Definition of tRNA
Transfer RNAs or tRNAs are molecules that act as temporary amino acid carriers, delivering the appropriate amino acids to the ribosome based on the nucleotide sequence of the messenger RNA (mRNA). In this way, they act as intermediaries between nucleotide and amino acid sequences.
tRNAs are ribonucleic acids and can therefore form hydrogen bonds with mRNA. In addition, they can also form ester bonds with amino acids, physically linking mRNA and amino acids together during the translation process. They bind to mRNA in a complementary and antiparallel manner, and each tRNA can bind to a three-nucleotide stretch in the mRNA. These sets of three nucleotides in mRNA are called codons, and the corresponding sequence in tRNA is called an anticodon. The base pairing between the codon and the anticodon confers specificity to the translation process. At one end of the tRNA, an appropriate amino acid is attached to its 3'-hydroxyl group based on the anticodon, and the ribosome catalyzes the formation of a peptide bond between that amino acid and the elongating polypeptide chain.
tRNA structure and function
Transfer RNAs are encoded by a variety of genes and are usually short molecules, between 70 and 90 nucleotides (5 nm) in length. The two most important parts of a tRNA are its anticodon and the 3'-terminal hydroxyl group, which can form an ester bond with an amino acid. However, there are other aspects of a tRNA's structure, such as the D arm and the T arm, that contribute to its high specificity and efficiency. Only 1 in 10,000 amino acids does not match a tRNA, which is a remarkable number given the chemical similarities between many amino acids.
Transfer RNAs, like all other cellular nucleic acids, have a sugar-phosphate backbone, and the orientation of the ribose sugar determines the direction of the molecule. One end of RNA has a reactive phosphate group attached to the fifth carbon atom of ribose, while the other end has a free hydroxyl group on the third carbon atom. This creates the 5' and 3' ends of the RNA, as all other phosphate and hydroxyl groups participate in phosphodiester bonds in the nucleic acid.
The last three bases at the 3' end of the tRNA are always CCA: two cytosines followed by an adenine base. This segment is part of the acceptor arm of the molecule, where an amino acid is covalently linked to the hydroxyl group of the ribose sugar of the terminal adenine nucleotide. The acceptor arm also contains portions of the 5' end of the tRNA, with a 7-9 nucleotide stretch from the opposite base-pairing ends of the molecule joined together.
The anticodon loop that pairs with the mRNA determines which amino acid binds to the acceptor rod. The anticodon loop is recognized by aminoacyl-tRNA synthetase (AATS), the enzyme that chemically links a tRNA to an amino acid via a high-energy bond. AATS "reads" the anticodon and also recognizes the D arm, which is downstream from the 5' end of the tRNA.
The D arm consists of a double-stranded stem region formed by internal base pairing and an unpaired nucleotide loop structure. The D arm is a highly variable region and plays an important role in stabilizing the tertiary RNA structure and also affects the kinetics and fidelity of translation at the ribosome.
The other structure that influences tRNA's role in translation is the T arm. Similar to the D arm, it contains a stretch of nucleotides that pair together and a loop that is single-stranded. The paired region is called the "stem" and contains mostly 5 base pairs. The loop contains modified bases and is also called the TΨC arm to specify the presence of thymidine, pseudouridine, and cytidine residues (modified bases). tRNA molecules are unusual because they contain a large number of modified bases and contain thymidine, which is normally found only in DNA. The T arm is involved in the interaction of the tRNA with the ribosome.
Finally, between the anticodon loop and the T arm is a variable arm of less than 20 nucleotides that plays a role in tRNA recognition by AATS but may be absent in some species.
The secondary structure of tRNA, which contains the acceptor region, the D and T arms, and the anticodon loop, is said to resemble a cloverleaf. After the RNA has folded into its tertiary structure, it is L-shaped, with the acceptor rod and T arm forming an elongated helix, and the anticodon loop and D arm similarly forming another elongated helix. These two helices line up perpendicular to each other, bringing the D and T arms closer together, while the anticodon loop and acceptor arm are at opposite ends of the molecule.
In this image, the CCA 3' region is yellow, the acceptor arm is purple, the variable loop is orange, the D arm is red, the T arm is green, and the anticodon loop is blue.
The type of tRNA
A tRNA can be classified according to the amino acid it carries, creating 20 different tRNAs. Alternatively, they can also be grouped by their anticodon. There are 64 possible codons, formed by a combination of four nucleotides. Of these, 3 are stop codons that signal the end of translation. As a result, an amino acid is represented by multiple codons and both AATS and tRNAs must take this redundancy into account. However, very few species have exactly 61 tRNAs, raising the question of how each codon is recognized by a given tRNA. In many species, the number far exceeds 61, and different tRNAs carrying the same anticodon can show different efficiencies in translation, adding a layer of regulation to the process of protein synthesis.
tRNAs interact with codons on the mRNA through their anticodon loop. Base pairing between the codon and anticodon ensures specificity during translation. However, the first base of the anticodon, which pairs with the "wobble" or third position in a codon, is often modified to allow the tRNA to bind to three bases instead of one. Therefore, a single tRNA has the ability to recognize and base pair with three codons that encode the same amino acid. There are 20 AATS, one for each amino acid. This group of enzymes can recognize all anticodons that represent a given amino acid, thus acting as the second arm of the machinery that takes care of the redundancy of the genetic code.
Finally, these molecules can also be divided into three categories: those that carry canonical amino acids linked to the correct tRNA, those that are incorrectly linked, and those that carry modified amino acids, such as selenocysteine, for non-canonical elongation.
Post-transcriptional modification of tRNA
There are about 500 genes encoding tRNA in the human genome and 300 gene fragments associated with these RNAs. These genes are transcribed by RNA polymerase III, and the transcript undergoes extensive modification, particularly in eukaryotes. Introns are spliced, endonucleases act at the intron-exon boundary, the 5' and 3' ends of the RNA are processed, and enzymes add the terminal CCA residues to the 3' end of the tRNA. CCA residues could be aminoacylated in the nucleus itself, and this charged tRNA could then be exported out of the nucleus.
In addition, many tRNA bases are also modified, primarily by methylation (addition of a methyl group) and deamidation (removal of an amide group). In particular, the first base of the anticodon, which corresponds to the "wobble" position in the codon, is modified to allow for unusual types of base pairing. Adenine can be modified to inosine, expanding the pairing possibilities for uracil, cytosine, and adenine. Pseudouridine is another common modified base derived from enzyme-mediated isomerization of uridine residues. It is believed to play a role in the structural integrity of the tRNA molecule, participate in the rigidity of the proximal sugar-phosphate backbone, and also affect the base stacking of proximal regions. Lysidine is an unusual base formed when a lysine amino acid is attached to a cytidine residue. Lysidine pairs specifically with adenosine, a property that isoleucine tRNA uses to ensure translation specificity.
AATS attach the appropriate amino acid to tRNA molecules based on their anticodon. These enzymes contain binding sites for the amino acid, tRNA, and ATP and hydrolyze ATP to AMP and link the amino acid to the ribose sugar of the last nucleotide in the tRNA. tRNA is now considered "charged" and can participate in protein synthesis reactions on the ribosome. This reaction usually occurs in the cytoplasm, although it has also been observed in the nucleus.
The enzyme binds to various regions of the tRNA to ensure high specificity in the reaction and even corrects its own reaction, as many amino acids have similar structures.
The mature tRNA is then linked to specific export factors using the RanGTP system, which exports it from the cell nucleus. The acceptor arm and T arm play important roles in this process, and there is extensive interaction between the export factors and the RNA molecule, allowing only complete and fully processed tRNAs to enter the cytoplasm.
Interaction of tRNA with the ribosome
The ribosome contains three important regions: the P (peptidyl) site, which contains the growing polypeptide, the A (acceptor) site, which receives a reloaded tRNA, and the E (egress) site, through which an unacylated tRNA leaves the ribosome. ribosome. These sites span both subunits of the ribosome and are called P/P or A/A sites, with the first letter referring to the site on the smaller subunit. For example, the P/P site binds tRNA that anchors a polypeptide chain, while the A/A site anchors an incoming charged tRNA. The peptidyl tRNA in the P/P site transfers the growing polypeptide to the tRNA in the A/A site and is deacylated. To continue the translation process, the ribosome advances one codon, causing the tRNA to switch from the P/P site to a transient P/E configuration and then to the E/E site before exiting the ribosome. Similarly, tRNA adopts a temporary A/P transition conformation at the A/A site before settling into the P/P site, ready for the next amino acid to continue translation.
- antiparallel– Parallel but facing opposite directions, like the two sugar and phosphate backbones of a DNA molecule.
- complementarity– The property of nitrogenous bases in nucleic acids to form specific and stable hydrogen bonds with other nitrogenous bases. For example, the interaction between adenine and thymine occurs through complementary hydrogen bonds.
- introns– Parts of an RNA molecule that are removed after transcription.
- transcription– The process of generating an RNA molecule from a DNA template.
to test
1. Which of these structures are found in tRNAs?
ONE.Anticodon-Schleife
B.codon
C.ATS
D.all previous
Answer to question #1
ONEthat's right. Only the anticodon loop is found in tRNAs. Codons are found in mRNAs and AATS are enzymes, not parts of an RNA molecule.
2. Which of these modified residues are found in tRNAs?
ONE.pseudouridina
B.shy
C.Citidine
D.all previous
Answer to question #2
Dthat's right. Transfer RNAs contain several modified bases, and these modifications are essential for their correct functioning. To date, they are the only class of RNA molecules known to contain thymidine, which is normally found only in DNA. Pseudouridine and cytidine are commonly seen on the T arm of tRNA.
3. Which of these modified bases is derived from adenine?
ONE.adenosine
B.Inosina
C.Citidine
D.all previous
Answer to question #3
Bthat's right. Inosine is derived from adenine. While adenosine can technically be considered a derivative of adenine, it is not considered a "modified" base. Cytidine nucleotide is formed when cytosine binds to a phosphorylated ribose sugar.
FAQs
What is the function of transfer RNA tRNA? ›
Transfer RNA (tRNA) has a long-established role in protein synthesis. The tRNA molecule serves as an adaptor [1] between the genetic instructions written in nucleic acid sequences and the protein products encoded in genes.
Are there 61 types of tRNA? ›Per cell, 61 tRNA types are required to provide one-to-one correspondence between tRNA molecules and codons that specify amino acids, as there are 61 sense codons of the standard genetic code.
Why are there 61 types of tRNA? ›The majority of cells have 40 to 60 types of tRNAs because most of the 61 sense codons have their own tRNA in the eukaryotic cytosol. The tRNAs, which accept the same amino acid are known as isoaccepting tRNAs.
Why are there 64 tRNA types? ›How many distinct tRNAs are required? In the genetic code, codons made of of three bases specify an amino acid. With three bases, there are 64 possible permutations. With three codons corresponding to STOP codons, this leaves 61 combinations that code for an amino acid.
What is the structure & function of tRNA? ›Transfer RNA (tRNA) is a short nucleotide RNA chain. With a L-shaped structure, tRNA functions as an 'adaptor' molecule that translates three-nucleotide codon sequence in the mRNA into the suitable amino acid of that codon. As the link between amino acids and nucleic acids, tRNAs determine the genetic code.
How many types of tRNAs are there? ›Types of tRNA. A tRNA can be classified based on the amino acid it carries, giving rise to 20 different tRNAs. Alternatively, they can also be grouped based on their anticodon. There are 64 possible codons arising from a combination of four nucleotides.
What are the parts of tRNA? ›Each tRNA contains a set of three nucleotides called an anticodon. The anticodon of a given tRNA can bind to one or a few specific mRNA codons. The tRNA molecule also carries an amino acid: specifically, the one encoded by the codons that the tRNA binds.
Where is tRNA found? ›tRNAs encoded by nuclear genomes are transcribed in the nucleus and are then exported to the cytoplasm where they perform their essential function of delivering amino acids to growing polypeptide chains as specified by mRNA codons.
What are 3 bases in tRNA called? ›Roughly in the middle of the tRNA molecule is a sequence of three bases called the anticodon. These three bases are hydrogen bonded to a complementary sequence in an RNA molecule— called messenger RNA, mRNA— during protein synthesis.
Who discovered tRNA? ›tRNA, discovered by Paul Zamecnik and collaborators [2], is a literal “adaptor” molecule [3] that mediates the translation of information from messenger RNAs (mRNAs). tRNA was the first non-coding RNA to be discovered.
Why is 45 tRNA? ›
There is a tRNA formed to match its codon with a single type of amino acid. Although there are 61 different codons that code for the 20 amino acids, there are only 45 different tRNAs because the third base in the tRNA anticodon can recognize two or more different codons on a mRNA.
Are there 20 different tRNA molecules? ›As each tRNA molecule will only carry a single amino acid, and there are 20 amino acids used by the cell to synthesize proteins, there will be exactly 20 different types of tRNA molecules in a human cell. Each of these will be unique to one amino acid.
What are the 4 bases of tRNA? ›Three of these bases, adenine (A), cytosine (C), and guanine (G), are the same as DNA. But instead of thymine (T), the fourth base is uracil (U). Each base has a complement -- another base that it can connect to.
How is tRNA formed? ›Transfer ribonucleic acid (tRNA) is primarily synthesized from tRNA gene through transcription by RNA polymerase and becomes the mature form via several steps: processing, splicing, CCA addition and posttranscriptional modification.
What are the four arms of tRNA? ›The tRNA possess four arms ( the acceptor, D, anti-codon and -arms), three loops (D, anti-codon and -loop ) and a variable region [4] .
Where is the first tRNA? ›Our first, methionine-carrying tRNA starts out in the middle slot of the ribosome, called the P site. Next to it, a fresh codon is exposed in another slot, called the A site.
Does tRNA have 3 end? ›Abstract. Cytoplasmic tRNAs undergo posttranscriptional 5' and 3' end processing in the eukaryotic nucleus, and CCA (which forms the mature 3' end of all tRNAs) must be added by tRNA nucleotidyl transferase before tRNA can be aminoacylated and utilized in translation.
What is the function of the 3 end of the tRNA? ›At the 3' end of the tRNA molecule, opposite the anticodon, extends a three nucleotide acceptor site that includes a free -OH group. A specific tRNA binds to a specific amino acid through its acceptor stem.
Why is it called tRNA? ›transfer RNA / tRNA
Transfer ribonucleic acid (tRNA) is a type of RNA molecule that helps decode a messenger RNA (mRNA) sequence into a protein. tRNAs function at specific sites in the ribosome during translation, which is a process that synthesizes a protein from an mRNA molecule.
Introduction. Transfer RNAs (tRNAs) range in length between 70 and 100 nucleotides. tRNAs are acylated with the cognate amino acid by their cognate aminoacyl-tRNA synthetase (aaRS), and the resulting aminoacyl-tRNAs are substrates for ribosomal protein synthesis.
Who named tRNA? ›
Francis Crick called the tRAN as adaptor molecule because it attaches itself via initiation and elongation factors to the ribosome- mRNA complex which facilitates the incorporation of the correct amino acid to the growing polypeptide chain by its specific anticodon to the mRNA codon.
Is tRNA 2d or 3d? ›All tRNAs conform to a secondary structure described as a “cloverleaf”, and fold in three-dimensional space into an “l-shaped” molecule, in which the amino acid and the anticodon are at opposite ends of the molecule.
Does tRNA have 5 and 3 ends? ›During maturation, tRNA molecules undergo a series of individual processing steps, ranging from exo- and endonucleolytic trimming reactions at their 5'- and 3'-ends, specific base modifications and intron removal to the addition of the conserved 3'-terminal CCA sequence.
Are there 64 different tRNA? ›Although there are 64 different codons ( 61 codons code for amino acid while 3 are stop codons), most cells have only 40 to 60 different tRNAs.
How many genes does tRNA? ›The human genome contains more than 500 tRNA genes to decode 61 codons.
How much tRNA is in a cell? ›A cell contains several hundred thousand tRNA molecules, each of which consists of only 70 to 90 nucleotides folded into a cloverleaf-like pattern.
Does tRNA have a 5 end? ›5′ tRNA halves are derived from the same part of tRNA molecules as 5′ tRFs, indeed they contain the 5′ tRF sequence. However, translation repression by 5′ tRNA halves requires a run of at least four guanosine residues at the 5′ end of the molecule, which is present in tRNAAla and tRNACys only.
What is the function of transfer RNA tRNA quizlet? ›The function of tRNA is to bring the amino acids and place them in the correct potsition to create the desired protein. The ribosomes are made up of rRNA and proteins. There are actually 2 subunits to each ribosome.
What is the main function of mRNA tRNA and rRNA? ›mRNA provides a template for gene coding during protein synthesis, tRNA carries the amino acids to the ribosomes, which has to be added to the polypeptide chain and rRNA forms ribosomes along with proteins.
What is the function of transfer RNA Quizizz? ›What is the function of transfer RNA? It is a part of the ribosome. It bonds to other RNA molecules, leading to their destruction. It delivers the correct amino acid to the ribosome.
What is the function of tRNA in the process of making proteins quizlet? ›
What is the role of tRNA in protein synthesis? To deliver the amino to deliver the amino acids. Picks up the amino acids and then delivers them to the ribosome. tRNA ensures the correct amino acid is delivered at the correct time by matching anticodons to mRNA strands.
What are the two important functions of tRNA molecules? ›Function of tRNA
The job of tRNA is to read the message of nucleic acids, or nucleotides, and translate it into proteins, or amino acids. The process of making a protein from an mRNA template is called translation.
Transfer ribonucleic acid (tRNA) is primarily synthesized from tRNA gene through transcription by RNA polymerase and becomes the mature form via several steps: processing, splicing, CCA addition and posttranscriptional modification.
What are the 3 functions of rRNA? ›Role of Ribosomal RNA in Translation
Translation of the mRNA sequence requires the involvement of rRNA at every step – initiation, elongation and termination.
transfer RNA / tRNA
Transfer ribonucleic acid (tRNA) is a type of RNA molecule that helps decode a messenger RNA (mRNA) sequence into a protein. tRNAs function at specific sites in the ribosome during translation, which is a process that synthesizes a protein from an mRNA molecule.
The role of tRNA is to read the message of nucleic acids, or nucleotides, and to convert it into proteins or amino acids. Note: The method of generating a protein from the mRNA prototype is called translation. tRNAs are ribonucleic acids and are thus able to form hydrogen bonds with mRNA.
What is the function of RNA short answer? ›The primary function of RNA is to create proteins via translation. RNA carries genetic information that is translated by ribosomes into various proteins necessary for cellular processes. mRNA, rRNA, and tRNA are the three main types of RNA involved in protein synthesis.