The eucaryotic cell

We have already seen that eucaryotic cells are, for the most part, larger and much more complex than procaryotes, containing a range of specialised subcellular organelles (Figure 3.13). Within the microbial world, the major groups of eucaryotes are the fungi and the protists (protozoans and algae); all of these groups have single-celled representatives, and there are multicellular forms in the algae and fungi.

Our survey of eucaryotic cell structure begins once more with the genetic material, and works outwards. However, since many internal structures in eucaryotes are enclosed in a membrane, it is appropriate to preface our description by briefly considering eucaryotic membranes. These are, in fact, very similar to the fluid mosaic structure we described earlier in this chapter, as depicted in Figure 3.5. The main difference is that eucaryotic membranes contain lipids called sterols, which enhances their rigidity. We shall consider the significance of this when we discuss the plasma membrane of eucaryotes below. Cholesterol, which we usually hear about in a very negative context, is a very important sterol found in the membranes of many eucaryotes.

TUMBLE

Figure 3.12 Running and tumbling. Anticlockwise rotation of the flagellum gives rise to 'running' in a set direction. Reversing the direction of rotation causes 'tumbling', and allows the bacterial cell to change direction

Figure 3.13 This example of eucaryotic cell structure shows a plant cell. Other eucaryotic cells may differ with respect to the cell wall and the possession of choroplasts. Note the much more elaborate internal structure compared to a typical procaryotic cell (Figure 3.3), in particular the presence of membrane-bounded organelles such as mitochondria, chloroplasts, endoplasmic reticulum and a true nucleus. From Nicklin, J, Graeme-Cook, K & Killington, R: Instant Notes in Microbiology, 2nd edn, Bios Scientific Publishers, 2002. Reproduced by permission of Thomson Publishing Services

Figure 3.13 This example of eucaryotic cell structure shows a plant cell. Other eucaryotic cells may differ with respect to the cell wall and the possession of choroplasts. Note the much more elaborate internal structure compared to a typical procaryotic cell (Figure 3.3), in particular the presence of membrane-bounded organelles such as mitochondria, chloroplasts, endoplasmic reticulum and a true nucleus. From Nicklin, J, Graeme-Cook, K & Killington, R: Instant Notes in Microbiology, 2nd edn, Bios Scientific Publishers, 2002. Reproduced by permission of Thomson Publishing Services

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