USMLE Forums banner
1 - 11 of 11 Posts

·
Registered
Joined
·
209 Posts
Discussion Starter · #1 ·
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
 

·
Registered
Joined
·
316 Posts
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
 

·
Registered
Joined
·
209 Posts
Discussion Starter · #3 ·
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
 

·
Registered
Joined
·
316 Posts
o... if they say so then it must be it... but if somebody xplains it more clearly it will be better otherwise its confusing
 

·
Registered
Joined
·
414 Posts
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:
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
 

·
Registered
Joined
·
154 Posts
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?
 

·
Registered
Joined
·
1 Posts
Answer

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

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
 
1 - 11 of 11 Posts
Top