Figure 6.9 The binary fission of a bacterium is outlined in five steps. When the new cell walls are in place, the daughter cells separate. A septum is formed between the nucleoids from the periphery toward the center of the cell. After the chromosomes have cleared the midpoint of the elongated cell, cytoplasmic separation begins. As the cell elongates, the growing membrane aids in the transport of the chromosomes. As the new double strands are formed, each origin point moves away from the cell-wall attachment toward opposite ends of the cell. Replication of the DNA is bidirectional-moving away from the origin on both strands of the DNA loop simultaneously. The starting point of replication, the origin, is close to the binding site of the chromosome to the plasma membrane ( Figure 6.9). The packing proteins of bacteria are, however, related to some of the proteins involved in the chromosome compaction of eukaryotes. As in eukaryotes, the DNA of the nucleoid is associated with proteins that aid in packaging the molecule into a compact size. The single, circular DNA chromosome of bacteria is not enclosed in a nucleus, but instead occupies a specific location, the nucleoid, within the cell. Because of the speed of bacterial cell division, populations of bacteria can grow very rapidly. The cell division process of prokaryotes, called binary fission, is a less complicated and much quicker process than cell division in eukaryotes. This type of cell division is called binary fission. Mitosis is unnecessary because there is no nucleus or multiple chromosomes. In bacterial cells, the genome consists of a single, circular DNA chromosome therefore, the process of cell division is simplified. The genomic DNA must be replicated and then allocated into the daughter cells the cytoplasmic contents must also be divided to give both new cells the machinery to sustain life. To achieve the outcome of identical daughter cells, some steps are essential. In unicellular organisms, daughter cells are individuals. In both prokaryotic and eukaryotic cells, the outcome of cell reproduction is a pair of daughter cells that are genetically identical to the parent cell. For unicellular organisms, cell division is the only method to produce new individuals. Prokaryotes such as bacteria propagate by binary fission. Explain how FtsZ and tubulin proteins are examples of homology.Describe the process of binary fission in prokaryotes.Here, in the cat’s system, the asexual parasite completes the sexual part of its life cycle.By the end of this section, you will be able to: This attraction causes it to seek out places populated with cats, and cat being the natural predator of rat, preys on the infected rat while also consuming the parasite. The parasite induces the production of a chemical within the rat that causes the rat to be attracted to (instead of being repelled by) the odor of cat urine. Mostly rats are carriers of this parasite since they live in sewers and ingest fecal matter. Any warm-bodied animal can be used as the initial host during its asexual phase. It requires two hosts for the completion of its life cycle. This is observed in the case of Toxoplasma gondii. This in turn allows the parasite to manipulate the behavior of the host in order to facilitate its transfer to the next host required to complete its life cycle. The infection by an obligate parasite that follows a complex life cycle modifies the cellular chemistry of the host. This leads to the lysis (death) of the host cell. After the parasite has reproduced itself multiple times, the progeny are released by rupturing the host cell’s membrane. These organisms infect the host cell and utilize the internal-cellular machinery of the host to replicate themselves. In contrast, an obligate parasite not only depends on the host for nutrition, but also for the purpose of reproduction. In other words, it grows and reproduces on its own, but depends on the host cell as a nutrient and energy source. On the other hand, if they penetrate the host cells, they are said to be intracellular parasites, and can be further divided into two types – obligate and facultative.įacultative parasite is an organism that does not rely on the host for completing its life cycle, but displays parasitism to derive nutrition from the host. If the parasitic organisms are present in the extracellular spaces between the cells of the host organism, they are said to be intercellular parasites. Parasites can be broadly divided into two categories based on their location within a host, post infection. It is a theory that explains the evolution of eukaryotes from prokaryotes by the formation of a mutualistic relationship with an intracellular parasite, which later transformed and evolved to become the present-day mitochondria.
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