Name: trna modified bases and function
Uploaded: 2020-11-23T11:47:37.000Z
Duration: 2 min 36 s
Channel: JoVE

Transfer RNAs, or tRNAs, are non-coding RNAs that play a major role in protein synthesis. Eukaryotic cells contain more than 50 distinct tRNAs, each carrying a specific amino acid.
The folded tRNA has three hairpin loops: an anticodon loop, a T loop, and a D loop. The 3&#8217; end of the molecule has a conserved CCA sequence that covalently binds an amino acid. Additionally, tRNAs contain many modified bases at several positions.
A tRNA gene is transcribed by RNA Polymerase III as a long precursor tRNA, or pre-tRNA. The pre-tRNA contains a 5&#8217; leader sequence, a 3&#8217; trailer sequence comprising a polyuridine tract, a 14-nucleotide long intron, and unmodified bases.&#160;
The precursor tRNA undergoes post-transcriptional processing and modifications before it yields a mature tRNA. The extent of processing varies significantly in order and kind for different tRNAs.&#160;
The first step in the tRNA processing involves the removal of the 5&#8217; leader sequence and is catalyzed by an RNA enzyme called Ribonuclease P, or RNase P. This enzyme contains a catalytically active RNA that removes the 5&#8217; leader sequence.
In the second step, the trailer sequence at the 3&#8242; end is trimmed by one or more nucleases, such a

transfer rna synthesis

Transfer RNA Synthesis

One of the unique features of tRNA is the presence of modified bases. In some tRNAs, modified bases account for nearly 20% of the total bases in the molecule. Altogether, these unusual bases protect the tRNA from enzymatic degradation by RNases.
Each of these chemical modifications is carried by a specific enzyme, post-transcription. All of these enzymes have unique base and site-specificity. Methylation, the most common chemical modification, is carried by at least nine different enzymes, with three enzymes dedicated for the methylation of Guanine at different positions.
The nature and position of these modified bases are species-specific. Thus, there are several bases that are exclusive to eukaryotes or prokaryotes. For instance, thiolation of Adenine is only observed in prokaryotes, whereas methylation of cytosine is restricted to eukaryotes. Overall, eukaryotic tRNAs are modified to a greater extent than those from prokaryotes.
Although the nature of modifications may vary, some regions of the tRNA are always heavily modified. Each of the three stem-loop regions or &#34;arms&#34;&#160;of the tRNA have modified bases that serve unique purposes. The T&#936;C arm, named after the presence of the nucleotides, thymine, pseudouridine and cytosine, is recognized by the ribosome during translation. The DHU or D arm that contains the modified pyrimidine dihydrouracil&#160;serves as a recognition site for the aminoacyl-tRNA synthetase enzyme, that catalyzes the covalent addition of an amino acid to the tRNA. The anticodon loop often has a queuine base, which is a modified guanine. This base creates a Wobble pair with the codon sequence on the mRNA, i.e. it forms a base pair that does not follow Watson-Crick base pair rules. Usually, a tRNA binds the mRNA more &#8220;loosely&#8221; in the third position of the codon. This allows several types of non-Watson&#8211;Crick base pairing or Wobble bases at the third codon position. It has been observed that the presence of queuine&#160;in the first position of the anticodon, which pairs with the third position of the codon, improves the translation accuracy of the tRNA.

One of the unique features of tRNA is the presence of modified bases. In some tRNAs, modified bases account for nearly 20% of the total bases in the ...

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JoVE Core

Molecular Biology

Unit 1

Transcription: DNA to RNA

KEY TERMS AND CONCEPTS

trna modified bases and function

Transfer RNA (tRNA) contains many modified bases that help it work during protein synthesis. In some tRNAs, these chemical changes make up nearly 20% of the total bases. They also help protect tRNA from breakdown by RNases, which are enzymes that cut RNA.

These modifications are added after transcription, meaning after the tRNA is made from DNA. Each change is carried out by a specific enzyme with its own base and site preference. Methylation is the most common modification, and at least nine enzymes can add it. Three of these enzymes methylate guanine at different positions.

The type and location of modified bases can differ between species. Some bases are found only in eukaryotes, while others are found only in prokaryotes. For example, thiolation of adenine is seen only in prokaryotes, and methylation of cytosine is restricted to eukaryotes. Overall, eukaryotic tRNAs tend to be modified more than prokaryotic tRNAs.

Even with these differences, some parts of tRNA are usually heavily modified. The TΨC arm contains thymine, pseudouridine, and cytosine, and it is recognized by the ribosome during translation. The DHU, or D, arm contains dihydrouracil and acts as a recognition site for aminoacyl-tRNA synthetase, the enzyme that attaches an amino acid to tRNA.

The anticodon loop often contains queuine, a modified guanine. Queuine helps form a wobble pair with the mRNA codon, which means the pairing does not always follow standard Watson-Crick rules. tRNA usually binds more loosely at the third codon position, so wobble pairing can occur there. The presence of queuine in the first anticodon position, which pairs with the third codon position, can improve translation accuracy.

tRNA Modified Bases and Function

what is gene expression?

Gene Expression: From DNA to Proteins

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RNA stability describes how long an RNA molecule stays intact in a cell. Cells do not let every RNA last the same amount of time. Instead, they control RNA lifetime to help regulate gene expression. Some RNAs are made to be short-lived, while others remain stable longer. This difference matters because RNA helps carry genetic information from DNA and supports protein production. When RNA breaks down faster or slower, the cell can change how much of a protein is made. The transcript also...

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transcription

Transcription and RNA Formation

Transcription is the process that makes RNA from DNA. It begins when RNA polymerase, the enzyme that copies genetic information, binds to a gene on the DNA strand. The DNA opens so the cell can read the template strand. As RNA polymerase moves along the template strand, it builds a complementary RNA copy. The RNA strand carries the message from DNA in a form the cell can use later. This step is a key part of gene expression. The process ends when the RNA molecule is released and the DNA...

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eukaryotic rna polymerases

RNA Polymerase II and mRNA Termination

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RNA Polymerase Pausing in Elongation

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pre-mrna processing

Pre-mRNA Splicing and RNA Protection

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chromatin structure regulates pre-mrna processing

chromatin-structure-regulates-pre-mrna-processing

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mRNA Quality Control Before Export

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ribosomal rna synthesis

How Ribosomes Are Assembled in Cells

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Transfer RNA (tRNA) contains many modified bases that help it work during protein synthesis. In some tRNAs, these chemical changes make up nearly 20% of the total bases. They also help protect tRNA from breakdown by RNases, which are enzymes that cut RNA. These modifications are added after transcription, meaning after the tRNA is made from DNA. Each change is carried out by a specific enzyme with its own base and site preference. Methylation is the most common modification, and at least nine...

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bacterial transcription

Bacterial RNA Polymerase Steps

Bacterial RNA polymerase carries out RNA synthesis from DNA. In bacteria, there is no membrane-bound nucleus. As a result, transcription and translation can happen at the same time on the same DNA template. Bacterial transcription has three main stages: initiation, elongation, and termination. These stages are guided by specific DNA sequences. The promoter regions lie 10 and 35 base pairs upstream of the gene and help RNAP begin transcription. Transcription starts at the DNA base pair labeled...

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RNA Polymerase Recruitment in Transcription

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key terms and concepts

Explore how modified bases shape tRNA stability, ribosome recognition, amino acid attachment, and wobble pairing in high school biology.

tRNA Modified Bases and Function | JoVE K12

molecular biology

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tRNA Modified Bases and Function

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