Transcription and Translation

Transcription and Translation


  • Transcription is the first step in protein synthesis where the DNA sequence of a gene is copied into messenger RNA (mRNA).
  • It occurs in the nucleus in eukaryotes and the cytoplasm in prokaryotes.
  • This process is catalysed by RNA polymerase, an enzyme that unwinds the DNA and synthesizes the RNA transcript.
  • Transcription elicits three main stages: initiation, elongation, and termination.
  • During transcription, only one DNA strand (template strand) is used to synthesise mRNA.
  • Transcription results in the replacement of the thymine (T) base in DNA with uracil (U) in mRNA.


  • Translation is the process that interprets the genetic information in mRNA to synthesise a protein.
  • This process occurs in the cytoplasm, specifically on the ribosomes.
  • Every three nucleotides on the mRNA form a codon, which corresponds to a specific amino acid.
  • The order of these codons determines the sequence of amino acids in the resulting protein.
  • Transfer RNAs (tRNAs) carry corresponding amino acids to the ribosome, based on the sequence of codons in the mRNA.
  • The amino acids are then joined together by peptide bonds in a process called peptide bond formation.
  • The chain of amino acids (polypeptide) continues to grow until a stop codon is reached, signalling the end of translation.

Post-Translational Modifications

  • After translation, many proteins undergo post-translational modifications to become fully functional.
  • This can include the addition of functional groups, cleavage of certain amino acids, or formation of disulphide bridges.
  • Proteins could also fold into their specific 3D structures, crucial for their function.
  • Some proteins require the addition of other chemical groups (like phosphates or carbohydrates) as part of their maturation process.
  • These modifications enhance the diversity of the protein functions that can be derived from the genetic code.