Electron Transport Chain (ETC) in Cellular Respiration: Definition, Location and Steps Simplified
Cellular
respiration is a catabolic process which involves the intracellular oxidation
of glucose or organic moleculesthrough
series of enzymatic reaction producing energy in the form of ATP with the
release of CO2 and H2O as byproducts.
This is the summarized video on Electron transport chain
3 stages of cellular respiration:
1. Glycolysis (Glyco=Glucose; lysis= splitting) is the
oxidation of glucose (C 6) to 2 pyruvate (3 C) with the formation of ATP and
NADH.
2.The
Krebs cycle, Citric acid cycle or TCA cycle is an eight step cyclic reactions
in which acetyl CoA is oxidized producing CO2, reduced coenzymes (NADH + H+ and
FADH2), and ATP.
3. Electron Transport Chain:
ETC is
the step by step transfer of high energy electrons through a series of electron
carriers located in multienzyme complexes, finally reducing molecular O2
to form water with the formation of ATP by chemiosmosis.
EXACT SITE OF REACTION
Organelle: Mitochondrion
Site of Electron transport chain: Mitochondrial Inner membrane
Proton (H+) pumped into the intermembrane space creating proton gradient
ATP synthesis occurs towards the matrix region (see the above figure)
Background info: At the beginning of electron transport
chain we have NADH and FADH2 synthesized during Kerb’s cycle and glycolysis.
Approximately only 4 ATP are synthesized directly (2 from glycolysis and 2 from
Krebs cycle) from a glucose molecule. The rest ~32-34 ATP are synthesized
during Electron transport chain (ETC) by chemiosmosis.
Now let as move into the detail
1. Electron flow and Energy release:
NADH and FADH2 donates high energy electrons
that pass through different protein complexes and electron carriers in the ETC.
As the electrons moves from high energy to low
energy level, some amount of energy is released. The final electron acceptor is
O2 which splits and takes up H+ to form water (H2O)
2. Proton movement and gradient formation
The energy released during electron flow is used
to pump proton (H+ ions) from matrix side to the intermembrane space of
mitochondrion. (see figure). This creates a proton gradient
or (Electrochemical gradient or proton motive force) across the inner
mitochondrial membrane (that is higher concentration of H+ ions in the
intermembrane space compared to the matrix).
3. Proton motive force (PMF) driven ATP
synthesis
The H+ ions should move to matrix to maintain
equilibrium (to balance H+ ion concentration). As phopholipid bilayer of inner
mitochondrial membrane is impermeable, the only way out is through the protein
complex called ATP synthase which spans the inner mitochondrial membrane and
has a proton channel.
The flow of H+ ions through ATP synthase
provides energy for the addition of phosphate to ADP thus forming ATP. (just
like turbine in hydroelectric power plant where water forces turbine movement,
here flow of H+ ions drives ATP synthesis)
The proton gradient (Proton motive force) driven
ATP synthesis is called Chemiosmosis.
Hope things are clear. Watch the video for
better understanding. Thank you and enjoy learning Biology
