Protein synthesis is one of the most fundamental biological processes by which individual cells build their specific proteins. Within the process are involved both DNA (deoxyribonucleic acid) and different in their function ribonucleic acids (RNA). The process is initiated in the cell’s nucleus, where specific enzymes unwind the needed section of DNA, which makes the DNA in this region accessible and a RNA copy can be made. This RNA molecule then moves from the nucleus to the cell cytoplasm, where the actual the process of protein synthesis take place.
What is protein synthesis – The details!
All cells function through their proteins. Protein function is defined by their molecular function , localization within cell and involvement in a particular biological process. All components of protein function are defined by the exact composition, structure and conformation of the proteins, which is encrypted within the DNA region (called locus) encoding that protein. With the process of protein synthesis biological cells generate new proteins, which on the other hand is balanced by the loss of cellular proteins via degradation or export.
Transcription is the first of overall two protein synthesis steps. During transcription, the information encoded in the DNA is copied to a RNA molecule as one strand of the DNA double helix is used as a template. The RNA molecule is sent to the cytoplasm, which helps to bring all components required for the actual protein synthesis together – amino acids, transport RNAs, ribosomes, etc. In the cytoplasm the protein polymers are actually “synthesized” through chemical reactions – that is why the process is known as “protein synthesis” or even more precisely – “protein biosynthesis”.
The RNA copy of the protein genetic information encoded in DNA molecule is produced in the nucleus and it is called messenger RNA (mRNA). Each mRNA encodes the information for a single protein and is much smaller in size compared to the DNA molecule. This makes possible for mRNA molecules to exit the nucleus through tiny openings called nuclear pores. Once it exits the nucleus and enters the cytoplasm, the mRNA could interact with a cellular structure known as a ribosome, which serves as the cell’s assembler within the process of protein synthesis. The ribosome consists of proteins and ribosome RNA molecules (rRNA), which are organized in two subunits. The mRNA initially binds to just one of the ribosome sub-units.
When the mRNA interacts with the big ribosome sub-unit, this triggers the approach of another RNA molecule, called transfer RNA (tRNA). The tRNA molecule possess a specific sequence of 3-bases (anti-codon), which hast to complement a corresponding sequence (codon) within the mRNA sequence. When it finds it, it attaches to the mRNA, as the other end of the tRNA is “loaded” with an amino acid. At this point arrives the other sub-unit of the ribosome and a complete structure is formed. The first tRNA binds to a so called “start codon”, which is one and the same for all proteins. As the complete ribosome structure is formed, another tRNA molecule approaches. The next tRNA differ from the first one and is carrying another amino acid. Again, the tRNA must have an anti-codon that matches complementary the second codon of the mRNA. The two amino acids carried by the first two tRNAs are bind together with help from the ribosome and using cellular energy in the form of adenosine triphosphate (ATP).
The above steps repeats until there are uncoupled codon sequences on the mRNA – thus the chain of amino acids grows longer. Once the sequence of amino acids is successfully assembled in a protein, the two ribosome sub-units separate from each other, to be joined again for later use.
The actual sequence of amino acids forms the so called primary structure of the proteins. Depending on the exact composition and order of the amino acids in the protein sequence, the chain folds into a three-dimensional shape. When this happens the protein is complete.
The process of protein synthesis takes place in multiple ribosomes simultaneous and all throughout the cell cytoplasm. A living cell can synthesize hundreds of different proteins every single second.