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1.2. At the heart of the cell: the DNA macromolecule
During the last session, we saw how at the heart of the cell there's DNA in the nucleus, sometimes of cells, or directly in the cytoplasm of the bacteria. The DNA is what we call a macromolecule, that is a very long molecule. It's Avery, in 1944, who discovered that the DNA was the support of genetic information. But the scientists who are most well-known for DNA are Francis Crick and James Watson who discovered together, with Maurice Wilkins and Rosalind Franklin, in 1953, the structure of DNA, the famous double helix, the two strands. Here are Crick and Watson explaining on a very crude wire model far away ... Voir la vidéo
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L'analyse des flux de matières à l'échelle des départements français
... Sabine Barles décrit le métabolisme de 2 régions: Paris et la Loire Atlantique. Elle analyse pour chacune d'entre elles les flux entrant, les flux sortant ainsi que les additions au stock. Sur cette base, elle montre les différences qui... Voir la vidéo
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Le cycle de l'azote à Paris
... contemporaine. Elle s’intéresse en particulier aux interactions entre sociétés et biosphère qu’elle analyse à travers leur métabolisme, base de l’écologie territoriale. Les autres semaines du MOOC Economie circulaire et innovation: « Les grands enjeux... Voir la vidéo
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Le choix de la distribution d'échantillonnage
Le choix de la distribution d'échantillonnage- Cours de statistiques inférentielle - Licence de psychologie deuxième année - Institut d'enseignement à distance. Université Paris 8 Voir la vidéo
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5.3. Building an array of distances
So using the sequences of homologous gene between several species, our aim is to reconstruct phylogenetic tree of the corresponding species. For this, we have to comparesequences and compute distances between these sequences and we have seen last week how we were able to measure the similarity between sequences and we can use this similarity as a measureof distance between sequences. So we will compare pairs of sequences, measure the similarity and store the value of distance, of similarity into what we could call a matrix or an array. Before going further, let's makemore explicit the use of these two terms, they are not equivalentbut some people mix them. The ... Voir la vidéo
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3.3. Searching for start and stop codons
We have written an algorithm for finding genes. But you remember that we arestill to write the two functions for finding the next stop codonand the next start codon. Let's see how we can do that. We are looking for triplets. We use the term triplets as long as wehave no proof that they are codons. You can have triplets outside genes. Within genes, they are called codons. In general, we arelooking for triplets. If you have a sequence like thisone and you are looking for occurrences of this triplet, whatyou have to do is: position your triplet at the beginning of the sequence. Compare the first letter. If it is not ... Voir la vidéo
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3.5. Making the predictions more reliable
We have got a bacterial gene predictor but the way this predictor works is rather crude and if we want to have more reliable results, we have to inject into this algorithmmore biological knowledge. We will use a notion of RBS, RBS stands for Ribosome Binding Sites. What is it? OK. Let's have a look atthe cell machinery or part of it here. You certainly see here that wedeal with a eukaryotes cell. Why? It's because you have anucleus and you remember that the difference between prokaryoticcell and eukaryotic cell lies n the existence of a nucleus. Within the nucleus you have the DNA. The DNA is transcribed into ... Voir la vidéo
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5.2. The tree, an abstract object
When we speak of trees, of species,of phylogenetic trees, of course, it's a metaphoric view of a real tree. Our trees are abstract objects. Here is a tree and the different components of this tree. Here is what we call an edge or a branch. We have nodes, a particular nodeis the root and other nodes are the leaves here terminal nodesand we see that when we draw a tree as an abstract object, we put the root upside and the leaves downside so it's the reverse of a classical natural tree. We need an expression to describe a tree and we will use this kind of expression, how ... Voir la vidéo
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