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5.3.1.1. Transfer RNA

Transfer RNA

The transfer RNA is a kind of ribonucleic acid that is responsible for transporting the amino acids to the ribosomes where, according to the specified sequence in messenger RNA (transcribed, in turn, of the DNA) are proteins synthesized .

The RNA soluble or transfer (tRNA) represents approximately 15% of the entire RNA. It is made up of about 80 nucleotides, and is dispersed in the cell cytoplasm.

There is a tRNA molecule for each amino acid, with a specific triplet of nitrogenous bases, the anticodon, which varies between the different tRNAs.

The tRNA is single-stranded, but it presents areas of intra-strand complementarity, that is, complementary areas within the same chain, which causes them to pair, giving a characteristic structure similar to that of a three-leaf clover. In the secondary structure of tRNAs the following characteristics are distinguished:

  • An arm called the D-arm and its handle. It is so named because it contains dihydrouridine.
  • T-arm (for carrying thymine) and its handle.
  • An arm called the anticodon and its loop, complementary to the specific codon of the mRNA .
  • An amino acid acceptor arm.

Although we speak of a cloverleaf-shaped structure, in reality, the tRNA molecule folds, acquiring a tertiary structure in the shape of an L.

In addition to the typical nucleotides of RNA, such as A, G, C and U, tRNA contains others that carry methylated bases, such as dihydrouridine (UH), ribothymidine (T), inosine (I), methylguanosine (GMe), etc., which constitute 10% of the total ribonucleotides of tRNA.

The RNA chain has two ends:

  • 5 'end: it has a triplet of nitrogenous bases in which there is always guanine (G) and a free phosphoric acid.
  • End 3': The triplet -CCA is always found. The -OH group of nucleotide A is the one that binds to the carboxyl group of the amino acid that transports the tRNA to the ribosome. The anticodon triplet corresponds to the amino acid that specifically binds each tRNA, and is complementary to the codon of the mRNA.

Therefore, the tRNA must fulfill two functions:

  • Recognize and transport specific amino acids to the ribosome.
  • Recognize the codons of the mRNA.

Fundamental ideas about transfer RNA or tRNA

The transfer ribonucleic acid or tRNA:

  • Formed by the union of ribonucleotides through phosphodiester bonds in the 5 '→ 3' sense.
  • Functions:
  • Structure:
    • An arm called the D-arm and its handle.
    • A  T-arm and its handle.
    • An arm called the anticodon and its loop, complementary to the specific codon of the mRNA.
    • An amino acid acceptor arm.
  • The RNA chain has two ends:
    • 5 'end: it  has a triplet of nitrogenous bases in which there is always guanine (G) and a free phosphoric acid.
    • 3 'end: With the -CCA triplet that binds to the amino acid that transports the tRNA to the ribosome.