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Gene Expression Overview

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Gene ExpressionGene Expression The Gene StructureThe Gene Structure Protein SynthesisProtein Synthesis

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Gene ExpressionGene Expression

Gene expressionGene expression

is the process by which the is the process by which the information contained in a information contained in a gene is converted into the gene is converted into the structures and functions of a structures and functions of a cell by producing a biologically cell by producing a biologically functional functional proteinprotein. .

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Eukaryotic CellEukaryotic Cell

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Gene StructureGene Structure

Eukaryotic gene Eukaryotic gene structure:structure: Most Most eukaryotic genes in eukaryotic genes in contrast to typical contrast to typical bacterial genes, bacterial genes, the the coding sequence coding sequence (exons)(exons) are interrupted by are interrupted by noncoding DNA noncoding DNA (introns).(introns).

The gene must have The gene must have ( Exon; start signals; stop ( Exon; start signals; stop

signals; regulatory control signals; regulatory control elements).elements).

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Protein SynthesisProtein Synthesis

Protein SynthesisProtein Synthesis is the process in which is the process in which cells build proteins fromcells build proteins from information in a DNA gene information in a DNA gene in a in a two major stepstwo major steps::

I-Transcription and

II-Translation

Transcription :: synthesis of an RNA synthesis of an RNA (mRNA)(mRNA) that is that is complementary to one of complementary to one of the strands of DNA.the strands of DNA.

Translation Translation :: ribosomes read a ribosomes read a messenger RNA and messenger RNA and make protein according to make protein according to

its instructionits instruction..

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Protein SynthesisProtein Synthesis

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TranscriptionTranscription

http://biology.unm.edu/ccouncil/Biology_124/Images/transcription.gif

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Transcription

RNA polymeraseRNA polymerase copies both the exons and the copies both the exons and the introns. The stretch of DNA that is transcribed into an RNA introns. The stretch of DNA that is transcribed into an RNA molecule is called a molecule is called a transcription unittranscription unit. .

A transcription unit that is translated into protein A transcription unit that is translated into protein containscontains codingcoding sequence that is translated into protein and sequence that is translated into protein and sequencessequences that direct and regulate protein synthesis; that direct and regulate protein synthesis;

Transcription proceeds in the 5' → 3' direction.Transcription proceeds in the 5' → 3' direction.

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RNA SplicingRNA Splicing

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TranslationTranslation

http://www.nature.com/embor/journal/v4/n9/images/embor923-f3.jpg

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TranslationTranslation

Translation is the process by which ribosomes read the Translation is the process by which ribosomes read the genetic message in the mRNA and produce a protein genetic message in the mRNA and produce a protein product according to the message's instruction.product according to the message's instruction.

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RibosomesRibosomes are the site are the site of of protein biosynthesisprotein biosynthesis using using the mRNA as a template, the the mRNA as a template, the ribosome traverses each ribosome traverses each codon of the mRNA, pairing codon of the mRNA, pairing it with the appropriate amino it with the appropriate amino acid. This is done using acid. This is done using molecules of molecules of transfer RNAtransfer RNA (tRNA) containing a (tRNA) containing a complementary complementary anticodonanticodon on on one end and the appropriate one end and the appropriate amino acid on the other.amino acid on the other.

http://www.molecularexpressions.com/cells/ribosomes/images/ribosomesfigure1.jpghttp://www.molecularexpressions.com/cells/ribosomes/images/ribosomesfigure1.jpg

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ElongationElongation

Transfer of proper Transfer of proper aminoacyl-tRNA from aminoacyl-tRNA from cytoplasm to A-site of cytoplasm to A-site of ribosome;ribosome;

Peptide bond formation;Peptide bond formation;

Peptidyl transferase Peptidyl transferase forms a peptide bonds forms a peptide bonds between the amino acid between the amino acid in the P site and the in the P site and the newly arrived aminoacyl newly arrived aminoacyl tRNA in the A site. This tRNA in the A site. This lengthens the peptide by lengthens the peptide by one amino acids.one amino acids.

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ElongationElongation

Translocation;Translocation; translocation of the new translocation of the new peptidyl t-RNA with its peptidyl t-RNA with its mRNA codon in the A site mRNA codon in the A site into the free P site occurs into the free P site occurs Now the A site is free for Now the A site is free for another cycle of another cycle of aminoacyl t-RNA codon aminoacyl t-RNA codon recognition and recognition and elongation. Each elongation. Each translocation events translocation events moves mRNA , one moves mRNA , one codon length through the codon length through the ribosomes. ribosomes.

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Protein Synthesis

http://bioinfo.bact.wisc.edu/themicrobialworld/lysozyme.gifhttp://bioinfo.bact.wisc.edu/themicrobialworld/lysozyme.gif

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Protein Synthesis

www.bseinquiry.gov.uk/report/volume2/fig1_2.htm

Reading the instruction means Reading the instruction means translating the code in the RNA translating the code in the RNA from from basesbases

))building block of DNA and RNAbuilding block of DNA and RNA ( (to to amino acidsamino acids (building block of (building block of proteins)proteins)..