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#1
07-16-2010
 USMLE Forums Veteran Steps History: 1 + CS Posts: 209 Threads: 34 Thanked 92 Times in 30 Posts Reputation: 122
Antibody Antigen Question

The amounts of protein precipitated in a series of tubes containing a constant amount of antibody and varying amounts of antigen are presented below. In which tube is antigen-antibody equivalence obtained?
Tube Antigen Precipitated (mg) Protein (mg)
A 0.02 1.1
B 0.08 2.1
C 0.32 3.1
D 1.0 3.7
E 2.0 2.9

A. A
B. B
C. C
D. D
E. E
 The above post was thanked by: Pixie (07-16-2010), Zagaris (07-16-2010)

#2
07-16-2010
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i think A... may be i m wrong but i thought this way... antibody which is a protein should be constant... the lowest amount shows more antibody has consumed and antigen and antibody are now in equilibrium
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#3
07-16-2010
 USMLE Forums Veteran Steps History: 1 + CS Posts: 209 Threads: 34 Thanked 92 Times in 30 Posts Reputation: 122

In tube d in the question presented, the maximum protein precipitate is observed. According to the rules governing precipitin reactions, maximum precipitation occurs at approximately antigen-antibody equivalence. In tubes a through c, antibody excess occurs; in tube e, antigen excess occurs

this is the explanation they gave but i didnt get the explanati0on can anyone explaina it if u understand the concept
#4
07-16-2010
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o... if they say so then it must be it... but if somebody xplains it more clearly it will be better otherwise its confusing
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#5
07-17-2010
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i used the same equilance basis.
E--as the amount of antigen ppt and protein are most equal to each other.
E--also there hhigest ppt in E it means more Ag-Ab equivalence.

is it not right please do correct me.:sorry:
Quote:
 Originally Posted by ecgram In tube d in the question presented, the maximum protein precipitate is observed. According to the rules governing precipitin reactions, maximum precipitation occurs at approximately antigen-antibody equivalence. In tubes a through c, antibody excess occurs; in tube e, antigen excess occurs this is the explanation they gave but i didnt get the explanati0on can anyone explaina it if u understand the concept
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#6
07-17-2010
 USMLE Forums Veteran Steps History: 1 + CS Posts: 209 Threads: 34 Thanked 92 Times in 30 Posts Reputation: 122

@kabutar actually i answered E but i dont no why the answer says D
but i still think its E
#7
07-17-2010
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someone should explain this
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#8
11-20-2011
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this is really tough question
#9
11-20-2011
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it's D
explanation given is right and i can't explain in a better way,,,see the graph given in immuno Kaplan . .

zone of equivalence = max amount of precipitate also known as window phase . .
#10
11-20-2011
 USMLE Forums Addict Steps History: Step 1 Only Posts: 154 Threads: 8 Thanked 134 Times in 62 Posts Reputation: 144

Quote:
 Originally Posted by zohaib it's D explanation given is right and i can't explain in a better way,,,see the graph given in immuno Kaplan . . zone of equivalence = max amount of precipitate also known as window phase . .
Hey Zohaib, i get the principle but the numbers are not clear to me. It D there is 1 mg precip. meaning 1 mg of ag bound to AB. What does the other number mean? is it the rest amount of AB?
#11
12-16-2012
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It's an old question but thought it could use an explanation:

SUBTRACT!!!!!
3.1 - 0.32 = 2.78 anti-body complex
3.7 -1.0 = 2.7 anti-body complex

JUST after 3.1 with anti-body complex 2.78 we begin to see a decrease in complex and a rise in antigen precipitation meaning excess antigen - meaning we have passed maximum equivalence, so like from old chemistry be have just hit the titration point

Quote:
 Originally Posted by ecgram The amounts of protein precipitated in a series of tubes containing a constant amount of antibody and varying amounts of antigen are presented below. In which tube is antigen-antibody equivalence obtained? Tube Antigen Precipitated (mg) Protein (mg) A 0.02 1.1 B 0.08 2.1 C 0.32 3.1 D 1.0 3.7 E 2.0 2.9 A. A B. B C. C D. D E. E

 Tags Immunology-, Step-1-Questions

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