Question: What does mRNA carry?
About the article "RNA", section "In translation".

Candidate passages:
 m6A describes the methylation of the nitrogen at position 6 of the adenosine base within mRNA.
Discovered in 1974, m6A is the most abundant eukaryotic mRNA modification.
The term "epitranscriptome" was coined following transcriptome-wide mappings of m6A sites, but does not necessarily exclude other post-transcriptional mRNA modifications.
m6A methylation regulates nuclear export of mature mRNA and mRNA stability.
How, and in response to what stimulus, the cell endogeneously regulates the level of m6A methylation remains unclear at present.  
Proteins are essential to life.
Cells produce new protein molecules from amino acid building blocks based on information coded in DNA.
Each type of protein is a specialist that usually only performs one function, so if a cell needs to do something new, it must make a new protein.
Viruses force the cell to make new proteins that the cell does not need, but are needed for the virus to reproduce.
Protein synthesis consists of two major steps: transcription and translation.
Transcription is the process where information in DNA, called the genetic code, is used to produce RNA copies called messenger RNA (mRNA).
These migrate through the cell and carry the code to ribosomes where it is used to make proteins.
This is called translation because the protein's amino acid structure is determined by the mRNA's code.
Information is hence translated from the language of nucleic acids to the language of amino acids.
Some RNA genes of viruses function directly as mRNA without further modification.
For this reason, these viruses are called positive-sense RNA viruses.
In other RNA viruses, the RNA is a complementary copy of mRNA and these viruses rely on the cell's or their own enzyme to make mRNA.
These are called negative-sense RNA viruses.
In viruses made from DNA, the method of mRNA production is similar to that of the cell.
The species of viruses called retroviruses behave completely differently: they have RNA, but inside the host cell a DNA copy of their RNA is made with the help of the enzyme reverse transcriptase.
This DNA is then incorporated into the host's own DNA, and copied into mRNA by the cell's normal pathways. 
Messenger RNP (messenger ribonucleoprotein) is mRNA with bound proteins.
mRNA does not exist "in vivo" "naked", mRNA is always bound by many different proteins while being synthesized, spliced, exported and while being translated in the cytoplasm.
When mRNA is being synthesized by RNA polymerase, this nascent mRNA is already bound by RNA 5′ end 7-methyl-guanosine capping enzymes.
Later mRNA is bound by exon and intron definition complexes, and splicing snRNPs.
The spliced mRNA is bound the other set of proteins which help in export from the nucleus to the cytoplasm.
In vertebrates exon-exon junction are marked by exon junction complexes which in the cytosol could trigger nonsense mediated decay if the exon-exon junction is downstream of the stop codon. 
A Transfer RNA (abbreviated tRNA and archaically referred to as sRNA abbreviating "soluble" RNA) is an adaptor molecule composed of RNA, typically 73 to 94 nucleotides in length, that serves as the physical link between the nucleotide sequence of nucleic acids (DNA and RNA) and the amino acid sequence of proteins.
It does this by carrying an amino acid to the protein synthetic machinery of a cell (ribosome) as directed by a three-nucleotide sequence (codon) in a messenger RNA (mRNA).
As such, tRNAs are a necessary component of protein translation, the biological synthesis of new proteins according to the genetic code.
The specific nucleotide sequence of an mRNA specifies which amino acids are incorporated into the protein product of the gene from which the mRNA is transcribed, and the role of tRNA is to specify which sequence from the genetic code corresponds to which amino acid.
One end of the tRNA matches the genetic code in a three-nucleotide sequence called the anticodon.
The anticodon forms three base pairs with a codon in mRNA during protein biosynthesis.
The mRNA encodes a protein as a series of contiguous codons, each of which is recognized by a particular tRNA.
On the other end of the tRNA is a covalent attachment to the amino acid that corresponds to the anticodon sequence.
Each type of tRNA molecule can be attached to only one type of amino acid, so each organism has many types of tRNA (in fact, because the genetic code contains multiple codons that specify the same amino acid, there are many tRNA molecules bearing different anticodons which also carry the same amino acid).
The covalent attachment to the tRNA 3’ end is catalyzed by enzymes called aminoacyl-tRNA synthetases.
During protein synthesis, tRNAs with attached amino acids are delivered to the ribosome by proteins called elongation factors (EF-Tu in bacteria, eEF-1 in eukaryotes), which aid in decoding the mRNA codon sequence.
If the tRNA's anticodon matches the mRNA, another tRNA already bound to the ribosome transfers the growing polypeptide chain from its 3’ end to the amino acid attached to the 3’ end of the newly delivered tRNA, a reaction catalyzed by the ribosome. 
Quantifying gene expression by traditional DNA detection methods is unreliable.
Detection of mRNA on a Northern blot or PCR products on a gel or Southern blot does not allow precise quantification.
For example, over the 20-40 cycles of a typical PCR, the amount of DNA product reaches a plateau that is not directly correlated with the amount of target DNA in the initial PCR.
Quantitative PCR can be used to quantify nucleic acids by two common methods: relative quantification and absolute quantification.
Absolute quantification gives the exact number of target DNA molecules by comparison with DNA standards using a calibration curve.
It is therefore essential that the PCR of the sample and the standard have the same amplification efficiency.
Relative quantification is based on internal reference genes to determine fold-differences in expression of the target gene.
The quantification is expressed as the change in expression levels of mRNA interpreted as complementary DNA (cDNA, generated by reverse transcription of mRNA).
Relative quantification is easier to carry out as it does not require a calibration curve as the amount of the studied gene is compared to the amount of a control housekeeping gene.
As the units used to express the results of relative quantification are unimportant the results can be compared across a number of different RT-Q-PCR.
The reason for using one or more housekeeping genes is to correct non-specific variation, such as the differences in the quantity and quality of RNA used, which can affect the efficiency of reverse transcription and therefore that of the whole PCR process.
However, the most crucial aspect of the process is that the reference gene must be stable.
The selection of these reference genes was traditionally carried out in molecular biology using qualitative or semi-quantitative studies such as the visual examination of RNA gels, Northern blot densitometry or semi-quantitative PCR (PCR mimics).
Now, in the genome era, it is possible to carry out a more detailed estimate for many organisms using DNA microarrays.
However, research has shown that amplification of the majority of reference genes used in quantifying the expression of mRNA varies according to experimental conditions.
It is therefore necessary to carry out an initial statistically sound methodological study in order to select the most suitable reference gene.
A number of statistical algorithms have been developed that can detect which gene or genes are most suitable for use under given conditions.
Those like geNORM or BestKeeper can compare pairs or geometric means for a matrix of different reference genes and tissues.