Why do cells want LOTS of glucose? Why do cells want lots of ATP?

1 Answer
Nov 13, 2017

ATP is the Energy carrier in (almost?) any organism.
Glucose is the main supplier of this Energy.


ATP is used to drive endothermic enzymatic reactions, i.e. reactions that cost energy to take place. ATP delivers this by means of the high-energy bond between its second and third Phosphate groups.

Note: besides this, ATP has many other roles in the cell, not ONLY Energy delivery....

The Energy mentioned has to come from somewhere, and it ultimately is extracted by means of 3 pathways/cycles:
1 Glycolysis (the Embden Mayerhof pathway);
2 Citric Acid Cycle (also known as " Krebs "-cycle);
3 Oxidative Phosphorylation.

Lets start with the first one:
No matter what sugar you consume, it will rapidly be converted to (D-) Glucose. this will be phosphorylated, and via a series of conversions broken down to Pyruvate. The enzyme Pyruvate Carboxylase converts it, by adding a Carboxyl group (organic acid-group), to OxaloAcetate, which then enters the Citric Acid cycle.

I want (need!) to keep this explanation short, so I won't explain in detail what is generated and where, but suffice it to say that in all 3 processes energy-carriers(ATP) and electron donors/acceptors (NADH, NADPH) are involved. The Carbon atoms ultimately end up in the #CO_2# that we exhale.:

#C_6H_(12)O_6 + 6O2rarr6CO_2 + 6H_2O #

The ELECTRONS (as well as the protons, or #H^+#) that are extracted via #NAD^+# and #NADP^+# are ultimately donated to #O_2#, resulting in the watermolecules in the formula presented above...

The whole process is extremely complex, and cannot possibly be described in detail in one answer. There is a map however, descibing the complete (human & otherwise) Metabolism.
They usually are given away for free at stands in Science Fairs, congresses etc. (at least they used to be in the past).

If you are interested, you can try and order them on-line from Roche who seem to be the new custodians of the Map(s).
Finally, there is an on-line version:


Can be a bit overwhelming at first sight, but there is a menu to steer you around I think...

Footnote: For Oxidative Phosphorylation, look in Map2...