Transcription and translation

Transcription & Translation 

We are going to try to explain to you the transcription processus 

To forms proteins, the DNA is first transcribed into RNA and then this RNA will be translated into protein.

We will explain how the transcription of DNA takes place.

first, we're going to define the DNA and then we will detail the steps of the transcription. We will continue with the translation and conclude with a global view of this presentation.

I- DNA:

DNA stands for deoxyribonucleic acid, and is the carrier molecule for hereditary genetic information.

Structure of the DNA:

DNA is a very long molecule, composed of a succession of nucleotides.  There are four different nucleotides: adenosine, cytidine, guanosine and thymidine. Each nucleotid is auxiliary which an other. Namely nucleotid A is associated with the T one and nucleotid C with the G.

The DNA consists of two complementary strands helically wound (double helix).

II-The transcription

We are going to explain the different step of the transcription but first of all we have to say that

 From the double-strand of DNA there is creation of a single strand of RNA. This synthetised RNA is auxiliary with DNA strand matrix but thymine is replaced by uracil

DNA is transcribed by RNA polymerase to form messenger RNA

thanks to RNA polymerase

Daniella:

RNA polymerase is composed of 5 subunits (alpha, beta, beta’, omega) with a specific function. They form the enzyme core.

There are two subunit alpha which have to fixe DNA  and assemble subunits beta and beta’

Subunit beta and beta’ contain catalytic site 

While subunit omega structures subunits beta’. 

RNA polymerase requires a sigma transcription factor to recognize the promoter and this forms the holoenzyme

[pic 1]

1) The initiation

First of all RNA polymerase binds to the promoter. The promoter is a part of the noncoding gene that carries the -35 and -10 consensus sequences

RNA polymerase + promoter form the closed complex

Then there is opening of the double helix and formation of the transcription bubble. The complex is then open

Next the sigma subunit dissociates from the RNA polymerase. 

It’s then that the elongation beginning.

2) the Elongation

In prokaryote cells there is only one RNA polymerase even if in eukaryote cells there are three. Moreother it doesn’t need primer. 

During this step the RNA polymerase associated with each nucleotide the nucleotide auxiliary (A-U and C-G)

The RNA polymerase moves on the 5 'to 3' DNA strand and it synthesizes the RNA from 5 'to 3'.

The RNA is synthetised into a simple chain. 

3) The Termination

To stop the transcription The RNA polymerase encounters/meet a termination site on the DNA which indicates the end of the discomfort to be transcribed. 

This site may be dependant or not of a rho factor. 

III- Translation

Now were are going to show you the translation. It allows to transform our strand of RNA into proteins. Ribosomal complex is composed of two subunits a big and a little one. The big subunit is composed of 3 differentes sites P,A,E 

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