Submitted by Prerak Juthani
The molecule above is known as FURA-2, and it is a dye that is used to bind to Ca(2+) ions within neurons. Based on the charges shown in FURA-2, how many Ca(2+) ions do you think it can bind to?
a) 0
b) 1
c) 2
d) 3
e) 4
a) 0
b) 1
c) 2
d) 3
e) 4
And the answer is…
C. If we look at the charge on the FURA-2 molecule, we can see that the total charge is -4, and if we look at the question, we see that the charge of the Ca(2+) is +2. Thus, to be electrically neutral when bindings (which is usually what we want since nature hates charge), we would have two COO- groups bind to one Ca(2+) ion. Thus, since we have four COO- groups in all, we can reason that FURA-2 must bind to 2 Ca(2+) ions.