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Immunoglobin / Muscle contraction

Discussion in 'MCAT: Medical College Admissions Test' started by akalin24, Apr 21, 2004.

  1. akalin24

    akalin24 Member
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    For whatever it worth...

    One of my classmates made a big deal about these two questions in class today (Immunolgy).

    Our professor just finished her Ph.D in molecular biology at M.I.T.

    Her answers to the questions were... hydrolysis of ATP, NOT Ca++!

    Antigens attach to the light variable strand of the Immunoglobulin

    6 hypervariable regions

    Figured I would share the info..
     
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  3. DO it right

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    lol...i never guessed so many questions right...i knew the ATP one..thanx :laugh:
     
  4. pateltr1

    pateltr1 Member
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    Purve's 6th Edition Life Sciences, it says "The variable regions of both light and heavy chains participitate in defining antigen-binding site."

    Just curious, "6 hypervariable region" question was in same passage as antigen binding site question? I can't seem to remember that question.
     
  5. IcedCube

    IcedCube Senior Member
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    i totally have blanked out trying to remember this passage...was it on DM??
     
  6. theDr.

    theDr. Senior Member
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    why oh why did I put Ca+++. I still think the wording of the question was bogus.
     
  7. SitraAchra

    SitraAchra Attending Anesthesiologist
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    Damnit, I put 12 hypervariable regions. The passage said two regions (3 loops per region) but in the diagram I saw four...and I went with the diagram. I hated that passage!
     
  8. UCLAstudent

    UCLAstudent I'm a luck dragon!
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    I think this is still up in the air.
     
  9. UCLAstudent

    UCLAstudent I'm a luck dragon!
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    I put that, too.
     
  10. DoogieHowserMD

    DoogieHowserMD Junior Member
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    i put the same

    if there is 0 calcium, then regardless of ATP, myosin can't bind to actin rite? something has to uncover the troponin binding sites.

    you can make a contraction and have actin bind to myosin without ATP.. but ATP is what releases the 2... to begin the cycle all over again.

    i.e. rigor mortis - there is no ATP in the body, and yet your muscles can contract in the presence of calcium... they just can't release because there's no ATP.
     
  11. duck2005

    duck2005 Member
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    im 99.9% sure the answer was ATP hydrolysis. recall that it asked what "POWERS" contraction, not what is essential for contraction. many things are essential for contraction- actin, myosin, Ca+.

    the power of contraction is a mechanical power derived from chemical energey harnessed from the hydrolysis of ATP. secondly, without ATP hydrolysis, myosin cannot bind actin. hydrolysis produces ADP + P.

    when mysoin is bound to ADP+P, it is the release of these that results in the contraction powerstroke. these are replaced with ATP to release myosin fr actin. and then, ATP hydrolysis results in the return of myosin to its normal form. without ATP hydrolysis, ATP would remain bound to myosin, myosin would remain in the cocked position, and would be unable to bind actin for future contraction.

    w/ rigor mortis, the contraction is caused by rapid release of Ca and is powered by ATP. there is no more ATP produced and relaxation cannot occur (you're right here). still, the contraction in rigor mortis itself is related to Ca and to ATP.
     
  12. ASDIC

    ASDIC The 9th Flotilla
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    for the immunoglobin question, even if you didnt know that the region had 6 hypervariable regions, you could figure it out form the picture.

    If you looked at the picture, there were 2 arrows pointing towards the 2 clefts where they heavy strand meets the light strand. And according to the passage, they said each cleft has 3 hypervariable regions.

    So an immunoglobin would have 2 x 3 = 6 hypervariable regions
     
  13. Remember you have to answer the questions according to the info. based in the passage. I had put 6 first (i think) then changed it to twelve based on ther material in the passage.
    In other words :eek: I don't want to discuss this thing anymore
     
  14. KHep

    KHep Senior Member
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    I too originally put 6, reread the passage and then changed my mind and put down 12.........urghhh! :smuggrin:
     
  15. duck2005

    duck2005 Member
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    in fact, the passage said there are 3 hypervariable regions on each of "ONE light chain and ONE heavy chain." that was in the passage. yet another instance where bio ends up being verbal.
     
  16. Big Bill

    Big Bill Senior Member
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    Duck 2005 you are right. there were one region for each light and heavy chain and there are two of each. This was definately a verbal type question. As for the ATP question ATP supplies energy in its Phosphodiester bonds. Ca2+ provides the trigger to start contraction by binding to Troponin C. Glad it is over, Bill
     
  17. akalin24

    akalin24 Member
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    What do you guys think about the antigen binding question. I chose the light variable region but I guess it binds to both light and heavy variable regions??? That was not an answer choice it was 1 or the other.

    ??
     
  18. duck2005

    duck2005 Member
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    i didnt have an antigen binding ?. i had one that asked where carbs would bind (cooh terminal end of consant region). another where a phagocytic cell would attach. that's constant region, heavy chain
     

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