Do Prokaryotes Have tRNA: Why, How And Detailed Insights

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Transfer RNA or simply tRNAs are present in prokaryotes.

To answer the question “Do prokaryotes have tRNA?”, the answer is obviously it does. Since all organisms require the help of tRNA to complete protein synthesis it is essential in prokaryotes as well.

tRNA is one of the varieties of RNA molecule that physically links mRNA and the amino acid sequence of the proteins it translates. This is done by the tRNA by transferring an amino acid to the ribosome hence the name.

ALL ABOUT tRNA:

  • tRNA, a  type of RNA molecule that is made up of 76- 90 nucleotides approximately.
  • tRNA or transfer-RNA was formerly referred to as sRNA or simply put as soluble RNA.
  • Every tRNA molecule has two functional areas: a trinucleotide region called the anticodon and a region for attaching a specific amino acid
  • Transfer RNA carries an amino acid to an organelle called the ribosome.
  • Complementing a 3-nucleotide codon in the transcribed mRNA by a 3-nucleotide anticodon in the tRNA is what results in translation (i.e. formation of protein molecule) based on the mRNA code.
  • Hence tRNAs are necessary for the process of translation in both prokaryotes and eukaryotes.
  • The D-loop, T loop, variable loop, and anticodon loop are all part of the secondary structure of tRNA that looks like a
  • cloverleaf.
  •  Through coaxial stacking of the T and D loops, the tRNA folds into an L-shaped tertiary structure.
do-prokaryotes-have-tRNA
Clover leaf structure of tRNA Image: Wikipedia

 Function of tRNA in prokaryotes:

The function of tRNA in prokaryotes is the same as that in other organisms.

The tRNA’s main function is to read nucleotides and convert them into the respective proteins or simply carry out protein synthesis via translation. tRNAs read the mRNA code in the form of 3 letter nucleoside fragments called codons.

Peptide syn.svg
How tRNA functions in translation
Image: Wikipedia

A total of 64 3 letter codons are present that read 21 amino acids. Some also start or stop the translation process – called start and stop codons respectively. They are present in specified locations. There are also more than 1 codon coding for the same amino acid.

Eg the codons CGT, CGC, CGA, CGG, AGA, AGG all code the same amino acid Arginine.

Arginin Arginine.svg
Structure of Arginine
Image: Wikipedia

Apart from translation, tRNA identifies the enzyme Aminoacyl tRNA synthetase, which grabs certain amino acids from the cytoplasm and transports them to the site of translation.

Why is initiator tRNA formylated in prokaryotes?

Translation Initiator tRNA or simply initiator tRNA is crucial in both eukaryotes and prokaryotes.

By using specialised base pairing between its anticodon triplet CAU and the general initiation codon AUG in the mRNA, tRNA plays a critical role in the commencement of protein synthesis in both prokaryotic and eukaryotic cells.

Protein translation can only start once the initiation complex along with the 30S ribosome unit recognizes the translation start site on the mRNA. This initiator complex comprises of formylmethionine or (fMet-tRNAfMet) and three proteins called initiation factor-1 (IF1), Initiation factor 2 or  IF2 and Initiation Factor or IF3 respectively.

1280px S N Formylmethionine V.1.svg
Structure of N-Formyl methionine Image: Wikipedia

The initiator tRNA formation is a compulsory step the allows to be able to the initiation factors and carry them to the mRNA and start the process of translation altogether. It is only after formylation that the tRNA can recognize the initiator codons on the mRNA.

tRNA processing in prokaryotes:

  • tRNA precursors often have additional nucleotides at both their 5′ and 3′ ends, as well as intervening sequences in the centre of the molecule in some cases.
  • Additional tRNAs may be included as part of the extra nucleotide sequences if the precursor is multimeric.
  • Furthermore, precursors frequently lack the 3′ terminal -CCA sequence seen in all working tRNAs, as well as the entire complement of changed nucleotides that define tRNA structure.
  • In various prokaryotic species, tRNA genes can be found in several settings. They are found as single genes in diverse systems,8 in clusters having several tRNA sequences (as many as 21 in Bacillus subtifi),” in the spacer and distal sections of rRNA operons, and in conjunction with protein genes.
  • Several tRNA gene transcripts have been discovered as a result of these different forms of gene organisation. As a result, tRNA precursors representing transcripts from a single tRNA gene or clusters of tRNA genes have been discovered.
  • Endonucleolytic cleavages, which serve to separate the tRNA sequences from extraneous nucleotide residues or other RNAs, are the key processing events in the development of tRNAs from all types of precursors.
  •  If RNaseP is used to do the main cleavage, the mature tRNA’s 5′ terminal is produced. When it comes to monomeric precursors, this is frequently the case.
  • Multimeric and polycistronic precursors containing tRNA sequences, on the other hand, are frequently cleaved by different endoribonucleases to produce smaller fragments, which are then further processed to provide the mature tRNA 5′ and 3′ termini.
  • In typically developing wild type cells, intact primary transcripts are not found, suggesting that endonucleolytic cleavages occur quickly during or soon after transcription. tRNA precursors can be detected in normal cells under particular conditions, such as when a processing system is overloaded by a high number of transcripts or when a transcript has a poor substrate.
  • When a tRNA gene cloned in a bacteriophage or plasmid is injected into bacteria or eukaryotic cells, this is something commonly seen.
  • The activity of the endonuclease RNase P can create the 5′ phosphoryl terminal of mature tRNAs from tRNA precursors.

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