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Table of Contents
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Optional Essay (12/03)
The Central Dogma
Dogma can be understood as a fixed idea that seems to be true, a belief. In molecular biology, the term central dogma was coined by Francis Crick in 1958, but this idea generated many contradictions, even in the author's own view. Considering that this idea plays an important role in the transfer of genetic information, Cricks in his work of 1970, decided to establish a new concept to the term "dogma". He emphasizes that previous analyzes had shown that the genetic information transfer system (DNA-RNA-Protein) could be divided into three groups, but at the time, none of them were explicitly expressed. Crick had a critical view about these groups, so he determined four points to formulate his concept of central dogma. He proposed three ideias that he called "general transfer, special transfer and unknown transfer". Finally, Cricks states that such information can not be transferred back from the protein to proteins or nucleic acids, the genetic information is a flow that starts in the DNA, is transferred to the RNA that makes as final product a protein.
Essay 1 - Comentários por Maria Catarina
The Central Dogma of Molecular Biology plays an important role in the understanding transfer of genetic information. Crick in his work of 1970, emphasizes that information can not be transferred back from the protein to proteins or nucleic acids, the genetic information transfer system flow occurs in the direction of DNA to RNA to Protein.
PS: In the first essay the teacher said that it had no theme, so I did not write about the Central Dogma
Essay 2 (26/03)
The Neutral Theory
The Neutral Theory of molecular biology suggests that evolutionary changes in populations results from mutations and genetic drift, not from natural selection. Kimura (1968) states that "the rate of radom fixation of neutral mutation in evolution (per species per generation) is equal to the rate of neutral mutations (per gamete per generation)".
In coding sequences of protein, changes between codons that encode the same amino acid (synonymous substitutions) are more frequent than changes leading to replacement of amino acids (non-synonymous substitutions). Most noncoding sequences evolves at a higher rate. These observations are contrary to the theory of natural selection. Regions that do not affect the phenotype has a smaller diference when the selection fixes the majority of substitutions.
Essay 3 (02/04) - Comentários por Letícia
- O texto está muito bom. Com frases curtas e objetivas
- Fiquei com dificuldade de entender a última frase "Regions that do not affect (…)". Acredito que tenha ficado ambígua.
Essay 4 (30/04)
Phylogenetic trees
Phylogenetic trees, which are the basis of Systematics, are hypothetical diagrams that represent evolutionary relationships among organisms. These cladograms are frequently misunderstood among scientists and / or educators. Prior knowledge of evolution is necessary to understanding a phylogenetic tree. The pattern in which the branches connect represents our understanding of how the species evolved from hypothetical common ancestors. Each node represents the last common ancestor of all descendant groups from this point forward.
The ability to read a phylogenetic tree is conceptualize evolution in phylogenetic terms. Unfortunately, many biologists are graduating without this basic knowledge, which leads them to misinterpretations of historical reconstructions. As a consequence, this is perpetuated for every generation of students who can not understand how and why organisms are related.
Essay 5 (07/05) - Comentários por Tamires Andrade
- O texto está muito bom e objetivo, mas acredito que a organização das frases poderia estar diferente, contextualizando melhor a ideia geral. O começo do parágrafo explica o que é a árvore da vida, e neste momento, a frase que explica o que cada nó representa já poderia estar conectada. A partir disso, a explanação sobre dificuldade de entendimento por parte de alguns cientistas poderia ser incluída.
Essay 6 (14/05)
Autoavaliação da escrita
As principais dificuldades que notei em relação a minha escrita foram ambiguidade, melhorar a contextualização das ideias, bem como a organização das frases. Notei que em alguns momentos o que estava claro para mim não estava lógico para o meu leitor.
Dentre as dificuldades que percebi em relação aos outros colegas, estão a ocorrência de frases longas, falta de direcionalidade na escrita e organização das ideias. Em alguns textos notei que a pessoa que estava escrevendo, não voltou para conferir a escrita, deixando o texto sem direcionamento.
Essay 7 (21/05)
Methods of tree-reconstruction
Nowadays, reconstruction of phylogenies often comprises nucleotide or aminoacid sequences. However, different types of molecular data can be used on this approach. As a consequence, scientists developed numerous methods of reconstruction trees in order to find the optimal tree and obtain measurements for every branch. The neighbour-joining algorithm is one of the most traditional method. It is a fast distance method to see if there is a relationship between evolutionary distance and a measure of pair-wise similarity between the lineages. The second popular approach is the parcimony, which utilizes character states to reconstruct the phylogenies. This method chooses the tree(s) with the fewest number of homoplasies. Recently, many researchers are also using the maximun likelihood approach. This is a statistical framework applied when we are assuming a stochastic model of evolution. Likelihood methods measure the probabilities of character state changes along a tree. These are the most used methods, but many others are useful to tree-reconstruction. There is no right or wrong approach, it is going to depend on the choice of your set of data and what you want to show on a tree.
Avaliação 2 - Tema 1
Outline (28/05)
- Arcabouço conceitual
- O que a sistemática hennigiana trouxe para a Evolução?
- Ruptura ou mudança dentro do paradigma filogenético?
- Considerações finais
Construção parágrafos Avaliação 2 (04/06)
Parágrafo 1: Definição de sistemática filogenética. Sistema de classificação. O que os cladogramas nos informam.
Phylogenetic systematics is a tool that provides more complete studies of comparative biology. A cladogram can be used as the basis for a classification system, as well as for tracing the biogeography of a group (Nelson & Platinik 1981)……
Parágrafo 2: Papel da proposta filogenética de Hennig.
Hennig (1950, 1966) based his method on the evolutionary history of the groups. Biological classifications had to reflect the kinship relationships between living beings, using the concept of common ancestry as the basis for the identification of monophyletism…..
Parágrafo 3: O que mudou na forma como a história evolutiva era contada.
Parágrafo 4: Como as novas técnicas de análise estão influenciando a reconstrução filogenética
Parágrafo 5: Conclusão.
Self-evaluation (11/06)
A disciplina me ofereceu um suporte de quais tópicos devo me aprofundar para seguir aprendendo sobre o assunto. Porém, esperava que o conteúdo de molecular fosse ser mais aprofundado, visto que já possuo um conhecimento sobre sistemática filogenética. Senti que já deveria ter vindo com os conceitos básicos de evolução molecular. Além disso, senti falta de mais ilustrações, pois meu tipo de aprendizado se baseia no visual. Talvez os tópicos apresentados deveriam ser explicitados mais claramente na ementa da disciplina.
Os textos disponibilizados com antecedência é um ponto muito positivo, porém acho que alguns deles deverão ser discutidos em sala de aula, através de uma leitura prévia por parte dos alunos. Acho que dessa forma, a discussão seria mais calorosa e com mais embasamento por parte da turma. A organização da aula também foi muito boa e concordo com a ordem que foi proposta do meio da disciplina para o fim, com os seminários no início e a aula expositiva no final. Concordo com o ponto de que os essays deveriam ser feitos em casa, porém com as correções feitas em sala, para gerar uma discussão em pares.
Nota autoavaliação: 1