The cell of any organism is one big factory for the production of chemicals. Here reactions take place in the biosynthesis of lipids, nucleic acids, carbohydrates and, of course, proteins. Proteins play an enormous role in the life of the cell, as they perform many functions: enzymatic, signaling, structural, protective, and others.
Protein biosynthesis: description of the process
The construction of protein molecules is a complex multi-stage process that occurs under the action of a large number of enzymes and in the presence of certain structures.
Synthesis of any protein begins in the nucleus. Information about the structure of the molecule is recorded in the DNA of the cell, from which it is read. Almost every gene in an organism encodes one, unique protein molecule.
What is the role of the cytoplasm in protein biosynthesis? The fact is that the cytoplasm of the cell is a "pool" for monomers of complex substances, as well as structures that are responsible for the process of protein synthesis. Also, the internal environment of the cell has a constant acidity andion content, which plays an important role in biochemical reactions.
Protein biosynthesis takes place in two stages: transcription and translation.
Transcription
This stage starts in the nucleus of the cell. Here the main role is played by such nucleic acids as DNA and RNA (deoxy- and ribonucleic acids). In eukaryotes, the unit of transcription is the transcripton, while in prokaryotes, this organization of DNA is called the operon. The difference between transcription in prokaryotes and eukaryotes is that an operon is a section of a DNA molecule that encodes several protein molecules, when the transcripton carries information about only one protein gene.
The main task of the cell at the stage of transcription is the synthesis of messenger RNA (mRNA) on the DNA template. To do this, an enzyme such as RNA polymerase enters the nucleus. It is involved in the synthesis of a new mRNA molecule, which is complementary to the deoxyribonucleic acid site.
For successful transcription reactions, the presence of transcription factors, which are also abbreviated as TF-1, TF-2, TF-3, is necessary. These complex protein structures are involved in the connection of RNA polymerase with the promoter on the DNA molecule.
The synthesis of mRNA continues until the polymerase reaches the end region of the transcripton, which is called the terminator.
The operator, as another functional area of the transcripton, is responsible for inhibiting transcription or, conversely, for accelerating the work of RNA polymerase. Responsible forregulation of the work of transcription enzymes special proteins-inhibitors or proteins-activators, respectively.
Broadcast
After mRNA has been synthesized in the cell nucleus, it enters the cytoplasm. To answer the question about the role of the cytoplasm in protein biosynthesis, it is worth analyzing in more detail the further fate of the nucleic acid molecule at the translation stage.
Translation occurs in three stages: initiation, elongation and termination.
First, mRNA must attach to ribosomes. Ribosomes are small non-membrane structures of the cell, which consist of two subunits: small and large. First, the ribonucleic acid attaches to the small subunit, and then the large subunit closes the entire translational complex so that the mRNA is inside the ribosome. Actually, this is the end of the initiation stage.
What is the role of the cytoplasm in protein biosynthesis? First of all, it is a source of amino acids - the main monomers of any protein. At the stage of elongation, a gradual build-up of the polypeptide chain occurs, starting with the start codon methionine, to which the remaining amino acids are attached. The codon in this case is a triplet of mRNA nucleotides that codes for one amino acid.
At this stage, another type of ribonucleic acid is connected to work - transfer RNA, or tRNA. They are responsible for delivering amino acids to the mRNA-ribosome complex by forming an aminoacyl-tRNA complex. tRNA recognition occurs through complementaryinteractions of the anticodon of this molecule with the codon on the mRNA. Thus, the amino acid is delivered to the ribosome and attached to the synthesized polypeptide chain.
Termination of the translation process occurs when the mRNA reaches the stop codon sections. These codons carry information about the end of peptide synthesis, after which the ribosome-RNA complex is destroyed, and the primary structure of the new protein enters the cytoplasm for further chemical transformations.
Special protein initiation factors IF and elongation factors EF are involved in the translation process. They are of various types, and their task is to ensure the correct connection of RNA with ribosome subunits, as well as in the synthesis of the polypeptide chain itself at the elongation stage.
What is the role of the cytoplasm in protein biosynthesis: briefly about the main components of biosynthesis
After the mRNA leaves the nucleus into the internal environment of the cell, the molecule must form a stable translational complex. What components of the cytoplasm must be present at the stage of translation?
1. Ribosomes.
2. Amino acids.
3. tRNA.
Amino acids - protein monomers
For the synthesis of a protein chain, the presence in the cytoplasm of the structural components of the peptide molecule - amino acids. These low molecular weight substances in their composition have an NH2 amino group and a COOH acid residue. Another component of the molecule - the radical - is the hallmark of each individual amino acid. What is the role of the cytoplasm inprotein biosynthesis?
AA occur in solutions in the form of zwitterions, which are the same molecules that donate or accept hydrogen protons. Thus, the amino group of amino acids is converted into NH3+, and the carbonyl group into COO-.
In total, there are 200 AAs in nature, of which only 20 are protein-forming. Among them, there is a group of essential amino acids that are not synthesized in the human body and enter the cell only with ingested food, and non-essential amino acids that the body forms on its own.
All AAs are encoded by some codon that corresponds to three mRNA nucleotides, and one amino acid can often be encoded by several such sequences at once. The methionine codon in pro- and eukaryotes is the starting one, because it begins the biosynthesis of the peptide chain. Stop codons include UAA, UGA and UAG nucleotide sequences.
What are ribosomes?
How are ribosomes responsible for the biosynthesis of proteins in the cell and what is the role of these structures? First of all, these are non-membrane formations, which consist of two subunits: large and small. The function of these subunits is to hold the mRNA molecule between them.
There are sites in ribosomes where mRNA codons enter. In total, two such triplets can fit between the small and large subunit.
Several ribosomes can aggregate into one large polysome, due to which the rate of synthesis of the peptide chain increases, and the output can be obtained immediatelyseveral copies of the protein. Here is the role of the cytoplasm in protein biosynthesis.
Types of RNA
Ribonucleic acids play an important role at all stages of transcription. There are three large groups of RNA: transport, ribosomal and informational.
mRNAs are involved in the transfer of information about the composition of the peptide chain. tRNAs are mediators in the transfer of amino acids to ribosomes, which is achieved by the formation of an aminoacyl-tRNA complex. Attachment of an amino acid occurs only with the complementary interaction of the anticodon of the transfer RNA with the codon on the messenger RNA.
rRNA are involved in the formation of ribosomes. Their sequences are one of the reasons why mRNA is held between the small and large subunits. Ribosomal RNAs are produced in the nucleoli.
Meaning of proteins
Protein biosynthesis and its importance for the cell are colossal: most of the body's enzymes are of a peptide nature, thanks to proteins, substances are transported through cell membranes.
Proteins also perform a structural function when they are part of muscle, nerve and other tissues. The signaling role is to transmit information about the processes occurring, for example, when light falls on the retina. Protective proteins - immunoglobulins - are the basis of the human immune system.
