Hey this is DrK from imedicalschool and today
we are going to talk about the electron transport
chain otherwise known as the ETC. In previous
videos we talked about glycolysis, pyruvate
decaroboxylation and the citric acid cyle.
Each of these steps was preparation for the
electron transport chain with the production
of NADH and FADH2. The purpose of producing
NADH and FADH2 was to use these electron carriers
to create ATP in a process called oxidative
phosphorylation.
Let's begin by talking about where the electron
trasnport chain takes place. The ETC is present
in the inner mitochondrial membrane. The inner
mitochondrial membrane is important because
it is selectively permeable to hydrogen, sodium,
and potassium ions. The selective permeability
is vital because it allows for the creation
of a hydrogen ion gradient which is the engine
for ATP production. In addition there are
folds in the inner mitochondrial membrane,
called cristae. Cristae increase the surface
area and increase the ability to produce ATP
by allowing more complexes to fit in the inner
mitochondrial membrane.
Now there are four complexes involved the
ETC with complex five being involved in oxidative
phosophorylation. They are conveniently named
Complex one, two, three, and four. Unfortunately
a few of these complexes have alternate names
which I will highlight as we go through the
ETC. Remember when we formed NADH we represented
it as NADH plus a hydrogen ion. This representation
reflects the fact there is a hybride ion represented
by the H in NADH and one hydrogen atom represented
as the H+. The hybride ion is passed as an
electron from complex to complex in the ETC,
while the hydrogen atom is shuttled by each
complex into the inter membrane space to create
a hydrogen gradient. This gradient will later
be used by oxidative phosphorylation to create
ATP.
NADH with H plus enters the ETC via the NADH
dehydrogenase complex, otherwise known as
complex one. As the name suggests NADH dehydrogenase
removes the electrons with the hydrogen atom
from NADH. NADH dehydrogenase contains a flavin
mononucleotide molecule that allows for the
acceptance of electrons and a hydrogen from
NADH. NADH Dehydrogenase shuttles the hydrogen
from NADH into the mitochondrial inter membrane
space and then passes the electrons down the
ETC. NADH dehydrogenase contains an iron sulfur
complex that allows transfer of electrons
to coenzyme Q, which is an intermediary complex
between complex one and complex two. An alternate
name for coenzyme Q is ubiquinone.
The improtance of coenzyme Q ia that not only
does it accepts hydrogen atoms from the NADH
dehydrogenase complex but it can also accept
protons from complex two. Complex two is also
called succinate dehydrogenaose or succinate-ubiquinone
oxidioreductase.
Succinate is one of the intermediate products
in the citric acid cycle. Succinate dehydrogenase
acts on succiante to create fumarate. In the
process an FAD molecule is reduced to FADH2.
FADH2 passes its electrons to conzyme Q. Coenzyme
Q, whether it accepts electrons from complex
one or complex two these electrons are passed
on to complex three. Complex three, four,
and five all contain a heme group. As the
electrons are accepted the ferric atom is
converted to it s 2 plus ferrous state. As
the electron passes from complex III, otherwise
known as cytochrome B & C, these electrons
are transported to complex four, otherwise
known as cytochrome a and a3.
Complex 4 is the only complex that interacts
with oxygen. In doing so the electrons reduce
the oxygen atom to H2O or water. This is a
key point because oxygen is the final electron
acceptor of the ETC to produce water.
In the entire electron transport chain electrons
are passed from complex to complex and in
the meantime each complex pushes hydrogen
atoms to the intermemebrane space. This si
the most important point about the ETC Cycle.
The shuttling of hydrogen atoms into the inter
membrane space creases a diffusion gradient.
This gradient that is created is like stretching
a rubber band in that there is a lot of energy
you are putting in. As soon as you let go
of the rubber band it will go flying because
of all the pent up energy. The hydrogen gradient
is the same way. In our next video we wilt
all about oxidative phsophorylation which
is the process where this gradient will be
relieved creating a large amount of ATP.
As a side note realize there are many chemicals
that can inhibit the electron transport chain
due to their interaction with the cytochromes
involved. For example antimycin A is a product
produced by some fungi and actually inhibits
the transport of electrons from cytochrome
b to cytochome c within the complex three.
In addition cyanide and carbon monoxide prevent
the final transfer of lecterns to oxygen.
If this occurs electrons build up in complex
four disrupting the gradient and movement
of electrons down the lectern transport chain
resulting in the cessation of the ETC.
Well that was a brief review of the electron
transport chain system. I hope you enjoyed
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and I will see you next time.
