Question

1.  Suppose you are a cellular biologist tracking cellular respiration in a cell.  You know that the cell has completed catabolism a certain number of glucose molecules and has partially catabolized another.  You have documented the following being produced:

                                    130 molecules of ATP

                                    44 molecules of NADH

                                    8 molecules of FADH₂

                                    26 molecules of CO₂

            a.  How many molecules of glucose have been completely catabolized?  (2)

            b.  How far along the cellular respiratory pathway has the remaining glucose been catabolized (hint, it is past the energy pay-off phase of glycolysis)?  Explain how you figured out the responses to questions 1a and 1b.  (4)

(Hint, your answer will be similar to: “a. 10 molecules of glucose have been completely catabolized” and “b. the remaining glucose has been catabolized through the energy investment phase of glycolysis”.)

2. Suppose a plant cell outputs 4 molecules of G3P.  (These 4 G3P can then be use do make 2 molecules of glucose).

            a.  How many total CO₂ does the plant cell have to take in to output 4 G3P and to keep the Calvin Cycle going (RuBP is also regenerated)?

            b.  How many total ATP does the plant cell use in order to output 4 G3P and to keep the Calvin Cycle going (RuBP is also regenerated)?

            c.  How many total NADPH does the plant cell use in order to output 4 G3P and to keep the Calvin Cycle going (RuBP is also regenerated)?

Answer 1

1. Cellular Respiration

a. Each molecule of glucose when completely catabolized produces six molecules of Carbon dioxide. In the given case, we observe that 26 molecules of CO2 have been produced which shows that four molecules of glucose have been completely catabolized which gave 6X4 = 24 CO2 molecules and the rest two molecules are produced during the catabolism of fifth glucose which is now partially catabolized. So, the answer to the question comes out to be 4.

b. Each cycle of respiration produces 10 molecules of NADH, 2 molecules of FADH2, and 6 molecules of CO2, which then ultimately give 32 molecules of ATP. In the given data, if we exclude the numbers formed in the first four cycles of respiration like this:

ATP = 130 - (32X4) = 2, Similarly,

NADH = 4, FADH2 = 0 , CO2 = 2

Above are the no. of molecules of each type formed in the fifth cycle. So, the step till which two ATP, four NADH, and two CO2 have been produced is the conversion of pyruvate to Acetyl Co-A. Also, no FADH2 is produced till then., which means that the remaining glucose has reached that state where it is converted into Acetyl Co-A