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  #1  
Old 08-29-2012
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Post biochem question

q) which of the following lipid soluble hormone/substance is exception from others in having seven transmembrane spanning domain proteins..?

a) cortisol
b) cholecalciferol
c) androstenedione
d) triiodothyronine
e) retinoic acid
f) ascorbate
g) somatomedins
h) vasopressin
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Old 08-29-2012
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Default my answer :)

f) ascorbate ?
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Old 08-30-2012
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Correct Answer E is the answer

the correct answer is E) retinoic acid( vitamin A)

seven transmembrane spanning domains are the charecteristic of trimeric G coupled receptors.....

water souble hormones uses these receptors for their signalling pathways(ex----Gs,Gq,Gi---used by glucagon,epinephrine,ANF etc)......

lipid soluble hormones uses DNA binding domain via ZN finger motifs mostly(ex-----vit.D,thyroxine,cortisol)...
except vit.A ,it uses both ZN finger motifs( for epithelium maintenance) and 7 spanning domains coupled to trimeric G protein ( for vision)..

trimeric G proteins include Gs,Gq,Gi and Gt(transducin)
Gt is for photoreceptor pathway for vision.....so, retinoic acid is the only lipid soluble hormone/substance which uses this pathway.....it is the most appropriate answer....
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Old 08-30-2012
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Quote:
Originally Posted by venky2600 View Post
the correct answer is E) retinoic acid( vitamin A)

seven transmembrane spanning domains are the charecteristic of trimeric G coupled receptors.....

water souble hormones uses these receptors for their signalling pathways(ex----Gs,Gq,Gi---used by glucagon,epinephrine,ANF etc)......

lipid soluble hormones uses DNA binding domain via ZN finger motifs mostly(ex-----vit.D,thyroxine,cortisol)...
except vit.A ,it uses both ZN finger motifs( for epithelium maintenance) and 7 spanning domains coupled to trimeric G protein ( for vision)..

trimeric G proteins include Gs,Gq,Gi and Gt(transducin)
Gt is for photoreceptor pathway for vision.....so, retinoic acid is the only lipid soluble hormone/substance which uses this pathway.....it is the most appropriate answer....
nice question but what about vasopressin which is also v1(Gs) and V2(Gq) coupled.... have you ruled it out bec its not lipid soluble hormone( or substance)
and same is the case with vit c which is water soluble ???(although i don't know its cellular mechanism of action?? so can you through light on that as well)
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Quote:
Originally Posted by offpiste View Post
nice question but what about vasopressin which is also v1(Gs) and V2(Gq) coupled.... have you ruled it out bec its not lipid soluble hormone( or substance)
and same is the case with vit c which is water soluble ???(although i don't know its cellular mechanism of action?? so can you through light on that as well)
yes, vasopressin is water soluble and Gs and Gq coupled receptors as you said.....ya, i ruled out them
cortisol, cholecalciferol, T3, androstenedione are lipid soluble----act via Zn motif(DNA binding domain)
vasopressin(Gs and Gq), somatomedins( IGF-1 by JAK/STAT pathway) are water soluble hormones....
as for vitamin C is concerned......it is water soluble hormone....it cannot be synthesized in humans due to deficiency of l-gluonolactone oxidase enzyme....so, all the digested vit.C is transported via GLUT 1 and 3 ,SVCT (sodium ascorbate co-transporters) transporter system......

hope it understands well.....
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Old 08-30-2012
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Quote:
Originally Posted by venky2600 View Post
q) which of the following lipid soluble hormone/substance is exception from others in having seven transmembrane spanning domain proteins..?

a) cortisol
b) cholecalciferol
c) androstenedione
d) triiodothyronine
e) retinoic acid
f) ascorbate
g) somatomedins
h) vasopressin
Ya its retinoic acid, I did this question somewhere in KV kamal or AAA.
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