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in the last lesson we pointed out
that in the presence of oxygen pyruvate
and reduced *** have
a different fate
they enter into the mitochondrion welcome again
in today's lesson we explain aerobic respiration
including the Link reaction the Krebs cycle
the role of NADH and H+
the electron transport chain
and the role of oxygen we explain
oxidative phosphorylation in terms of
chemiosmosis and we explain the relationship
between the structure of the mitochondrion
and its function pyruvate
is the end product of glycolysis
in the absence of oxygen pyruvate
becomes the final acceptor
for the hydrogens on reduced
*** but when oxygen is present
both the pyruvate and the ***
have a different fate pyruvate
enters by active transport in
to the matrix of the mitochondrion
once in the matrix pyruvate
associates with coenzyme A
in this process a
decarboxylation or a loss carbon dioxide
occurs in addition there is
an oxidation or a loss
of hydrogen from the pyruvate as
as *** plus the acceptor is
reduced the link reaction
for it links glycolysis which occurs
in the cytoplasm of the cell with
a cycle or reactions that
occur first in the matrix
of the mitochondrion and then
leads on to reactions that happen
on the cristae of the mitochondria
this cycle of reactions that happens
in the matrix begins with the
two carbon structure that forms from
pyruvate and its association with coenzyme A
combining with
of four carbon molecule
to produce a six carbon molecule
it's important to note that this is a simplification
and that several enzymes are associated with
these reactions the six carbon structure
or the citric acid undergoes
several transformations at some stages
there are decarboxylations and
at several stages there is the
reduction of *** this cycle
or Krebs Cycle can be summarized
in this way with 3 reductions
of *** and another
acceptor FAD also associated with the process
and at one of the stages sufficient energy is released
to allow for the direct combination of
adenosine diphosphate with
inorganic phosphate the so-called
substrate level phosphorylation
which also happens in glycolysis
in the series of reactions the process can continue
as more pyruvate enters and more
acetyl coenzyme A is formed
it can combine with the four carbon structure
to continuously produce a supply
of the six carbon citric acid
and to allow for the continuous rotation
of the Krebs cycle the significant
event in this cycle is the removal of hydrogen
the oxidation of the molecules
in the cycle and the reduction of
*** + the significance
of the reduction of the hydrogen acceptor
*** plus becomes obvious
when we consider the events occuring
in these little foldings or the
cristae of the mitochondrion
for it is in here that the significant
process which yields energy for the cell
occurs if we were to magnify this membrane
several times and
look at the outside the crista
which is the matrix of the mitochondrion
the membrane itself
and the space within the membrane
then it would be possible to see
the structures involved in the process
of chemiosmosis
as the electrons from the hydrogens
accepted by *** become
passed through a series of
acceptors each one having
a stronger affinity or attraction for electrons
has these electrons flow from one
acceptor to the next
sufficient energy is released
to allow for the hydrogen ions
here in the matrix
to be moved or pumped
against a concentration gradient
and to build up higher concentration
in this tiny area
between the membranes there are several such
infoldingss which increase the surface area
and the fact that the pockets are very small
means that the ion concentration becomes high
at a faster rate once this concentration is high enough
then the hydrogen ions move through
a special transmembrane
channel which comprises
the enzyme ATP synthase
and as the ions flow
from the high concentration that was built
inside of the crista out into the matrix
ATP is produced from ADP
and inorganic phosphate with the use
of the energy of the moving
hydrogen ions chemiosmosis
a very similar if not identical process
happens across the thylakoid membranes
of chloroplasts but just as pyruvate
worked as the final acceptor of glycolysis
removing the hydrogens picked up by
*** plus in the mitochondrion in
in aerobic respiration there is the need for
a final acceptor
for where would the electrons transferred
here through these series of acceptors
ultimately go and where would all of the
hydrogen ions ultimately go
if there is no final stage in this
conveyor belt then
the entire process could come
to a grinding halt this
final stage in the manufacturing
of ATP requires
the consumption of oxygen
a very highly electronegative
element oxygen quickly associates
with the two electrons acquiring a negative charge
the summary equation
for respiration reads this way
with glucose seemingly
reacting with oxygen to produce carbon dioxide
water and energy but it is certainly not
a case of oxygen being added
to glucose to oxidize it
for the oxidations and reductions
that occur in both the mitochondria
and the chloroplasts involve
losses of electrons losses of hydrogen
but there are no examples of gains of
oxygen or losing oxygen
so the definition
of oxidation and reduction in biological systems
could be simplified to look at oxidation
as the Los and reduction
as the gain a loss of hydrogens
and electrons in oxidation and
a gain of hydrogens and electrons
in reductions through a series of
oxidations by the removal of hydrogen
glucose is stripped in a very gradual process
beginning with glycolysis and continuing in the matrix of the mitochondrion
as this happens carbon dioxide is
also released eventually all the hydrogens
are disposed of by combining with
oxygen the final acceptor
in aerobic respiration consider some final questions
and bring together the two keep organelles
the mitichondrion and the chloroplast
consider aerobic respiration and
anaerobic respiration