REVIEW. Cholesterol oxidation Health hazard and the role of antioxidants in prevention. ALFONSO VALENZUELA, JULIO SANHUEZA and SUSANA NIETO. STRUCTURE AND FUNCTION OF THE CELL All Materials Cmassengale I. All Organisms are Made of Cells A. The cell is the basic unit of structure function B. The cell. Class Activities STEM Activity Build a Cell Membrane and Color an Animal Cell Animal Cell Color page Build a Membrane. Describe The Role Of The Nucleus In Cell Activities For 5th' title='Describe The Role Of The Nucleus In Cell Activities For 5th' />Describe The Role Of The Nucleus In Cell Activities For ElementaryAre Viruses Alive Scientific American. Editors Note This story was originally published in the December 2. Scientific American. In an episode of the classic 1. The Honeymooners, Brooklyn bus driver Ralph Kramden loudly explains to his wife, Alice, You know that I know how easy you get the virus. Half a century ago even regular folks like the Kramdens had some knowledge of virusesas microscopic bringers of disease. Yet it is almost certain that they did not know exactly what a virus was. They were, and are, not alone. For about 1. 00 years, the scientifi c community has repeatedly changed its collective mind over what viruses are. First seen as poisons, then as life forms, then biological chemicals, viruses today are thought of as being in a gray area between living and nonliving they cannot replicate on their own but can do so in truly living cells and can also affect the behavior of their hosts profoundly. The categorization of viruses as nonliving during much of the modern era of biological science has had an unintended consequence it has led most researchers to ignore viruses in the study of evolution. Finally, however, scientists are beginning to appreciate viruses as fundamental players in the history of life. Coming to Terms. It is easy to see why viruses have been diffi cult to pigeonhole. They seem to vary with each lens applied to examine them. The initial interest in viruses stemmed from their association with diseasesthe word virus has its roots in the Latin term for poison. In the late 1. Because they were clearly biological themselves and could be spread from one victim to another with obvious biological effects, viruses were then thought to be the simplest of all living, gene bearing life forms. Their demotion to inert chemicals came after 1. Wendell M. Stanley and his colleagues, at what is now the Rockefeller University in New York City, crystallized a virus tobacco mosaic virusfor the fi rst time. They saw that it consisted of a package of complex biochemicals. But it lacked essential systems necessary for metabolic functions, the biochemical activity of life. Stanley shared the 1. Nobel Prize in chemistry, not in physiology or medicinefor this work. Further research by Stanley and others established that a virus consists of nucleic acids DNA or RNA enclosed in a protein coat that may also shelter viral proteins involved in infection. By that description, a virus seems more like a chemistry set than an organism. But when a virus enters a cell called a host after infection, it is far from inactive. It sheds its coat, bares its genes and induces the cells own replication machinery to reproduce the intruders DNA or RNA and manufacture more viral protein based on the instructions in the viral nucleic acid. The newly created viral bits assemble and, voil, more virus arises, which also may infect other cells. These behaviors are what led many to think of viruses as existing at the border between chemistry and life. More poetically, virologists Marc H. V. van Regenmortel of the University of Strasbourg in France and Brian W. J. Mahy of the Centers for Disease Control and Prevention have recently said that with their dependence on host cells, viruses lead a kind of borrowed life. Interestingly, even though biologists long favored the view that viruses were mere boxes of chemicals, they took advantage of viral activity in host cells to determine how nucleic acids code for proteins indeed, modern molecular biology rests on a foundation of information gained through viruses. Molecular biologists went on to crystallize most of the essential components of cells and are today accustomed to thinking about cellular constituentsfor example, ribosomes, mitochondria, membranes, DNA and proteinsas either chemical machinery or the stuff that the machinery uses or produces. This exposure to multiple complex chemical structures that carry out the processes of life is probably a reason that most molecular biologists do not spend a lot of time puzzling over whether viruses are alive. For them, that exercise might seem equivalent to pondering whether those individual subcellular constituents are alive on their own. This myopic view allows them to see only how viruses co opt cells or cause disease. The more sweeping question of viral contributions to the history of life on earth, which I will address shortly, remains for the most part unanswered and even unasked. To Be or Not to Be. The seemingly simple question of whether or not viruses are alive, which my students often ask, has probably defi ed a simple answer all these years because it raises a fundamental issue What exactly defi nes life A precise scientifi c defi nition of life is an elusive thing, but most observers would agree that life includes certain qualities in addition to an ability to replicate. For example, a living entity is in a state bounded by birth and death. Living organisms also are thought to require a degree of biochemical autonomy, carrying on the metabolic activities that produce the molecules and energy needed to sustain the organism. This level of autonomy is essential to most definitions. Viruses, however, parasitize essentially all biomolecular aspects of life. That is, they depend on the host cell for the raw materials and energy necessary for nucleic acid synthesis, protein synthesis, processing and transport, and all other biochemical activities that allow the virus to multiply and spread. One might then conclude that even though these processes come under viral direction, viruses are simply nonliving parasites of living metabolic systems. But a spectrum may exist between what is certainly alive and what is not. A rock is not alive. A metabolically active sack, devoid of genetic material and the potential for propagation, is also not alive. A bacterium, though, is alive. Although it is a single cell, it can generate energy and the molecules needed to sustain itself, and it can reproduce. But what about a seed A seed might not be considered alive. Yet it has a potential for life, and it may be destroyed. In this regard, viruses resemble seeds more than they do live cells. They have a certain potential, which can be snuffed out, but they do not attain the more autonomous state of life. Another way to think about life is as an emergent property of a collection of certain nonliving things. Both life and consciousness are examples of emergent complex systems. They each require a critical level of complexity or interaction to achieve their respective states. A neuron by itself, or even in a network of nerves, is not consciouswhole brain complexity is needed. Yet even an intact human brain can be biologically alive but incapable of consciousness, or brain dead. Similarly, neither cellular nor viral individual genes or proteins are by themselves alive. The enucleated cell is akin to the state of being braindead, in that it lacks a full critical complexity. A virus, too, fails to reach a critical complexity. Breaking Bad Season 4 Free Watch Online. So life itself is an emergent, complex state, but it is made from the same fundamental, physical building blocks that constitute a virus. Approached from this perspective, viruses, though not fully alive, may be thought of as being more than inert matter they verge on life. In fact, in October, French researchers announced fi ndings that illustrate afresh just how close some viruses might come.