DNA

DNA Structure

  • DNA, or Deoxyribonucleic Acid, is the molecule that stores and carries the genetic information of an organism.
  • It’s composed of two long chains of nucleotides that twist around each other to form a double helix structure.
  • Each nucleotide consists of a sugar, a phosphate group, and one of four nitrogenous bases: adenine (A), thymine (T), cytosine (C), or guanine (G).
  • The bases form pairs and always pair up in the same way - A with T, and C with G. These are known as base pairs making up the ‘rungs’ of the DNA ladder.

DNA Replication

  • DNA replication is the process by which DNA makes an exact copy of itself. This is critical for cell division.
  • The double helix of DNA uncoils and the base pairs split apart, assisted by a group of enzymes called DNA helicases.
  • Each separate strand of DNA acts as a template for building a new strand. New nucleotides arrive and match up with their complementary bases on the template - A with T and G with C.
  • The new DNA molecules rewind into the classic double helix structure.

DNA and Protein Synthesis

  • The sequence of bases in a DNA molecule codes for the sequence of amino acids in a protein - this is known as a gene.
  • The process of protein synthesis involves two key stages: transcription and translation.
  • In transcription, the DNA unwinds and an RNA molecule is formed from one of the DNA strands, a process involving the enzyme RNA polymerase.
  • The RNA molecule (messenger RNA or mRNA) leaves the nucleus and moves to the cytoplasm.
  • In translation, the mRNA molecule is ‘read’ by structures known as ribosomes and a protein is assembled based on the code.

DNA and Genetic Variation

  • Genetic variation is made possible due to the endless combinations possible in the DNA sequence.
  • Mutations, or changes in the DNA sequence, can lead to genetic variation and evolution.
  • However, not all mutations have an effect. Only those that occur in genes that code for proteins are likely to influence an organism’s characteristics.
  • These mutations can be caused by exposure to radiation, certain chemicals, or can occur randomly during DNA replication.