VIRUSES (Lectura grado 9)

Viruses are tiny particles composed largely on nucleic acid and protein, but lacking may of the features of living cells. They were discovered in the late nineteenth century, with the observations that the infections agents responsible for small and tobacco mosaic were to small to be seen with the ligth microscope and would even pass through filters that stopped all known bacteria, it was also found that viruses reproduced only inside living cells.

Viruses occupy a estrange limbo somewhere between the living and nonliving worlds. They are like linving organisms in  possesing genetic material, composed of nucleic acids and capable of mutation and recombination. Viruses can be the before evolve and adapt  to their changing enviroments. On the other hands, viruses are not cellular, they have no ribosomes, nor the metabolic machinery of protein synthesis and energy generation.

Lacking these components, viruses can reproduce only inside host cell, and even her there reprodution is unique. Cell reproduce by growing and eventully dividing into to new cell, each containing a complete set of the components needed for life. Viruses, by contrast ares disassembled into their separate nucleic acid and protein components; the host's metabolic machinery then produces a few dozen to hundred of new viral genomes and thousand of protein subunits to make new viral coats, and then these components are assembled into new viral particles. These particles are the same size as the original: unlike cells, viruses do not grow. Another bizarre feature of viruses is that many of them can be crystallized a common enough property of minerals and even of fairly complex organic molecules, but certainly not of living cells. Furthermore, crystalizer viruses, when wetted an exposed to living host cells, soon establih infections and get back to the business of producing more virus particles. As a result of all these odd characteristics, viruses are not considered real living organisms an do not belong in the five kingdoms. Nevertheless, since viruses are active only inside the cells of living organisms, and indeed may have devastating effects on their hosts, the study of viruses is clearly in the province of the biology.

Much of our knowledge of viruses comes from word on bacteriopha-ges (often shortened to phages) viruses that infect only bacteria. Phages have long produced by the millions in cultures of bacteria. With recently developed methods of culturing many of the viruses that infect humans and other animals, a field of obvius economics importance as well as scientific interest.

ACTIVIDAD

1. ¿El virus es un ser vivo? ¿Por qué? Dibújalo y señala sus partes.

2. ¿Cuál es la diferencia entre la reproducción celular y la reproducción viral?

3. Investiga cinco enfermedades de origen viral y descríbalas.