Protein Synthesis

Protein synthesis is divided into two phases: transcription and translation.

In transcription, RNA polymerase unzips DNA and reads it in the 3' to 5' direction. Free RNA nucleotides are base paired with the exposed DNA nucleotides and assembled into mRNA. The mRNA then leaves the nucleus and moves to the ribosomes in the cytoplasm. Transcription ends and translation begins.

Translation has four stages.

• In the amino acid activation stage amino acids are attached to the appropriate tRNA molecules. A molecule of ATP is used to activate the tRNA.
  
  
• In the initiation stage the ribosome moves along the mRNA strand until it reaches the code for formyl methione (AUG).
  
  
• In the elongation stage the tRNA matches its anti-codon (three nucleotides) with the mRNA codon (three nucleotides). The amino acid on the previous tRNA is transferred to the newly arrived tRNA and the empty tRNA leaves. This is repeated over and over as the ribosome moves along the mRNA strand.
  
  
• In the termination stage a nonsense code is reached and the protein is released.