8.3, 9.2 - 9.3, 9.4 Flashcards

Question

eukatotic mRNa processing

Answer 1

introns interupt eukaotic but not prokatic genes such that splciing of primary trasncipt is needed for eukaytic gene expression otehr types of RNA procesisng taht occur in eukaotes but not prokayotes add a methylated cap and a poly A tail, repretcly to teh 5' and 5' ends

Answer 2

info in DNA is starting point of gene expression cell trasnrbibes it into mRNa then translate into protein muattions thta later the base pairs of DNA can modify any of teh steps or products of gene expression

Answer 3

bc of the nature of genetic code, mutations in a genes aa encoding exons geenrate range of reprocusison whenever the aa seqeunce is changed by mutation that encodes protein, reuslt is unpredicatble alterted proteins can function normally, less efficiently, more efficnetly, not at all or have new functions

Answer 4

a conseqeunce of codesdegnecry is some mutations known as silent mutations can change a codon into a mutant codon that specifies exactly the same aa the majority of silent mutations chnage the third nucelotide of a codon, the position at which most codons for teh same aa differ bc silent mutations dont alter the aa, such mutations dont affect gene expression or phenotype

Answer 5

mutations that chnage a codon into a mutant codon that specifies a diff aa are clled missense mutations if substituted aa has chemcial rpoerties similar to one it replaces then it mya have little or no effect - conservative mutations nonconservative mutations, missense mutations that cause substiution of aa with diff properties, are likely to have notciable conseqeunces effect on pheontype depends on which aa is usbsutietd and teh lcoation of the aa in three d structure of protein and how change affects the strcuture and function

Answer 6

nonsense mutatiosn change an aa specifying codon to a premature stop codon nonsense mutatiosn result in prodction of shortened truncated proteins lacking aa between aa endoced by mutant codon and the c terminus of a normal polypeptide mutant is unable to function if it needed the missing aa for actvity

Answer 7

frameshift mutations result from the insertion or deletion of nucelotides within the coding sequence if the number of extra or missing nucelotides isnt divisble by 3 the insertin or deltion skews reading frame it results in truncated porteins with inccorect aa at c termini

Answer 8

mutations that prdoceu a variant pheontype arent resttced to alterations in codons bc gene expression depends on many signals other than the coding seqeunce, changs in any crucial signals can disurpt process promoters and termination signals in the dnaof prokaryotes instrcut rna pol to start and stop transcription changes in seqeuence of promoter can make it hard for rna pol to associate with teh promoter- whch stop transicription mutations in promoters or enhancers that prevent recog by trasncirption factors can stop transcription in eukaryotic genes mutations in termination signal can diminsih mRNA rpoduced and amount of gene product in eukaryotes, most prmary trasncripts have splice acceptor sites, donor sists and bracnh sites that allow splicing to join exons together with precision in the mature mRNA chnages in any one of these sites can obstruct splicing the splicing errors can yeild spliced mRNA that encode altered form of protein in prokarotes, mutations afefct ribsome bnding site can lower affinity of mRNa for smal ribsomal subunit diminiting translation and amount of protein product mutations in UTR of eukaryotic mRNA affect transaltion - ex. muation in 5' utr can create a AUG upsteram that results in premature initation of translation - if out of frame then no normal protein produce - if in frame the N terminus contaisn additional aa AAUAAA in 3' utr of eukaytes signals addition of poly A tail polyA needed for mRNA transaltion so mutation affecting seequnce can stop translation otehr thinsg in 3' utr help stability mutations in stop codon could produce longer than normal protens or may be unstable or nonfunctional

Answer 9

mutations affect pgeontype by changing aa seqeunce of protein or amount of gene product produced any muation on inside or outside coding region that reduces protein actvity in any way is a loss of function mutation

Answer 10

loss of function alleles that block function of a protein compeletkly are null or amorphic mutations for protein encoding egnes, mutations eitehr prevent syntehsis of polypetide or result in synthesis of a mutatnt protein thats inactive amorphic alleles are usually recessive to wild type condiser A+a1 hetrozygote hwere wildtype give functional and null a1 doesnt if amount of protein rpdocues by single widltype is above trheshold amount sufficent to fufil biochem requirement then pheontype of hetrozygote is wild type usually homozygous dom make more thantwice as much protein needed for normal pheontype a hypomorphic mutation is loss of ufnction allee that prodcues either less of wild type proetin or mutant protein that less efefctive than wildtype hypomorphic are usually recesisve to wildtype for same reasn as amorphic

Answer 11

for some proetin ecndoing egnes, the output of biochem pathay inw hcih protein woks is proprtional to amount ofprotein actvity for tehse genes, diff combos of alleles can generate phenotypes that vary continously w the amount of functional geen product, giving rise to incompelet dominance ex. loss of function mutation in single pigment producing gene can geenrate a red to white spetcrum of flowers with the white resulting from absence of enzyme in biochem pathway

Answer 12

with charcertic exquistive sentsite to amount of functinal protein rpoduced, even smallc hange can cause switch between phenotypes a hertozygote for an amorphic allele and normal allele may look diff than wildtype geneticst use term haploinsufficieny to describe relatevly rare situations in which one wild type alleel deosnt provide enough of a gene rpoduct to avoid a mutant phenotype 800 of tehse genes exist an example is human haploinsofcient gene is GLI3 - trasncirption factor for specification of digist - hertozygote for loss of fucntion muattion causes polydactly - presence of extra finegrs or toes

Answer 13

bc many ways exist to inetrfere w genes ability to make sufficent protein, majoriy are usually loss of function alleles some rare muatiosn can enhance or confer new actvity on protein/protein expression or expres protein at worng time or place - gain of function alleles bc allele by istelf usually rpoduces protein that can alter pheontype even in presence of normal protein, these gain of function are usually domto wild types gain of function alelles w dom affects on visible pheontypes ar elethal when homozygous bc they are pelotripic ltehality results from absence of normal geen function or two doses of alter protein are responsible for invaiability

Answer 14

hypermorphic muattion generates eitehr more nromal protein product than wild type or more effeicent mutant protein ex. the human FGFR2 genes reuslts in achondoplasia - short limbs - encodes a singaling protein that inhbits bone growth the protein is nrmally actviated onlyw hen amsall protein called fgf bidns to it most ppl with achodnrpplasia carry mutant alle which encoes the protein with argnane - this cause sit to become activve without FGF mutant protein is constinutively active receptor that is active all time its dom to wildtpe bc muatnt protein inhits boen rbwoth even if nromal prtein present

Answer 15

rare class of dom gain function is neomporphic mutation that egenrate a novel characetric some produce mutant protein w new function while other causee genes to rpdouce nromal proetin but at innaproaite time or place (ectopic expression) huntingtoons disease is neomphic allee with mutant protein mutant has expanded run of Q aa and reuslt in neural degenation HD disease allele is dom bc rpescne of normal HD doesnt stop mutant ex. of neopmorphic allele that expresses normal protein ectopically is AntpNS mutant alleel in drosphila the wild type usually givs the flys legs mutation causes the alleek to express normal protein not only in leg cells but in cells that become antanenae the mutant is dom bc the normal allele doenst prevent the ectopic expression

Answer 16

some dom alleles of genes encode ppriteins that not only fail to provide the atcivty of the wild type protein btt also prevent nromal protein from functioning such alleles are dom neg or antimorphic alleles ex. gene encoding polypeptide that associates w three other idnetcial polypetide in 4unit enzyme all 4 units are products of same gene if dom munat allele D directs synetshis of poison subunit whose rpesence even as one subunit abolsehs enzyme. function then atcive tetramers comsposed of wild type are only 1/16 alle tetratemetr produces as a reuslt, totale enyme atcivty in hetrozgotes is less than in wild type homzygotes of wildtype the kinky allele of axin in mice is example of dom neg muation

Answer 17

predicting afefcts are hard most mutations consitute loss of function this is bc most aa changes are likley to diminsh protein function and that most alterations in gene regulatory sistes will make the sites less efficient rare muattion in any gene cn casue a gain of function u cant predict whethr mutant alleel will be dom or recessive most loss of function are recessive and most gain of function are dom to normal alleles domiancne relations between wild tupe and muatnt alleels of gene nn diploid organism depnd on how drstcially a mutation infleucnes protein prdction or atcivty and ow throughly pehontype depdns on the wild type level fo protein loss of funcyion: amorphic (null) or hypomorpic (leaky) - but are common, recessive, can be incompelet dom is pheontype varies continosuly w gene atcivty, can be dom in cases of haploisfufcieny gain of function alleles: hypermorephc - rare - dom or incompelet dom neomrophic - rare-usually dom antimorphic (dom neg) - rare - dom or incompelte dom

Answer 18

gene expresison depdns on diff number of proteins and RNA genes for all proteins are trascnribes and transalted same way as otehr genes genes for all rRNA , tRNA and snRNA are noncoding genes that are trasncirbes not trasnlated mutations in any of these genes wheteh protein coding or noncoding can have dramtic affetc on peontype lethal muation affetcing machienry of gene expression: loss of function muattions in genes for moelcules that implrement gene expression like ribsomabl proteins are often lethal in homozygotes bc muatn affect syntehsis of all proteins - even 50% rection in some proetisn or RNA needed for gene expresison can have huge afefcts ex. in dropshila, null muattions in genes encoding for varius ribsomal proteins are lethal in homozygotes supressor muattions in tRNA genes: if more than one gene encodes the same moelcule with a role in gene expression, amutation in one gene doensnt mean lethality bacterial geentcist found that muations in some tRNa genes can supress efefcts of nonsesne muattions in otehr geens the tRNA gene mutations that haev this affect give rise to nonsense supressor tRNAs ex. in wildtype e coli pop with in frame UAG nonsen muattion in tryptphan syntahse gene all cells have truncated nofnucntional enzyme and are auxotrophs unable to synethzie enzyme subseunet exposure of them to mutagens can generate some trp+ cllls with two mutations - one with orgnail nonsense and one is in gene that speciies tRNA for aa tyrosine mutation in tRNa genes supresses efefct of nonsense mutation, retsoring function in the gene (altered anticdon) basis of nonsense supression is tRNA muattion changes anticodn that reocgnizes codon for tyrsoine to anticodn copleamtry to the stop codon mutant tRNA inserts the tyrosine into polpetide in the inframe nosnnse muattion allowing a full length muation cells ith nnsense muattion in tRNA gene can survive only if two codnitions coexist - cell must have otehr tRNA that reocgnizes same codon that the supressing tRNA reocgnized befor emutation aleted the codon w/p those tRNA then u couldnt have way to isnetr proepr aa too that codon - supresisng tRNa must repsond only ineffciently to stop codon found at the ends of mRNA coding regions if not case then tRNA would wreak havock causing polyeptides to be longer then noral to gaurd this, two stop codons are placed in a row - bc supressing tRNa insetring aa at both codons is low