Protein Synthesis

Protein Synthesis

  • Protein synthesis is the biological process of building proteins based on the information carried in DNA.

Transcription

  • Transcription is the first step in protein synthesis. During this process, a segment of DNA serves as a template for mRNA synthesis.
  • Transcription takes place in the nucleus where RNA polymerase binds to a specific region of the DNA molecule, the promoter region.
  • RNA polymerase moves along the DNA strand, creating an RNA molecule from free nucleotides, following the base pairing rules.

Translation

  • Once an mRNA molecule has been transcribed, it leaves the nucleus and enters the cytoplasm.
  • In the cytoplasm, it binds to a ribosome, where translation occurs.
  • During translation, the ribosome moves along the mRNA, reading the codons.
  • Each codon codes for an amino acid. These are brought to the ribosome by molecules of tRNA, each of which has an anticodon corresponding to a codon on the mRNA.
  • The tRNA molecules release their amino acids, which join together in a chain, forming a polypeptide chain.

Role of Ribosomes

  • Ribosomes are the sites of protein synthesis. They consist of two subunits, which sandwich the mRNA and tRNA during protein synthesis.
  • Large ribosomal subunit carries out peptidyl transferase activity, which forms peptide bonds between amino acids.
  • Small ribosomal subunit reads the mRNA and binds to the tRNAs.

Protein Folding and Processing

  • After synthesis, the amino acid chain begins folding into its functional shape, aided by chaperone proteins.
  • The folding and any required modifications, such as phosphorylation or glycosylation, occur in the endoplasmic reticulum (ER) and Golgi apparatus.
  • After these processing steps, the protein can be shipped off to fulfil its role elsewhere in the cell.

Regulation of Protein Synthesis

  • The rate of protein synthesis is controlled at multiple levels, including regulating transcription, controlling mRNA degradation, and modification of finished proteins.
  • Gene expression can be altered by DNA methylation and histone modification, two forms of epigenetic regulation.
  • The turning on and off of genes can have a profound impact on protein synthesis and the ultimate function of the cell and organism.