Ensaio Opcional - 12/03/19
Francis Crick has proposed the central dogma of molecular biology on 1958, however only on 1970 your ideas were published(1). The central dogma is fundamentally based on DNA e how the genetic information flow in biology systems. The genetic information transfers is unidirectional and can be divided in 3 groups: (a) DNA to DNA, process called replication; (b) DNA to RNA, process called transcription; (c) RNA to Protein, process called translation. Besides the unidirectionality of the genetic information, the central dogma has other three main basic rules: (I) it is universal (II) central (III)conservative (due to ribosome sequence conservative in different organism). The genetic code witch is evolve by the central dogma, is a sequence of nucleotides compound by adenine, cytocine, guanine and timine, and different three sets of them determine a 64 possible condon that specify aminoacids (excluding 3 stop codons, remaining 61 codons for 20 aminoacids). The term "degeneration of genetic code" comes from the process that different codons (or synonyms codons) specify the same aminoacid. Considering the 3 codon bases, the wobble position refers to the 3rd nucleotide in a codon, witch is the less conservative and some non-Watson-Crick base paring is usual to occur (3rd base redundancy). Thus, the first two bases in a code shows the specificity, allowing (during the evolution course) more efficiency of translantion with less number of RNAt syntheses. With all this knowledge, it is useful to apply codon usage bias to specify codon witch are more present than other synonyms codon in different species, witch may contribute to molecular evolution(2)
[1]CRICK, F. (1970). Central Dogma of Molecular Biology. Nature, 227(5258), 561–563. https://doi.org/10.1038/227561a0
[2] Behura, S. K., & Severson, D. W. (2013). Codon usage bias: causative factors, quantification methods and genome-wide patterns: with emphasis on insect genomes. Biological Reviews, 88(1), 49–61. https://doi.org/10.1111/j.1469-185X.2012.00242.x
Ensaio 1 - 19/03/2019
Correção Ensaio opcional por Rafaela
The Central Dogma was proposed in 1958 by Francis Crick. It is fundamentally based on DNA and how the genetic information flow in biological systems: (a) DNA to DNA, a process called replication; (b) DNA to RNA, a process called transcription; (c) RNA to Protein, a process called translation. In addition to this unidirectional transfer the central dogma has three other basic rules: (I) it is universal, (II) central and (III) conservative (due to ribosome sequence conservative in the different organism). The genetic code evolved by the central dogma is a sequence of nucleotides composed by adenine, cytosine, guanine, and thymine. Each set of three nucleotides determine a codon, resulting in 64 possible codons that encode 20 amino acids (with the exception of three stop codons). The term "degeneration of genetic code" comes from the process that different codons (called synonyms codons) specify the same amino acid. Considering the three codon bases, the 3rd nucleotide is the less conservative and most usual to occur a non-Watson-Crick base pairing. Thus, the first two bases in a code show the specificity, allowing (during the evolution course) more efficiency of translation with less number of tRNA syntheses. With all this knowledge, it is useful to apply codon usage bias to specify which codon is more present than other synonyms codon in different species, which may contribute to molecular evolution(2)
Ensaio 2 - 26/03/2019
Teoria Neutra da Evolução Molecular
DNA is a molecule constantly changing due polimerase error process, called substitutions and mutations.Mutations fixed within a population is called substitutions and as a consequence of both process, evolution theory can be articulated. For more than one century, evolution theory was based on Darwin's arguments[1]. Basically, genetic variability generated by mutations, affect population fitness due negative selection (natural selection). On the other hand, changes in frequency of alleles over time promote high non-synonyms mutations rates in genome of individuals that are positively selected (adaptation). With molecular advances, Kimura has observed that the majority of evolutionary changes at the molecular level are not caused by selection[2]. The neutral theory of molecular evolution proposes: randomized genetic variation caused by genetic drifs and no functional consequences of them on progeny survival. After fifty years of Kimura's theory, discussions had rebound and no consensus are already established. Some "neutralists" emphasizes how import is to detect how much of the genome is directly or indirectly influenced by natural selection. This test called Mc Donald-Keitman Test (MK)combines polymorphism and divergences data to test action of positive selection against null hypothesis neutral theory)[3]. MK test could be considered more powerfull than dn/ds, which consider only divergence factors.
[1]Darwin, C. On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life (London, John Murray, 1859)
[2] Kimura, M. Evolutionary rate at the molecular level. Nature 217, 624–626 (1968) doi:10.1038/217624a
[3]Kern. A. The Neutral Theory in Light of Natural Selection. Molecular Biology and Evolutuion, 1366-1371(2018)
Ensaio 2 - 02/04/2019
Correção Ensaio opcional por Hugo
Teoria Neutra da Evolução Molecular
A Teoria Neutra da Evolução Molecular propõe que a maioria das mudanças evolutivas no nível molecular não são causadas por seleção natural[2]. Variações genéticas aleatórias causados por drifts genéticos, não têm consequências na sobrevivência da prole. Afirmação bastante polêmica ainda nos dias atuais. Os defensores do neutralismo enfatizam a importância de se quantificar a influência da seleção natural no genoma. Uma métrica utilizada para isso é o Teste MK, que combina polimorfismo e dados divergentes para testar a ação da seleção positiva contra a hipótese nula da Teoria Neutra[3].
Os erros de processamento da polimerase causam alterações constantes no DNA. Mutações são