According to le chatelier's principle, when a change is introduced into a system in chemical equilibrium, the equilibrium shifts?

Yes it shifts depending on if the equation is product or reactant favored. Factors that can determine which way the equilibrium shifts could be pressure, movement, heat, a rise or fall in temperature, a catalyst (only if in the equation already), a gain or loss of a reactant, and a gain or loss of a product

the equilibrium shifts in the direction that relieves the stress on the system

Explanation:

DNA is basically the hard copy. It is double stranded and found in every cell. It contains a library of EVERY single protein that the body makes. Cells supress bits of the DNA because every protein does not apply to every cell. 

mRNA is the portable version that is taaken away from the hard copy to make the actual protein. It is single stranded and codes for 1 protein (although in bacteria one mRNA can code for many proteins). It is the actual bit that gets TRANSCRIBED in the nucleas (copied) and TRANSLATED (written) into proteins in the cytoplasm on ribosomes (which are incidently another form of RNA...rRNA). 

DNA functions include getting copied to every daughter cell too