Protein synthesis is a very important process. It is he who helps our body grow and develop. It involves many cell structures. After all, first you need to understand what exactly we are going to synthesize.
What protein needs to be built at the moment - enzymes are responsible for this. They receive signals from the cell about the need for a particular protein, after which its synthesis begins.
Where is protein synthesis
In any cell, the main place of protein biosynthesis is the ribosome. This is a large macromolecule with a complex asymmetric structure. It consists of RNA (ribonucleic acids) and proteins. Ribosomes can be located one by one. But most often they combine with EPS, which facilitates the subsequent sorting and transport of proteins.
If ribosomes are sitting on the
endoplasmic reticulum , it is called a rough EPS. When translation occurs intensively, several ribosomes can move along one matrix at once. They follow each other and in no way interfere with other organelles.
What is needed for protein synthesis
For the process to take place, it is necessary that all the main components of the protein synthesizing system are in place:
- A program that sets the order of amino acid residues in the chain, namely, mRNA, which transfers this information from DNA to ribosomes.
- Amino acid material from which a new molecule will be built.
- The tRNA that delivers each amino acid to the ribosome will take part in decoding the genetic code.
- Aminoacyl-tRNA synthetase.
- Ribosomes are the main site of protein biosynthesis .
- Energy.
- Ions of magnesium.
- Protein factors (for each stage its own).
Now we will consider each of them in more detail and find out how proteins are created. The biosynthesis mechanism is very interesting, all components act unusually harmoniously.
Synthesis program, matrix search
All information about which proteins our body can build is contained in DNA. Deoxyribonucleic acid is used to store genetic information. It is securely packed in the chromosomes and is located in the cell in the nucleus (if we are talking about eukaryotes) or floats in the cytoplasm (in prokaryotes).
After DNA research and recognition of its genetic role, it became clear that it is not a direct matrix for translation. Observations have suggested that RNA is associated with protein synthesis. Scientists decided that it should be an intermediary, transfer information from DNA to ribosomes, serve as a matrix.
At the same time, ribosomes were discovered; their RNA makes up the vast majority of cellular ribonucleic acid. To check whether it is a matrix for protein synthesis, A. N. Belozersky and A. S. Spirin in 1956-1957. conducted a comparative analysis of the composition of nucleic acids in a large number of microorganisms.
It was assumed that if the idea of a DNA-rRNA-protein scheme is correct, then the composition of total RNA will change in the same way as DNA. But, despite the enormous differences in deoxyribonucleic acid in different species, the composition of total ribonucleic acid was similar in all bacteria considered. From this, scientists concluded that the main cellular RNA (i.e., ribosomal) is not a direct mediator between the carrier of genetic information and the protein.
Discovery of mRNA
It was later discovered that a small fraction of RNA repeats the composition of DNA and can serve as an intermediary. In 1956, E. Volkin and F. Astrachan studied the process of RNA synthesis in bacteria that were infected with the bacteriophage T2. After getting into the cell, she switched to the synthesis of phage proteins. In this case, the bulk of the RNA did not change. But in the cell, the synthesis of a small fraction of metabolically unstable RNA began, the nucleotide sequence in which was similar to the composition of phage DNA.
In 1961, this small fraction of ribonucleic acid was isolated from the total mass of RNA. Proof of her intermediary function was obtained from experiments. After infection of the cells with T4 phage, a new mRNA was formed. She associated with the old host ribosomes (no new ribosomes were detected after infection), which began to synthesize phage proteins. This “DNA-like RNA” was complementary to one of the phage DNA strands.
In 1961, F. Jacob and J. Mono expressed the idea that this RNA transfers information from genes to ribosomes and is a matrix for the sequential arrangement of amino acids in the process of protein synthesis.
The transfer of information to the site of protein synthesis is carried out by mRNA. The process of reading information from DNA and creating messenger RNA is called transcription. After it, RNA undergoes a number of additional changes, this is called "processing". In the course of it, certain regions can be excised from matrix ribonucleic acid. Next, the mRNA goes to the ribosomes.
Protein Building Material: Amino Acids
There are 20 amino acids in total , some of them are indispensable, that is, the body cannot synthesize them. If some acid in the cell is not enough, this can lead to a delay in translation or even a complete stop of the process. The presence of each amino acid in sufficient quantity is the main requirement for protein biosynthesis to proceed correctly.
Scientists received general information about amino acids in the 19th century. Then, in 1820, the first two amino acids were isolated - glycine and leucine.
The sequence of these monomers in a protein (the so-called primary structure) completely determines its next levels of organization, and hence its physical and chemical properties.
Amino acid transport: tRNA and aa-tRNA synthetase
But amino acids cannot line up on their own in the protein chain. In order for them to get to the main place of protein biosynthesis, transport RNA is necessary .
Each aa-tRNA synthetase recognizes only its own amino acid and only the tRNA to which it needs to be attached. It turns out that 20 varieties of synthetases are part of this family of enzymes. It remains only to say that amino acids are attached to tRNA, more precisely, to its hydroxyl acceptor tail. Each acid must have its own transport RNA. This is followed by aminoacyl-tRNA synthetase. It not only compares amino acids with the correct transport, it also regulates the reaction of the formation of ester bonds.
After a successful attachment reaction, tRNA follows the site of protein synthesis. This is where the preparatory processes end and the broadcast begins. Consider the main stages of protein biosynthesis :
- initiation;
- elongation;
- termination.
Synthesis Steps: Initiation
How does protein biosynthesis and its regulation occur? Scientists have been trying to find out for a long time. Numerous hypotheses were put forward, but the more modern the equipment became, the better we began to understand the principles of broadcasting.
The ribosome — the main site of protein biosynthesis — begins to read mRNA from the point at which its part encoding the polypeptide chain begins. This point is located at a certain distance from the beginning of the messenger RNA. The ribosome must recognize the point on the mRNA from which reading begins and connect to it.
Initiation - a complex of events that provide the beginning of the broadcast. It involves proteins (initiation factors), initiator tRNA, and a special initiator codon. At this stage, the small subunit of the ribosome binds to the initiation proteins. They prevent her from contacting the large subunit. But they allow you to connect with the initiator tRNA and GTP.
Then this complex "sits" on the mRNA, namely on the site that is recognized by one of the initiation factors. There can be no mistake, and the ribosome begins its path along the messenger RNA by reading its codons.
As soon as the complex reaches the initiating codon (AUG), the subunit stops moving and, using other protein factors, binds to the large subunit of the ribosome.
Stage of synthesis: elongation
Reading mRNA involves sequential synthesis of a protein chain by a polypeptide. It goes by adding one amino acid residue after another to the molecule under construction.
Each new amino acid residue is added to the carboxyl end of the peptide, the C-terminus is growing.
Stage of synthesis: termination
When the ribosome reaches the termination codon of messenger RNA, the synthesis of the polypeptide chain ceases. In his presence, the organelle cannot accept any tRNA. Instead, termination factors come into play. They release the finished protein from the stopped ribosome.
After termination of translation, the ribosome can either descend from the mRNA or continue to slide along it without translation.
The meeting of the ribosome with a new initiating codon (on the same chain while continuing to move or on a new mRNA) will lead to a new initiation.
After the finished molecule leaves the main site of protein biosynthesis, it is marked and sent to the destination. What functions it will perform depends on its structure.
Process regulation
Depending on its needs, the cell will independently control the translation. Regulation of protein biosynthesis is a very important function. It can be carried out in various ways.
If the cell does not need some kind of connection, it will stop the biosynthesis of RNA - protein biosynthesis will also cease to occur. Indeed, without a matrix, the whole process will not begin. And old mRNAs quickly decay.
There is another regulation of protein biosynthesis: the cell creates enzymes that interfere with the initiation phase. They interfere with translation, even if a reading matrix is available.
The second method is necessary when protein synthesis needs to be turned off right now. The first method involves the continuation of sluggish translation for some time after the cessation of mRNA synthesis.
A cell is a very complex system in which everything rests on the balance and precise operation of each molecule. It is important to know the principles of each process in the cell. So we can better understand what is happening in the tissues and in the body as a whole.