The new synthesis of proteins in organisms is called protein biosynthesis. Along with fats and carbohydrates, proteins are one of the basic building blocks of cells in all living things. In addition to structural functions, various proteins take on a variety of different tasks in our body.
As a basic knowledge for this article, it is important to know the basic structure and composition of DNA. If you are new to DNA, you can refresh your knowledge in our article on the subject.
Proteins and protein biosynthesis – definition
Protein biosynthesis is the new synthesis of proteins in our cells. But what are proteins anyway? And why do they play such an essential role in our bodies and cells?
proteins
Proteins (also proteins) are biological macromolecules, which consist of so-called amino acids are constructed. The corresponding amino acids are linked to one another via specific peptide bonds. Amino acid chains will also polypeptides called. A protein can consist of one or more polypeptides.
For a deeper insight into the structure and functions of proteins, see ‘s articles on protein structure and biological functions of proteins. Come around!
Proteins take on important structural functions in cell construction, as well as a variety of different tasks in our cells. Proteins are as so-called biocatalysts involved in a large part of the metabolic processes taking place in our body. Proteins, which act as biocatalysts enzymes called.
biocatalysts are molecules that speed up or slow down biochemical reactions by decreasing or increasing the amount of energy required for a reaction to occur (activation energy). Some biochemical reactions require biocatalysts to take place.
protein biosynthesis
Our cells synthesize proteins according to a specific blueprint, which is in our genome (DNA) is included. Protein biosynthesis can be divided into two sub-steps.
the protein biosynthesis is the new synthesis of proteins in living cells. It is a central and essential intracellular process for all living beings. During protein biosynthesis, new proteins are built from amino acids according to the specifications of genetic information (DNA).
In a first step, the information for the corresponding protein in the cell nucleus is read out and put into a so-called messenger RNA (mRNA) rewritten. This step will transcription called.
Messenger RNA (mRNA), like DNA, is a nucleic acid. Unlike DNA, RNA can leave the cell nucleus. In the course of protein biosynthesis, the mRNA serves as a transport molecule for the blueprint of the proteins.
In the second step of protein biosynthesis, the mRNA is translated into a corresponding polypeptide (protein). This step will translation called. Each gene is involved in the process of protein biosynthesis in a translated polypeptide. One speaks of the so-called «One Gene One Polypeptide Hypothesis».
Figure 1: Simplified representation of protein biosynthesis
Protein biosynthesis eukaryotes and prokaryotes
Prokaryotes (bacteria and archaea) do not have a cell nucleus. In prokaryotes, all protein biosynthesis takes place in the cytoplasm of the cells. In eukaryotes, on the other hand, the individual steps of protein biosynthesis are spatially separated from one another.
Protein biosynthesis – process
In the following section you will get a deeper insight into the individual steps of protein biosynthesis.
transcription
the transcription is the transcription of a gene into an mRNA. A gene contains the information for building a polypeptide.
transcription is the synthesis of RNA, using the DNA as a template and transcribing the base sequence of the DNA into the base sequence of the RNA.
In order for a gene to be read and transcribed, the coiled DNA for transcription must be uncoiled at the appropriate section and separated into two single strands.
By means of a corresponding protein complex, the so-called codogenic single strand of the gene is read and transcribed into an mRNA. The decisive enzyme for the construction of the mRNA single strand (transcript) is the so-called RNA polymerase.
Of the codogenic strand is the single strand of the protein-coding gene, which is used by RNA polymerase as a template to form mRNA.
During transcription, a codogenic strand is formed complementaryright RNA strand. While DNA from the base pairs adenine thymine (AT) and guanine cytosine (GC) is constructed, RNA molecules consist of the base pairs adenine uracil (AU) and guanine cytosine (GC). Corresponding thymine bases are swapped in the RNA by uracil bases.
Of the coding strand is the DNA strand of the gene, which Not used by RNA polymerase. It corresponds to the base sequence of the emerging mRNA single strand (transcript).
Figure 2: Schematic representation of the transcriptionSource: micorbiologynotes.org
RNA processing
After the gene has been transcribed into an mRNA transcript, certain processes must take place so that the corresponding mRNA can function as a transport molecule. These processes are referred to as the so-called RNA processing or from Rmaturation process the mRNA. RNA processing ensures that the correct sections of mRNA are translated into a polypeptide and protects the mRNA from enzymatic degradation.
RNA processing is a process in eukaryotic cells. Due to the gene structure, no mRNA maturation process is necessary in prokaryotes.
You can get a deeper insight into the transcription process and the most important enzymes involved in a separate article.
translation
The translation is the second step of protein biosynthesis.
translation is the synthesis of proteins, whereby the base sequence of the mRNA is translated into an amino acid sequence of a protein.
The translation takes place at the so-called ribosomes instead of. Ribosomes consist of a large and a small subunit. The mRNAs attach themselves to a ribosome and are processed with the help of so-called transfer RNAs (tRNAs) translated into polypeptides.
ribosome
Ribosomes are made up of proteins and ribosomal RNA (rRNA). The small subunit recognizes and binds the corresponding mRNA. The large subunit has three binding sites for tRNAs and is responsible for the formation of the polypeptide chain.
The three tRNA binding sites of the ribosome are A-(aminoacyl), P-(peptidyl) and E-(Exit) binding site called. Each binding site has space for one tRNA molecule. The binding sites become equally important when it comes to the translation process.
tRNA
Transfer RNAs (tRNAs) Like mRNAs, they are nucleic acids and consist of a sequence of bases. Due to interactions between the bases, tRNAs have a so-called cloverleaf structure. On one side, tRNAs have a binding site for a specific amino acid. On the other side is a recognition sequence for the mRNA.
The recognition sequence for the mRNA consists of three bases and is anticodon called. The tRNAs transport specific amino acids that match their anticodons. The tRNAs can therefore bind to corresponding mRNA sections that complementary to their recognition sequence (anticodon).
A anticodon is a triplet of bases (nucleotides) on tRNA that are complementary to a codon on mRNA.
Figure 3: Representation of a tRNA with anticodon Source: Quora.com
Thus, three bases on the mRNA always correspond to one amino acid. Following this scheme, the mRNA can be translated into a polypeptide. This principle of translation is called genetic code designated.
genetic code
Human proteins consist of 21 different amino acids. Certain codons in the genetic code correspond to specific amino acids. So-called base triplets or codons (Base sequence consisting of 3 bases) correspond to the different amino acids. In addition to triplets, which code for amino acids, there are so-called Begin- and stop codons.
A codon is a sequence of three (triplet) on the mRNA that determines the position of an amino acid in a protein or encodes the translation stop.
start codons initiate the start of synthesis of a polypeptide chain, while stop codons lead to termination of synthesis and release of the polypeptide chain.
The genetic code is degenerate. This means there are more possible base triplets than the total number of possible amino acids. Therefore, multiple codons code for the same amino acid. For example, the codons CGG, CGA, CGC, CGU, AGG, and AGA code for the amino acid arginine (Arg).
The so-called code sun shows you which codons the RNA which amino acids correspond.
Figure 4: Code sun for translating the genetic codeSource: Wikipedia.de
With the help of the article on the genetic code, you can further deepen your knowledge on this topic.
Translation process
The information for the amino acid chain is on the gene and was transcribed to an mRNA during transcription. The mRNA is then translated into an amino acid chain (polypeptide chain) on the ribosome. Three base pairs each (base triplets or codon) on the mRNA correspond to an amino acid.
1. At the beginning of translation, the ribosome binds to the mRNA and moves along it until a start codon (AUG) is present.
2. There is a triplet of mRNA bases at each of the three binding sites on the ribosome. At the beginning of translation, the start codon is located at the A binding site of the ribosome. Now a tRNA with a matching anticodon can bind at the A site and at the start codon.
3. Now the ribosome migrates one base triplet on the mRNA. Now the start codon with the bound tRNA is in the P binding site. A new unbound triplet of bases is located at the A-binding site. A suitable tRNA can now bind to it. Accordingly, there are two tRNAs in the P and A binding site next to each other. Both tRNAs carry an amino acid.
4. The amino acid of the tRNA in the P-binding site is now transferred to the amino acid of the tRNA in the A-binding site. The ribosome then migrates another base triplet. The tRNA without the amino acid is now at the E-binding site (Exit binding point) and will then leave the ribosome. At the P binding site is the tRNA with the resulting amino acid chain. The A binding site is empty and ready to accept a new tRNA.
5. The substeps 3 and 4 are now repeated with the ever-migrating ribosome and an ever-longer amino acid chain is formed.
6. At a certain point, the ribosome gets to a stop codon. There are no tRNAs with matching anticodons for the corresponding stop codons. As a result, translation is terminated and the resulting amino acid chain detaches from the ribosome and the tRNA. In this way, the mRNA can be translated into a polypeptide.
Figure 5: Schematic representation of the translation Source:…