DNA and Protein Synthesis

DNA and Protein Synthesis

DNA Structure and Replication

DNA Structure

  • DNA is a type of nucleic acid made up of two polynucleotide chains that twist around each other to form a double helix.
  • Each polynucleotide strand is made up of repeating units called nucleotides.
  • A nucleotide consists of a deoxyribose sugar, a phosphate group, and one of four possible nitrogenous bases: adenine (A), thymine (T), guanine (G), or cytosine (C).
  • DNA has a complementary base pairing rule, where A pairs with T, and C pairs with G via hydrogen bonds.

DNA Replication

  • DNA replication is a semi-conservative process where each of the two strands act as a template on which a new complementary strand is synthesized.
  • The process begins at origins of replication and progresses in both directions, forming a replication fork.
  • The enzyme DNA helicase unwinds the double helix by breaking the hydrogen bonds between the pairs of bases.
  • DNA polymerases then add nucleotides to the exposed strands following the base pairing rules.
  • The synthesis occurs in a 5’ to 3’ direction, with leading and lagging strands due to the antiparallel nature of DNA.

Protein Synthesis

Transcription

  • Protein synthesis begins with transcription, where the DNA is used as a template to create a messenger RNA (mRNA) molecule.
  • RNA polymerase binds to the promoter region on the DNA strand and begins to synthesise the RNA strand.
  • Unlike in DNA, in RNA, uracil (U) replaces thymine.

Translation

  • Translation occurs at the ribosome, where the mRNA is used as a template to build a protein.
  • The process involves transfer RNA (tRNA) molecules which carry the appropriate amino acids that match the codons on the mRNA.
  • Three stages occur in this step: initiation, in which the ribosome subunits assemble; elongation, where the amino acids are added to the growing chain; and termination, when the protein synthesis is complete and the new polypeptide is released.
  • Translation is an example of the genetic code being ‘read’ and turned into a polypeptide chain.

The structure of DNA and the process of protein synthesis are fundamental to all life, and understanding these processes leads to a deeper comprehension of many aspects of biology.