transcription

where does this occur

nucleus for eukaryotes, throughout the cell in prokaryotes

template strand

• 3’ → 5’

• used by RNA polymerase to build the RNA strand

• complimentary to template strand

coding strand

• 5’ → 3’

• same sequence as RNA, except T instead of U

• matches mRNA

• lowk irrelevant

how is mRNA made?

• 5’ to 3’ direction

• reads the template strand 3’ → 5’ so makes it in 5’ → 3’ direction

what does RNA polymerase bind to?

• the promoter region

• recognizes the TATA box in eukaryotes

  • easy to break b/c two hydrogen bonds, requiring less energy

initiation stage of transcription

• RNA polymerase bonds to the promoter region

• recognizes the TATA box

• RNA polymerase unwinds a small section of this DNA

• that region is then transcribed into RNA (mRNA)

elongation stage of transcription

• reads DNA 3’ → 5’ to build RNA 5’ → 3’

• RNA nucleotides added one by one

• multiple RNA polymerases can transcribe simultaneously

termination stage of transcription

• when RNA polymerase reaches the DNA sequence called the termination sequence

• many adenines

• A’s on the DNA template strand become U’s on the RNA strand

• these proteins recognize the U’s and tell them to stop working

• RNA strand is released

exons vs introns

• exons - important sequences that code for proteins

• introns - unnecessary sequences that must be removed

why must introns be removed

• the mRNA might not form the correct protein

• spinal muscular atrophy can occur, leading to muscle weakness and shrinking

three important modifications before mRNA leaves the nucleus

• splicing

  • removing introns and exons join together by the enzyme spliceosome

• adding a 5’ cap

  • 7 guanine molecules

  • help ribosomes recognize mRNA for protein production

• adding a 3’ poly-A-tail

  • chain of A’s that prevent mRNA from being broken down