CELLULAR RESPIRATION
The essential purpose of cellular respiration is to carefully extract ENERGY
from a fuel molecule (like glucose, though many other molecules can be used as
fuel molecules for cells) and transfer as much of that ENERGY into ATP
molecules. Those 36 ATP molecules can then be used to run most cellular
machines.
The first step does NOT require oxygen (it is “anaerobic”) is GLYCOLYSIS
which occurs in the cytosol. The glucose molecule (6C) is cracked in half and
some ENERGY is stored as 2 ATP molecules profit. The two pyruvic acid
molecules (3C each) still have plenty of stored ENERGY and they will be used as
reactants for the CITRIC ACID CYCLE (Krebs Cycle).
The second step is the CITRIC ACID CYCLE (CAC, Krebs Cycle). Both the CAC
and the ELECTRON TRANSPORT SYSTEM (ETS) require oxygen (thay are
“aerobic”) and occur inside mitochondria. The CAC takes place deep inside the
MATRIX of mitochondria During the CAC the remaining 3C molecules are
completely taken apart and the carbon products are carbon dioxide CO . The CO2 2
will diffuse out of the cell and eventually be exhaled out the lungs. Of course,
ATP and other ENERGY-carrier molecules (NADH, FADH ) are produced.2
The third step is the ELECTRON TRANSPORT SYSTEM (ETS) which occurs
around, and inside, the inner membrane of mitochondria. A famous enzyme
(ATP Synthase) will make most of the ATP in this step. Oxygen atoms play an
important role as electron acceptors here and the oxygen atoms end up as
part of the water which is a product of cellular respiration.
During GLYCOLYSIS, a 6-carbon Glucose molecule is “cracked” in half to form two 3-carbon molecules
of Pyruvic Acid. It takes a little to do this [2 ATP’s of ACTIVATION ENERGY] but much more ENERGY
ENERGY is released.
All types of cells [prokaryotes and eukaryotes] will store some of this in ATP molecules, but ENERGY
eukaryotic cells can store some additional in molecules of NADH, another nucleotide energy-carrier ENERGY
that can carry the in HIGH ENERGY ELECTRONS.ENERGY
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These HIGH ENERGY ELECTRONS will need to be carried over to the ELECTRON TRANSPORT
SYSTEM [ETS] in the mitochondria where the ENERGY is transferred to ATP’s.
At the end of GLYCOLYSIS, a Net Profit of 2 ATP is released and the Pyruvic Acid molecules, still
containing lots of will be used for FERMENTATION by many prokaryotes OR be shuttledENERGY
over to the mitochondria for more extraction.ENERGY
During the CITRIC ACID CYCLE [Krebs Cycle] the pyruvic acid molecules from GLYCOLYSIS will be
completely disassembled and the will be stored in ATP or in molecules of NADH or FADH . This ENERGY 2
will result in the production of 6 CO molecules that will leave the cell by diffusion [remember internal 2
respiration?]. A total of 2 ATP molecules, 2 FADH2 molecules and 8 NADH molecules are produced.
In the ELECTRON TRANSPORT SYSTEM [ETS], the HIGH-ENERGY
ELECTRONS carried by NADH and FADH are transferred to the first protein in the ETS. As the2 HIGH-
ENERGY ELECTRONS are transported from one membrane protein to the next, the in those ENERGY
electrons is used to run protein pumps that pump PROTONS [H+ ions!] from the MATRIX of the
mitochondria into the OUTER COMPARTMENT. This creates a sort of “biological battery” that has a
surplus of positive charges [Hydrogen protons] in the outer compartment. These protons can only flow
back through ATP Synthase embedded in the inner membrane. ATP Synthase is a molecular machine
that uses the KINETIC ENERGY ENERGY [the of MOVEMENT] to form ATP. Most of the ATP produced in
cellular respiration is
generated in the . These ATP molecules are actively transported out of the mitochondria for use ETS
all over the cell.
The Anatomy of a Mitochondria
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