Transcription and translation flashcards exam III.txt

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  1. RNA v DNA
    • 1. RNA has ribose (DNA deoxiribose sugar)
    • 2. RNA is single stranded (but can form 2nd structures)
    • 3. RNA has uracile base (DNA has thymine)
  2. Transcription role and steps
    • transcribes DNA-->RNA (RNA chain grows 5-3')
    • 3 steps:
    • 1. Initiation: 5' region of gene binds to CORE & SIGMA
    • 2. Elongation: RNA synth starts (binds to promoter, NO primer needed) & sigma DISSOCIATES from CORE
    • 3. Termination: RNA synth stops when polymerase rec. a certain sequence OR when a Rho factor helps to dissociate the 2
  3. 3 types of RNA
    • 1. mRNA: messenger - carries code for aa seq of protein. UNSTABLE
    • 2. rRNA: ribosomal - associates w/protein to form ribosome. STABLE
    • 3. tRNA: transfer - small RNA's that serve as carriers for AAs
  4. 3 types of RNA polymerases
    • RNA pol I: synthesizes ribosomal RNA
    • RNA pol II: synthesizes mRNA
    • RNA pol III: synthesizes tRNA & other small RNAs
  5. in Eukaryotes, how is RNA processed for transcription to occur?
    • CAP added to 5' end
    • poly-A-tail added to 3' end
    • SPLICING of introns, bringing EXONS together
  6. Translation role and steps
    • RNA --> protein synthesis
    • E,P,A sites (from 5'-3' of mRNA seq)
    • tRNA becomes charged when aa at ACC
    • Elongation
    • Termination
    • Components can be reused for new pro synth
  7. Elongation in Tranlsation
    • 1. requires BINDING of next aa tRNA: requires elongation factors and hydrolysis of GTP
    • 2. peptide bond formation: catalyzed by peptidyl transferase
    • 3. Translocation: ribosome (RNA pol I) moves down to 3'end, moving peptidyl tRNA to P site, leaving A site free
  8. Termination in Translation:
    • 1. UAA, UAG, UGA codons (on mRNA) STOP bc no tRNA have anticodons to these codes
    • 2. Rib recognition stops thru Release factors, and polypeptide is released
  9. Controlling Expression in EUK
    • 1. Promoters
    • 2. Enhancers: activators bind to DNA when enzyme binds to its allosteric site
    • 3. Transcription factors
    • 4. Repressors: released when lac present to bind to repressor, for example
    • 5. RNA regulation
  10. Controlling Expression in PRO
    • Regulation predominantly at TRANSCRIPTION level, but still at Translational and post-translational levels
    • Antisense RNA also aids by binding to ssRNA and then dicer breaking it up to turn off expression
  11. Post-translational regulation
    Feedback inhibition: final product can act to inhibit the enzyme that acts in the early pathway
  12. 2 allosteric binding sites
    • Regulatory site: binds final product of pathway
    • Catalytic site: binds substrate
  13. Lac operon:
    • Lactose (gal + glu) induces this
    • 1. Gene I makes a repressor to this operon (DIFFUSIBLE-moves around to act on other operators)
    • 2. Lactose BINDS to repressor
    • 3. When glucose is low, cAMP will be INCREASED and binds to CAP, which BINDS to promoter
    • Need both Repressor released and Low glucose
  14. 3 enzymes encoded by lac operon:
    • 1. Lac Z: makes b-galactosidase - breaks lac up and aids in making allolactose to induce lactose
    • 2. Lac Y: makes permease - in cell membrane to allow lactose INTO cell
    • 3. Lac A: makes Transacetylase
  15. Symbols for lac operon
    • I -: mutant repressor does NOT bind to operator, constitutive transcription (always ON when glu is low)
    • I +: WT, DOMINANT to I- (due to diffusible repressor)
    • I s: Repressor w/deformed allosteric site, so no chance for repressor to leave (always UNABLE), DOMINANT to I-
    • P -: mutant promoter(not diffusible) always UNABLE, no binding of RNA to promoter
    • O c: mutant operator so repressor can't bind, constitutive transcription (always ON when glu is low)
  16. trp operon
    • form of feedback inhibition
    • involved in biosynth of Tryptophan
    • trpR: fxns in repression
    • trpL: fxns in attenuation (encoded by a Leader peptide)
    • when there is a lot of TRP present, NO pausing of transcription: loop forms b/w 3&4 and STOPS ribosome from transcribing
    • when there is not much TRP, ribosome has to pause: loop forms b/w 2&3, but ribosome can continue transcription
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Transcription and translation flashcards exam III.txt
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