Cellular Respiration
1. Glycolysis
The glycolytic pathway begins with a 6-carbon molecule of glycolysis, the glucose is 'set up' by adding
. During the first 5 steps of
, and split into two of provided by the
[PGAL]. The first steps of glycolysis thus require an initial investment of energy,
.

Mitochondria

2. Pyruvate Oxidation
Pyruvate Oxidation is the step which molecules from glycolysis and transports them from the membranes into the matrix. Once inside a
. It takes the two
, through the two three changes:
1. a CO
2
portion of the
2. a is removed. by two hydrogen atoms (which are obtained from food)
3. is attached to the acetic acid portion (acetyl group)
The newly formed now moves on to the .

3
.
K REB ’ S C YCLE

Aerobic Respiration
I. steps:
A. The three carbon releases energy such that reacts whereby a carbon is lost as CO
2
. The reaction
. The remaining two carbon compound is not allowed to be free but rather binds a special molecule
This is essentially an reaction due to the loss of .
1. This reaction is probably more than one step, considering all of the reactants.
However, even to this day the intricacies of this reaction are not well understood.
2. It is not clear in eukaryotic cells exactly what carbon form passes from the cytoplasm to the (pyruvate? acetyl CoA? an intermediate?) The process looks very complex.
3. The binding of to the two carbon molecule is probably a type of handle making it easier for enzymes to act upon it.
B. The two carbon chain is released from to make the six carbon and binds to the four carbon
( a tricarboxylic acid )
1. The six carbon molecule is much more manageable by enzymes. (analogy :
). The two carbon molecule will eventually be totally decomposed to again regenerate , the later of which can be reused again.
C. The next reaction removes which is followed by a reaction which adds back water!!! The purpose is to rearrange the molecule to make it more convenient to extract the energy.
D. The next reaction releases energy to form
E. The reaction of (6 carbon molecule) to
.
(5 carbon molecule) leads to the release of gaseous
F. The next reaction again utilizes also released again as
. as a handle for one reaction. Energy is
. At this point we also lose the last in the form of CO
2
.
G. The reaction of molecule can be easily converted to an ATP by one more reaction.
H. Succinic acid to fumaric acid yields a passed to and used in the oxygen) to presumably yield two molecules.
. This
. A GTP can be
(in the presence of
I. The final step of our original glucose. The regenerated acetyl is now ready to react with another and the whole cycle can be repeated.
J. Frequently wrings out the last bit of energy (as NADH) of are quoted because it is known that in that the reduced NAD formed by glycolysis in the cytoplasm must be actively cells transported across the mitochondrial membrane to be made available to the
. The cost of such active transport is one ATP for each NADH transported.
Thus, the net for each cytoplasmic is only two ATP rather than three. However if one plays this game, then one should also consider the active transport of other molecules as well (pyruvate? phosphate? Mg++? etc.). The actual net gain of ATP is unknown but must be regarded as less than .
II. In eukaryotic cells the Kreb's cycle occurs in the liquid part of the the electron transport chain occurs in the .
The outer membrane is very can almost be ignored. and has almost no while
; it seems to have no function and

Anaerobic Respiration
•
is not available to serve as the final electron acceptor, the is unable to function.
• will remove hydrogens and electrons from end product pyruvate. Together, these actions will allow
Two different a) pathways are known.
is common in bacteria and yeast cells. and will remove the to continue.
• pyruvate is first
Acetaldehyde is then reduced as to yield a 2-carbon substance are transferred from NADH to acetaldehyde to produce .
•
Once the NAD has been , glycolysis can continue.
. b) The same result is reached by
.
• pyruvate is used as the
• end product is a molecule of respiration in cells. cells through the process of of the hydrogens removed from is a common by-product of
.

The steps of value is that, by permitting the recovered in the absence of do not themselves produce any additional ATP. Their sole
.
, they allow at least some energy to be
Some bacteria are . They are entirely dependent on anaerobic pathways. Most other organisms are aerobic, but some organisms, and some tissues are able to function in a state. That is, they are able to manufacture enough ATP through anaerobic processes to sustain themselves when for aerobic events.
Alternate Pathways
Many other pathways link to the basic pathways of
Organic materials other than glucose can be fed into the pathways, i.e. and .
• broken down during within the cell to form
.
•
Any of the or .
. can be readily transformed into either
, proteins, to their monomeric units, and may be reassembled
, such as , starch, and
•
Triglycerides are also readily glycerol, which is converted to into their constituent monomer, 3-carbon
.
•
Proteins can be hydrolyzed to their to form short chain carbon compounds and enter the respiratory pathway at different points, e.g. pyruvate, acetate, , succinate, fumarate, or .
When an of nutrient fuels are available, the excess can be diverted into storage molecules and held until resources are scarcer.
•
Carbohydrates is processed to and
, then converted to form which are assembled to provide the .

Key Products of glycolysis transition
Krebs cycle
Total
ATP CO
2
NADH FADH
2

Total ATP Production at End of Electront Transport System in source glycolysis transition
Krebs cycle total direct ATP from NADH from FADH
2
Total ATP Production at End of Electron Transport System in source glycolysis transition
Krebs total direct ATP from NADH from FADH
2
Cells
ATP
Cells
ATP

In cells, all
ATP can be recovered. In cells only ATP are recovered. This reduction occurs because takes place in the steps of and the occur inside the . The 2 produced during glycolysis must be passed across the membrane to the . They enter the ETS at the level of FAD -- that is, they each pass through only two couplings instead of the expected . This accounts for the two 'lost' ATP in cells.