viernes, 16 de diciembre de 2016

QUESTION 25: HOW MANY GENES DOES A HUMAN HAVE?

Until the 1990s, the idea generally accepted by the scientific community was that in the genome of any human could be on the order of 100,000 genes. But as the Human Genome Project was shedding light on our DNA sequence, that number went down. Thus, when in the year 2000 the scientific parents of the Project together with politicians Bill Clinton and Tony Blair presented the first draft of the human genome, the estimate lowered the number of genes to 25,000-30,000. But that draft was only the beginning. Since then we have been working on the huge amount of information obtained and the latest estimates put the number of genes present in each of our nucleated cells in about 20,500.

The next question that should be asked is, are these few or many compared to other living organisms? And the answer can not be any other: they are, exactly, the ones we need. Sometimes - too often - journalists and scientists often play to confront the number of genes, the size of the genome, the number of chromosomes, the similarity between DNA and other characteristics linked to our genetic material with that of some animals for arrive to really absurd situations. And it would be as if knowing that the number of pieces that have a computer we ask ourselves if they are few or many compared to other elements like a motorcycle, a toaster or a mechano. The conclusion we could reach would be as ridiculous as it was meaningless. DNA is the same.

However, in order to satisfy the curiosity of those who may still have it and without the intention of entering into comparisons that we have already said that they can not do, I will show in the following table the number of genes of some species more or less distant from ours.

Species                                                    No. genes
Human being (Homo sapiens)                 20,500
Water flea (Daphnia pulex)                     31,000
Mouse (Mus musculus)                           23,000
Bacteria E. coli                                          4,377
Rice (Oryza sativa)                                  28,000
Yeast (S. cerevisiae)                                  5,800
Fly (Drosophila melanogaster)                17,000
Worm (C. elegans)                                   21,733
Arabidopsis (A. thaliana)                         25,500
Dog (Canis lupus)                                    19,300
Mycoplasma genitalium                               485
EBV virus, which causes mononucleosis      80

QUESTION 12: WHERE IS THE RNA?

Although to answer the question of where the DNA is, we only have to know if we were talking about a eukaryotic cell (with differentiated nucleus) or a prokaryotic cell (without differentiated nucleus), when the question arises for RNA, the answer is complicated. And this is so because there is no single RNA and because the place where it is synthesized and the place where it performs the function that has to fulfill is not always the same.

But, let's start with the simplest case. In prokaryotes, as we have said, there is no nucleus understood as an independent compartment. Therefore, the genetic material is not enclosed in any isolated structure. In this way there is no other possibility than to find the RNA, regardless of the type in question, in the cytoplasm.

In eukaryotes, the situation is more complex. First, we must bear in mind that the synthesis of RNA, whatever the type, is in the nucleus, but the translation of that sequence into a sequence of proteins occurs in the cytoplasm. In addition, both processes (transcription and translation) take place both the maturation of the RNA and its transport to the exterior of the nucleus. Therefore, if we consider that the rRNA and tRNA perform their function in the synthesis of proteins and this takes place in the cytoplasm, it is immediate to conclude that it will be here where we can find them both. On the other hand, the regulatory RNA or RNAs plays an important role in the maturation of the mRNA, and as this is carried out in the nucleus, it will be where we find it. Finally, the mRNA can be found both inside the nucleus and in the cytoplasm. Finding it to a greater or lesser extent inside or outside the nucleus will depend on the half-life of the synthesized mRNA, and this, ultimately, will depend on the maturation process that the molecule has undergone.

QUESTION 3: WHERE IS THE DNA?

DNA is found inside cells, but to answer this question more accurately, it will be necessary to first clarify how many types of cells exist. Thus, considering the presence or absence of nucleus, it can be said that there are two large groups of cells. On one side, the eukaryotic cells (from the Greek eu-karyon, with true nucleus) and on the other side, the prokaryotic cells (from the Greek pro-karyon, withe real nucleus). The basic difference between these two types of cells is that the former have a membranous structure called nucleus, while the latter have no nucleus.

To the group of eukaryotic cells belong the animal cells, vegetables, fungi and an extensive group called protista, in which the microalgae, amoebas, molds are, whereas the group of eukaryotic cells belong both archeobacteria and eubacteria.

Well, in eukaryotic cells the DNA is inside of its nucleus whereas in the prokaryotic cells the DNA is dispersed by the inner región, the cytoplasm. Importantly, considering a eukaryotic organism such as a human, absolutely all somatic cells in his body have the same genetic information -not the germ cells, ova and sperm, which present only half of it-. That is, the DNA that we can find in a somatic cell of a person's eyelid is the same as the one that this same individual will have in a cell of his liver.

A separate mention requires viruses. These are not considered living organisms since they are not capable of performing a number of basic functions by themselves, but they have genetic material that can be in the form of DNA or RNA. In this case, the DNA is located inside a protein structure called capsid.