Asexual reproduction takes place when ample nutrients are available, while sexual reproduction takes place under conditions of starvation. Paramecia can reproduce either asexually or sexually, depending on their environmental conditions. "In other words, if something foreign got into the micronuclear genome, then when the next macronucleus is made, it would removed and not included in the expressed version of the genome." Forney notes that this has been described by some as a primitive DNA immune system that is, surveying the genome and trying to keep out invading elements. "In the case of ciliates, there's a mechanism in which, if a piece of DNA is in the micronucleus but it's not in the macronucleus, it will be removed from the next macronucleus that is made," Forney explained. Why the presence of two distinct nuclei? One evolutionary reason is that it is a mechanism by which paramecium and other ciliates can stave off genetic intruders: pieces of DNA that embed themselves into the genome. He gives the example of the Paramecium aurelia species complex, which have two micronuclei and Paramecium multimicronucleatum, which have several. However the number of micronuclei can vary by species. (Image credit: Designua Shutterstock )Īll paramecium species have one macronucleus, according to Forney. "So it's the nucleus that is transcribed to make mRNAs and proteins from those mRNAs." The macronucleus is polyploid, or contains multiple copies of each chromosome, sometimes up to 1000 copies, according to Encyclopedia of Microbiology. "It is the transcriptionally active nucleus," he added. On the other hand, the macronucleus contains a subset of DNA from the micronucleus, according to Forney. "It's the DNA that is passed from one generation to the another during sexual reproduction," he said. Forney notes that the micronucleus contains all of the DNA that is present in the organism. The micronucleus is diploid that is, it contains two copies of each paramecium chromosome. The two types of nuclei are the micronucleus and macronucleus, according to the Encyclopedia of Microbiology. "They have two types of nuclei, which differ in their shape, their content and function." " Paramecium along with the other ciliates have this rather unique feature," said James Forney, a professor of biochemistry at Purdue University. Perhaps the most unusual characteristic of paramecia is their nuclei. When the contractile vacuole collapses, this excess water leaves the paramecium body through a pore in the pellicle. Depending on the species, water is fed into the contractile vacuoles via canals, or by smaller water-carrying vacuoles. Contractile vacuoles are responsible for osmoregulation, or the discharge of excess water from the cell, according to the authors of " Advanced Biology, 1st Ed." (Nelson, 2000). They then fuse with organelles called lysosomes, whose enzymes break apart food molecules and conduct a form of digestion. Food vacuoles encapsulate food consumed by the paramecium, according to the University of Chicago. These are membrane-enclosed pockets, which in plants and animals handle waste product, store water and offer structural support for cells, according to the National Human Genome Research institute Vacuoles take on specific functions with a paramecium cell. This region contains the majority of cell components and organelles, including vacuoles. Research published in the journal Zoological Science found that trichocysts of Paramecium tetraurelia were effective against two of the three predators that were tested: the Cephalodella species of rotifers and the Eucypris species of arthropods.īelow the ectoplasm lies a more fluid type of cytoplasm: the endoplasm. Trichocysts are a network of telescopic organelles that are used to repel and shield from any predatory attacks and propel the paramecium in unpredictable directions, according to Cell Biology magazine. When they discharge their contents, they become long, thin and spiky, according to "Biology of Paramecium." This region consists of spindle-shaped organelles known as trichocysts. Under an external covering called the pellicle is a layer of somewhat firm cytoplasm called the ectoplasm. However, the organism also contains some unique organelles. Paramecia have many organelles characteristic of all eukaryotes, such as the energy-generating mitochondria. The defining features of eukaryotic cells are the presence of specialized membrane-bound cellular machinery called organelles and the nucleus, which is a compartment that holds DNA, according to Washington University. In contrast to prokaryotic organisms, such as bacteria and archaea, eukaryotes have well-organized cells. (Image credit: Getty Images) Cell structure Paramecium and amebae under a microscope.
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