In HelpHippo's Intro to biochemistry metabolism, we said this:
There are 10 steps in glycolysis with long names and much detail.
This simplified intro is a start: Butt, “O”, head, chop, and change,
Hat on, hat off, move, lose, done
Start with glucose: a sugar with six carbons, numbered from head to butt.
One: On the butt: add a phosphate. Two: make it fructose on carbon 2.
Three: On the head: Add another phosphate....
Four: chop the big carbon sugar in half - the butt half is easy, it just gets a hat.
Five: make the “difficult head half” look like “the easy butt half.”
Butt “O” head, “chop (and change)”
Now that we're halfway through glycolysis, how much ATP have we made?
None.
That's right, so far we've actually lost two ATP,
that's where the phosphate on the butt... and head came from.
This is the “investment” part of glycolysis - just like you need a match to release more
fire from gasoline, you need to “invest” 2 ATP to release
more energy from glucose.
Speaking of investment steps, now - we'll explain this frequently tested factoid:
Step 3 (Phosphofructokinase) is the major committed step of glycolysis.
If you burn one ATP to stick a phosphate on the butt, this “butt sugar” can go down
other pathways.
But after “investing another ATP” and “sticking another phosphate on the head”?
There are... no other pathways for “butt AND head fructose”
you have to finish glycolysis.
So we committed...and chopped and changed so we now have two “easy bottom halves”.
We're in the pay-off phase, where we make high energy bonds:
Six,, on the hat, add a phosphate (and make a high energy bond in NADH)
Seven, off that hat phosphate, to make an ATP
Eight, move the phosphate from the butt to the middle, and now there's an OH on the butt.
Nine, lose that OH from the butt
Ten, And we use that middle phosphate to make our last ATP...leaving pyruvate
for the next part of cellular respiration: the citric acid cycle!
HelpHippo - Help your Hippocampus
