| 词汇 | 细胞核 |
| 释义 | 细胞核 For70 years scientists have reasoned that evolution of nucleus was the key to complex life. We are family: Scientists suspect that a large DNA-based virus took up residence inside a bacterial cell more than a billion years ago to create the first cell nucleus. Brown supports scientists who want to create hybrid embryos in which the nuclei of human cells are inserted into animal eggs and allowed to grow for a few days. Previous research has shown that testosterone boosts the number of nuclei in muscle cells beyond the amount produced by working out. Third, the head of a sperm cell is almost all nucleus. Gunderson's team examined individual cells in the wasting muscles and found that there is apoptosis going on, but that other cells are dying, not the muscle fibers or their extra nuclei. “ If you have nuclei that last forever, then you would also have an advantage that could last forever,” Gundersen says. So how do you store all that DNA in a tiny nucleus? However, something similar could probably be made by inserting the nucleus of a human cell into the egg of another species, such as a rabbit. Chromosomes, which are found in the nucleus of a cell, are thread-like structures that contain genes which determine the characteristics of an individual. What has some doctors and ethicists upset is that this so- called nuclear- transfer technique has also been used to produce clones, starting with Dolly the sheep. As the muscle atrophied, the cells deflated to about40 percent of their bulked-up volume, but the number of nuclei in the cells did not change. The difference is the amount of DNA that could be supported in the nucleus, not as repetitive copies of the same old genes, but as the raw material for new evolution. One of its jobs is to act as a messenger carrying genetic information from a cell's nucleus to the machinery which makes proteins. The transmission of an extracellular signal from the surface of the cell to the nucleus by a relay of protein- protein and protein- ligand interactions. Bacteria, rather than having complex nuclei, carry their genes on simple rings of DNA which float around inside their cells. The researchers compared sequences of DNA from the nuclei of African and Asian elephants, and from woolly mammoths and the American mastodon. But the big finding is that the cell nucleus has two compartments— and genes are only active in one. Since the extra nuclei don't die, they could be poised to make muscle proteins again, providing a type of muscle memory, he says. IVF often fails in older women because there are abnormalities in the outside of their eggs, known as cytoplasm, which surrounds the nucleus. This trio can then dock with select segments of DNA in the cell’s nucleus to inappropriately turn on genes that can poison the host animal. The new study suggests that pumping muscles full of nuclei early in life could help stave off muscle loss with age. The technique, which produced the famous sheep Dolly, involves replacing the nucleus of an egg cell with a nucleus from an adult cell that contains new genes, then implanting the egg into a female. To make a cloned embryo would require a human egg into which a cell nucleus from the progenitor could be inserted. The researchers also made what they say are the first sequences of nuclear DNA from the extinct American mastodon. These are the animals, the plants, the fungi and also a host of single-celled creatures, all of which have complex cell nuclei divided into linear chromosomes. |
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