RNA transcription: the process of making and RNA copy from a gene’s DNA called the mRNA

• The DNA code is transferred form a strand of DNA to mRNA in the nucleus and then the mRNA can take the code into the cytoplasm for protein synthesis.

• Transcription only occurs in the nucleus and the mitochondria

• Initiation

  • Unwind the double stranded DNA by locating the initiation point by a group of proteins called initiation factors

  • They move along the DNA strand until they reach the promoter region.

    • The promoter region is a special sequence of DNA nucleotides

      • it signals the RNA polymerase to begin the synthesis of DNA to join the protein complex

  • The most common DNA sequence in promoter region: consensus sequence

• Elongation

  • Once RNA polymerase combines with initiation factors to unwind DNA, it creates a transcription bubble.

    • Transcription bubble: region where two DNA strands are separated and exposed

    • only one DNA strand is used to synthesize the RNA molecule

  • RNA polymerase moves across the double strand that runs from the 3’ to 5’ direction

    • uses the anti sense strand to direct the synthesis of RNA molecule

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  • RNA is copied from the template strand, RNA polymerase can only read beginning at 3 end ending at 5 end.

  • RNA strand: template strand/antisense strand

  • DNA strand: coding strand/non template strand.

• The nucleotides found on the sense strand is similar to the ones found in the RNA strand T is replaced with A.

RNA processing:

• In eukaryotic cells they found that the mRNA code is significantly shorter than the DNA code.

• the newly synthesized mRNA consists of non coding regions called introns/intervening sequences and coding regions called exons. (PREMRNA molecule)

• Splicosome - essential for removing the introns while gluing and splicing together the exons

• Processing of the mRNA:

  • adding a protective cap on the 5’ end and adding a tail of many adenine nucleotides called the polyadenosine tail tot he 3’ end of the mRNA.

  • connects the exon by forming proper phosphodiesther linkages

RNA polymerase

• In prokaryotic organisms, there’s only 1 RNA polymerase

• In eukaryotic organisms, there’s three different types of RNA polymerases.