NBME Answers : varunmehru's page

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submitted by sugaplum(487), visit this page

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This question is asking about VDJ rearrangement which happens in the bone marrow. The genes are all chopped up because the B cell is trying to generate a unique combination for its receptor
simple concepts... odd wording

Chapter 3 of "how the immune system works" - awesome book

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varunmehru in the question stem, they are asking about a constant region. VDJ rearrangement is for the variable. It doesn't make sense :( +4

sallz Both the constant (heavy chains) and the light chains undergo gene rearrangement. The heavy chain undergoes V(D)J random recombinations, while the light chain undergo VJ random recombinations. So gene rearrangement could work for both regions. +13

azibird The constant region does not undergo recombination. That's why it's called constant. It's just right next to the variable region though, so they get expressed together as one protein. That's why the constant-labeled DNA region is variable length here. +4

chaosawaits You're right that the constant region is not undergoing recombination. The multiple bands are not do to constant region rearrangement; it's due to the variable chain rearranging and then the cDNA probe that is specific to the constant region attaches to each of these rearrangements, since it hasn't changed +

submitted by sklawpirt(34), visit this page

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I think the idea here is simply that one should think about where vesicles are coming from on their way to the golgi complex.

"Two steps forward and one step back." Specfically the question may be referring to a rare craniofacial disorder. an awarenesss of that disease is not necessary. What is necessary is understanding the origin from where vesicles are traficked to the Golgi apparatus.

COPI protein is needed to coat vescles from the RER to send to golgi. Thus, with a mutation in that protein, the packaged proteins that should bleb off and be sent to the golgi, instead accumulate in the RER and dilate it. Thus the answer.

https://www.cell.com/ajhg/pdf/S0002-9297(16)30214-2.pdf

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hayayah pg. 47 on FA got the good visuals! +6

notadoctor COPII* proteins are needed to coat vesicles from the RER to Golgi. "Two(COPII) steps forward; one(COPI) step back." Anterograde goes RER -> Golgi -> Lysosomes/Secretory Vesicles -> Plasma membrane +27

titanesxvi why not small lysosomes? +5

varunmehru and I thought large lysosomes due to lack of enzymes to degrade +1

samsam3711 The size of the lysosome is not affected by the presence or absence of protein, but its function is compromised (eg. protein is getting stuck in the RER) +2

fattyacid I hope this helps to whomever was lost like me Null mutation: A mutation (a change) in a gene that leads to its not being transcribed into RNA and/or translated into a functional protein product. For example, a null mutation in a gene that usually encodes a specific enzyme leads to the production of a nonfunctional enzyme or no enzyme at all. +3

pingra I think you made a typo: COPII (RER -> cis-Golgi); COPI (trans-golgi -> cis-golgi and cis-golgi -> RER), clathrin (endocytosis and trans-golgi -> lysosome) +2

kevin So my thought process was if there is no COP signal then instead of going to Golgi it would be sent astray into cytoplasm, akin to how in I-cell Dx the enzymes get sent out of the cell since there is no trafficking signal (therefore I presumed large lysosome due to eating the aggregated protein). Are we saying without COP or Clathrin that the vesicle will simply stay put where it is? If I can get a reply before my exam (2 weeks) that'd be much appreciated +2