What Is a Geniculate Nucleus?
Nucleus is the largest and most important cell structure in eukaryotic cells. It is the regulatory center of cellular genetics and metabolism. It is one of the most significant signs that eukaryotic cells are different from prokaryotic cells. Mammalian mature red blood cells, higher plant mature sieve cells, etc.). [1] (Old junior high school textbooks, high school textbooks, or some foreign textbooks think that the nucleus is not an organelle, and university cell biology considers it as an organelle, which is based on university textbooks.) ), Nucleolus, nuclear matrix, etc.
- The nucleus is the main place for the storage, replication and transcription of genetic information in the cell. It was discovered and named by British scientist Brown in 1831. Most are spherical or oval. Usually one or two or more. Separated from the cytoplasm by a double-layered porous nuclear membrane. The nucleus contains nuclear fluid, chromatin (or chromosomes) and nucleoli [2]
- The nucleus is the earliest organelle found.
- The nucleus is the control center of the cell.
- Chromatin and chromosome are not different in chemical composition, but only in different configurations at different functional stages.
- The nuclear backbone is made of fibrin
- From its structure, we can derive the function of the nucleus: controlling the heredity, growth and development of the cell. Germany
- In October 1837,
- The origin of the nucleus remains an unsolved mystery. The main theories so far are: syntrophic model, autogenous model, viral eukaryogenesis model, exomembrane hypothesis, compression and structured hypothesis ( packing and structurization hypothesis), and so on.
- The co-operating model believes that some ancient archaea similar to modern methanogens invaded and lived in bacteria similar to modern myxobacteria, forming early cell nuclei. The similarity of archaea and eukaryotes in specific protein (such as histone) genes is considered to be evidence supporting the theory of archaeal-based nuclear origin.
- The auto-evolution model believes that proto-eukaryotic cells evolved directly from bacteria and did not need to pass through endosymbiosis. The evidence comes from a class of obligate aerobic bacteria-Planctomycete. They have a clear intracellular membrane structure. Among them, there is a sprouting fungus called Gemmata obscuriglobus whose chromatin is surrounded by a double-layered nuclear membrane , Similar to the structure of the nucleus of a eukaryote, while the nucleus of Pirellula staleyi is enveloped by a single layer of the cytoplasmic inner membrane ICM. However, this model does not further explain how verification was developed.
- Viral eukaryotic origin models suggest that viral infection of prokaryotes results in the production of membrane-bound nuclei and other eukaryotic features. The evidence is that there are certain similarities in the macromolecular structure of eukaryotes and viruses, such as linear DNA strands, capping of mRNAs, and tight binding to proteins (the coat of the virus is similar to histones). One of the hypotheses of this hypothesis is that phagocytosis formed the early cellular "predator" and subsequently evolved the nucleus.
- The outer membrane hypothesis believes that the nucleus originates from a single early cell that evolved from the second outer cell membrane, while the inner membrane surrounding the original cell is transformed into a nuclear membrane and gradually evolves a delicate nuclear pore structure to facilitate the internal ( Such as ribosomal subunits) are sent out of the nucleus.
- The compression and structuring hypothesis holds that the nucleus originates from the large size of the prokaryotic cell's genome (including DNA replication errors or doublings, lateral gene transfer methods, endosymbiotic fusion, etc.). The formation of nuclei and the emergence of mitosis are mainly to meet the needs of accurately distributing huge DNA molecules to their offspring. Therefore, how to effectively compress (with the help of histones) long-chain DNA into several chromosomes and how to divide multiple Simultaneous separation of chromosomes (with the help of a spindle) is the key to nuclear evolution. From prokaryotes to eukaryotes, the total amount of DNA in the genome has increased by about 3.5 orders of magnitude, which is surprisingly consistent with the DNA packing ratio of modern eukaryotes. The inner cell membrane system, including the nuclear membrane, is to achieve the orderly control of complex biochemical systems, or to say, ordering is achieved through the internal modularization of cells [2] .