BIO1022 Lecture Notes - Lecture 1: Stop Codon, Polysome, Start Codon
30 May 2018
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BIO1022 Lecture 1 – DNA transcription, translation and mutation
- two strands of DNA are reverse complement
• T - A, C - G
• base pair joined by hydrogen bonding
- RNA single stranded
- DNA to RNA - transcription
- DNA - RNA - protein
- viruses can produce DNA from RNA - reverse transcription
- production of mRNA - nucleus
- translation - cytoplasm
- transcription
• the DNA directed synthesis of RNA
• RNA polymerase - splits double helix - starts producing RNA - 5-3 prime
direction -
• formed covalent bonds between RNA nucleotides - complementary base
incorporated into mRNA.
• transcription unit - area being transcribed
• promotor - RNA polymerase binds to the promotor and the DNA strands
unwind and the polymerase initiates RNA synthesis at the start point on
the template strand
• elongation -
• termination - RNA transcript is released and the polymerase detaches
from the DNA
• eukaryotic specific difference
•
o promotor has a TATA box
o transcription factors bind to TATA - RNA polymerase attaches -
unwinds DNA
o additional processing steps to RNA
o
▪ pre mRNA - addition of methyl cap - added enzymatically to
the 5 prime end - 3 prime end - addition of adenines - poly-
A tail.
▪
▪ both required for stability
▪ prevent it from being degraded
▪ methyl cap required for exit from nuclear pore into
the cytoplasm
o splicing
o
▪ introns cut out and exons spliced together
▪ UTR - untranslated regions
▪
▪ regulate translation
▪ splicing forms coding sequence CDS = open reading frame
ORF
▪ spliceosome - a complex of proteins and RNAs
▪ alternative splicing
▪
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