Gene expression Gene expression The information encoded in

Gene expression

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 1. Transcription 2. Translation 3. Protein folding 4. Functional protein

1. DNA’s information is copied into messanger RNA (m. RNA) molecule in transcription

2. m. RNA directs synthesis of a protein with amino acid sequence determined by the base sequence of the codons in m. RNA 3. Translation

Folded Unfolded 3. Correct folding of a protein is needed to achieve functional activity

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

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

From a m. RNA to a protein… • Decoding m. RNAs codon sequence to protein is dependent on transfer RNAs (t. RNA) • All t. RNAs have similar structure • amino acid part • anticodon part Amino acid • Anticodon part base pairs with it’s anticodon structure in m. RNA • Amino acid part carries correct amino acid to the place of protein synthesis t. RNAs are needed for recognition and transport m. RNA

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

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

• 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 m. RNA is released Step 5. Following the translation proteins are folded and sometimes also chemically modificated

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 • 3 D structure can be predicted from the aa-sequence • The function of a protein can be predicted from it’s structure

Protein folding…

Expression control • The action of a cell is dependent on it’s proteins • Amount of the proteins are determined by: 1. Concentration of the RNA 2. Frequency at which the RNA in translated to the protein 3. 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…

• 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

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

• 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

Thank you all for your attention!