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le (5m11s)

1.5. Counting nucleotides

In this session, don't panic. We will design our first algorithm. This algorithm is forcounting nucleotides. The idea here is that as an input,you have a sequence of nucleotides, of bases, of letters, of characters which ends with a star symbol, here. And, you want to count the number of A,C, G and T, and then the frequencies. To write an algorithm in thispseudo code language, you need first to declare on which objector variables you will work. Here, we declare severalinteger variables. What does it mean integer variables? That is a variable, the value of which can be an integer: 1, 2, 3, minus 9 and so on. So, integer ...
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le (4m29s)

1.6. GC and AT contents of DNA sequence

We have designed our first algorithmfor counting nucleotides. Remember, what we have writtenin pseudo code is first declaration of variables. We have several integer variables that are variables which cantake as a value an integer. One, two, three minus five and so on. We have the sequence of characters we want to interpret, declare as a character string oflengths and define. Then we have the initializationof our different variables. This symbol is a symbol for assignment, it means that zero becomes the value of total nb, nbT and soon and so on and here we say: index takes the value one. It means that we position at the beginning of ...
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le (6m7s)

1.7. DNA walk

We will now design a more graphical algorithm which is called "the DNA walk". We shall see what does it mean "DNA walk". Walk on to DNA. Something like that, yes. But first, just have a look again at the typical, also quite short sequence of DNA, a long text offour letters: A, C, G, T, T and so on. When the first sequence of DNA were obtained, the idea of using computers very quickly emerged but people didn't know exactly what to do with this sequence of characters. Again, there is a meaning behind the sequence because it is genetic information. It means it is the information ...
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le (6m25s)

1.8. Compressing the DNA walk

We have written the algorithm for the circle DNA walk. Just a precision here: the kind of drawing we get has nothing to do with the physical drawing of the DNA molecule. It is a symbolic representation. It is a way of representing the information content of the sequence as a drawing. Remember that the problem of the algorithm we designed is that it supposes the capacity of drawing several millions or billions of segments on the screen. This is not feasible. No screen will be large enough for that. So, how can we deal with this hardware constraint? Compression is the answer. Let's see that in more details. Remember, for each ...
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le (9m8s)

1.9. Predicting the origin of DNA replication?

We have seen a nice algorithm to draw, let's say, a DNA sequence. We will see that first, we have to correct a little bit this algorithm. And then we will see how such as imple algorithm can provide biological results. Again, this is the aim of bioinformatics: analysing the genomic texts and providing biological results. So, you remember that we had to deal with the problem of the screen size and for that, we decided to change the first version of the algorithm and we introduced a window of fixed length. And we get this algorithm. So, in this algorithm, we repeat the analysis within the window and ...
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le (6m10s)

2.4. A translation algorithm

We have seen that the genetic codeis a correspondence between the DNA or RNA sequences and aminoacid sequences that is proteins. Our aim here is to design atranslation algorithm, we make thehypothesis that the genetic codehas been implemented as an array as presented in the lastslide of the previous session. We have seen transcriptions and translationsfrom DNA to RNA and proteins. An important thing to notice hereis that most of the time computer scientists and bioinformaticiansjust forget about RNA. When they speak about translating,they say translating from DNA to proteins directly becausethe differences between the DNA and RNA is only T and U sowhat they do is this ...
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le (5m51s)

2.5. Implementing the genetic code

Remember we were designing our translation algorithm and since we are a bit lazy, we decided to make the hypothesis that there was the adequate function forimplementing the genetic code. It's now time to see this lookupfunction but just before that come back on this condition herewhich is a bit more complex than the first attempt in writing the algorithm. Here you see the keyword OR, itmeans that this condition is true if this one is true or thisone is true or this one is true. Why do we need this morecomplex condition? Imagine our sequence and there washere the last triplet we translated. Now we increase our index ...
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