Cell Respiration
Overview:
If all the
energy in glucose was released at once, it couldn't be harnessed to make
ATP. So the breakdown of glucose
is done in steps.
Each step
releases a little of the energy contained in the chemical bonds in glucose by
transferring high-energy electrons from one molecule to another.
Respiration
is divided into 3 stages:
1.
Glycolysis
2.
The
Kreb's Cycle
3.
Electron
Transport Chain
1. Glycolysis
Takes
place in the cytoplasm of the cell:
Overall:
Used
2 ATP + Made 4 ATP 2 ATP total
Made
2 NADH
Made 2 pyruvate
Before the pyruvates can
enter the KrebŐs cycle, it must be modified:
Each
of the pyruvate molecules produced in glycolysis combine with a cofactor called
coenzyme A to produce acetyl-CoA (a 2-carbon molecule) and giving off CO2.
During this reaction
a molecule of NADH is also produced, which will also later be used to generate
ATP.
Overall: since we have 2
pyruvates-
Made 2 NADH
Gave off 2 CO2
2.
Krebs
Cycle
Within the matrix of the mitochondria, each acetyl-CoA
(with 2 carbons) will combine with a 4-C molecule called oxaloacetate. The resulting 6-C molecule will then go
through a series of reactions, each releasing a bit more energy. The result will be CO2,
NADH, and FADH2.
Eventually, oxaloacetate will be remade, to start the cycle all over
again:
Overall: 6 NADH, 2 FADH2, 2 ATP, 4 CO2
3.
Electron
Transport Chain
We have now made a total of 4 ATP molecules (2 from
glycolysis, 1 from each of two turns of the Krebs cycle). The rest of the high-energy electrons
from our original glucose have now been transferred to 10 NADH and 2 FADH2. These electrons in NADH and FADH2
will be used in the Electron Transport Chain (ETC) to produce even more ATP.
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