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Understanding
Applications & Skills
Important Words/Phrases
 Glycolysis
 Krebs Cycle
 Electron Transport Chain
 Oxidation
 Reduction
 Redox
 Phosphorylation
 Isomerisation
 Mitochondrion
 Decarboxylation
Introduction
 You have already learned the basics of cellular
respiration. In fact, you knew the formula before you
started this course
 But this is a tremendous oversimplification of the
process
 Now we’re going to learn the details
Oxidation and Reduction
 All chemical reactions either require energy or release
it
 Many reactions can be described using the terms
“oxidation” or “reduction”
 These reactions are often coupled together and are
known as “redox” reactions
Oxidation and Reduction
Oxidation and Reduction
 To help you remember:
OIL RIG (Oxidation Is Losing electrons,
Reduction Is Gaining electrons)
OR
LEO says GER
(Losing Electrons is Oxidation,
Gaining Electrons is Reduction)
Redox and Electron Carriers
Electron Carriers
NADH and FADH2
 Both of these molecules are Nucleic Acids. In their
reduced forms they have a tremendous amount of
energy that gets released during oxidation
FADH2
Oxidized
Reduced
Overview
 Cell Respiration can be divided into 4 parts:
 Glycolysis
 Pyruvate Oxidation (also called the “linking” reaction)
 Krebs Cycle (also called the citric acid cycle)
 The electron transport chain (oxidative phosphorylation)
Overview (Continued)
 Glycolysis takes place in the cytoplasm and is anaerobic
 The other three parts occur in the mitochondria and
require oxygen
(aerobic)
 Each step either produces
ATP or reduces NAD
or FAD
Glycolysis
Some Key Points:
 Starts with Glucose, ends with Pyruvate
 Two ATP molecules are used, 4 are made
 Net production is 2 ATP per molecule
of glucose
 Also produces two molecules of NADH
Can be divided into 3 General Parts
1. Energy expenditure (steps 1-4)
2. Splitting (steps 4 & 5)
3. Energy production (steps 6-10)
Reactions are named according to what
happens
Glycolysis Step by Step
Types of Reactions:
 Phosphorylation – adding a phosphate group





(steps 1 and 3)
Isomerase – an isomer is created
(step 2, 5 & 8)
Redox – the substrate is oxidized while
NAD+ is reduced to NADH (6)
Dephosphorylation – A phosphate group is
removed from the substrate, ATP is
produced (7 & 10)
Dehydration – Water is removed (9)
Decomposition – A large molecule is broken
down (4)
Glycolysis Odds and Ends
 Every step is controlled by an enzyme
 Pyruvate will enter the mitochondria if oxygen is
available. If not, it will be reduced to lactate (in
animals). This causes NADH to be oxidized
Glycolysis
1. Substrate includes Glucose, ATP, ADP, Pi , NAD+ and H+
2. Main products include Pyruvate, ATP and NADH (H2O)
3. One Glucose molecule yields 2 Pyruvate, 2 ATP and
2 NADH
4. Pyruvate is converted to lactate if oxygen is not available
Simulations
http://www.science.smith.edu/departments/Biology/Bio231/glycoly
sis.html
http://highered.mheducation.com/sites/0072507470/student_view0
/chapter25/animation__how_glycolysis_works.html (try quiz!)
Linking Reaction (Pyruvate Oxidation)
This is a one step reaction, but lots of stuff is happening!
It begins in the cytoplasm
and ends up in the
mitochondria
Linking Reaction
Three Things are Happening:
1. Pyruvate combines with Coenzyme A to form Acetyl
Coenzyme A
2. NAD+ is converted to NADH
3. CO2 is released as a waste product (decarboxylation)
Linking Reaction Summary
1. Substrates include pyruvate, coenzyme A, NAD+ & H+
2. Products include Acetyl Coenzyme A, NADH & CO2
3. Acetyl Coenzyme A is produced in the matrix of the
mitochondria
Inside the Mitochondria
 The mitochondrion is an extremely complex organelle
Mitochondrion Diagram
Labeled Diagram
The Krebs/Citric Acid Cycle
 This is an 8 step process
 Technically it has no start or finish since it’s a cycle but the point
that Acetyl Coenzyme A enters the cycle (where oxaloacetate is
converted to citrate) is usually referred to as step #1
step 1
Krebs Cycle
Key Points
 Redox reactions in steps 3, 4, 6
and 8 produce 3 molecules of
NADH and 1 molecule of
FADH2
 ATP is produced in step 5 by
the dephosphorylation of
Succinyl CoA
 CO2 is produced as a waste
product in steps 3 and 4
(decarboxylation)
 *when we determine the
products that come from
one molecule of glucose, we
have to realize that two
pyruvate molecules were
produced so we have two
turns of the Krebs cycle per
glucose molecule
Krebs Cycle Summary
Key Substrates
Key Products
 Acetyl Coenzyme A
 ATP
 Oxaloacetate
 NADH
 NAD+
 FADH2
 FAD
 CO2
 GDP
 ADP
Krebs Cycle – By the Numbers
For each loop of the Krebs Cycle we get:
 1 molecule of ATP
 3 molecules of NADH
 1 molecule of FADH2
But the products of glucose allow for 2 loops of the cycle. So 1
molecule of glucose produces:
 2 molecules of ATP
 6 molecules of NADH and
 2 molecules of FADH2
In the Krebs cycle
Recap
 So if we combine glycolysis, the link reaction and the
Krebs cycle what do we have?



4 ATP (net)
10 NADH
2 FADH2 per glucose molecule
The Electron Transport Chain
 So far, a lot of NADH has been made but not much
ATP
 That problem is taken care of in the final step of the
respiratory chain; the Electron Transport Chain
Electron Transport Chain
 The Electron Transport Chain (ETC) takes place along
the inner membrane of the mitochondria.
 A series of electron carriers line up in order of their
affinity for electrons
Electron Transport Chain
 The reduced NADH molecules
contain large amounts of energy
and some of this energy is
released when the first electron
carrier (NADH dehydrogenase)
breaks NADH up into NAD+,
H+ and 2 electrons.
 Energy is released as the two
electrons get taken up by the
carrier and passed on down the
line (carrier I to carrier II to
carrier III to carrier IV)
 Each time electrons are
transferred, more energy is
released
ETC
Where Does the Energy Go?
 Each time the energy is released it is used to actively
transport protons (H+) out of the matrix into the
intermembrane space through pumps that are located in
three of the carriers
 For NADH, 3 H+ ions get
pumped out
 For FADH2, only two H+
ions are pumped out
because it gets oxidized
by electron carrier II
(ubiquinone or q for short)
ETC and Chemiosmosis
 As the H+ gradient increases, there is
pressure for them to diffuse back into
the matrix. This pressure is based on
concentration and electrical gradient.
It is called an electrochemical
gradient
 There is another structure adjacent to
the electron carriers called ATP
synthase. ATP synthase is an
enzyme and a membrane channel
that H+ ions can diffuse through
 As they diffuse into the matrix, the
kinetic energy they possess is used to
combine ADP and P to form ATP
ETC (Oxidative Phosphorylation)
 Since each NADH molecule provides enough energy to pump 3
H+ into the intermembrane space, 3 ATP get made.
 Similarly, each FADH2 molecule will result in the synthesis of 2
ATP molecules
ATP Count
Let’s do some Math
Each glucose molecule makes
10 NADH
3 x 10 = 30
2 FADH2
2x2=4
4 ATP
=4
_____________________________
Total ATP from one molecule of glucose is 38 ATP
At least in theory. In reality that number is closer to 30
because it doesn’t work as perfectly as it should
What About Oxygen
Last Question:
What Does Oxygen Do?
The final electron carrier, carrier IV (cytochrome oxidase) has
a very high affinity for electrons. But it can only hold two
electrons. If it isn’t oxidized (i.e. able to lose the electrons)
then it won’t be able to accept any more electrons and the
ETC will grind to a halt. Fortunately, there is something that
has an even higher affinity for electrons than cytochrome
oxidase
OXYGEN!!!
Role of Oxygen
 Oxygen takes the electrons
from carrier IV and then
combines with two H+ ions to
make a molecule of water
 As more ATP gets made, more
oxygen is needed on a
continual basis
 The availability of Oxygen is
usually what limits our ability
to make ATP.
Now watch this
https://www.youtube.com/watc
h?v=VER6xW_r1vc