Eukaryotic cell division organisms

The nuclei of eukaryotic cells contain multiply coiled DNA bound with proteins in bodies called chromosomes. The number of chromosomes varies with the organism. Humans have 46 chromosomes in their body cells (somatic cells) and 23 chromosomes in each germ cell, the eggs and sperm that fuse to initiate sexual reproduction. During cell division, each chromosome is duplicated and the DNA in it is said to be replicated. The production of duplicates of a molecule as complicated as DNA has the potential to go wrong and is a common mode of action of toxic substances. Uncontrolled cell duplication is another problem that can be caused by toxic substances and can result in the growth of cancerous tissue. This condition can be caused by exposure to some kinds of toxicants. 

Prokaryotic microorganisms that are distinct from fungi, which are eukaryotic. Prokaryotic organisms lack a true nucleus. Their DNA is present within the cytoplasm. Bacteria are usually unicellular and have a rigid cell wall. Cell division usually occurs by binary fission. 

The posttranslational modification of proteins is required for the specific function of the proteins, as well as their stability, degradation, and control of various biological processes. For example, certain proteins must be phosphorylated, i.e., one or more PO4 groups are added to the protein chain. After phosphorylation, proteins become active in the signal transduction pathway, cell division, and other systems in an organism. In higher eukaryotes, one third of all proteins are phosphorylated. 

Energy production in mitochondria and the mechanisms behind cell division are very similar in all eukaryotic organisms. Furthermore, some inhibitors of enzymes have so little specificity that many different enzymes in a great variety of organisms may be targets. Many of the pesticides with such general modes of action have considerable historic interest. Not all of them are simple in structure, and many are used for purposes other than combating pests. 

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