1. Transcription and
Translation

2. Central Dogma
• One gene = One polypeptide
• DNA  RNA  Protein
• DNA  RNA is called transcription
• RNA  Protein is called translation
• Prokaryotes and Eukaryotes process
genetic information differently

3. How are genes switched on and off?
Cells only use some of their genes most of the time
You do not want nerve cells making liver cell proteins
Most genes can be switched on or off
Example
Gene
Operator region Structural region
Length of (code for protein)
DNA
Repressor RNA polymerase
binding site binding site

4. The enzyme RNA polymerase attaches
ON itself to its binding site…
… and moves down the
strand of DNA decoding the
RNA polymerase gene
Repressor protein attaches itself to its
OFF binding site…
RNA polymerase is blocked
and cannot attach to DNA
Repressor
protein

5. If the … the repressor
repressor protein cannot
binding site bind to the DNA
is lost…
There is nothing to stop … so the gene is
DNA polymerase
binding…
permanently
ON
Having a healthy copy of this gene will not
switch the defective copy off, so…
… the disease caused by the defective
allele is… … dominant

6. • Promoter:
TATA Box
• Transcription
factors
• RNA poly-
merase
• Transcription
initiation
complex

7. Transcription
• Creation of pre-mRNA
• DNA is read from 3’ to 5’
• mRNA is made from 5’-3’
• 3 phases
– Initiation
– Elongation
– Termination

8. Elongation

9. Finishing the pre-mRNA
• Introns-intruding, spliced out
• Exons-kept, will be expressed

10. • snRNP’s identify
introns
• Introns are cut
out at a
Spliceosome
• Final mRNA has
only genes that
will be tran-
scribed in cell
• Introns used to
be considered
“junk” but may no
longer be the
case!

11. Translation
• The production of
polypeptides
• On a Ribosome
• tRNA, transfer RNA
carries in the amino
acids to the
ribosome
– (transfers the A.A)
Read 5’ to 3’

13. mRNA code
• 21 different
AA’s
• 64 codon
combinations
• Note
redundancy

14. APE
• Aminoacyl-
tRNA
synthetase
• Peptidyl
tRNA
binding site
• Exit

16. Termination of the
translation

17. The wrong protein
Nothing formed