Translational control of gene expression
Translational control of gene expression is the regulation of the process of translation. In other words, this is the control of the conversion of mRNA into a polypeptide chain.
Translational control is most relevant in eukaryotes, as prokaryotic genetic regulation occurs mostly during transcription.
Translational control prevents the cell wasting resources on the production of unwanted proteins.
Translation is mainly controlled through altering the amount of mRNA present within the cytoplasm. Capping and polyadenylation, two types of post-transcriptional modification, are both vital for this.
The cell can control how much of the newly transcribed mRNA receives a methylguanosine cap and poly (A) tail. This in turn dictates how much mRNA enters the cytoplasm and how long it will remain before being broken down.
A type of RNA called small interfering RNA (siRNA) controls the amount of mRNA available for translation. siRNA binds to mRNA and prevents it from being translated.
Some proteins, called translational factors, directly regulate translation by binding to the translational machinery.
These regulatory protein factors can bind to specific sequences on mRNA and prevent ribosomes from attaching. This prevents translation.
Post-translational modification is the alteration of proteins and polypeptides after they have been synthesised.
In many cases, the polypeptide chain (amino acid sequence) produced after translation is not yet a functional protein. It must undergo further modification.
Post-translational modifications include adding functional groups, folding and covalently modifying the protein.
Protein degradation (the breakdown of proteins) is also involved in gene expression. If a certain type of protein becomes too prevalent, digestive enzymes are able to break them down.
Degradation can reduce the levels of certain proteins in cells if the environment changes, or if proteins become old or damaged.
All of these processes are part of the control of gene expression. They ensure that only the required amount of protein is present within the cell.