1. Gene expression

2. Gene expression
The information encoded in a gene is converted into a protein
 The genetic information is made available to the cell
Phases of gene expression
Transcription
2. Translation
Protein folding
 Functional protein

3. DNA’s information is copied into messanger RNA (mRNA) molecule in transcription

4. mRNA directs synthesis of a protein with amino acid sequence determined by the base sequence of the codons in mRNA
Translation

5. Folded
Unfolded
Correct folding of a protein is needed to achieve
functional activity

6. Transcription: a mRNA copy of a DNA sequence is produced
RNA polymerases make RNAs
Other strand is used as a template
mRNA copy has one strand
Beside the coding area also other
information is added to mRNA
molecule
Sequence is complementary for DNA
Ts are replaced with uracils, U

7. mRNA is produced and
processed in the nucleus:
1.Introns are cutted off
2.Methyl cap is added to 5’ end
3.Poly A tail is added to 3’ end
Nucleus
Cytoplasm
The ready mRNA molecule is
transported to the cytoplasm

8. From a mRNA to a protein…
Decoding mRNAs codon sequence to protein is
dependent on transfer RNAs (tRNA)
All tRNAs have similar structure
amino acid part
anticodon part
Anticodon part base pairs with it’s
anticodon structure in mRNA
Amino acid part carries correct amino
acid to the place of protein synthesis
tRNAs are needed for recognition
and transport
Amino acid
mRNA

9. Protein synthesis Protein synthesis takes place in the ribosomes
Ribosomes are located to the
cytoplasm
Ribomes recognize the
initiation codon from mRNA
Elongation of a protein chain
includes three steps main steps

10. Step 0.
mRNA arrives to the ribosome and the ribosome
starts to ”read” mRNAs code
Step 1.
tRNA forms a pair with the corresponding
codon in mRNA
Step 2.
A bond is formed by ribosome between the
adjacent amino acids
Step 3.
The ribosome translocates to the next mRNA codon
and the ”used” tRNA is discharged from the ribosome

11. Previous steps are repeated until the ribosome
arrives to the stop codon
Step 4.
Termination is carried out with the help
of termination factors
After termination the nascent protein is released from
the ribosome, the ribosome dissociates and the mRNA
is released
Step 5.
Following the translation proteins are folded and
sometimes also chemically modificated

13. Protein folding
Protein´s folding is dictated by it’s amino acid sequence
Correct folding is needed for the protein to achieve proper functional properties
Proteins assisting in the folding process are known
3D structure can be predicted from the aa-sequence
The function of a protein can be predicted from it’s structure

14. Protein folding…

15. Expression control The action of a cell is dependent on it’s proteins
Amount of the proteins are determined by:
Concentration of the RNA
Frequency at which the RNA in translated to the protein
Stability of the protein
Only a small portion of the genes in a cell are expressed
 Depends on the cell type, developmental stage, environmental factors…

16. Regulation can happen at any stage of gene expression
Control of the transcription initiation is the most important
Different kind of control elements are found
In eukaryotes, the control elements of transcription can be
found from the inside and outside the gene area
Most important control element is the promoter
 Initiation place
 Directs binding of the enzymes
needed to produce RNA

17. Control of the initiation of transcription
5’ regulatory sequences  control the site of
transcription initiation  The promoter
RNA polymerase can`t recognise transcription start sites
Start sites are positioned 25 bp to 3’ direction from a
nucleotide sequence motif called the TATA BOX
General transcription factors guide RNA polymerase
to the start site
 TFIID-protein binds to TATA BOX
 Directs the binding of the RNA polymerase

18. Other transcription factors are also needed
 TFIIA, TFIIB, TFIIE and TFIIH bind close
to the start site
Some transcription factors bind to the RNA polymerase
Critical properties are brought by transcription factor
 needed for example to unwind the DNA
Also enhancer are needed for activation of transcription
 Are found from the genome
 Binding sites for activators

19. Thank you all for
your attention!