Protein Synthesis

Protein Synthesis

  • Protein synthesis is the biological process of creating proteins in cells.
  • This process comprises two stages: transcription and translation.

Transcription

  • Transcription takes place in the cell’s nucleus where the DNA is found.
  • Here, a segment of the DNA, called a gene, is used as a template to create a molecule of messenger RNA (mRNA).
  • The enzyme RNA polymerase attaches to the DNA, splitting the two strands apart and copying one to make an mRNA strand.
  • The mRNA carries the genetic code from the DNA to the ribosomes, which are the site of protein synthesis.

Translation

  • In this stage, carried out in the cytoplasm by ribosomes, the mRNA binds to a ribosome and is ‘read’.
  • This ‘reading’ process generates a sequence of amino acids which link together to form a polypeptide chain, the building blocks of proteins.
  • This is guided by molecules called transfer RNA (tRNA), which carry amino acids to the ribosome and match them to the appropriate codon on the mRNA.
  • Each set of three bases on the mRNA, known as a codon, codes for one specific amino acid.
  • The polypeptide chain continues to grow until a stop codon is reached, at which point it folds into its final shape to form a protein.

Protein Folding

  • Once polypeptide chains are formed, they need to fold to become functional proteins.
  • The folding process is facilitated by cell structures named chaperones.
  • If the protein doesn’t fold correctly, it can lead to diseases such as Alzheimer’s, Parkinson’s, and cystic fibrosis.

Importance of Proteins

  • Proteins play an essential role in almost all biological processes, including cell signalling, immune responses, and the catalysis of metabolic reactions.
  • Proteins also provide structural support for cells and tissues and enable cells to move.
  • The proteins are assembled according to the information encoded in the DNA; any errors in this information can lead to genetic disorders.

Key Terms

  • DNA: Deoxyribonucleic acid, holds the genetic information in cells.
  • RNA: Ribonucleic acid, carries information from the DNA to the ribosome.
  • mRNA: Messenger RNA, carries the genetic code from the DNA in the nucleus to the ribosomes in the cytoplasm.
  • tRNA: Transfer RNA, assists in translation by carrying and aligning amino acids for polypeptide synthesis.
  • Amino Acids: The building blocks of proteins.
  • Proteins: Complex macromolecules that perform numerous roles in the body, manufacturing, breaking down, and transporting a wide range of substances.
  • Codon: A sequence of three nucleotides which together form a genetic code for the synthesis of a specific amino acid or a stop signal.
  • Chaperones: Proteins in the cell that assist in the folding of other proteins into their proper three-dimensional structures.
  • Polypeptide Chain: A chain of amino acids linked by peptide bonds, which folds to form a protein.