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Molecular Biology


Actual synthesis of a protein under the direction of mRNA.

  • mRNA is translated into the amino acid sequence of a protein

  • mRNA- template for translation (information)

  • Ribosome- coordinate recognition & catalyze bond formation

  • tRNAs- physical interface between amino acid & codon

  • Aminoacyl-tRNA synthetases- Couples amino acid to tRNAs

mRNA: "messenger" RNA

Carries the code for protein from DNA

  • Codon: an ordered series of 3 nucleotide-long unit in the protein coding region of the mRNA or DNA​

RNA Codon.png
  • Open Reading Frame (ORF): protein coding region of mRNA located within the mRNA

    • Start Codon: 1st amino acid; defines the reading frame​

    • Stop Codon: Termination; defines the end of the ORF​

Start & Stop codons.gif

tRNA: "transfer"RNA

Transports amino acids to ribosomes during translation

  • Provides the physical interface between the amino acids being added to the growing polypeptide chain & the codons in the mRNA

trna structure.jpeg

rRNA: Ribosomal ribonucleic acid or Ribosomal RNA

RNA component of the ribosome

  • Structural component

  • Directly responsible for the key functions of the ribosome

    • provides a mechanism for decoding mRNA into amino acids  

    • interacts with tRNAs during translation by providing peptidyl transferase activity


Prokaryotes- Ribosome-binding site (RBS)

Eukaryotes- 5' cap

  • Untranslated Region (UTR): untranslated sequences located in eukaryotic mRNA


RNA + Proteins= functional ribosome

Composed of 2 Subunits: 

  • Large Subunit: contains the peptidyl transferase center for the formation of peptide bonds

  • Small Subunit: contains the decoding center for charged tRNAs read or decode the codon units of the mRNA


Aminoacyl-tRNA Synthetases: 

"Charging" the tRNA with the amino acid

Enzyme that catalyst of the esterification of a specific amino acid to 1 or more its compatible cognate tRNAs to form an aminoacyl-tRNA.

  1. Amino acid react with ATP to become adenylylated with the release of AMP- Adenyllation of amino acid

  2. Transfer of the adenylylated amino acid to tRNA

aminoacyl tRNA Synthetase.jpg

Translation Steps​

  1. Initiation

    • Formation of an initiation complex in which the ribosome is bound to the specific initiation (start) site on the mRNA while the initiator tRNA is annealed to the initiator codon & bind to the ribosome​

  2. Elongation

    • Amino acids join to the growing polypeptide chain according to the sequence specified by the mRNA.

    • Same steps are repeated over & over again until the termination codon is reached in the mRNA. 

  3. Termination

    • Termination codon gives the signal to release the ready-made protein from the ribosome.

  4. Ribosome Recycling

    • Critical last step in translation after the release of the polypeptide chain

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