1. 8.2 Cell Respiration

2. Understanding

3. Applications & Skills

4. Important Words/Phrases
Glycolysis
Krebs Cycle
Electron Transport Chain
Oxidation
Reduction
Redox
Phosphorylation
Isomerisation
Mitochondrion
Decarboxylation

5. 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

6. 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

7. Oxidation and Reduction

8. 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)

9. Redox and Electron Carriers

10. Electron Carriers

11. 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

12. FADH2
Oxidized Reduced

13. 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)

14. 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

15. 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
Energy expenditure (steps 1-4)
Splitting (steps 4 & 5)
Energy production (steps 6-10)
Reactions are named according to what
happens

16. 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)

17. 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

18. Glycolysis Substrate includes Glucose, ATP, ADP, Pi , NAD+ and H+
Main products include Pyruvate, ATP and NADH (H2O)
One Glucose molecule yields 2 Pyruvate, 2 ATP and NADH
Pyruvate is converted to lactate if oxygen is not available
Simulations
(try quiz!)

19. 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

20. Linking Reaction Three Things are Happening:
Pyruvate combines with Coenzyme A to form Acetyl Coenzyme A
NAD+ is converted to NADH
CO2 is released as a waste product (decarboxylation)

21. Linking Reaction Summary
Substrates include pyruvate, coenzyme A, NAD+ & H+
Products include Acetyl Coenzyme A, NADH & CO2
Acetyl Coenzyme A is produced in the matrix of the mitochondria

22. Inside the Mitochondria
The mitochondrion is an extremely complex organelle

23. Mitochondrion Diagram

24. Labeled Diagram

25. 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

26. 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

27. Krebs Cycle Summary Key Substrates Key Products Acetyl Coenzyme A
Oxaloacetate
NAD+
FAD
GDP
ADP
ATP
NADH
FADH2
CO2

28. 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

29. 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

30. 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

31. 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

32. 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

33. 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)

34. 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

35. 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

36. ATP Count
Let’s do some Math Each glucose molecule makes 10 NADH 3 x 10 = 30 2 FADH2 2 x 2 = 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

37. What About Oxygen 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!!!

38. 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