Question

Step 2 of the Citric Acid Cycle converts citrate to isocitrate.

This moves the functional group (-OH) to convert a ______________alcohol to a _____________alcohol, which can then be oxidized to an a-ketone in the next step along with a decarboxylation reaction.

Write the molecular formula for citric acid (citrate with the hydrogens put back on those carboxyl groups): ___________________

From the molecular formula, calculate the molar mass for citric acid:_______________g/mol.

How is citrate related to isocitrate?

a. They are constitutional isomers.

b. Citrate has a higher molar mass.

c. Isocitrate and citrate are diastereomers but not enantiomers.

d. They are inter-convertible by a change in conformation.

Answer 1

Step II of citric acid cycle converts citrate to isocitrate is the isomerisation of citrate. This moves the functional group -OH to convert a tertiary (3⁰) alcohol to a secondary alcohol(2⁰), which can then be oxidised to a ketone in the next step along with a decarboxylation reaction.

Molecular formula of citric acid is C₆H₈O₇ or C₆H₅O₇^3- (trisodiumcitrate).

Molar mass of citric acid :-Atomic number of carbon, C = 6 ; Hydrogen, H = 1 ; Oxygen ,O = 8

Mass number of carbon, C = 12 ; Hydrogen, H = 1 ; Oxygen ,O = 16

      Molecular mass of citric acid = 12 (6) + 8 (1) + 16 (7)

                                                  = 72 + 8 + 112

So, Molecular mass of citric acid = 192 g/mol.

Citrate and isocitrate are constitutional and structural isomers. Both show position isomer because there is difference in position of -OH functional group. Both have same molecular mass.Isocitrate is chiral because it has two (C2 & C3)chiral carbon but citrate is achiral because there ia no chiral carbon in citrate.So these are neither diastereomer nor enantiomers.

Yes they are interconvertable and interconversion is isomerisation.