Many eukaryotic cells have a cell wall. The composition of the cell wall differs with each organism. For example, the cell walls of many fungi are composed of chitin cellulose. Chitin is a polysaccharide, which is a polymer of N-acetylglu-cosamine (NAG) units. The cell wall of other fungi is made of cellulose, which is also a polysaccharide. Cellulose is also found in the cell wall of plants and many algae. Yeast has a cell wall composed of glucan and mannan, which are two polysaccharides.
In contrast, protozoa have no cell wall and instead have a pellicle. A pellicle is a flexible, proteinaceous covering. Eukaryotic cells of other organisms (such as animals) that lack a cell wall have an outer plasma membrane that serves as an outside cover for the cell. The outer plasma membrane has a sticky carbo hydrate called glycocalyx on its surface. Glycocalyx is made up of covalently bonded lipids and proteins in order to form glycolipid and glycoprotein in the plasma membrane. Glycolipid and glycoprotein anchor the glycocalyx to the cell, giving the cell strength and helping the cell to adhere to other cells. Glycocalyx is also a molecular signature used to identify the cell to other cells. White blood cells use this to identify a foreign cell before destroying it.
A eukaryotic cell lacks peptidoglycan, which is critical in fighting bacteria with antibiotics. A bacterium is a prokaryotic cell. Peptidoglycan is the framework of a prokaryotic cell's cell wall. Antibiotics such as penicillin attack peptidoglycan resulting in the destruction of the cell wall of a bacterium. Eukaryotic cells invaded by the bacterium remain unaffected because eukary-otic cells lack peptidoglycan.
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