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    • #330
      Antje
      Participant

      What is PNA? My bio teacher gave us an article for class and it talked about a DNA like substance called PNA and I just wondered, what is it? 😕

      Antje

    • #19198
      Poison
      Participant

      I do not have an exact info but one of my teacher say that-according to his hypothesis- PRION is the PNA.
      PNA: primary nucleic asid

    • #19227
      mbab
      Participant
      quote Poison:

      I do not have an exact info but one of my teacher say that-according to his hypothesis- PRION is the PNA.
      PNA: primary nucleic asid

      you are wrong. PNA ( Peptide nucleic acids), is a nucleic acid mimics in which the sugar phosphate backbone of natural nucleic acid is replaced by a synthetic peptide backbone formed by N-(2_aminoethyl)-glycine units. PNA can recognize DNA and RNA specifically and PNA-DNA, PNA-RNA complexes is more stable than corresponding DNA-DNA, DNA-RNA. PNA is superior to DNA and RNA in recognize single nucleotide polymorphism.

    • #19235
      Poison
      Participant

      OK. I see. that was not my hypothesis. I only told my teacher’s.
      Thanx for correcting. 🙂

    • #19465
      RobJim
      Participant

      Do prions have nucleic acid? I thought they were just proteins that catalyzed their own creation. They self replicate, kind of like DNA.

    • #19494
      canalon
      Participant
      quote :

      Do prions have nucleic acid? I thought they were just proteins that catalyzed their own creation. They self replicate, kind of like DNA.

      Yep, prions have no nucleic acids. Theyr are just proteins.
      But they do not self replicate. They catalyze the folding of a protein (itself, but folded differently) made by the cell into another form (the pathogenic, autoreplicative folding).

    • #19502
      thank.darwin
      Participant
      quote Canalon:

      They catalyze the folding of a protein (itself, but folded differently) made by the cell into another form (the pathogenic, autoreplicative folding).

      When you say “folding of a protein” do you mean – they catalyze the folding of a protein by adding bonds, such as disulfide bridges and hydrogen bonds?

    • #19524
      RobJim
      Participant

      Yep, prions have no nucleic acids. Theyr are just proteins.
      But they do not self replicate. They catalyze the folding of a protein (itself, but folded differently) made by the cell into another form (the pathogenic, autoreplicative folding).

      I guess they don’t assemble the polypeptides like DNA assembles other strands of DNA. They sort of self replicate, but not to the same extent I guess.

    • #19528
      thank.darwin
      Participant

      What do you mean – “They sort of self replicate , but not to the same extent”
      please explain more…

    • #19543
      RobJim
      Participant
      quote thank.darwin:

      What do you mean – “They sort of self replicate , but not to the same extent”
      please explain more…

      Well, DNA can catch and hold nucleotide triphosphates and put them in position to esterify into a new strand of DNA. That is, the DNA can create new molecules of DNA from smaller molecules.

      Prions are protein enzymes that catalyze the refolding of other proteins into prion arrangements. Therefore they transform one protein to a prion at a time. However they don’t assemble the protein chains from amino acids.

    • #19564
      canalon
      Participant
      quote :

      Well, DNA can catch and hold nucleotide triphosphates and put them in position to esterify into a new strand of DNA. That is, the DNA can create new molecules of DNA from smaller molecules.

      Prions are protein enzymes that catalyze the refolding of other proteins into prion arrangements. Therefore they transform one protein to a prion at a time. However they don’t assemble the protein chains from amino acids.

      DNA do not self replicate. It needs quite a complex enzymatic machinery to do so… But, yes, provided the right enzymes it can make a copy of itself. As for prion you need the nucleic acids necessary to produce the protein, then the prion to catalyse the folding of the protein in th eprionic form. A prion cannot be replicated just from itself, the gene coding for the “pre-prion” protein must be present in the cell first.

    • #20495
      abhay
      Participant

      Prion protein has got two isoforms: PrPc (prion cellular) and PrPSc(prion scrapie).
      when we say diseased protein then we are referring it to PrPSc. this protein can change the conformation of PrPc and not any other proteins. one more important thing to keep in mind is that these two proteins have got same DNA sequence.. so its just conformation which makes them different from each other in the terms of proteinase K resistant and infectivity.
      as such no other protein has been detected which mediates the above conversion though presence of hypothetical protein X (factor X) has been mentioned in litt.

      presence of DNA in this conversion is still highly debated. few researchers are still backing the presence of nucleic acids in scrapie deposits and its role in prion conversion. but “Portein Only” hypothesis given by Stanley B. Prusiner (1997, Nobel Laureate) is still lobbying prion biology. acc. to it, its the scrapie protein which induces conformational change onto normal cellular prion protein.

    • #20498
      2810712
      Participant

      From this conversation, prions are proteins, they change the conformation of
      theis isomers[ differing in conformation] , right. But, then , I think, those changedPrPcs become PrPSc’s , isn’t it???
      ❓ Does those prions have any physiological IMP???
      OK they can induce the pritein kinase K resistance etc. which prevents the degradation of that protein as its binding site changes due to conformational change.
      ❓ But, we can’t say that this leads them to continue their all functions, as the conformational change will also affect the functioning of that protein.
      💡 But, this may be useful to block a cascade of reactions,; if we add some prions for a specefic protein in the cell then the digestion of that protein will not occur, or get reduced. { I think, prions are potent conformation changers] So, the path of biochem. reaction, which requires the digested parts of that protein , will not occur, isn’t it???

      Oh I’ve been a bit complicated here, sorry. 😥

      hrushikesh

    • #20678
      abhay
      Participant

      Well too many questions??? a bit stuffy but let us sort it out one by one…

      Does those prions have any physiological IMP???
      Yes of course it has got some role as is evident from its constitutive nature of expression. over and above it is found abundantly inside Central nervous system.. but then its exact nature of its function is not properly understood.
      workers have found its role in copper homeostasis, response to oxidative stress. exact function is still an enigma for science.

      OK they can induce the pritein kinase K resistance etc. which prevents the degradation of that protein as its binding site changes due to conformational change.
      let me correct u for proteinase K. its an serine endoproteases which acts non specifically on proteins. result is massive proteolysis. this enzyme is used as an assay for detection of scrapie protein as this protein is not degraded by proteinase K enzyme. reason behind this in ability may be attributed to inaccessibility of peptide bond to this enzyme..(as u have mentioned in u’r post).

      But, we can’t say that this leads them to continue their all functions, as the conformational change will also affect the functioning of that protein

      surely, it is not able to function properly. after its conformation changes it is shed off from cell membrane and thus it deposits extracellularly causing formation of amyloid plaques. this shedding is done by a phospholipase which specifically cuts GPI anchor of this protein.

      But, this may be useful to block a cascade of reactions,; if we add some prions for a specefic protein in the cell then the digestion of that protein will not occur, or get reduced. { I think, prions are potent conformation changers] So, the path of biochem. reaction, which requires the digested parts of that protein , will not occur, isn’t it???

      well there i disagree with u’r point.. pricipally if it can change conformation of any other proteins it should act in the way u have mentioned.. but unfortunately sytem is not as simple as assumed..
      in case of prion protein “species barrier” is reported. that means prion of human wont transform mouse prion.. this give a sense of a very high specificity. moreover no body has reported any cross conformation changes among different proteins. reason lies behind the structure of beta sheet formed by different proteins. if we assume this structure as a platform or any protein domain.. then only those proteins having same domain/platform can sit and can enjoy the priviledge of conformational changes.. and in this case it is possible for same protein.. thus we should always look the system keeping in view of high specificity of this protein.. thus u’r biochemical reaction wont stop even if u add this protein. nevertheless it will affect reaction by crowding or quenching metal ions or bybinding to substrate or enzymes( incase if it has got property to bind to it.)

      I’ll suggest to everybody if they are really interested in Prion biology please visit Nobel prize site and read lecture of Prusiner (1997).
      or follow this link:
      http://nobelprize.org/medicine/laureates/1997/prusiner-lecture.html

    • #20679
      abhay
      Participant

      Well too many questions??? a bit stuffy but let us sort it out one by one…

      Does those prions have any physiological IMP???
      Yes of course it has got some role as is evident from its constitutive nature of expression. over and above it is found abundantly inside Central nervous system.. but then its exact nature of its function is not properly understood.
      workers have found its role in copper homeostasis, response to oxidative stress. exact function is still an enigma for science.

      OK they can induce the pritein kinase K resistance etc. which prevents the degradation of that protein as its binding site changes due to conformational change.
      let me correct u for proteinase K. its an serine endoproteases which acts non specifically on proteins. result is massive proteolysis. this enzyme is used as an assay for detection of scrapie protein as this protein is not degraded by proteinase K enzyme. reason behind this in ability may be attributed to inaccessibility of peptide bond to this enzyme..(as u have mentioned in u’r post).

      But, we can’t say that this leads them to continue their all functions, as the conformational change will also affect the functioning of that protein

      surely, it is not able to function properly. after its conformation changes it is shed off from cell membrane and thus it deposits extracellularly causing formation of amyloid plaques. this shedding is done by a phospholipase which specifically cuts GPI anchor of this protein.

      But, this may be useful to block a cascade of reactions,; if we add some prions for a specefic protein in the cell then the digestion of that protein will not occur, or get reduced. { I think, prions are potent conformation changers] So, the path of biochem. reaction, which requires the digested parts of that protein , will not occur, isn’t it???

      well there i disagree with u’r point.. pricipally if it can change conformation of any other proteins it should act in the way u have mentioned.. but unfortunately sytem is not as simple as assumed..
      in case of prion protein “species barrier” is reported. that means prion of human wont transform mouse prion.. this give a sense of a very high specificity. moreover no body has reported any cross conformation changes among different proteins. reason lies behind the structure of beta sheet formed by different proteins. if we assume this structure as a platform or any protein domain.. then only those proteins having same domain/platform can sit and can enjoy the priviledge of conformational changes.. and in this case it is possible for same protein.. thus we should always look the system keeping in view of high specificity of this protein.. thus u’r biochemical reaction wont stop even if u add this protein. nevertheless it will affect reaction by crowding or quenching metal ions or bybinding to substrate or enzymes( incase if it has got property to bind to it.)

      I’ll suggest to everybody if they are really interested in Prion biology please visit Nobel prize site and read lecture of Prusiner (1997).
      or follow this link:
      http://nobelprize.org/medicine/laureates/1997/prusiner-lecture.html

    • #20680
      abhay
      Participant

      oops i’m sorry for sending two posts having same but minor differences in the content.

    • #20698
      2810712
      Participant

      ABHAY WROTE-
      well there i disagree with u’r point.. pricipally if it can change conformation of any other proteins it should act in the way u have mentioned.. but unfortunately sytem is not as simple as assumed..
      in case of prion protein “species barrier” is reported. that means prion of human wont transform mouse prion.. this give a sense of a very high specificity. moreover no body has reported any cross conformation changes among different proteins. reason lies behind the structure of beta sheet formed by different proteins. if we assume this structure as a platform or any protein domain.. then only those proteins having same domain/platform can sit and can enjoy the priviledge of conformational changes.. and in this case it is possible for same protein.. thus we should always look the system keeping in view of high specificity of this protein.. thus u’r biochemical reaction wont stop even if u add this protein. nevertheless it will affect reaction by crowding or quenching metal ions or bybinding to substrate or enzymes( incase if it has got property to bind to it.)

      WHat if we introduce a prion specefic for a target protein to stop the functioning of that orotein ? ? ? Can we obtain prions specefic for some protein ? ? ?
      Also if it is possible then other problems like binding to substrate or enzyme will, i think, not ocur, as their affinity for binding prions would be lesser than that specefic protein, what do U think???

      hrushikesh

      @ Abhay
      that prion paper was good ,but I didn’t read it completely . sorry but it was too long .

    • #20699
      abhay
      Participant

      WHat if we introduce a prion specefic for a target protein to stop the functioning of that orotein ? ? ?
      well its not possible to rule out the possibility of making prion specific to any protein.. but i feel the word usage is a bit wrong .. rather than saying prion specific to any protein u can tag any protein with prion sequence (responsible for aggregation) and then see whatever happens to it. its just like tagging any protein with GFP to observe that protein in live cells using fluorescence microscopy…
      so if u tag any protein with this prion.. outcome will be crowding of u’r protein as this sequence will aggregate and in that case u’r local protein concentartion will increase…
      again hypothetically if this happens.. u’r protein activity will increase even in nanomolar concentration .. thus saving much of u’r protein.. but other side of the story is u’r protein may not feel happy in crowded condition or u’r substrate may not be accessible to all proteins due to overcrowd and thus u’ll have reduced activity or u’r protein may precipitate out.. so u can see if u mangae to go for the optimum concentration of course u’ll get something but again that will vary protein to protein…

      over and above this protein is highly dangerous as it owes infectivity.. it needs P4/BSL4 facility.. so playing around with this protein may invoke ethical issue landing u in court..
      but again these are just another aspects.. and nothing is impossible..

    • #20707
      2810712
      Participant

      Thanks , questioning helps me understand better. Although I am not required to study this, questioning and trying to understand such topics helps even college students like me.
      THank you Abhay, good to see [ see the name] somebody from my country here.
      Thanks.

      hrushikesh

    • #20709
      abhay
      Participant

      no need to mention that. i’m impressed with your curious nature.. well i know this forum is not meant to ask any personnal questions but i’ll be glad to know u’r whereabouts esp. u’r combi in college.. to avoid this forum with personnal details u can send me mail in following address..
      abhay@ccmb.res.in

      further queries in this topic are always welcome.

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