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Unformatted text preview: Nucleus Prokaryotic cells lack a nucleus; the word prokaryotic means primitive nucleus. Eukaryotic cells, on the other hand, have a distinct nucleus. The nucleus of eukaryotic cells is composed primarily of protein and deoxyribonucleic acid, or DNA. The DNA is organized into linear units called chromosomes, also known as chromatin when the linear units are not obvious. Functional segments of the chromosomes are referred to as genes. Approximately 100,000 genes are located in the nucleus of all human cells. Nuclear proteins belong to a class of proteins called histones. The chromosome is coiled around the histones. The nuclear envelope, an outer membrane, surrounds the nucleus of a eukaryotic cell. The nuclear envelope is a double membrane, consisting of two lipid layers (similar to the plasma membrane). Pores in the nuclear envelope allow the internal nuclear environment to communicate with the cell...
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- Fall '07