In one laboratory experiment, bacteria exposed to high levels of pathogenic bacteria over several hundred generations eventually adapted "their progeny became dependent on having the formerly pathogenic bacteria in food vacuoles...(Jeon, 1991)" (Armstrong) There are several ways in which bacteria may subsume other bacteria, including ingesting them and maintaining them in food vacuoles as in the Jeon experiment, or they may become infected by bacteria that are acting as parasites. Mitochondria, for example, could have been parasitic and fed off the host at the same time that they proved useful to it. Chloroplasts, because they are significantly self-supporting, are more likely to have been introduced as food. This theory continues to suggest that after many generations of true symbiosis, the mitochondria and chloroplasts lost their independence. If the endosymbiosis theory was correct, there are many things which should hypothetically prove true in experimentation. For example, it should be evidenced that single-celled organisms can indeed subsume other organisms and become dependent upon them for survival, and that subsumed organisms can surrender their own DNA and become dependent. These have both been seen to be true. For example, Margulis and Swartz found "an anaerobic organism that has adapted...
"Gene loss is also known to have happened in other endosymbiotic organisms, like Buchnera aphidicola, a symbiont of aphids that supplies "essential" amino acids and other nutrients to their hosts, and Rickettsia prowazekii, which causes the disease typhus." (Smith et al.) Another test would be to see whether or not the membranes surrounding the organelles appear to have originated as vacuoles formed from the introduction of foreign matter to the cell. Once again, the findings are consistent with the outer membrane surrounding these organelles having what appears to be an exterior side facing inward toward the mitochondria's second membrane, and its interior side touching the rest of the cell. The appearance of differently sized ribosomes, independent reproduction and movement of these organelles, and the lack of intermediate stages all also point to this conclusion.
Stem cells are cells that can develop into other forms of cells; Evans's cells could develop into entire mice. Evans eventually began altering the genetic material in the stem cells, creating mice that had genetic material from other creatures and could pass that material on to their offspring" (313). These findings, together with the research conducted separately by Capecchi and Smithies, enabled several teams of researchers to develop knockout
G Protein-Linked Receptors An organism must respond appropriately to its internal and external environments day after day in order to survive. The organism's cells respond to internal and external stimuli much like tiny computers that process numerous inputs and also produce numerous outputs in daily existence (Kennedy 2004). These stimuli are signals that come from the general environment or the cells of other or co-existing organisms, proximate or distant, and this
In the tissue culture, they usually proliferate indefinitely. The normal constraints which limit the growth of the cells absent in the cancerous state and are also characterized by the division ability for number of generations which is unlimited. Cell cycle and cancer With millions of chemical reactions taking place concurrently and in specific areas, the human body can be thought of as a small laboratory. It is the only "machine" with
Cell Junctions - Tight Junctions and Adherens Junctions There are a number of specialized junctional complexes in epithelial cells, formed by molecules that are different from CAMs and SAMs. These comprise of tight junctions, gap junctions, adherens junctions, and desmosomes; gap junctions can in addition form stuck between cell aggregates in condensing mesenchyme. All of these are well-formed and sometimes elaborate supramolecular structures carrying out various functions, ranging from electrical and
CELL & ITS COMPONENTS Biology Biologists, researchers, and professionals of many disciplines study the nature of the cell. The drive to understand the nature of the cell aligns with urges to understand the nature of the atom, the molecule, DNA and other entities of astronomically small size. In many instances, studying the extremely small provides profound insight and clarification on how bodies of much larger sizes including societies and galaxies work
They are composed of a double membrane, one side of which separates it from the cytosol, and the other side of which contains the material that it is transporting. Their membranes can be joined with the plasma membrane to deliver material into and out of the cell, and can be fused with other organelles to gather material for digestion, storage, or transport. Cilia: Along with the flagella, the cilia are
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