oxidation and reduction examples

1. oxidation and reduction
pbl G5
case 4

2. objectives
1. define the oxidation and reduction and compare between them
2. explain the mechanism of catabolism of food and know the difference in alcohol
metabolism case.
3. define both of NAD and FAD and ATP the chemical structure for each one
4. explain how NAD and FAD involved in metabolism of food
5. explain the synthesis of FADH2 and NADH

3. Oxidation-Reduction
The key chemical event in an oxidation-reduction reaction is the net movement of
electrons from one reactant to another reactant. The movement occurs from the reactant
with less attraction of electrons to the reactant with more attraction for electrons.
Some Redox Terminology
Oxidation: is loss of electrons
Reduction is gain of electrons

4. Example

5. Oxidation Number
An oxidation state is a number that is assigned to an element in a chemical combination.
This number represents the number of electrons that an atom can gain, lose, or share when
chemically bonding with an atom of another element.

7. Reducing and Oxidizing Agents

8. NAD
NADH, short for nicotinamide adenine dinucleotide, is an
important pyridine nucleotide that functions as an oxidative
cofactor in eukaryotic cells. NADH plays a key role in the
production of energy through redox reactions. NAD serves as a
cofactor for dehydrogenases, reductases and hydroxylases, making
it a major carrier of H+ and e- in major metabolic pathways such as
glycolysis, the tricarboxylic acid cycle, fatty acid synthesis and
sterol synthesis

9. NAD
structure
C21H27N7O14P
2
663.43 g/mol

10. CONVERSION OF NAD TO NADH
This is an oxidation reaction where 2 hydrogen atoms (or 2 hydrogen ions and 2 electrons)
are removed from the organic metabolite. (The organic metabolites are usually from the
citric acid cycle (krebs cycle) and the oxidation of fatty acids).
One hydrogen is removed with 2 electrons as a hydride ion (H−H−) while the other is
removed as the positive ion (H+H+). Usually the metabolite is some type of alcohol which
is oxidized to a ketone.

15. FAD
Flavin adenine dinucleotide (FAD) is a condensation product of riboflavin and adenosine
diphosphate. It is the coenzyme of various aerobic dehydrogenases, e.g., D-amino acid
oxidase and L-amino acid oxidase. In biochemistry, flavin adenine dinucleotide (FAD) is
a cofactor in redox reactions. There are two main portions of FAD: (1) adenine and (2)
Flavin mononucleotide. The two portions are joined together at their phosphate groups.
FAD occurs in different redox states: quinone, semiquinone, and hydroquinone. It
converts between one state to another either by accepting or donating electrons. FAD can
be produced by the reduction and dehydration of flavin-N(5)-oxide.

16. Structure of FAD
Molecular Formula:
C27H33N9O15P2
Molecular Weight:
785.557 g/mol

17. FAD conversion into FADH2
The conversion of FAD to FADH2 is
an example of a reduction reaction. In
this case flavin adenine dinucleotide
(FAD) gains 2 electrons and 2
hydrogen atoms. The reaction is:
FAD+2e−+2H+↔FADH2
FAD can be seen as a carrier for
electrons. This reduction reaction
happens in the citric acid cycle when
fumarate is formed from succinate.

18. •Flavoproteins are enzymes that catalyze redox reactions using
either flavin mononucleotide (FMN) or flavin adenine dinucleotide
(FAD) as coenzymes.
•These coenzymes are derived from the vitamin riboflavin.
•Although the flavin coenzymes are water soluble, they are bound
tightly to the enzyme. Tightly bound coenzymes are called
prosthetic groups. As a result the flavin coenzymes do not transfer
electrons from one enzyme to another, but allow the flavoprotein to
temporarily hold the electrons to catalyze an electron transfer from
a substrate to the electron acceptor.

19. •The fused ring shown in red is an isoalloxazine ring which
undergoes reversible reduction. The isoalloxazine ring can accept
either one electron or two. The fully reduced flavins are abbreviated
FADH2 or FMNH2.
•FAD the oxidized or quinone form. FADHx the radical or
semiquinone form. FADH2 the reduced or hydroquinone form

20. •FAD the oxidized or quinone
form.
• FADHx the radical or
semiquinone form.
•FADH2 the reduced or
hydroquinone form

21. •FAD accepts and donates 2 electrons with 2 protons (2 H):FAD + 2
e
-
+ 2 H
+
FADH2

22. ADENOSINE TRIPHOSPHATE (ATP)
All living things, plants and animals, require a continual supply of energy in order to
function. The energy is used for all the processes which keep the organism alive. Some of
these processes occur continually, such as the metabolism of foods, the synthesis of large,
biologically important molecules, e.g. proteins and DNA, and the transport of molecules
and ions throughout the organism. Other processes occur only at certain times, such as
muscle contraction and other cellular movements.However, before the energy can be used,
it is first transformed into a form which the organism can handle easily. This special
carrier of energy is the molecule adenosine triphosphate, or ATP.

23. STRUCTURE OF ATP
The ATP molecule is composed of three
components. At the centre is a sugar molecule,
ribose (the same sugar that forms the basis of
RNA). Attached to one side of this is a base (a
group consisting of linked rings of carbon and
nitrogen atoms); in this case the base is
adenine. The other side of the sugar is attached
to a string of phosphate groups. These
phosphates are the key to the activity of ATP.

24. HOW IT WORKS
The bonds between the phosphate groups of ATP’s tail can be broken by hydrolysis
Energy is released from ATP when the terminal phosphate bond is broken
This reaction releases a lot of energy, which the organism can then use to build proteins,
contact muscles, etc. The reaction product is adenosine diphosphate (ADP), and the
phosphate group either ends up as orthophosphate (HPO4) or attached to another
molecule.
This release of energy comes from the chemical change to a state of lower free energy,
not from the phosphate bonds themselves
When the organism is resting,the reverse reaction takes place and the phosphate group
is reattached to the molecule. Thus the ATP molecule acts as a chemical 'battery',
storing energy when it is not needed, but able to release it instantly when the
organism requires it.

25. Glycolysis
*The first stage of respiration.
*Glycolysis takes place in the cytoplasm of cells.
*During this process one molecule of glucose (6 carbon molecule) is degraded into two
molecules of pyruvate (three carbon molecule).

26. krebs cycle
Following glycolysis, the mechanism of cellular respiration involves another multi-step process—the Krebs cycle, which is also
called the citric acid cycle or the tricarboxylic acid cycle. The Krebs cycle uses the two molecules of pyruvic acid formed in
glycolysis and yields high-energy molecules of NADH and flavin adenine dinucleotide (FADH2), as well as some ATP.
Steps
In order for pyruvate from glycolysis to enter the Kreb's Cycle it must first be converted into acetyl-CoA by the pyruvate
dehydrogenase complex which is an oxidative process wherein NADH and CO2 are formed. Another source of acetyl-CoA is beta
oxidation of fatty acids.
1. Acetyl-CoA enters teh Kreb Cycle when it is joined to oxaloacetate by citrate synthase to produce citrate. This process requires
the input of water. Oxaloacetate is the final metabolite of the Kreb Cycle and it joins again to start the cycle over again, hence
the name Kreb's Cycle. This is known as the committed step
2. Citrate is then converted into isocitrate by the enzyme aconitase. This is accomplished by the removal and addition of water to
yield an isomer.
3. Isocitrate is converted into alpha-ketogluterate by isocitrate dehydrogenase. The byproducts of which are NADH and CO2.
4. Apha-ketogluterate is then converted into succynl-CoA by alpha-ketogluterate dehydrogenase. NADH and CO2 are once again
produced.
5. Succynl-CoA is then converted into succinate by succynl-CoA synthetase which yields one ATP per succynl-CoA.

27. 1. Succinate coverts into fumarate by way of the enzyme succinate dehydrogenase and
[FAD] is reduced to [FADH2] which is prosthetic group of succinate dehydrogenase.
Succinate dehydrogenase is a direct part of the ETC. It is also known as electron
carrier II.
2. Fumarate is then converted to malate by hydration with the use of fumarase.
3. Malate is converted into oxaloacetate by malate dehydrogenase the byproducts of
which are NADH.

29. Electron Transport Chain
The energy released in these e- transfers is used to pump H+ (protons) out of the matrix
into the intermembrane space. This produces a proton gradient (different [H+] on each
side) – a state of high potential energy.
1a. At enzyme complex I, NADH is oxidized to NAD+ and e- are transferred between
different proteins in this cluster, then to coenzyme Q (CoQ or Ubiquinone). Protons are
pumped.
1b. FADH2 is oxidized (transfers its e-) to the CoQ at enzyme complex II. The reduced
CoQ joins the rest of the “chain”.
2. The reduced CoQ travels to enzyme complex III where the e- are transferred between
proteins and then to cytochrome c. Protons are pumped.

30. 3. Cytochrome c travels to the enzyme complex IV where the e- are transferred between
proteins and then to O2 to form water. More protons are pumped.
The H+ ions that have been pumped into the intermembrane space can only get back into
the matrix through ATP Synthase. The energy released as H+ flow back to the matrix is
coupled with the formation of ATP:
ADP+Pi →ATP+H2O (oxidative phosphorylation 1)
Each NADH that enters the electron transport chain produces 3 ATP molecules (i.e H+
ions are pumped at complexes I, III and IV) whereas each FADH2 (that joins the “chain”
at complex two) produces 2 ATP molecules (i.e H+ ions are pumped only at complexes III
and IV)

31. Synthesis of ATP
A cell has two ways of generating ATP:
Chemiosmosis
Substrate level phosphorylation
Chemiosmosis is the production of ATP due to hydrogen ion gradient across a
membrane. According to chemiosmotic model, the electron transport chain in the
inner mitochondria has proton pumps. In 1961, Peter Mitchell realised that the
buildup of hydrogen ions on one side of a membrane would be a source of potential
energy and that the movement of ions across the membrane, down an electrochemical
gradient, could provide the energy needed to power the formation of ATP from ADP
and Pi. He called this chemiosmosis theory.

32. Structure of Mitochondria
Mitochondria have an inner and outer phospholipid membrane.
The outer membrane is smooth and the inner membrane is folded into cristae
Between the inner and outer membranes is the intermembrane space.
The matrix is enclosed by the inner membrane, its where the link reaction and Krebs
cycle takes place
The inner membrane is impermeable to most small ions, including hydrogen ions
(protons) and has embedded in it many electron carriers and ATP synthase enzymes.
Some of the electron carriers have a coenzyme that pumps (using energy released from
the passage of electrons) protons from the matrix to the intermembrane space.

33. Because the inner
membrane is
impermeable to small
ions, protons accumulate
in the intermembrane
space, building up a
proton gradient – a
source of potential
energy.

34. Chemiosmosis
The ATP synthase enzymes are large and protrude from the inner membrane into the
matrix and allow protons to pass through them.
Protons flow down a proton gradient, through the ATP synthase enzymes, from the
intermembrane space into the matrix. This flow is called chemiosmosis.
The force of this flow drives the rotation of part of the enzyme and allows ADP and Pi
(inorganic phosphate) to be joined to make ATP.
Oxidative phosphorylation is the formation of ATP by the addition of inorganic
phosphate to ADP in the presence of oxygen.
Hence production of ATP by chemiosmosis is Oxidative phosphorylation.
4H+
+ 4 e–
+ O2
→ 2H2 O

35. Question
An average adult human with a typical weight of 70 Kg consumes about 65 Kg of
ATP per day. How could you explain this?
Answer :
The average adult human consumes approximately 11,700kJ (2800 Calories) per day.
About 50% of metabolic pathways leads to production of ATP ,thus of the 11,700 kJ a
person consumes , about 5850 kJ ends up as ATP. The hydrolysis of 1 mole of ATP
produces 50 kJ of energy . This means the body cycles through 5850/50 =117 moles of
ATP each day . The disodium salt of ATP has a molecular weight of 551 g/mol .

36. So , an average person hydrolyzes about :
117 moles 551 g/mole = 64,467 g of ATP per day✖
64,467 / 1000 = 64 Kg
The average adult human ,with a typical weight of 70 kg consumes approximately 64
kg per day, an amount nearly equal to the person’s weight .

37. Anaerobic respiration
Anaerobic respiration is the metabolic process in which oxygen is absent, and only the
stage of glycolysis is completed. This process occurs mostly in microorganisms, but it can
also be a temporary response to anoxic, or oxygen-less, conditions in the cells of
multicellular organisms .
In the absence of oxygen . pyruvate can follow one of two metabolic pathways:
lactate (lactic acid) fermentation.
alcoholic fermentation :occurs in plants and yeasts which are respiring anaerobically

38. lactate fermentation.
● The pyruvate from glycolysis is
converted in a single step to
lactate (lactic acid).
● The reaction is catalysed by
lactate dehydrogenase and the
process requires hydrogen from
NADH

39. alcoholic fermentation
● Pyruvate is first converted to
ethanal by decarboxylation
(removal of carbon dioxide).
● The carbon dioxide is released as
a gas.
● Acetaldehyde (Ethanal)is then
reduced to ethanol using
hydrogen from NADH.

40. references
books:
❖ Advanced biology , Michael Kent , Oxford , chapter 6:Respiration , 6-2 glycolysis and fermentation , page
102 and 103 .
❖ Introduction-to-organic-and-biochemistry-7th-edition Guyton and Hall Textbook of Medical Physiology 12th
Edition

41. references
wibesites:
❖ https://highered.mheducation.com/sites/dl/free/0073525502/930160/mad25502_ch08.pdf
❖ http://www.pearsonschoolsandfecolleges.co.uk/AssetsLibrary/SECTORS/Secondary/PDFs/Science/HeinemannScience/OCRALevelSampleLessons/OCRA2Biology_StudentBook97804356
❖ https://www.slideshare.net/scuffruff/glycolysis https://www.youtube.com/watch?v=FE2jfTXAJHg
❖ https://www.khanacademy.org/science/biology/cellularfermentation/glycolysis/a/glycolysis
❖ https://www.google.com.sa/url?sa=t&rct=j&q=&esrc=s&source=web&cd=8&cad=rja&uact=8&ved=0ahUKEwjg-p3a2pnTAhXGUBQKHVw5A_wQFghaMAc&url=http%3A%2F%2Fwe
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❖ https://pubchem.ncbi.nlm.nih.gov/compound/flavin_adenine_dinucleotide#section=Top
❖ http://www.biology-nline.org/dictionary/Flavin_adenine_dinucleotide
❖ http://www.laney.edu/wp/cheli-fossum/files/2012/01/Electron-transport-chain.pdf
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❖ http://www.nslc.wustl.edu/courses/Bio2960/labs/Metabolism%20Lecture.pdf
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❖ https://chem.libretexts.org/Core/Biological_Chemistry/Vitamins,_Cofactors_and_Coenzymes/Nicotinamide_Adenine_Dinucleotide_(NAD)

42. thank you
pbl G5