BMSC 220 6a transcription and RNA

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BMSC 220 6a transcription and RNA
2013-10-18 16:38:32
BMSC 220 transcription RNA

BMSC 220 7 transcription and RNA
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  1. Gene expression:
    production of a particular mRNA from a gene (DNA sequence)
  2. Changes in gene expression are involved in:
    -Response of cells to their environment

    -Regulation of cell cycle

    • -Distinct activities of different cell types in tissue and organ function
    • -Cell differentiation and development
  3. Variable Gene Expression:
    Response of cells to their environment
    -Heat shock protein genes are expressed when cells exposed to elevated temperatures
  4. Variable Gene Expression:
    Regulation of cell cycle
    Mutations causing a reduction in expression of tumour suppressor genes such as Rb or p53 is a major contributing cause in some cancers
  5. Variable Gene Expression:
    Distinct activities of differentiated cell types and co-ordination of different cell types in tissue and organ function
    -Mutation that changes the regulation of the human apolipoprotein A-I gene promoter (encodes a serum lipid transport protein) affects blood LDL/HDL ratios
  6. Variable gene expression:
    Cell differentiation and development
    Many genes are expressed only once during the life of an organism, for only a short period of time during embryonic development in only one or a few cell types, yet are critical for proper formation of the adult form
  7. RNA polymerases
    • -principal enzymes responsible for RNA synthesis (transcription)
    • –synthesize RNA from a DNA template.
    • -complex enzymes made up of multiple polypeptide chains.
    • -Do not require a primer sequence to initiate RNA synthesis
  8. promoters
    • -the DNA sequence with which RNA polymerase and other proteins interact to initiate and regulate transcription of a gene
    • -molecular dimmer switch
  9. Transcription
    RNA synthesis using a DNA template
  10. Translation
    protein synthesis using an mRNA template
  11. Transcription in Eukaryotes vs Prokaryotes
    Chromatin: In eukaryotes, takes place on DNA that has chromatin (nucleosomes must be displaced), takes place on free DNA in prokaryotes


    Extensive RNA Processing

    Multiple nuclear RNA polymerases in euk:
  12. eukaryotic RNA polymerase
    • an enzyme that catalyzes the synthesis of RNA from a DNA template. Three different nuclear RNA polymerases each responsible for different cellular RNAs
    • RNA polymerase I
    • RNA polymerase II
    • RNA polymerase III
  13. In prokaryotes there is _ RNA polymerase
  14. RNA polymerase I
    Ribosomal RNA (rRNA): 5.8S, 18S, 28S
  15. RNA polymerase II
    ALL Messenger RNAs (mRNAs)

    -smallest proportion of RNA but greatest regulatory complexity

    -regulatory mechanisms have evolved to ensure that the correct gene is transcribed in the correct cell type at the correct time and in the correct amount
  16. RNA polymerase III
    Ribosomal RNA (rRNA): 5S

    ALL Transfer RNAs (tRNAs)
  17. rRNAs and tRNAs:  make up well over __% of the total RNA (by mass) in any given cell
  18. DNA sequence element
    -term used to denote a specific short sequence of DNA base pairs within a gene promoter for which a specific functional property with respect to regulation of transcription of that particular gene has been ascertained
  19. •Cis-acting DNA sequences
    (also called promoter and enhancer elements) regulate expression of genes
  20. molecular dimmer switch
    • -combination of DNA sequence element and cis-acting DNA sequences
    • -regulate transcription
  21. •Basal or core promoter
    Genes transcribed by RNA polymerase II contain core promoter elements, including the TATA box  (others also exist), and an initiator (Inr) DNA sequence
  22. •Upstream promoter, and enhancers
    transcriptional regulatory sequences that can be located at a significant distance from the promoter.
  23. reporter genes

    • example:
    • -(GFP) causes cells that express it to glow green under blue light
  24. Transcription factors
    2 categories
    -proteins that are required for RNA polymeraseII to initiate transcription.

    • -General transcription factors
    • -gene-specific transcription factors
  25. General transcription factors
    Found where?
    • -involved in transcription from all polymerase II promoters.
    • -constitute part of the basic (or general) transcription machinery
    • -involved in formation of the transcription initiation complex

    -Found in the core or basal promoter
  26. gene-specific transcription factors
    found where?
    • -transcription factors that are not part of the general machinery.
    • -bind to promoter and enhancer elements (with specific DNA sequences) of one or a small number of different genes,
    • -direct activity of the general transcription factors

    -found in upstream promotor
  27. How do gene specific transcription factors work
    by either

    -modifying the rate of transcription initiation by the basal transcription complex,


    -the rate of basal transcription complex assembly
  28. Where does the transcription initiation complex/pre-initiation complex bind?
    core or basal promoter
  29. TATA box
    a regulatory DNA sequence found in the promoters of many eukaryotic genes transcribed by RNA polymerase II
  30. TATA-binding protein, or TBP,
    is a basal transcription factor that binds directly to the TATA box (DNA sequence-specific binding properties).
  31. •TBP-associated factors, or TAFs,
    • polypeptides associated with TBP in the general transcription factor, TFIID.
    • (transcription factor II D)
  32. •TFIIB
    associates with TFIID at the core promoter,
  33. Steps to formation of inititiation complex
    • -TBP binds to the TATA box
    • -TFIID associates with TBP
    • -TFIIB associates with TFIID
    • -Recruitment of RNA polymerase and TFIIF
    • -Binding TFIIE and TFIIH
  34. proximal and distal promoter elements
    -binding sites for gene specific transcription factors that modulate activity of the basal transcription complex

    -same as enhancers
  35. the recognition and binding sites of most transcription factors consist of short DNA sequences, typically spanning __-__ base pairs
  36. Two example transcription factors
    • SP1
    • CBTF
  37. What specifies the amount of transcriptional initiation by RNA pol II at a gene in a particular cell type?
    a combination of transcription factors interacting at a specific gene’s promoter/enhancer sequences at any one point in time
  38. DNA-affinity chromatography
    a method used to isolate transcription factors based on their binding to specific DNA sequences in order to study them further
  39. Steroid hormone receptors
    (contain a zinc finger domain) are transcription factors that regulate gene transcription in response to hormones such as estrogen and testosterone
  40. •Homeodomain proteins
    (contain a helix-turn-helix DNA binding domain) play critical roles in the regulation of gene expression during embryonic development.
  41. Reporter gene:
    • -a gene that is easily visualized (once it is translated into a protein) whose gene sequence is placed upstream of the gene whose expression you actually want to visualize
    • -sometimes placed using plasmids

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