From Gene to ProteinFrom Gene to Protein

• The connection between genes The connection between genes and proteinsand proteins

• The synthesis and processing of The synthesis and processing of RNARNA

• The synthesis of proteinThe synthesis of protein

The Connection between The Connection between Genes and ProteinsGenes and Proteins

• The study of The study of metabolic defects metabolic defects provided evidence provided evidence that genes specify that genes specify proteinsproteins

• One-gene-one-One-gene-one-enzyme hypothesisenzyme hypothesis

Transcription and Transcription and Translation: Two Main Translation: Two Main ProcessesProcesses

• DNA synthesizes DNA synthesizes RNA: RNA: TranscriptionTranscription

• RNA synthesizes RNA synthesizes Protein: Protein: TranslationTranslation

The Genetic CodeThe Genetic Code

• Triplet sequence Triplet sequence of nucleotidesof nucleotides

• smallest units of smallest units of uniform length to uniform length to allow translation allow translation of all 20 amino of all 20 amino acidsacids

• codon- triplet in codon- triplet in mRNAmRNA

Synthesis and Processing Synthesis and Processing of RNAof RNA

• Three types of RNA: mRNA, tRNA, and Three types of RNA: mRNA, tRNA, and rRNArRNA

• eukaryotes have three polymeraseseukaryotes have three polymerases• RNA polymerase II responsible for mRNA RNA polymerase II responsible for mRNA

synthesissynthesis• Transcription subdivided into three Transcription subdivided into three

stages: Initiation, elongation and stages: Initiation, elongation and terminationtermination

• RNA must be processed before it can RNA must be processed before it can function function

TranscriptionTranscription

• InitiationInitiation: RNA polymerase binds to : RNA polymerase binds to promoter region,TATA box plays critical promoter region,TATA box plays critical role during initiationrole during initiation

• ElongationElongation: RNA polymerase unwinds : RNA polymerase unwinds DNA and adds nucleotides, 10 bases DNA and adds nucleotides, 10 bases long, long, growsgrows 5 5'' to 3 to 3' ' direction.direction.

• Termination:Termination: terminator sequence terminator sequence (AAUAAA) stops transcription(AAUAAA) stops transcription

• DNA reforms double helix, RNA “peals” DNA reforms double helix, RNA “peals” off template DNA (gene)off template DNA (gene)

TranscriptionTranscription

Transcription AnimationsTranscription Animations

• http://www.youtube.com/watch?v=-ygpqVr7_xs&feature=related

• http://www.johnkyrk.com/DNAtranscription.html

• http://vcell.ndsu.nodak.edu/animations/transcription/movie.htm

Post Transcriptional Post Transcriptional ModificationModification(RNA Processing)(RNA Processing)

• Capping: modified GTP Capping: modified GTP added to 5added to 5' end of mRNA' end of mRNA

• Poly (A) tail: 20-200 Poly (A) tail: 20-200 adenine nucleotides adenine nucleotides added to 3' end of mRNAadded to 3' end of mRNA

• RNA splicingRNA splicing

Functions of the 5Functions of the 5' Cap' Cap

• Protect mRNA from hydrolytic Protect mRNA from hydrolytic degradationdegradation

• Identifies mRNA to the small Identifies mRNA to the small ribosomal subunitribosomal subunit

Functions of the Poly (A) Functions of the Poly (A) tailtail

• Inhibit degradation if mRNA in the Inhibit degradation if mRNA in the cytosolcytosol

• Facilitate mRNA export from the Facilitate mRNA export from the nucleusnucleus

• Separated from the stop codon by Separated from the stop codon by trailer sequencetrailer sequence

RNA SplicingRNA Splicing

• IntronsIntrons: noncoding sequences that are : noncoding sequences that are removedremoved

• ExonsExons: coding sequences that are : coding sequences that are splicedspliced together together

• Small nuclear ribonucleoproteinsSmall nuclear ribonucleoproteins (snRNPs): identify and help bring about (snRNPs): identify and help bring about the splicing processthe splicing process

• SpliceosomeSpliceosome: catalyzes splicing : catalyzes splicing reactionsreactions

RNA SplicingRNA Splicing

Role of IntronsRole of Introns• May control gene May control gene

activityactivity• May allow a single May allow a single

gene to synthesize gene to synthesize several different several different proteinsproteins

TranslationTranslation(The synthesis of proteins)(The synthesis of proteins)

• tRNAtRNA• RibosomesRibosomes• Aminoacyl-tRNA Aminoacyl-tRNA

synthasessynthases

tRNAtRNA

• Interpreter between Interpreter between base sequence of base sequence of mRNA and amino mRNA and amino acid sequence of acid sequence of proteinprotein

• 45 different types45 different types• About 80 nucleotides About 80 nucleotides

longlong• Anticodon base pairs Anticodon base pairs

with codon of mRNAwith codon of mRNA

RibosomesRibosomes

• Coordinate the Coordinate the pairing of tRNA with pairing of tRNA with mRNAmRNA

• Two subunitsTwo subunits• Constructed in the Constructed in the

nucleusnucleus• Three binding sites: Three binding sites:

P site, A site and E P site, A site and E sitesite

Aminoacyl-tRNA SynthaseAminoacyl-tRNA Synthase

• 20 different types20 different types• Two steps:Two steps: 1) activation of 1) activation of

amino acid with amino acid with AMPAMP2) attachment of 2) attachment of the amino acid to the amino acid to tRNAtRNA

Building a polypeptideBuilding a polypeptide(Translation)(Translation)

• InitiationInitiation: brings mRNA, tRNA, and the two : brings mRNA, tRNA, and the two ribosomal subunits togetherribosomal subunits together

• ElongationElongation: three-step cycle that adds : three-step cycle that adds amino acids one by one to the initial amino acids one by one to the initial amino acid, requires cooperation of amino acid, requires cooperation of several several

• TerminationTermination: release of the polypeptide : release of the polypeptide chain from the complex.chain from the complex.

InitiationInitiation

• 55' cap attaches to ' cap attaches to small ribosome small ribosome subunitsubunit

• tRNA carrying tRNA carrying methionine methionine attaches to mRNA attaches to mRNA codoncodon

• Large ribosomal Large ribosomal subunit attachessubunit attaches

ElongationElongation• Codon recognitionCodon recognition: :

tRNA directed into the tRNA directed into the A site by an elongation A site by an elongation factorfactor

• Peptide bond forms Peptide bond forms between adjacent between adjacent amino acidsamino acids

• TranslocationTranslocation: amino : amino acid in the A site is acid in the A site is moved to the P sitemoved to the P site

• mRNA moves through mRNA moves through the ribosome 5the ribosome 5''3' 3' directiondirection

TerminationTermination• Termination Termination

sequence is sequence is encounteredencountered

• Release factor binds Release factor binds to sequenceto sequence

• Release factor Release factor separates separates polypeptide and polypeptide and tRNAtRNA

Videos and WebsitesVideos and Websites• http://www.johnkyrk.com/DNAtranscription.html• http://www.youtube.com/watch?v=-ygpqVr7_xs&feature

=related• http://vcell.ndsu.nodak.edu/animations/transcription/mo

vie.htm• http://vcell.ndsu.nodak.edu/animations/transcription/inde

x.htm• http://vcell.ndsu.nodak.edu/animations/mrnaprocessing/i

ndex.htm• http://vcell.ndsu.nodak.edu/animations/mrnasplicing/ind

ex.htm• http://vcell.ndsu.nodak.edu/animations/translation/index.

htm

Videos and Websites (2)Videos and Websites (2)

• http://www.sumanasinc.com/webcontent/animations/content/lifecycleprotein.html

• http://www.sumanasinc.com/webcontent/animations/content/lifecyclemrna.html

• http://www.sumanasinc.com/webcontent/animations/content/proteinsecretion_mb.html

• http://www.sumanasinc.com/webcontent/http://www.sumanasinc.com/webcontent/animations/content/polyribosomes.htmlanimations/content/polyribosomes.html

• http://www.sumanasinc.com/webcontent/http://www.sumanasinc.com/webcontent/animations/content/translation.htmlanimations/content/translation.html

• http://www.sumanasinc.com/webcontent/http://www.sumanasinc.com/webcontent/animations/content/mRNAsplicing.htmlanimations/content/mRNAsplicing.html

VideosVideos

• http://vimeo.com/13497169http://vimeo.com/13497169• http://www.dnatube.com/video/544/http://www.dnatube.com/video/544/

Signal-Recognition-Particle-SRPSignal-Recognition-Particle-SRP• http://www.wehi.edu.au/education/http://www.wehi.edu.au/education/

wehitv/dna_central_dogma_part_1_-wehitv/dna_central_dogma_part_1_-_transcription/_transcription/

• http://www.wehi.edu.au/education/http://www.wehi.edu.au/education/wehitv/dna_central_dogma_part_2_-wehitv/dna_central_dogma_part_2_-_translation/_translation/