Transcription vs
Translation
Central Dogma
Chargaff’s Rule
States that base ratio is 1:1
A=T
CΞG
Therefore if there are 300 Adenines
there should also be 300 Thymines in
DNA
Transcription
Initiation – RNA polymerase attaches to
the promoter region on the DNA and
begins to unzip the DNA. Promoter
normally contains TATA box, sequence
of T-A-T-A
Transcription
Elongation occurs as
RNA polymerase
unzips the DNA and
assembles RNA
nucleotides using one
strand of the DNA as a
template.
This occurs in the 5’
 3’ direction
Transcription
Termination occurs when the RNA
polymerase reaches a special sequence of
nucleotides that servers as a termination
point. In eukaryotes the termination
region is often AAAAAAAAAAA.
mRNA processing
Before mRNA can leave the nucleus several
things happen:
5’ cap is added, cap is guanine nucleotide
with 2 extra phosphates
Poly A tail added to 3’ end. Tail has about
200 adenine nucleotides.
RNA splicing – introns are removed, exons
are spliced together. Small nuclear
ribonucleoproteins or snRNP’s delete the
introns
Alternative splicing
RNA splicing
Appropriately joined
Protein
Introns
Exons
Translation
Initiation begins when the small ribosomal
subunit attaches near the 5’ end of mRNA
A tRNA carrying an amino acid attaches to the
mRNA at the start codon AUG.
The large ribosomal subunit attaches to the
mRNA forming a complete ribosome
Elongation begins when the next tRNA binds
Translation