Protein Synthesis
Protein Synthesis:
- Protein synthesis is the process in which polypeptide chains are synthesised from DNA in the ribosomes.
- Transcription: Where small sections of DNA are replicated as mRNA in order to leave the nucleus through nuclear pores.
- Translation: The assembly of polypeptide chains in the ribosome.
- DNA Helicase 'unzips' the DNA double helix by breaking the hydrogen bonds between the base pair nucleotides, exposing the sense strand (the code) and the antisense strand (the complementary sequence of base pairs for the code).
- Free nucleotides move to bond to the exposed sense strand nucleotide bases. In mRNA, thymine is replaced by uracil.
- RNA polymerase forms phosphodiester bonds between the complementary bases, 'zipping up' the complementary nucleotides.
- Once the mRNA strand is complete, it detaches from the sense strand template and leaves nucleus through nuclear pore.
Translation:
- mRNA binds to ribosome at the 'AUG' start codon.
- Complementary tRNA binds to start codon on mRNA.
- Another complementary tRNA anticodon binds to the next codon on the mRNA.
- A peptide bond is formed between the two amino acids.
- Once a peptide bond is formed, the first amino acid exits the ribosome, and the ribosome moves onto the next codon and this process repeats.
- This process ends when a stop codon is reached, and the primary structure of the protein is completed. Post-translational modification may occur in the golgi apparatus before the folding of the polypeptide chain into secondary and tertiary structure begins.