Gene expression

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Gene expression
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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

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• DNAs information is copied into messanger RNA
  (mRNA) molecule in transcription

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• mRNA directs synthesis of a protein with amino
  acid sequence determined by the base sequence of
  the codons in mRNA
• ?Translation

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Folded
Unfolded

• Correct folding of a protein is needed to achieve
  
• functional activity

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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

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• 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

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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 its
• 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
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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

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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
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• 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

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Protein folding

• Proteins folding is dictated by its 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
  its structure

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Protein folding
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Expression control

• The action of a cell is dependent on its
  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

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• 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

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Control of the initiation of transcription

• 5 regulatory sequences ? control the site of
• transcription initiation ? The promoter
• RNA polymerase cant 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

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• 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

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