Cells and genes

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Cells and Genes

Cells are the basic building blocks of all organisms and they come in a range of shapes and sizes. The largest single cell today is an ostrich egg: the smallest are visible only under the most powerful microscopes. Unlike those of plants, fungi and bacteria, animal cells generally speaking do not have cell walls. Similarly in complex organisms the cells of different organs vary immensely, but in each cell there is a control centre, or nucleus, and cytoplasm which performs the function. All cell nuclei contain DNA, a material which contains four nucleitides, known as A, T, G and C. Different combinations of these letters form genes which encode specific traits. These in turn are organised in strings called chromosomes and the set of chromosomes within a cell governs the way the cell grows and develops. The complete set of genetic material within an organism is termed the genome.