ka5: structure of the genome

• The genome of an organism is its entire hereditary information encoded in DNA.
• A genome is made up of genes and other DNA sequences that do not code for proteins.

  • Most of the eukaryotic genome consists of non-coding sequences.
• DNA sequences that code for protein are defined as genes. Other sequences regulate transcription and others are transcribed but never translated.

  • Details of regulation of transcription (for example Jacob–Monod hypothesis) not required.
  • tRNA and rRNA are non-translated forms of RNA.
• The genome of an organism is its entire hereditary information encoded in DNA.
• Genes are DNA sequences that code for protein. However, a genome is not made up exclusively of genes. Genomes of eukaryotes only contain a tiny proportion of genes. The remainder of the genome is composed of DNA sequences that do not code for protein.
• Most of the genome is made up of non-coding sequences. Some have no function at all, some are yet to be discovered. However the known roles played by some non-coding sequences are:

   

  • Protection:

  Some of the repetitive sequence makes up a telomere at the ends of the chromosome. This prevents them from fraying at the ends.

   

  • Regulation of transcription

  RNA polymerase requires the assistance of transcription factors (known as activators) to begin transcription.
• The activators are bound to non-coding sequences of DNA called regulators. The DNA strand bends to bring the activators into contact with other transcription factors near the promoter region of the gene to form a molecular complex. Transcription can now begin.

  
• Some non-coding sequences code for forms of RNA other than mRNA.  These types of RNA have specific functions but are never translated into protein e.g. transfer RNA, ribosomal RNA and RNA fragments.