The most important idea is that the genetic material of any organism must be able to accurately replicate itself at least every generation (or for multicellular organisms at each cell division).
Base pairing (A-T or U and C-G)allows DNA and RNA (eg in polio virus, see Wikipedia page on RNA dependent RNA polymerase) to create a copy of themselves, when the appropriate enzymes are present. Proteins have no way of making a copy of themselves.
Stability is probably the main reason DNA is the most common genetic material. DNA has no enzymatic activity and was probably selected for to maintain the integrity of the genetic material (rather than having to perform a function for the cell/virus, during which it may be destroyed). The double helix structure also protects its integrity, and proofreading enzymes have also evolved which correct most of the mistakes made at DNA replication. RNA viruses don't have this mechanism- which could be said to be an advantage (as they can rapidly change and therefore avoid their hosts' immune systems), however in non-parasitic organisms most mutations in a gene would lead to a loss of an essential function and the extinction of that genome.
I don't think either of these reasons are relevant, but I think the main reasons retroviruses convert their RNA to DNA are so they can use the host cell's replication machinery (this was they do not need to encode as many genes), and secondly they need avoid the antiviral mechanisms of the cell, which would destroy any double stranded RNA molecules found (even if the virus was single stranded, dsRNA would have to be produced at replication).
Normal cells have a reset phase where they don't divide if there is n need for them unlike cancer cells where they divide rapidly and they don't have that reset phase
Of course, this is not true. An important function of the stomach is to serve as a temporary holding chamber. You can ingest a meal far more quickly than it can be digested and absorbed by the small intestine. Thus, the stomach holds food and parses only small amounts into the small intestine at a time.
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Explanation:
En biología, se llama organismo o ser vivo a un individuo singular y diferenciado, compuesto por un conjunto de materia orgánica jerarquizada y especializada. Lo constituyen sistemas de transmisión y comunicación bioquímica, que le permiten conservar su equilibrio interno a la vez que intercambiar materia y energía con el entorno que lo rodea. Dicho en otras palabras, un organismo es una entidad viviente, dotada de la capacidad de nutrirse, crecer, reproducirse y morir.
Todos los organismos conocidos, con excepción de los virus, están formados por células, y poseen un metabolismo que les permite garantizar su existencia y dar pie a sus procesos biológicos a cambio de intercambiar energía con el medio ambiente. El fin último de todo organismo parece ser la reproducción, esto es, la perpetuación de su especie y la transmisión de su material genético (herencia).
Químicamente hablando, los seres vivos se distinguen de la naturaleza que los rodea en su composición casi exclusiva a base de carbono, hidrógeno, oxígeno y nitrógeno, es decir, a base de moléculas orgánicas, estructuradas de manera muy diferente a las moléculas inorgánicas de la materia inerte.
