[ScienceDinoswar]

A worker in a radioisotope laboratory was accidentally exposed to high levels of ¹⁴CO₂ during a routine experiment.  When tests of the worker were run and analyzed it was discovered that the glucose in his blood contained ¹⁴C.

a. Based on what you now know about metabolism, show how ¹⁴CO₂ can become incorporated into glucose in the worker, being sure to indicate where in glucose the ¹⁴C resides (i.e., in which carbons the ¹⁴C is found).  You do not need to show every enzymatic transformation, but you do have to show the key steps in a way that clearly demonstrates you understand what is happening.

• At first I approached this using the Calvin cycle, but realized that wouldn't work as the worker is not a plant (as far as I know). Then I approached drawing the mechanism in terms of CO₂ production with ethanol in anaerobic fermentation to go back to acetaldehyde, back to pyruvate, and ultimately forming glucose with the ¹⁴C. Is this a possibly acceptable way for the ¹⁴CO₂ to be incorporated into glucose where the ¹⁴C is C3 and C4?

b. Does this unfortunate accident reveal that humans are actually capable of utilizing CO₂ for glucose synthesis, enabling us, like plants, to satisfy our metabolic needs simply by inhaling CO₂?  Explain.

• I've written:
  No because gluconeogenesis requires a lot of ATP to make glucose to be able to be used for metabolic needs, but oxygen releases more energy to give ATP for metabolism. Gluconeogenesis would be inefficient and a lot of work to process. This is the one I'm more so confused about explaining why CO₂ being inhaled can't just be used like plants in humans.