2024-01-24T14:57:50+03:00[Europe/Moscow] en true <p>distinguish between lac(inducible) &amp; trp(repressible) operons</p>, <p>define regulatory gene</p>, <p>suggest advantages of bacteria arranging genes in operons</p>, <p>define operon </p>, <p>define structural gene</p>, <p>describe main structural features of lac operon</p>, <p>describe main structural features of trp operon</p>, <p>how lactose, glucose regulate lac operon expression</p>, <p>how tryptophan regulate trp operon expression</p> flashcards
H2 Biology 17 - Regulation of GE in prokaryotes

H2 Biology 17 - Regulation of GE in prokaryotes

Customize
collection saved
Share
Long Term Learning Spaced Repetition
Add to Long Term Learning Desk
Fast learning Repeat this set of flashcards
Preview Test Spell
Play
Match
Review

  • distinguish between lac(inducible) & trp(repressible) operons

    effector molecule

    lac - allolactose, inducer; trp - tryptophan, co-repressor

    default state of repressor

    lac - active; trp - inactive

    default state of operon expression

    lac - switched off; trp - switched on

    products

    lac - protein pdt involved in lac breakdown; trp - protein pdt involved in trp a.a. synthesis

    structure

    lac - cluster of 3 structural genes coding for enzymes, proteins involved in lac breakdown; trp - cluster of 5 structural genes coding for enzymes in trp biosynthesis pathway

    when repressor bind to operator

    lac - active form, r&b operator; trp - co-repressor(trp) r&b allosteric site of repressor, repressor r&b operator

  • define regulatory gene

    region of DNA, codes for specific protein pdt that regulates expression of structural genes >

    constitutively expressed, i.e always transcribed

  • suggest advantages of bacteria arranging genes in operons

    allow simultaneous regulation of related genes w/ related fn/ involved in same metabolic activity >

    genes coding for related proteins/enzymes in single biochemical pathway/related fn/same metabolic activity grouped into operon, easier control >

    bacteria able to utilise variety of carbohydrates as respiratory substrate >

    operons allow bacteria to adapt, respond to env changes >

    operon genes only expressed when required, prevents wastage of energy, resources >

    bacteria @ selective advantage

  • define operon

    segment of DNA containing cluster of structural genes, make up single transcription unit, controlled by same promoter, operator >

    structural genes code for enzymes/functionally related proteins involved in single metabolic pathway

  • define structural gene

    region of DNA, codes for protein/RNA molecule that forms part of structure/has enzymatic fn

  • describe main structural features of lac operon

    segment of DNA, contains cluster of 3 SG; lacZ, lacY, lacA; makes up single t/c unit controlled by same promoter, operator >

    regulatory gene lacl lie upstream operon, codes for lac repressor >

    lac operon consists of promoter; RNA pol binding site, operator; lac repressor binding site, CAP binding site; catabolite activator protein binding site beside promoter >

    promoter, operator, CAP binding site lie upstream 3 SG >

    3 SG codes for enzymes for lac metabolism >

    lacZ; B-galactosidase(hydrolyse lactose->glucose+galactose)

    lacY; lac permease(membrane protein for transport of lactose into cell)

    lac A; lactose transacetylase >

    terminator; termination seq, marks end of operon

  • describe main structural features of trp operon

    segment of DNA, contains cluster of 5SG; trpE, trpD, trpC, trpB, trpA; make up single t/c unit controlled by same promoter, operator >

    regulatory gene trpR lie upstream operon, codes for trp repressor >

    trp operon consists of promoter; RNA pol binding site, operator; trp repressor binding site >

    promoter, operator lie upstream 5SG >

    5 SG codes for enzymes for trp synthesis >

    terminator; termination seq, marks end of operon

  • how lactose, glucose regulate lac operon expression

    lac absent

    lac repressor synthesised in active conf; r&b operator >

    operon switched off >

    RNA pol unable r&b promoter, unable t/c lac operon genes; mRNA not synthesised > BG, LP, LT not produced

    lac present

    BG convert lac -> allolac >

    allolac r&b allosteric site of lac rep, change 3D conf, becomes inactive, unable r&b operator >

    operon switched on >

    RNA pol able r&b promoter, able t/c lac operon genes; mRNA synthesised >

    BG, LP, LT produced

    low [glucose], lac present

    [cAMP] inversely proportional [glucose] >

    CAP activator synthesised inactive >

    high [cAMP] r&b allosteric site of CAP, CAP changes 3D conf, becomes active, able r&b CAP binding site >

    bends DNA, recruits RNA pol to promoter >

    RNA pol binds promoter @ high affinity >

    high lac operon t/c -> lactose used as temp substrate

  • how tryptophan regulate trp operon expression

    trp absent

    trp repressor synthesised in inactive conf >

    operon switched on >

    RNA pol able r&b promoter, able t/c trp operon genes; mRNA synthesised, translated into 5 polypeptides >

    enzymes that synthesise trp produced, trp synthesised

    trp present

    trp r&b allosteric site of trp rep, changes 3D conf, becomes active, able r&b operator >

    operon switched off >

    RNA pol unable r&b promoter, unable t/c trp operon genes; mRNA not synthesised >

    enzymes that synthesise trp not produced, trp not synthesised