The process of protein synthesis starts in the nucleus of the cell.
The first step is called "transcription"
The DNA's double helix is unwound so that the enzyme called RNA polymerase can read the DNA template strand, by binding to a region called promoter, and synthesize a single stranded molecule called mRNA.
After the mRNA molecule is synthesized by the RNA Polymerase, it undergoes a series of changed:
- "Splicing": during this process, sections of non coding RNA called "introns" are removed from the strand.
- "Editing" during this process, some nucleotides of the sequence are changed.
- "Polyadenylation" during this process a tail formed by adenine bases is attached to the mRNA string. This tail stabilized and protects the mRNA molecule from enzymatic degradation.
Once the mRNA molecule is ready, it leaves the nucleus and enters the cytoplasm. The mRNA travels to the ribosomes (these can be found free in the cytoplasm or attached to the walls of the endoplasmic reticulum).
Once the mRNA is in the ribosomes the second step of the protein synthesis begins, this phase is called "translation".
In this process, three molecules work together, the ribosomes, the mRNA, and the tRNA. The ribosomes have 3 binding sites, in one site the mRNA binds to the ribosome and the sequence is available for the tRNA to read. Then the tRNA molecules read the sequence of the mRNA and attach the corresponding amino acid, forming a chain of amino acids. This chain represents the primary structure of the protein.
Once the complete sequence of the mRNA was translated into the amino acid chain, the three molecules separate.
The mRNA is recycled into nucleobases, and the ribosome and tRNA are ready to start the translation process with the next mRNA molecule.
Finally, the amino acid chain undergoes several modifications so that the final protein is made.