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Structure and function of membrane systems in Eukaryotic cells.

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Introduction

Structure and Function of Membrane Systems in Eukaryotic Cells Fatimah Jilani There are two types of basic cells, one of which is the Eukaryotic cell. The eukaryotic cell has a true ('eu') nucleus ('karyo'). The eukaryotic cell contains the following features: * A true nucleus * True organelles which are membrane bound * And the well known plasmamembrane. In this essay, I shall explore the structure and function of cell membranes in eukaryotic cells. There is unknown to biologists any cell that does not have a membrane surrounding it and in eukaryotic cells most of the cell components are surrounded by a membrane too. It is an extremely thin cell structure and is only visible through the electron microscope measuring only up to 10nm thick. However small it is, the membrane makes up and plays an important function in living organisms. Both the cell surface membrane and the membranes surrounding certain organelles have the same basic structure. The cell membrane is made up from a phospholipid bilayer. The phosphate heads are polar molecules and so are water-soluble. The lipid tails are non-polar and therefore are not water-soluble. This means that the phospholipids are arranged with the heads in contact with the cytoplasm or extra-cellular fluid, both of which are watery environments. The tails are protected from this, by being as far from the cytoplasm and extra-cellular fluid as possible. ...read more.

Middle

everything else that would be normally be outside of the cell membrane and therefore the cell would never be able to stay in existence. However much the cells are in isolation cells still need a regular supply of substances required for structural functions and energy sources which are both part of cell life processes. Alongside that, unwanted waste materials need to be removed as well. Furthermore, the plasmamembrane acts a control mechanism controlling the entry and exit of materials and there are various methods of movement across the cell surface membrane and they are the following: * Diffusion * Osmosis * Facilitated Diffusion * Active Transport * Cytosis - Endocytosis and Exocytosis Diffusion is the net movement of molecules or ions from a region of higher concentration to a region of lower concentration. Diffusion occurs because of the constant movement of molecules and ions that bump into each other and then rebound in different directions. The energy needed for this movement is provided by the kinetic energy that each molecule or ion contains. Eventually this movement of molecules/ions will distribute them evenly. Fat-soluble molecules, such as glycerol, can diffuse through the membrane easily. They dissolve in the phospholipid bilayer and pass through it in the direction of the concentration gradient. Water, oxygen and carbon dioxide can also diffuse through the bilayer, passing easily through the temporary small spaces between the 'tails' of the phospholipids. ...read more.

Conclusion

Exocytosis is the movement of substances out of a cell. A vesicle that contain unwanted material moves towards the plasmamembrane and fuses with the cell membrane releasing whatever the contents of that vesicle were to the surroundings. Cytosis adds or subtracts the surface membrane of a cell and a balance is kept to determine the surface area of them membrane. Another important function carried out by the plasmamembrane is to do with cell recognition. Without the recognition of other cells within our body, we would be invaded by microorganisms so it is very important that our cells do so. The features of the cell's membrane that differentiate between cells are the proteins, carbohydrates, glycoproteins or glycolipids. The cells within our body have a certain set of chemicals on the surface and our immune system refers to these as being 'self'. Cells with different surface chemicals are regarded as being 'non-self' and are furthermore attacked. This whole system of cell recognition is yet to be fully discovered however, this is the basic knowledge that we know up to this point in time. Overall it is actually quite amazing to see how an extremely minute component of cell which itself is so small it cannot be seen by the naked eye, can play such important yet complex roles. We are yet to discover more about this cell ultrastructure however it would be of much interest to see what more the cell surface membrane can do. ...read more.

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