t RNA | Anatomy2Medicine
t RNA

t RNA

    • Structure
      • 75–90 nucleotides

 

  • 2º structure, cloverleaf form
  • anticodon end is opposite 3′ aminoacyl end.

 

      • All tRNAs, both eukaryotic and prokaryotic, have CCA at 3′ end along with a high percentage of chemically modified bases. (Remember : CCA Can Carry Amino acids. )

 

  • The amino acid is covalently bound to the 3′ end of the tRNA.
  • T-arm: contains the TΨC (thymine, pseudouridine, cytosine) sequence necessary for tRNA ribosome binding.

 

      • D-arm: contains dihydrouracil residues necessary for tRNA recognition by the correct aminoacyltRNA synthetase.

 

  • Acceptor stem: the 3′ CCA is the amino acid acceptor site.

 

The reaction proceeds in two steps. In the first step, the substrate amino acids are activated consuming ATP (part a), and in the second step, the reaction intermediate, aminoacyladenylate (aminoacyl-AMP), is transferred to the acceptor end of tRNAs (part b)

 

  • Charging

 

      • Aminoacyl-tRNA synthetase (1 per amino acid; “matchmaker”; uses ATP) scrutinizes amino acid before and after it binds to tRNA.
      • If incorrect, bond is hydrolyzed.
      • The amino acid-tRNA bond has energy for formation of peptide bond.

 

  • A mischarged tRNA reads usual codon but inserts wrong amino acid.
  • Aminoacyl-tRNA synthetase and binding of charged tRNA to the codon are responsible for accuracy of amino acid selection.
  • tRNA wobble
  • Accurate base pairing is required only in the first 2 nucleotide positions of an mRNA codon, so codons differing in the 3rd “wobble” position may code for the same tRNA/amino acid (as a result of degeneracy of genetic code).

 

Exam MCQ

Which of the following becomes convalently attached to tRNA during protein synthesis?

  1. amino acid
  2. eIF3
  3. mRNA
  4. 30S ribosomal subunit
  5. 50S ribosomal subunit

Ans A

Exam MCQ

autoantibodies against aminoacyl-tRNA synthetases (ARS) are strongly associated with interstitial lung disease (ILD) development in

  1. SLE
  2. Rhuematoid arthritis
  3. polymyositis and dermatomyositis
  4. Sjogren’s syndrome

Ans C

In the treatment of polymyositis and dermatomyositis (PM/DM), the complication of interstitial lung disease (ILD) is an important prognostic factor. It has been reported that autoantibodies against aminoacyl-tRNA synthetases (ARS) are strongly associated with ILD.

Exam MCQ

An 22-year girl pustular acne having these lesions over the past several years, which resolved spontaneously. However, the lesions have increased in quantity recently. The dermatologist prescribes an oral antibiotic for the treatment of these lesions. The drug most likely acts by which of the following mechanisms?

o A. Blocks ribosomal initiation complex formation

o B. Causes misreading at translation initiation

o C. Interferes with translocation during translation

o D. Inhibits ribosomal peptidyl transferase

o E. Prevents binding of aminoacyl-tRNA to ribosomes

Ans e

The drug belongs to the Tetracycline class which inhibits protein synthesis by preventing binding of Aminoacyl tRNA to the ribosomal 30S subunit