The document is an assignment submission on the electron transport chain. It provides details on the electron transport chain, including that it is a series of protein complexes in the mitochondrial inner membrane that sequentially transfers electrons, pumping protons out in the process. This generates a proton gradient that is then used by ATP synthase to produce ATP via chemiosmosis, making oxidative phosphorylation the most efficient ATP producer in aerobic respiration. The assignment covers the components, steps, and purpose of the electron transport chain in detail over multiple pages.

1. Course Code: BIO-CHEM 207
Course Title: Metabolism-1
Assignment on #1
Electron Transport Chain
Submitted To:
Name: Mahbuba Ferdous
Lecturer
Department of Biochemistry
PRIMEASIA UNIVERSITY
Submitted By:
Name: Najmul Hasan Forhad
ID: 181-038-033
Section: Friday Batch Department: Biochemistry
PRIMEASIA UNIVERSITY
Date of Submission:15-04-2020
A missionwith a vision

2. Metabolism-1
AssaingmentNo- 1
Electron Transport Chain
Introduction
The electron transport chain is a series of proteins and organic molecules found in the inner membrane
of the mitochondria. Electrons are passed from one member of the transport chain to another in a series
of redox reactions. Energy released in these reactions is captured as a proton gradient, which is then
used to make ATP in a process called chemiosmosis. Together, the electron transport chain and
chemiosmosis make up oxidative phosphorylation.
The mitochondrial electron transport chain is a series of enzymes and coenzymes in the crista
membrane, each of which is reduced by the preceding coenzyme, and in turn reduces the next, until
finally the protons and electrons that have entered the chain from either NADH or reduced flavin reduce
oxygen to water.
Fundamentals
Aerobic cellular respiration made up of 3 parts: glycolysis, the Krebs cycle, and oxidative
phosphorylation. In glycolysis, glucose is metabolized into 2 molecules of pyruvate, with an output of
ATP and nicotinamide adenine dinucleotide (NADH). The pyruvate is oxidized into acetyl CoA and
NADH and carbon dioxide (CO2). The acetyl CoA is then used in the Krebs cycle, also known as the
citric acid cycle, which is a chain of chemical reactions that produce CO2, NADH, flavin adenine

3. dinucleotide (FADH2), and ATP. In the final step, the NADH, FADH2 amassed from the previous steps
is used in oxidative phosphorylation, to make water and ATP.
Oxidative phosphorylation is made up of 2 parts: the electron transport chain (ETC) and chemiosmosis.
The ETC is a collection of proteins and organic molecules, which electrons pass through in a series of
redox reactions, and release energy. The energy released forms a proton gradient, which is used in
chemiosmosis to make a large amount of ATP.
Photosynthesis is a metabolic process that converts light energy into chemical energy, to build sugars. In
the light-dependent reactions, light energy and water are used to make ATP, NADPH, and oxygen (O2).
The proton gradient used to make the ATP is formed via an electron transport chain. In the light-
independent reactions, sugar is made from the ATP and NADPH from the previous reactions.
Components of ETC:
 NAD & Flavoprotein : H-carriers in celluiar respiration
 Non heme metalloprotein (Fe-S- Protein):iron cycles between 3+ and 2+ states.
 Ubiquinone or CoQ: region serves as an anchor to inner mitochondrial membrane.
 Cytochromes : Electron-transfer proteins that contain a heme prosthetic group
Composition of ETC
Four large protein complexes.
 Complex I - NADH-Coenzyme Q reductase
 Complex II - Succinate-Coenzyme Q reductase
 Complex III - Cytochrome c reductase
 Complex IV - Cytochrome c oxidase
 Many of the components are proteins with prosthetic

4.  groups to move electrons
Steps of Oxidative phosphorylation & Electron Transport Chain
Oxidative phosphorylation is the process where energy is harnessed through a series of protein
complexes embedded in the inner-membrane of mitochondria (called the electron transport chain and
ATP synthase) to create ATP. Oxidative phosphorylation can be broken down into two parts: 1)
Oxidation of NADH and FADH2, and 2) Phosphorylation - the production of ATP
1.Oxidation of NADH and FADH2.- losing elctrons via high energy molecules :
Step 1
Oxidative phosphorylation starts with the arrival of 3 NADH and 1 FADH2 the citric acid cycle,
which shuttle high energy molecules to the electron transport chain. NADH transfers its high energy
molecules to protein complex 1, while FADH2 2, transfers its high energy molecules to protein
complex 2. Shuttling high energy molecules causes a loss of electrons from NADH and FADH2
called oxidation (other molecules are also capable of being oxidized).
 The opposite of oxidation is reduction, where a molecule gains electrons (which is seen in the
citric acid cycle)

5. Step 2 -
Hitting the gym to pump some serious hydrogens ;
 The process of NADH oxidation leads to the pumping of protons through protein complex 1
from the matrix to the intermembrane space. The electrons that were received by protein
complex 1 are given to another membrane-bound electron carrier called ubiquinone or Q.
 This process of transferring electrons drives the pumping of protons, which is seen as
unfavorable. Electron transfer driving proton pumping is repeated in complexes 3 and 4 (which
we will discuss in steps 2 - 5). As this action is repeated, protons will accumulate in the
intermembrane space. This accumulation of protons is how the cell temporarily stores
transformed energy.
Step-3
The rest of the steps are now the same for the high energy molecules from NADH and FADH2 in
earlier steps. Inside the nonpolar region of the phospholipid bilayer UQH2 (which is also a nonpolar

6. compound) transports the electrons to protein complex 3. UQH2 also carries protons. When end UQH2
dlivers electrons to protein complex 3, it also donates its protons to be pumped.
Step 4
The electrons that arrived at protein complex 3 are picked up by cytochrome C(or “cyt C”), the last
electron carrier. This action also causes protons to be pumped into the intermembrane space.
Step-5
Cytochrome C carries the electrons to the final protein complex, protein complex 4. Once again, energy
released via electron shuttling allows for another proton to be pumped into the intermembrane space.
The electrons are then drawn to oxygen, which is the final electron acceptor. Its important to note that
oxygen must be present for oxidative phosphorylation to occur. Water is formed as oxygen receives the
electrons from protein complex 4, and combines with protons on the inside of the cell.

7. 2. Phosphorylation - the production of ATP
Step 6
As a result of part 1 (Oxidation of NADH and , FADH2 an electrochemical gradient is created, meaning
there is a difference in electrical charge between the two sides of the inner mitochondrial membrane.
The outside, or exterior, of the mitochondrial membrane is positive because of the accumulation of the
protons), and the inside is negative due to the loss of the protons. A chemical concentration gradient has
also developed on either side of the membrane. The electrochemical gradient is how the cell transfers
the stored energy from the reduced NADH and FADH2.

8. Synthase of ATP :
When there is a high concentration of protons on the outside of the mitochondrial membrane, protons
are pushed through ATP synthase. This movement of protons causes ATP synthase to spin, and bind
ADP and Pi, producing ATP. Finally, ATP is made!
ATP synthase uses the proton gradient across the mitochondrial membrane to form ATP. It is made up
of F0 and F1 subunits which act as a rotational motor system. F0 portion is embedded in the
mitochondrial membrane and is protonated and deprotonated repeatedly causing it to rotate. This
rotation catalyzes the formation of ATP from ADP and Pi. The F1 portion works to hydrolyze the ATP.
A proton pump is any process that creates a proton gradient across a membrane. Protons can be
physically moved across a membrane; this is seen in mitochondrial Complexes I and IV. The same
effect can be produced by moving electrons in the opposite direction. The result is the disappearance of
a proton from the cytoplasm and the appearance of a proton in the periplasm. Mitochondrial Complex III
uses this second type of proton pump, which is mediated by a quinone (the Q cycle).
Some dehydrogenases are proton pumps; others are not. Most oxidases and reductases are proton pumps,
but some are not. Cytochrome bc1 is a proton pump found in many, but not all, bacteria (it is not found
in E. coli). As the name implies, bacterial bc1 is similar to mitochondrial bc1 (Complex III).
Proton pumps are the heart of the electron transport process. They produce the transmembrane
electrochemical gradient that enables ATP Synthase to synthesize ATP.

9. Summary
 Oxidative phosphorylation is comprised of the electron transport chain and chemiosmosis.
 It is the most efficient producer of ATP in the process of aerobic respiration
 Electrons carried from previous steps of respiration enter the electron transport chain, and are
sequentially passed through membrane bound proteins
 The final member of the chain is oxygen, which forms water upon accepting the electron
 The electron transport chain generates a protein gradient
 The protein gradient drives ATP synthase activity, which generates ATP
Nazmul Hasan Forhad
BSc. In Biochemistry
Prime Asia University,Dhaka
Email: forhad1767@gmail.com
Mobi:+8801926249001