DNA and RNA Basics

DNA and RNA Basics

DNA and RNA: An Overview

  • DNA (Deoxyribonucleic Acid) and RNA (Ribonucleic Acid) are the central molecules of life which carry the genetic information.
  • DNA is a double-stranded molecule while RNA is usually single-stranded.
  • DNA is contained within the nucleus, while RNA can be found in the nucleus as well as the cytoplasm.

The Nucleotides: DNA and RNA’s Building Blocks

  • Both DNA and RNA are made up of nucleotides, comprising a phosphate group, a sugar (deoxyribose in DNA and ribose in RNA), and a nitrogenous base.
  • The DNA bases are adenine (A), thymine (T), guanine (G) and cytosine (C), while those of RNA are adenine (A), uracil (U), guanine (G) and cytosine (C).
  • Adenine always pairs with thymine in DNA and with uracil in RNA, while guanine always pairs with cytosine.

DNA Structure

  • The structure of DNA is a double helix, resembling a twisted ladder, with phosphate and sugars forming the backbone and base pairs forming the rungs.
  • Hydrogen bonds between the complementary bases maintain the structure of the DNA helix.
  • The sequence of bases in the DNA molecule codes for the sequence of amino acids in proteins.

RNA Structure

  • RNA molecules are usually single-stranded, but can fold into complex three-dimensional structures.
  • There are several types of RNA, including mRNA (Messenger RNA), tRNA (Transfer RNA) and rRNA (Ribosomal RNA), each with distinct roles in protein synthesis.

DNA Replication

  • During DNA replication, the DNA helix unwinds and each strand serves as a template to synthesise a new, complementary strand.
  • DNA replication is semi-conservative, each new DNA molecule consists of one old strand and one new strand.

Protein Synthesis: From DNA to Protein via RNA

  • The process of transcription makes a copy of a gene as an mRNA molecule.
  • The mRNA then moves from the nucleus to the cytoplasm and serves as a template for protein synthesis in a process called translation.
  • Each group of three bases on the mRNA (a codon) corresponds to a specific amino acid. Each codon is ‘read’ sequentially, and corresponding amino acids are joined together to form the protein.