Gene expression - Transcription

• The central dogma of molecular biology is a principal that describes the flow of genetic information, from DNA to functional groups.
• Gene expression is a process by which the information encoded in a gene is used to produce a functional gene product (can be a protein or non-coding) RNA molecule.
• 1. DNA replication
  2. Transcription
  3. Translation
• A gene is a specific region or sequence of DNA that contains instructions for producing a functional RNA molecule.
• Describe DNA

  A) Gene

  B) mRNA

  C) Protein

  D) function

  E) non-coding RNA

  F) tRna

  G) function

  
• A gene can have various roles. It is responsible for regulation of the synthesis of RNA and responsible for further processing of RNA.
• Transcription is the synthesis of RNA using information in the RNA.
• Transcription process

  The two nucleic acids are written in different forms of the same language, which is transcribed from DNA to RNA, providing a template strand.
• Transcription process

  After providing a template strand, it is used to create a complimentary strand during DNA replication.
• Transcription process

  After creating a complimentary strand, for protein coding gene, the resulting RNA molecule is a transcript of genes protein building instructions called mRNA.
• mRNA carries genetic message from the DNA to protein synthesising machinery of the cell and does this by catalysing the information of phosphodiester bonds between ribonucleotides.
• Transcription process

  RNA polymerase selects the correct nucleotides to incorporate into mRNA based on the sequence of the DNA, which is being transcribed.
• 5' -> 3' direction is the coding strand.
• 3' -> 5' is the template strand.
• DNA is transcribed to mRNA that runs a 5' -> 3' direction.
• Transcription has 3 stages:

  1. Initiation
  2. Elongation
  3. Termination
• Initiation is regulated by specific DNA sequences. Transcription factors bind to TATA box and other regions of the promoter.

  RNA Pol || binds, forming a transcriptional initiation complex.

  Then the two DNA strands seperate and RNA Pol || starts mRNA synthesis without a need of a primer.
• Label initiation

  A) promoter

  B) non-template strand

  C) template strand

  D) start point

  E) TATA box

  F) transcription factors

  G) RNA polymerase ||

  H) RNA transcript

  
• Elongation is producing RNA. RNA Pol || uses the template strand. which runs 3' - 5' direction, as a template strand and inserts complimentary RNA nucleotides in 5' - 3' direction.
• Coding sequence (DNA) -> Transcription (mRNA) -> Translation (protein)
• Coding sequence is a portion of genes DNA that is translated into a protein.
• The promoter is DNA sequence recognised by RNA polymerase to initiate transcription.
• UTR (untranslated regions) is transcribed, but not translated. They contain regulatory elements that influence gene expression. 3' UTR facilitates of poly-Atail.
• 5' cap prevents mRNA degration, promotes intron excision and provides a binding site for small ribosomal unit.
• Pony-A tail prevents mRNA degration and facilitates export of mRNA from nucleus to cytoplasm.