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Extension task 5

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Introduction

Extension task 5 (b) The terms prokaryote and eukaryote refer to the differences in the location of the DNA. In prokaryotes the DNA is not enclosed by nuclear membranes and lies free in the cytoplasm. The cells therefore lack true nuclei. The cells of eukaryotes, however, do contain true nuclei. Prokaryotic cells are smaller and less complex than eukaryotic cells. Prokaryotic cells have no nuclear membrane; the nuclear membrane is a very porous membrane that allows molecules to easily pass freely from the cytoplasm. The chromosomes in a prokaryotic cell are in direct contact with the cytoplasm. In comparison the chromosomes are enclosed in a double-layered nuclear membrane. They also have a much more complicated chromosome structure compared with prokaryotic cells. The cell division that takes place in a prokaryotic cell doesn't involve the process of meiosis. However, a eukaryotic cell will divide using mitosis and meiosis, yet another difference between these two types of cells. ...read more.

Middle

The prokaryotic cells only contain one type of ribosome of one size. The size of these two types of cells is different too. Eukaryotic cells have up to one thousand times more volume than a prokaryotic cell. Many cells have specialized cytoskeletal structures called flagella and cilia. Flagella usually occur one per organism whereas cilia are present as many, many per cell. Flagella are long, hairlike organelles that extend from the cell, permitting it to move. In prokaryotic cells, such as bacteria, the flagella rotate like the propeller of a motorboat. In eukaryotic cells, such as certain protozoa and sperm cells, the flagella whip about and propel the cell. Cilia are shorter and more numerous than flagella. Cilia use a molecule called kinesin, which has an ATPase activity, i.e. it uses the energy in ATP for its 'engine'. This energy is used to let kinesin bind to microtubules, long molecules present in nearly every eukaryotic cell, used for movement. ...read more.

Conclusion

Centrioles called 'basal bodies' form cilia and flagella. A basal body is like a centriole except that it is found at the base of a cilium or flagellum. Both centrioles and basal bodies are similar in that they consist of an outer ring of nine paired tubulin tubes Cilia and flagella have a similar structure except that in the centre of the ring of tubulin tubes is an additional pair of tubulin tubes. This arrangement is universal among all eukaryotes, such as protists, that have cilia and flagella. Cilia and flagella move in a whip like fashion, which is accomplished using a separate set of proteins that form arms attached to the tubulin. These protein arms allow neighbouring tubulin tubes to slide past each other and bend the cilium. Since eukaryote flagella and cilia move using kinetic energy generated within the structure some scientists have proposed the term undulapodia for these structures to distinguish them clearly from bacterial flagella. Ibrar ...read more.

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