler, (2011) What is Life? Introduction to Metabolic Biochemistry

·         Harvey Lodish, Arnold Berk, et al,(2000) Molecular Cell Biology, New York, Media Connected

·          Del Mar (1972), Biology Today, California, CRM Books.

·         Dr. Ken James (1998), Nutriology-Nutrition for Therapy and Rehabilitation, New Orleans, Paper-mill Press.

·         Tsuji M (2006) et al, Cell and Molecular Life Sciences, USA.

·         H.Gabius and S.Gabius (2002) Glycosciences: Status and Perspectives, Germany, Wiley-VCH.

·         Joeb J (December 1904) The Recent Development of Biology.

·         Fricke H (1925) The Electrical Capacity of Suspensions with Special Reference to blood: Journal of General Physiology.

·         Dooren LJ, Wiedemann LR (1986), On Bimolecular Layers of Lipids on the Chromocytes of the Blood: Journal of European Journal of Pediatrics.

·         Yeagle Philip (1993) The Membranes of Cells (2^nd ed.), Boston, Academic Press.