hottie99
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good question, i have no idea    
honestly, i dont even know how to approach ques like this? salvage pathway has enzymes like DTP and UMP rite?? i thought it has something to do with nucleotides and such, so replicating cells maybe.. and on that basis i'd think lymphocytes?? so not sure about this one, uugghh!!! damn biochem!! hehee
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| new_n_lost
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C. pneumocytes type 2 ??
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| sigh
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Nice thought Hottie99! Lymphocytes - correct. I don't have explanation...that's why I posted the question...so someone can explain ...
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| hottie99
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thx, i guess i was just thinking that the only one out of those that doenst replicate (not that i know of) would have been lymphocytes so that was my logic, who knows if it's rite or wrong, i wish i could explain it sigh with 100% confidence, but this was my simple minded logic  (not sure if u are making fun of my logic, hehehee)
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| new_n_lost
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ok
I have a confusion here when you say the salvage pathway of purine synthesis that means the question is asking you about >> A salvage pathway that exists for the purpose of utilizing the free purine bases from the nucleotide degradation back into making nucleotides. The specific enzymes that are part of the Salvage system are HGPRT and APRT ( adenine phosphoribosyl transferase), which convert the following reactions.
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Adenine phosphoribosyl transferase
Adenine + PRPP  adenylate + PPi
- Hypoxanthine-guanine phosphoribosyl transferase
Hypoxanthine + PRPP inosinate + PPi
Guanine + PRPP guanylate + PPi
Now we do know that ADA or Adenosine Deaminase is the causative factor of SCID in which the proliferative ability of lymphocytes is severely distrubed.
So i cant agree to this answer.
Lets discuss this, if anyone wants to .....................
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| new_n_lost
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Sorry forgot to add a step
ADA is also a part of Salvage pathway. where it regenerates Inosine form Adenosine
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| sigh
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Hottie I think any logic is fine if you got the right answer (just based on our IQ)
New and lost I have the question and the right answer...no explanation.I did not get it right... no idea what is going on... confusing ... agree
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| hottie99
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thx sigh for not bursting my bubble of confidence, very much appreciated!! 
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| new_n_lost
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sigh wrote:
New and lost I have the question and the right answer...no explanation.I did not get it right... no idea what is going on... confusing ... agree
The question seems to ask about Purine Salvage Pathway the 3 major enzymes of it are
1. HGPRT
2. ADA
3. APRT
Thats the defining point of the question. I maybe getting it wrong but to me its asking which cells lack the ability to salvage free purines bases and therefore require a de novo synthesis.
The enzymes in the De novo synthesis are different than the salvage one.
To me thats the whole point of the question and SCID is a prime example of the absence of purine salvage synthesis pathway.
So to me the answer given is not right unless i m missing something.
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| hottie99
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i see what ur saying as well, but if it's not the lymphocytes as u believe, then why any of the others?? dont the remaining lack enzymes of salvage pathway? what would direct u to pick type 2 pneumocytes over the others? just curious... thx!
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| silver
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where does it say that lymphocytes don't replicate? we're not born with the entire lot of lymphocytes that will last us our entire life.
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| hottie99
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i agree, i dont know if it is or has it ever been written that, im just saying, what other logic is there for the other answers? dont get so defensive, just back up what ur saying or if u dont know, then say that too.. im not claiming to know it all, i was just explianing my thought process if one wanted to follow, but i didnt say i was rite in it. the person who posted the question said the answer is D, but wat the reasoning is, no one knows, which is why he posted it in the first place...
i guess my logic compared to the others choices listed, others replicate, and i didnt think lymphocytes themselves replicate, i thought upon the 'death' of the lymphocyte, more produced from ur thymus or no?? not sure about that either..
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| new_n_lost
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hottie99 wrote:
i see what ur saying as well, but if it's not the lymphocytes as u believe, then why any of the others?? dont the remaining lack enzymes of salvage pathway? what would direct u to pick type 2 pneumocytes over the others? just curious... thx!
Cos so far from what i know Pneumocytes dont replicate and are usually destroyed and replaced with other cells. eg fibrosis. But for lymphocytes to be out of the salvage pathway was a bit tough for me cos of ADA def. in SCID. unless we say that ADA is not in the Salvage pathway.
And i also m looking thru materials which somehow mention that lymphocytes dont use salvage pathway. so far not much success. So if you believe that lymphocytes should be the answer then some reference that helped to derive your conclusion will definitely help me in understanding your reasoning for the answer.
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| hottie99
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i dont have reference, otherwise i would have gladly posted how i came to that, like i said i was just 'thinking outloud' again.. i didnt' google/answers.com/wikipedia it yet.. hahaa.. just hearing out wat everyone had to say. also i was curious wat the rationale was if u didnt think it was lymphocytes.. i agree ADA is in salvage pathway, so that's not to dispute, and yes ADA is deficient in SCID; i guess i just think of SCID as deficiency in B and T cells, never really thought about the lymphocytes in that situation.
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| new_n_lost
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And as to why i chose Pneumocytes. i made a guess or rather an educated guess( based on my very limited knowledge) or lets say answered by exclusion.
For my knowledge i always say inches covered and miles to go.
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| hottie99
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hahaa. yes as should everyone say that same thing, knowledge is just one of those things that is very difficult to know it all..
that's all i did, essentially i went down the list and eliminated options.. and left with that answer..
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| sigh
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I did some thinking/research about this...here what I got
I hope everybody knows what is MPA (mycophenolate mofetil)...yep... immunosuppressor which we use in transplant recepients, it inhibits IMPDH (inosine monoP dehydrogenase) which is enzyme in de novo pathway of G nucleotide s-s
so de novo s-s is inhibited...Now I will quate here from my resourse "because T- and B-lymphocytes are critically dependent for their proliferation on de novo synthesis of purines, whereas other cells types can utilize salvage pathways, MPA has potent cytostatic effects on lymphocytes"
I still can't put SCID together with this info...
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| hottie99
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hey sigh, where did u get this question from? is it from some bank?? just curious.. thankx!
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| new_n_lost
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sigh wrote:
I did some thinking/research about this...here what I got
I hope everybody knows what is MPA (mycophenolate mofetil)...yep... immunosuppressor which we use in transplant recepients, it inhibits IMPDH (inosine monoP dehydrogenase) which is enzyme in de novo pathway of G nucleotide s-s
so de novo s-s is inhibited...Now I will quate here from my resourse "because T- and B-lymphocytes are critically dependent for their proliferation on de novo synthesis of purines, whereas other cells types can utilize salvage pathways, MPA has potent cytostatic effects on lymphocytes"
I still can't put SCID together with this info...
Mate you missed an essential quote from that part of the article. The authors in the Nutrition and Immunology book have proved that by inhibiting the de novo synthesis of purines, the PROLIFERATIVE RESPONSE of the Lymphocytes is stopped. Whereas the normal day to day activity of the lymphocytes is handled by the salvage pathway.
Your reference is in the context of MPH drug and its function in/and as an anti cancer drug where the cells are in high proliferative mode and therefore they have both pathways working in overdrive.
But in the everyday function the salvage pathway is adequate for the lymphocytes.
Cheers and Respects.
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| sigh
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 So, do you think the question/answer may be wrong? I don't have any other explanation...
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| new_n_lost
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sigh wrote:So, do you think the question/answer may be wrong? I don't have any other explanation...
Bro i m mystified as much as you. But from the knowledge we have attained so far is that Lymphocytes DO PROLIFERATE. And they have both de novo synthesis and salvage pathway. APRT, HGPRT and ADA are a part of the purine salvation pathway and therefore it cant be said that lymphocytes dont have the salvage pathway.
Can you tell us the source of the question so that someone can shed light on it and we can all understand what the question was really asking/looking for us to know and memorise.
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| sigh
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The question was posted on another USMLE forum...They seems to be ok with the answer and they did not question it at all...95% it came from somebody's real exam... maybe under hormonal influence the guy was not able to understand this one correctly...
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| hottie99
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i see.. yeah seems like one of those chaotic uninterpretable questions like on the exam
no wonder we're all like wtf? well at least i am
thx sigh
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| new_n_lost
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sigh wrote:The question was posted on another USMLE forum...They seems to be ok with the answer and they did not question it at all...95% it came from somebody's real exam... maybe under hormonal influence the guy was not able to understand this one correctly...
Sorry i have another problem here.
Guys by nature are not HORMONAL Girls/Women are. Guys are usually more of a catecholamines sort of persons.   And to quote a very good friend of mine (a sentence she frequently uses to dispel adversaries i.e guys) I m not pmsing its just that i cant stand the sight of you.
My apologies to all the feminists who would take offense and respects to female equalists.
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