Introduction to Biochemistry - Quiz 3.4.4

The major goal of citric acid cycle is to produce the electron donors for the oxidative phosphorylation step, which means

To produce NADH
To produce FADH2

That's what I answered for the first time and I get partial credits, so I make another trial. I was thinking about it could be the production of GTP, after all it is for the energy.

But I learn a lesson here, citric acid cycle is also used to make precursors for bio synthesis of fatty acids and amino acids.

It is Fatty acids, Amino acids and pyruvate.

The problem is that pyruvate to acetyl coenzyme A released a lot of energy and is essentially irreversible, so there is no hope there. But once it enters the cycle, we cannot escape from the fate that two carbons will be decarboxylated away through the decarboxylation. So while it is possible to get glucose out of the oxaloacetate, the glucose is not made from the acetyl coenzyme A because there is no net conversion of acetate to oxaloacetate.

Iso-citrate to alpha-ketoglutarate and alpha-ketoglutarate to succinyl-coA.
This two oxidative decarboxylation tooks the carbons away.

A single turn in the glyoxylate cycle consume one and produce two oxaloacetate molecules, so it is a net production one one oxaloacetate molecule. To produce two oxaloacetate molecules and therefore 2 PEP molecules, we need two full turns.

Bacteria upregulate the glyoxylate cycle and down regulate the citric acid cycle.

I got this all wrong :(

I thought if the bacteria is feeding on pyruvate, there is no glucose around and it must build glucose, but that was false. Pyruvate itself can be an entry point to gluconeogenesis, therefore the cell can do citric acid cycle.

Once we decided it is the citric acid cycle, the rest follows:

Down regulate glyoxylate cycle
Down regulate gluconeogenesis
Up regulate citric acid cycle
Down regulate isocitrate lyase
Down regulate malate synthase
Unregulated citrate synthase
Upregulate phosphatase of AceK

Note: AceK can be used to phosphatase (i.e. remote the phosphate group) of the isocitrate dehydrogenase, that allows the citric acid cycle to move forward.