The second function of DNA is to provide the information needed to construct the proteins necessary so that the cell can perform all of its functions.
A process called translation takes the code from the mRNA to form aProtein.
Through the processes of translation and transcription, a specific sequence of amino acids in the DNA is used to build a new molecule.
The details of transcription are discussed in this module.
The flow of genetic information in cells is described by the central dogma, which states that genes specify the sequence of mRNAs, which in turn specify the sequence of proteins.
The central dogma states that there is a difference between the two.
One nucleotide is added to the mRNA strand for every other nucleotide in the DNA strand.
The translation is more complex because of the groups of three mRNA nucleotides.
In the next module, we will see that the translation is still systematic, such that the first, second, and third letters of the alphabet correspond to the first, second, and third letters of the alphabet.
The same process of transcription is performed by both prokaryotes and eukaryotes.
The nucleus of the cell has genes bound in it and the transcript must be taken to the cytoplasm.
The prokaryotes, which includebacteria and archaea, don't have a nucleus and transcription occurs in the cell's cytoplasm.
The region of mRNA synthesis is partially undone by the double helix.
In most cases, the genes they regulate are upstream of the promoter's genes.
The specific sequence of a promoter is very important because it determines whether the corresponding gene is transcribed all of the time, some of the time, or hardly at all.
When DNA is not wound, it forms a transcription bubble.
The promoter is involved in transcription.
The core enzyme is rewound behind the unwound DNA as elongation proceeds.
During the process of elongation, the polymerase tracks along the DNA template, synthesizing the mRNA in the 5' to 3' direction, and then rewinding the DNA as it is read.
Once a gene is transcribed, the prokaryotic polymerase needs to be told to free the newly made mRNA.
Depending on the genes being transcribed, there are two types of signals, one of which involves repeated nucleotides in the DNA template and the other of which involves freeing the transcript.
The process of transcription is done.
The transcript would already have been used to synthesise multiple copies of the encoded protein because the processes can occur concurrently using multiple ribosomes.
The presence of a nucleus precludes simultaneous translation and transcription.
Multiple genes can be transcribed by multiple polymerases and multiple ribosomes at the same time.
A high concentration of a specificProtein can be reached in this way.
The newly transcribed eukaryotic mRNAs must undergo several processing steps before they can be transferred from the nucleus to the cytoplasm.
A molecule that is more stable than a prokaryotic one is created by the additional steps in the maturation process.
The typical prokaryotic mRNA lasts no more than five seconds.
While the transcript is being processed and exported out of the nucleus, it is first coated in a protective coating.
While the pre-mRNA is being synthesised, a special nucleotide cap is added to the 5' end of the transcript.
The cap helps initiate translation by ribosomes and is involved in preventing synthesis.
The poly-A tail is the result of 200 adenine residues being added to the 3' end.
The modification protects the pre-mRNA from degradation and signals to cellular factors that the transcript needs to be exported to the cytoplasm.
During the processing of the pre-mRNA, introns are removed.
Functional proteins are not found in the intron sequence.
All of the pre-mRNA's introns need to be removed before the exons can code for the correct amino acids.
The sequence of the rejoined exons would be shifted if the process deviated from a single nucleotide.
While the pre-mRNA is in the nucleus, introns are removed and degraded.