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 protein synthesis takes place
In any cell, the main site of protein biosynthesis is the ribosome. It is a large macromolecule with a complex asymmetric structure. It consists of RNA (ribonucleic acids) and proteins. Ribosomes can be located singly. But most often they are combined with EPS, which facilitates the subsequent sorting and transport of proteins.
If ribosomes sit on the endoplasmic reticulum, it is called rough ER. When translation is intense, several ribosomes can move along one template at once. They follow each other and do not interfere with other organelles at all.
What is needed for synthesissquirrel
For the process to proceed, 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 will transfer this information from DNA to ribosomes.
- Amino acid material from which a new molecule will be built.
- tRNA, which will deliver each amino acid to the ribosome, will take part in deciphering the genetic code.
- Aminoacyl-tRNA synthetase.
- Ribosome is the main site of protein biosynthesis.
- Energy.
- Magnesium ions.
- Protein factors (each stage has its own).
Now let's look at each of them in more detail and find out how proteins are created. The mechanism of biosynthesis is very interesting, all components act in an unusually coordinated manner.
Synthesis program, matrix search
All the 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 the recognition of its genetic role, it became clear that it is not a direct template for translation. Observations have led to suggestions 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 there wereribosomes are open, 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 the "DNA-rRNA-protein" scheme is correct, then the composition of total RNA will change in the same way as DNA. But, despite the huge differences in deoxyribonucleic acid in different species, the composition of the total ribonucleic acid was similar in all bacteria considered. From this, scientists concluded that the main cellular RNA (that is, ribosomal) is not a direct intermediary between the carrier of genetic information and the protein.
Discovery of mRNA
Later it was 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 T2 bacteriophage. After it enters the cell, it switches to the synthesis of phage proteins. At the same time, the main part of 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. Evidence of its mediating function has been obtained from experiments. After infection of cells with T4 phage, new mRNA was formed. She connected with the old mastersribosomes (no new ribosomes are found after infection), which began to synthesize phage proteins. This "DNA-like RNA" was found to be complementary to one of the phage's DNA strands.
In 1961, F. Jacob and J. Monod suggested that this RNA carries information from genes to ribosomes and is a matrix for the sequential arrangement of amino acids during protein synthesis.
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, the RNA undergoes a series of additional changes, this is called "processing". In the course of it, certain sections can be cut out of the matrix ribonucleic acid. Then mRNA goes to ribosomes.
Building material for proteins: amino acids
There are 20 amino acids in total, some of them are essential, that is, the body cannot synthesize them. If some acid in the cell is not enough, this can lead to a slowdown 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.
General information about amino acids was obtained by scientists in the 19th century. Then, in 1820, the first two amino acids, glycine and leucine, were isolated.
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.
Transport of amino acids: tRNA and aa-tRNA synthetase
But amino acids cannot build themselves into a protein chain. In order for them to get to the main site of protein biosynthesis, transfer RNA is needed.
Each aa-tRNA synthetase recognizes only its own amino acid and only the tRNA to which it must be attached. It turns out that this family of enzymes includes 20 varieties of synthetases. It only remains to say that amino acids are attached to tRNA, more precisely, to its hydroxyl acceptor "tail". Each acid must have its own transfer RNA. This is monitored by aminoacyl-tRNA synthetase. It not only matches amino acids to the correct transport, it also regulates the ester bonding reaction.
After a successful attachment reaction, tRNA goes to the site of protein synthesis. This ends the preparatory processes and the broadcast begins. Consider the main steps in protein biosynthesis :
- initiation;
- elongation;
- termination.
Synthesis steps: initiation
How does protein biosynthesis and its regulation take place? Scientists have been trying to figure this 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, starts reading mRNA from the point at which its part encoding the polypeptide chain begins. This point is located on a certainaway from the start of messenger RNA. The ribosome must recognize the point on the mRNA from which reading begins and connect to it.
Initiation - a set of events that provide the start 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 initiation proteins. They prevent it from contacting the large subunit. But they allow you to connect with the initiator tRNA and GTP.
Then this complex "sits" on the mRNA, exactly on the site that is recognized by one of the initiation factors. There can be no mistake, and the ribosome begins its journey through messenger RNA, reading its codons.
As soon as the complex reaches the initiation codon (AUG), the subunit stops moving and, with the help of other protein factors, binds to the large subunit of the ribosome.
Synthesis steps: elongation
Reading mRNA involves sequential synthesis of a protein chain by a polypeptide. It proceeds 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.
Synthesis steps: termination
When the ribosome reaches the termination codon of messenger RNA, the synthesis of the polypeptide chain stops. In its presence, the organelle cannot accept any tRNA. Instead, termination factors come into play. They release the finished protein from the stopped ribosome.
Aftertranslation termination, the ribosome can either leave the mRNA or continue to slide along it without translating.
The meeting of the ribosome with a new initiation codon (on the same strand during the continuation of movement or on a new mRNA) will lead to a new initiation.
After the finished molecule leaves the main site of protein biosynthesis, it is labeled and sent to its destination. What functions it will perform depends on its structure.
Process control
Depending on their needs, the cell will independently control the broadcast. Regulation of protein biosynthesis is a very important function. It can be done in many ways.
If a cell doesn't need some kind of compound, it will stop RNA biosynthesis - protein biosynthesis will also stop happening. After all, 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 the 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 is kept in balance and the precise work of each molecule. It is important to know the principles of each process occurring in the cell. So we can better understand what is happening in the tissues and in the body as a whole.
