The interaction and structure of mRNA, tRNA, rRNA - the three main nucleic acids, is considered by such a science as cytology. It will help to find out what is the role of transport ribonucleic acid (tRNA) in cells. This very small, but at the same time undeniably important molecule takes part in the process of combining the proteins that make up the body.
What is the structure of tRNA? It is very interesting to consider this substance “from the inside”, to learn its biochemistry and biological role. And also, how are the structure of tRNA and its role in protein synthesis interconnected?
What is tRNA, how is it arranged?
Transport ribonucleic acid is involved in the construction of new proteins. Almost 10% of all ribonucleic acids are transport. To make it clear from which chemical elements the molecule is formed, we will describe the structure of the secondary structure of tRNA. The secondary structure considers all the basic chemical bonds between elements.
This is a macromolecule consisting of a polynucleotide chain. Nitrous bases in it are connected by hydrogen bonds. As in DNA, RNA has 4 nitrogen bases: adenine, cytosine, guanine, and uracil. In these compounds, adenine is always associated with uracil, and guanine, as usual, with cytosine.
Why does the nucleotide have a ribo prefix? Simply, all linear polymers having ribose instead of pentose at the base of the nucleotide are called ribonucleic. And transport RNA is one of 3 types of just such a ribonucleic polymer.
The structure of tRNA: biochemistry
Let's look into the deepest layers of the structure of the molecule. These nucleotides have 3 components:
- Sucrose, ribose is involved in all types of RNA.
- Phosphoric acid.
- Nitrous bases. These are purines and pyrimidines.
Nitrous bases are interconnected by strong bonds. It is customary to divide the bases into purine and pyrimidine.
Purines are adenine and guanine. Adenine corresponds to an adenyl nucleotide from 2 interconnected rings. And guanine - corresponds to the same "single-ring" guanine nucleotide.
Pyramidines are cytosine and uracil. Pyrimidines have a single ring structure. There is no thymine in RNA, since it is replaced by an element such as uracil. This is important to understand before paying attention to other structural features of tRNA.
Types of RNA
As you can see, the structure of tRNA cannot be briefly described. It is necessary to delve into biochemistry in order to understand the purpose of the molecule and its true structure. What other ribosomal nucleotides are known? Matrix or informational and ribosomal nucleic acids are also distinguished. Abbreviated as mRNA and rRNA. All 3 molecules work closely with each other in the cell so that the body receives properly structured protein globules.
It is impossible to imagine the work of one polymer without the help of 2 others. The structural features of tRNAs become more clear when considered in conjunction with functions that are directly related to the operation of ribosomes.
The structure of mRNA, tRNA, rRNA is very similar in many respects. All are based on ribose. However, their structure and functions are different.
The discovery of nucleic acids
Swiss Johann Miescher found macromolecules in the nucleus of the cell in 1868, which were later called nucleins. The name "nucleins" comes from the word (nucleus) - the nucleus. Although a little later it was found that in unicellular creatures without a nucleus, these substances are also present. In the mid-20th century, the Nobel Prize was awarded for the discovery of nucleic acid synthesis.
The functions of tRNA in protein synthesis
The name itself - transport RNA talks about the main function of the molecule. This nucleic acid “brings” with it the necessary amino acid required by ribosomal RNA to create a specific protein.
The tRNA molecule has few functions. The first is recognition of the IRNC codon, the second function is the delivery of building "bricks" - amino acids for protein synthesis. Some other experts highlight the acceptor function. That is, covalent amino acid addition. An enzyme such as aminocyl-tRNA synthase helps to “attach” this amino acid.
How is the structure of tRNA related to its functions? This particular ribonucleic acid is designed so that on its one side there are nitrogenous bases that always combine in pairs. These are elements known to us - A, U, C, G. Exactly 3 “letters” or nitrogenous bases make up the anticodon — the inverse set of elements that interacts with the codon according to the principle of complementarity.
This important structural feature of the tRNA ensures that there will be no errors in decoding the template nucleic acid. After all, the exact protein that is needed for the body is currently being synthesized depends on the exact amino acid sequence.
Structural features
What are the structural features of tRNA and its biological role? This is a very ancient structure. Its size is somewhere between 73 and 93 nucleotides. The molecular weight of the substance is 25,000–30,000.
The structure of the secondary structure of tRNA can be disassembled by studying the 5 main elements of the molecule. So, this nucleic acid consists of the following elements:
- loop for contact with the enzyme;
- loop for contact with the ribosome;
- anti-codon loop;
- acceptor stem;
- anticodon itself.
And also a small variable loop is isolated in the secondary structure. One shoulder in all types of tRNA is the same - a stem of two cytosine residues and one - adenosine. It is in this place that there is a connection with 1 of the 20 available amino acids. For each amino acid, a separate enzyme is designed - its own aminoacyl-tRNA.
All information that encrypts the structure of all nucleic acids is contained in the DNA itself. The structure of tRNA in all living things on the planet is almost identical. It will look like a sheet when viewed in 2-D format.
However, if you look at the volume, the molecule resembles an L-shaped geometric structure. This is considered the tertiary structure of tRNA. But for the convenience of studying it is customary to visually “unwind” it. The tertiary structure is formed due to the interaction of the elements of the secondary structure, those parts that are mutually complementary.
The shoulders of tRNAs or rings play an important role. One arm, for example, is necessary for chemical bonding with a particular enzyme.
A characteristic feature of the nucleotide is the presence of a huge number of nucleosides. There are more than 60 species of these minor nucleosides.
The structure of tRNA and coding of amino acids
We know that anticodon tRNA is 3 molecules. Each anticodon corresponds to a specific, "personal" amino acid. This amino acid is connected to the tRNA molecule using a special enzyme. As soon as 2 amino acids combine, the bonds with the tRNA break down. All chemical compounds and enzymes are needed until the required time. This is how the structure and functions of tRNA are interconnected.
A total of 61 types of such molecules are present in the cell. There can be 64 mathematical variations. However, 3 types of tRNAs are absent due to the fact that precisely such a number of stop codons in the mRNA does not have anticodons.
The interaction of mRNA and tRNA
Consider the interaction of a substance with mRNA and rRNA, as well as structural features of tRNA. The structure and purpose of the macromolecule are interconnected.
The structure of the mRNA copies information from a single DNA site. DNA itself is too large a combination of molecules, and it never leaves the nucleus. Therefore, an intermediary RNA is needed - informational.
Based on the sequence of molecules that the mRNA has copied, the ribosome builds a protein. Ribosome is a separate polynucleotide structure, the structure of which needs to be clarified.
Ribosomal tRNA: interaction
Ribosomal RNA is a huge organelle. Its molecular weight is 1,000,000 to 1,500,000. Almost 80% of the total amount of RNA is ribosomal nucleotides.
She kind of captures the mRNA chain and waits for anticodons, which will bring tRNA molecules with them. Ribosomal RNA consists of 2 subunits: small and large.
The ribosome is called the "factory", because in this organelle the whole synthesis of the substances necessary for everyday life takes place. It is also a very ancient cell structure.
How is protein synthesis in the ribosome?
The structure of tRNA and its role in protein synthesis are interrelated. The anticodon located on one of the sides of the ribonucleic acid is suitable in its form for the main function - the delivery of amino acids to the ribosome, where the protein is phased in stages. In essence, tRNA acts as an intermediary. Her task is only to bring the necessary amino acid.
When information is read from one part of the mRNA, the ribosome moves further down the chain. A matrix is only needed to transmit encoded information about the configuration and function of a single protein. Next comes another ribosome to the ribosome with its nitrogenous bases. It also decodes the next part of the mRNA.
Decoding is as follows. Nitrogen bases are combined according to the principle of complementarity in exactly the same way as in DNA itself. Accordingly, the tRNA sees where it needs to be "moored" and in which "hangar" to send the amino acid.
Then, in the ribosome, the amino acids selected in this way are chemically bonded, and a new linear macromolecule is formed step by step, which, after the end of the synthesis, is twisted into a globule (ball). Used tRNAs and mRNAs, having fulfilled their function, are removed from the “factory" of the protein.
When the first part of the codon is connected to the anticodon, a reading frame is determined. Subsequently, if, for some reason, a frame shift occurs, then some sign of the protein will be rejected. The ribosome cannot intervene in this process and solve the problem. Only after the completion of the process, 2 subunits of RRNA are combined again. On average, for every 10 4 amino acids there is 1 error. For 25 already collected proteins, at least 1 replication error is necessarily encountered.
TRNA as relic molecules
Since tRNAs may have existed at the time of the origin of life on earth, it is called a relict molecule. RNA is thought to be the first structure that existed before DNA, and then evolved. RNA World Hypothesis - formulated in 1986 by laureate Walter Hilbert. However, it is still difficult to prove this. The theory is supported by obvious facts - tRNA molecules are able to store blocks of information and somehow implement this information, that is, do the work.
But opponents of the theory argue that a short life span of a substance cannot guarantee that tRNA is a good carrier of any biological information. These nucleotides decay rapidly. The lifespan of tRNA in human cells ranges from several minutes to several hours. Some species can last up to a day. And if we talk about the same nucleotides in bacteria, then the terms are much shorter - up to several hours. In addition, the structure and functions of the tRNA are too complex for the molecule to become the primary element of the Earth's biosphere.