Transcription

• Transcription


  The conversion of DNA to mRNA, a prerequisite to protein synthesis. It involves copying a gene's DNA sequence to make an RNA molecule.
• Steps in Transcription


  1. Initiation

  2. Elongation

  3. Termination
• Initiation


  • The DNA's recognition sites attract the RNA polymerase. RNA polymerase binds to a sequence of DNA called the promoter, found near the beginning of a gene.
• Recognition Sites


  DNA segment that attracts the RNA Polymerase
• DNA Template


  Nucleic Acid used in transcription
• RNA Polymerase


  Enzyme that plants / lays the promoter
• Coding Strand / Non-Template Strand


  The upper strand (5' → 3' directionality), the unused strand in transcription
• Template Strand / Non-Coding Strand


  The lower strand (3' → 5' directionality), the template used to create the mRNA
• Only a 3' → 5' DNA template is used in transcription
• This is because of the anti-parallel rule where the RNA Polymerase has 5' → 3' directionality
• Elongation


  The addition of nucleotides to the mRNA strand. RNA polymerase reads the unwound DNA strand and builds the mRNA molecule using complementary base pairs.
• Components Needed in Termination

  • RNA Polymerase
  • Template Strand
  • mRNA
• The RNA polymerase has a 5' to 3' directionality, which is why the TEMPLATE STRAND is used since it is anti-parallel to the direction of the template strand: 3' to 5'
• Chargaff Rule


  RNA will always be coded with the following bases: Adenine (A) → Uracil (U), Guanine (G) → Cytosine (C)
• RNA Start Codon


  The fixed starting codon of a transcribed RNA, it will always be AUG
• RNA Stop Codon


  The fixed ending codon of the RNA, it can be any of the following: UAG, UAA, UGA
• Termination


  Sequences called terminators signal that the RNA transcript is complete. Once they are transcribed, they cause the transcript to be released from the RNA polymerase.
• Pre-mRNA


  The pre-mature mRNA that must undergo GENE SPLICING to maturate and become a mRNA
• Post-Transcription Process


  The maturation of transcribed RNA shall be processed through GENE SPLICING
• Exon


  The useful RNA Gene
• Intron


  The useless RNA Gene that the Spliceosome will remove
• Spliceosome (snRNPs - small nuclear ribonucleoproteins)

  Proteins that remove the Introns