Gene Structure

• The genetic code is stored as a three letter code of nucleotides


  In DNA these are called triplets

  In RNA these are called codons
• • DNA triplets in a gene are transcribed into a polymer called mRNA
• • mRNA codons correspond to a specific amino acid, resulting in translation of mRNA to a protein at the ribosome
• List all components of a gene:

  Promoter region

  Introns

  Exons

  Termination sequences

  Operator regions
• Promoter sequences are DNA sequences that define where transcription begins
• The promoter region is upstream (5’ end) of the gene being transcribed
• • RNA polymerase and the necessary transcription factors bind to the promoter sequence and initiate transcription.
  • In eukaryotes the promoter region often consists of a sequences of bases TATAAA – the TATA box
• Introns are the non-coding regions of DNA

  
• Each triplet or codon codes for one specific amino acid
• The termination sequence is a sequence of DNA that signals the end of transcription
• The Operator is typically only found in prokaryotic genes and serves as a binding site for repressor proteins
• • Repressor proteins act to inhibit gene expression
• The leader region is a section of DNA just upstream of the coding region and downstream of the promoter and operator
• The coding region of a gene is the part where the RNA polymerase binds to and transcribes the gene
• • Transcription factors are proteins that can attach to DNA and regulate gene expression
• Transcription factors can induce or repress the transcription of a gene

  
• Some prokaryotes organise genes of similar function into a structure known as an operon.


  This allows them to more efficiently control gene expression and save cellular energy.
• An operon is a cluster of linked genes that all share a common promoter and operator and are transcribed at the same time
• An operator region is a short region of DNA that interacts with repressor proteins to alter the transcription of an operon
• What are the differences between Eukaryotic and Prokaryotic genes?

  Eukaryotic genes:

  One promoter per gene 

  No operator region

  The open reading frame consists of introns and exons 

  Genes found on linear chromosomes

  Prokaryotic genes:

  One promoter and operator for multiple genes - operon

  Include an operator region where repressor proteins bind 

  The open reading frame consists only of exons 

  Genes found on a circular chromosome