Gene expression from dna to protein
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Gene Expression: From DNA to Protein. Background. Watson & Crick Beedle & Tatum. How Genes are Expressed. Processes: Transcription (DNA to mRNA) Translation (mRNA to protein) Importance of location Eukaryotes Prokaryotes. RNA. Review Types of RNA in Gene Expression

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Gene Expression: From DNA to Protein

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Gene expression from dna to protein

Gene Expression: From DNA to Protein


Background

Background

  • Watson & Crick

  • Beedle& Tatum


How genes are expressed

How Genes are Expressed

  • Processes:

    • Transcription (DNA to mRNA)

    • Translation (mRNA to protein)

  • Importance of location

    • Eukaryotes

    • Prokaryotes


Gene expression from dna to protein

RNA

  • Review

  • Types of RNA in Gene Expression

    • mRNA (messenger)-provides code for protein

    • tRNA (transfer)-carries amino acids

    • rRNA (ribosomal)-directs translation


Transcription

Transcription

  • Requires DNA-dependent RNA Polymerase

    • Core enzyme + sigma factor = holoenzyme

  • Three forms in Eukaryotic Nuclei

    • RNA Pol I –Pre-rRNA

    • RNA Pol II**--Pre-mRNA

    • RNA pol III –Pre-tRNA


Stage one intiation

Stage One: Intiation

  • RNA recognizes region to be transcribed

    • Promotor regions

      • TATA box

      • CAAT box


Stage two elongation

Stage Two: Elongation

  • Complementary mRNA produced from DNA


Stage three termination

Stage Three: Termination

  • Often zones with high GC levels

  • Loop and release of mRNA

  • Protection

    • 5’ capped with 7-methyl G

    • 3’ tail polyadenylation


Translation

Translation

  • Prokaryotic cells translate immediately into protein

  • Eukaryotic cells process mRNA before translation occurs

    • Cutting out Introns

    • Protecting transcript


Processing mrna

Processing mRNA

  • Splicing occurs by sequence

    • snRNA and snRNP (spliceosomes), and/or ribozymes (self-splicing enzymes)

    • Many different proteins can result from one transcript


Requirements for translation

Requirements for Translation

  • mRNA

    • Transcript

  • tRNA

    • Carrier for amino acids

  • Ribosomes

    • Two sub-units of protein with three pieces of RNA


Nucleotide sequence to protein

Nucleotide Sequence to Protein

  • Codons- 3 nucleotide codes for amino acids

    • 20 amino acides

    • 64 codons

    • 3 stop codons (UGA, UAA, UAG)

    • 1 Start codon (AUG-methionine)

  • Each codon brings in a tRNA anti-codon that contributes one amino acid to the protein


Stage one initiation

Stage One: Initiation

  • Small sub-unit of ribosome binds to mRNA

  • Methionine “start”

  • Large sub-unit of ribosome enters

  • Initiation factors involved


Stage two elongation1

Stage Two: Elongation

  • Connection

    • Next tRNA enters

    • 1sttRNA “hands” amino acid to 2ndtRNA, then leaves

    • Ribosome slides to free the next space

    • Continuationfor length of protein

    • Elongation factors involved


Stage three termination1

Stage Three: Termination

  • Stop Codon is reached

    • RF’s bind to stop codon

    • Protein is released

    • Ribosomal units disassociate


For our next session

For our next session:

  • Exploring factors influencing gene expression

  • Expression and repression of genes


References

References

  • Brooker, R. J. (2011). Concepts of Genetics + Connect Plus Access Card. McGraw-Hill Science Engineering, New York, NY.

  • Brooker, R. J., (2012). Genetics: analysis and principles. 4th Ed. McGraw-Hill Higher Education, New York, NY.

  • King, M. D. (2013). The Medical Biochemistry Page. Retrieved from: http://themedicalbiochemistrypage.org/home.html.

  • McClean, P. E. (2013). Transcription. Retrieved from: http://www.ndsu.edu/pubweb/~mcclean/plsc731/transcript/transcript1.htm

  • Unknown (2013). Three types of RNA polymerase in eukaryotic nuclei. Retrieved from: http://mcb.berkeley.edu/courses/mcb110/ZHOU/lec.5-7.euk_trxn_apparatus.pdf


Image sources

Image Sources

  • Cap & Tail http://classconnection.s3.amazonaws.com/681/flashcards/894681/jpg/coding1330783434942.jpg

  • RNA Elongation http://limbiclab.files.wordpress.com/2012/12/limbic_lab_dna_transcription_diagram1.png

  • RNA Initiation http://9e.devbio.com/images/ch05/0503fig1.gif

  • Processing http://www.genomebc.ca/glossary/Alternative%20Splicing%20(colourful)_Image.gif

  • Translation Initiation http://kvhs.nbed.nb.ca/gallant/biology/translation_initiation.jpg

  • Translation Elongation http://kvhs.nbed.nb.ca/gallant/biology/translation_elongation.jpg

  • Translation Termination http://utminers.utep.edu/rwebb/assets/images/17.17_Termination_of_transla.jpg


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