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what happens when highly reduced substrates such
as glucose are oxidized

the hydrogens (with their electrons) that are lost, must be gained by other chemicals. These other chemicals are therefore reduced as they gain hydrogens.



can receive these hydrogens (become reduced) to make enzymatic reactions work. These same coenzymes
will later become oxidized when they donate their hydrogens to allow other enzymatic reactions to


Glucose is a

highly reduced substrate (many hydrogens). It has the potential to go through many oxidation reactions yielding much energy


Energy is captured in ATP by

the process of phosphorylation


Substrate level phosphorylations

occur when high energy phosphates are directly transferred from phosphorylated compounds to ADP


oxidative phosphorylations

Phosphorylations that occur as part of the electron transport chain (system)


reduced coenzymes and hydrogens

Hydrogens that deliver their electrons to the electron transport chain (system) for oxidative
phosphorylation are transported on reduced coenzymes (NAD and FAD)


Where do reduced coenzymes give up their hyrdogens and now what can they do

Here the reduced coenzymes give up their hydrogens (with their electrons) to ETC compounds and become oxidized in the process.
Coenzymes are now free to undergo reduction and pick up hydrogens once again.



is any energy yielding oxidation in which the terminal hydrogen acceptor is an inorganic
compound. Gaseous oxygen is not necessarily involved.


Aerobic Respiration

-any energy yielding oxidation in which the terminal hydrogen acceptor is
the inorganic compound oxygen. (Highest energy yield)


Anaerobic Respiration

any energy yielding oxidation in which the terminal hydrogen acceptor is
an inorganic compound other than oxygen. Terminal hydrogen acceptors include compounds
such as nitrate (NO3-1), sulfate (SO4-2) or carbonate (CO3-2).



is any energy yielding oxidation in which the terminal hydrogen acceptor is an organic compound. This does not require oxygen. In fact, this is anaerobic. The Electron Transport Chain is not used. (Lowest energy yield)


three major reaction pathways used in the complete oxidation of glucose

Glycolysis, Krebs Cycle (Citric Acid Cycle or Tricarboxylic Acid Cycle) and the Electron Transport System or Chain
(Cytochrome System)


Enzymatic reactions for ATP production occur

on the plasma (cell) membranes of prokaryotes


Features of Glycolysis

A. Net gain of 2 ATPs from substrate level phosphorylation. Actually 2 ATPs are used to
prime reactions, but 4 ATPs are actually produced.
B. 2 hydrogen pairs (2H will be used to represent a hydrogen pair) are produced. Each 2H
is attached to the coenzyme NAD. Therefore, 2 NAD each with a hydrogen pair is produced. The reduced NAD has the potential to carry the 2H to the ETC (later) for ATP
production by oxidative phosphorylation.
C. Glycolysis is anaerobic it does not require or use oxygen whether oxygen is present or not.
D. Glycolysis is a series of 10 separate enzymatic reactions. The 6 carbon glucose is eventually split into two 3 carbon pyruvic acids.


Before entering the Krebs Cycle, each pyruvic acid must

lose one molecule of CO2 and become a
2 carbon unit (acetyl group)


Intermediate or Preparatory Step-follows glycolysis

Since 2 pyruvic acids are produced from each glucose that entered glycolysis, 2CO2’s are produced in this step per glucose. Furthermore, for each pyruvic acid that
is converted to an acetyl, a 2H (hydrogen pair) is removed (oxidation reaction) and attached to
NAD (becomes reduced). Again, there are two pyruvic acids per glucose so 2 NAD’s each with a
2H is created per glucose in this preparatory step. Each acetyl group is now attached to the
coenzyme called CoA to become acetyl CoA. The acetyl CoA delivers the 2 carbon acetyl group
to the Kreb’s Cycle reactions.


Krebs Cycle

Series of biochemical reactions in which the large amount of potential chemical energy
stored in acetyl CoA is released in steps. Intermediate compounds in the Krebs Cycle
are oxidized and the hydrogens are added to the coenzymes NAD and FAD (they
become reduced) along the way. Remember that reduced NAD and FAD will carry the
hydrogens along with their electrons to the ETC for ATP production


Feature of Krebs Cycle

Acetyl CoA delivers its acetyl group (2C) to a 4C compound in the Krebs Cycle called
oxaloacetic acid. Citric Acid a 6C compound is formed.
C. In step 3, a hydrogen pair (2H) is added to NAD. Also a CO2 is removed
(decarboxylation). The compound now has 5 carbons.
D. In step 4, another 2H is added to NAD and another CO2 is removed. We now have a 4C
E. In step 5, ATP is produced through substrate level phosphorylation.
F. In step 6, succinic acid (succinate) is converted to fumaric acid (fumarate). This
dehydrogenation reaction adds 2H to FAD (thus reducing FAD). FAD like NAD will carry
the hydrogen pair to the ETC for ATP production.
G. In step 8, another 2H is added to NAD. The compound oxaloacetic acid is formed and
the cycle can be repeated.


The entire Krebs Cycle turns

Note, for each glucose, 2 acetyl groups are formed. The above features (A-G) are repeated for
each acetyl group. The entire Krebs Cycle turns once per glucose.