Cell communication (biology)
In cells, DNA is housed in the nucleus and it never leaves. The DNA within the nucleus is transcribed by tRNA, and the transcriptions of the DNA become RNA. The RNA (ribonucleic acid) leaves the nucleus to float freely around the cytoplasm, and it contains the instructions of the DNA that are vital to the coding, decoding, regulation and expression of genes. The ribosomes then take the RNA messages and turn them into proteins that build cells. When a virus enters a cell and inserts its DNA code into the nucleus, it gets transcribed and released into the cell for the ribosome to make it into a protein. This is how viral infections occur. The cell then explodes with the overproduction of the virus, releasing it into the body to infect any and all other cells it finds. It is theorized that through evolution, cells developed a defense system called RNAi (RNA interference) to stop the production of the proteins that have suspicious mirror image messages of the RNA. They don’t just destroy the suspicious messages, but the correct messages as well to stop all production of that message. This is a cell’s self-destruct mechanism and every cell, plant and animal, have RNAi: a way to turn off the production of a certain gene inside the protein.
Cell nucleus
At a certain point during the cell cycle in open mitosis, the cell divides to form two cells. In order for this process to be possible, each of the new daughter cells must have a full set of genes, a process requiring replication of the chromosomes as well as segregation of the separate sets. This occurs by the replicated chromosomes, the sister chromatids, attaching to microtubules, which in turn are attached to different centrosomes. The sister chromatids can then be pulled to separate locations in the cell. In many cells, the centrosome is located in the cytoplasm, outside the nucleus; the microtubules would be unable to attach to the chromatids in the presence of the nuclear envelope. Therefore, the early stages in the cell cycle, beginning in prophase and until around prometaphase, the nuclear membrane is dismantled. Likewise, during the same period, the nuclear lamina is also disassembled, a process regulated by phosphorylation of the lamins by protein kinases such as the CDC2 protein kinase. Towards the end of the cell cycle, the nuclear membrane is reformed, and around the same time, the nuclear lamina are reassembled by dephosphorylating the lamins.