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In the matrix of the mitochondria of all our cells
Is the cycle of reactions that won Hans Krebs the Nobel Prize
This cycle takes the energy in food
And makes it into other forms that your cells can use.

Krebs Cycle makes the electron carrier NADH
Which later brings electrons to the electron transport chain.
And Krebs makes FADH2 its function is the same,
Krebs also makes some ATP another claim to fame.


(we’re talking) KREBS!
It’s the Citric Acid Cycle
Tricarboxylic Acid Cycle
Krebs– each cycle makes
One ATP, three NADH, one FADH2

Right before the cycle’s a transitional part
Links Krebs to glycolysis, so Krebs can start
Enzymes break a CO2 off a Pyruvate
Yields an NADH and Acetyl-CoA

Acetyl-CoA carries carbons two
With all the energy that derives from food
It’s a highly reduced molecule with energized electrons
It fuels up the Krebs cycle as it cycles on.

Now at the start of Krebs this Acetyl-CoA
Has the two carbons it carries in ripped away
Enzymes put these on oxaloacetate with carbons four,
Makes six-carbon citric acid who could ask for more?

Notice three carboxyl groups on that citric acid
It’s why the cycle’s also named for Tricarboxylic Acid
Or TCA Cycle, if it’s acronyms that you prefer
Or Krebs in honor of its discoverer!


Enzymes work on Citric Acid and remove a CO2
and other enzymes modify and oxidize it too,
The five carbon result is ?-Ketoglutarate.
Krebs cycle, it’s so great!

Every oxidation, can power the reduction,
of NAD plus which gains electron carrying function,
Becoming NADH, that energy sensation
Which later on in respiration powers ATP creation

Another oxidation follows, another  CO2 removed
Leaving us with a four carbon molecule
Another NADH results from this oxidation
As Krebs does its energy transformations

This four carbon molecule (Succinyl CoA),
Still has lots of energy, enzymes can take away
A series of reactions yield one ATP
The cell’s main energy currency.

Leavin’ just enough energy for enzymes to reduce
And one last NAD+ will also get reduced
As the final ‘lectron carrier NADH gets produced.

We’ve harvested what energy came in at Krebs’s start,
Now we have oxaloacetate at this final part
Oxaloacetate is the commencement and finale
Ready to meet acetyl CoA, and here at the final tally



Krebs goes round and round, such an ancient cycle,
Spinning like the wheels of my bicycle.
Krebs is like the axle of aerobic respiration,
I breathe out its CO2 with every exhalation!

We’ve walked through the cycle, so now lets review
Input is Acetyl-CoA with carbons two
The carbons get removed, releasing CO2
Exhaling sends this CO2 out of you.

The cycle’s function’s energy transformation
Three NADH, one FADH2 creation
And also synthesis of one ATP
Which cells directly utilize for energy

For every glucose cells absorb the cycle runs two times
As long as cells get fuel, Krebs is running just fine,
It precedes electron transport chain, it follows glycolysis
It’s spinning round and round in the mitochondrial matrix