1. Cellular Respiration Cell Respiration Step 1 :Krebs Cycle
Step 2: Electron Transport Chain (oxidative phosphorylation)
*Much more energy is released than in fermentation so
if an organism has a choice- will use cell respiration
*Note: your book separates Krebs into 2 steps: “Pyruvate
Processing” and “Krebs”. My lecture combines them as “Krebs”
in attempt to simplify the steps.

2. Cellular Respiration Recall: Glycolysis left us with pyruvate
If O2 is present, pyruvate is converted to acetyl Co-A
which enters the Krebs cycle
Krebs
CO2 + NADH +
Consequences of this oxidation rxn:
1 of the 3 C atoms in pyruvate converted to CO2
The other 2C atoms are converted to Acetyl CoA
Energy released from this rxn used to reduce NAD+ to NADH

3. Acetyl CoA enters the Krebs Cycle:
Cellular Respiration
Acetyl CoA enters the Krebs Cycle:
The Big Picture
acetyl Co-A
Successive oxidation
of 8 Carbon molecules
Enough energy
released from this
to generate ATP,
NADH and FADH
(similar role as NADH)
(higher energy)
(lower energy)

4. Cellular Respiration Krebs Cycle: The Big Picture
Fig 9.19
CO2 also produced as a result of oxidizing C molecules
(5C sugar 4 C sugar + CO2)

5. Cellular Respiration Krebs Cycle: The Big Picture
(e-carriers/donors)
Acetyl Co-A  CO2 + NADH + FADH + ATP
exhaled/
used for
photosynthesis
Can immediately
be used for energy
(ATPADP+ energy) O2
(e-acceptor)
H2O
This happens in next step- electron
transport chain

6. Cellular Respiration Where is this happening in the cell?
Glycolysis and
fermentation:
cytosol
Prokaryotes
Respiration:
mitochondria
Eukaryotes
Glycolysis,
Fermentation, and
respiration:
cytosol

7. Cellular Respiration After glycolyis, pyruvate is
Where is this happening in the cell?
After glycolyis, pyruvate is
transported into matrix of
the mitochondria where
the Krebs cycle occurs

8. Cellular Respiration What happens to the Krebs Cycle Products?
CO2 gas released
from cell (passes
through mitochondria
and cell membranes)
Electron carriers (NADH &
FADH) carry their
electrons to the inner
membrane where many molecules
that make up the electron transport chain are embedded.

9. inner membrane
outer
membrane
inner
membrane
space

10. Electron Transport Chain Big Picture
“chain” refers to a series of molecules that receive and then pass off electrons.
(NADH or FADH)
(O2)
H2O
With each transfer, energy is released
The final e- acceptor in the chain in O2. The diff. in potential energy between NADH and O2 is large. The difference is what is released.
energy released
energy released
When O2 receives
e- it gets reduced to
water. This is water
is a byproduct of
respiration
this is why
O2 needed

11. Electron Transport and Chemiosmosis
Most of the ETC molecules are proteins containing chemical groups that facilitate redox reactions. All but one of these proteins are embedded in the inner mitochondrial membrane.
In contrast, the lipid-soluble ubiquinone (Q) can move throughout the membrane.
During electron transport, NADH donates electrons to a flavin-containing protein at the top of the chain, but FADH2 donates electrons to an iron-sulfur protein that passes electrons directly to Q.

12. 12

13. 13

14. Unlike in Glycolysis and Krebs where ATP is directly generated from the change in free energy, there is another step between release of energy and ATP in the ETC: Oxidative Phosphorylation
ATP
*Released energy from ETC used to pump H+ into inner memb space (against gradient) where high [H+] accumulates (much potential energy in this space). As those H+ move down gradient through ATP synthase, the energy is release and that energy is used
to make ATP from ADP

15. Glycolysis, Krebs Cycle and ETC
(Cell Respiration)
C6H12O O2 +
6 H
CO2 +
ATP
produced in Krebs cycle
Gets converted to pyruvate (after many intermediate C molecules),
then acetyl Co-A, then a series of more oxidized C molecules
and eventually all the carbons in glucose become C in CO2 (oxidized)
used as the final electron acceptor in the electron transport
chain, without it-- fermentation
from reduction
of O2 in ETC
26 net/
glucose
ENERGY!

16. Feedback Inhibition
Feedback inhibition occurs when an enzyme in a pathway is inhibited by the product of that pathway.
Cells that are able to stop glycolytic reactions when ATP is abundant can conserve their stores of glucose for times when ATP is scarce.

17. 17

18. Regulation of Glycolysis
ATP = product of glycolysis
ATP inhibits glycolysis
So if there is enough ATP, no glycolysis
Remember, glycolysis does require some energy input.
Natural selection favors organisms that can conserve glucose when ATP is not needed.

19. Feedback Inhibition Regulates Glycolysis
During glycolysis, high levels of ATP inhibit the enzyme phosphofructokinase, which catalyzes one of the early reactions.
Phosphofructokinase has two binding sites for ATP:
The active site, where ATP phosphorylates fructose-6-phosphate, resulting in the synthesis of fructose-1,6-bisphosphate
A regulatory site
High ATP concentrations cause ATP to bind at the regulatory site, changing the enzyme’s shape and dramatically decreasing the reaction rate at the active site.

20. Regulation of Krebs cycle
The enzyme that converts acetyl CoA to the first product in the Krebs cycle is inhibited directly by ATP.
There are other places where NADH or ATP directly inhibits the Krebs cycle.

21. Regulation of pyruvate (before entering Kreb (citric acid) cycle
High levels of ATP, acetyl CoA, and NADH all inhibit PDH (pyruvate dehydrogenase).
High levels of NAD+, CoA, or AMP (aka low ATP) speeds rxn

22. The cell can use other carbon compounds in these processes
Carbohydrates first, then fats, then proteins

23. 23

24. Cellular Respiration
What if there is an over-flow of pyruvate: (more made by glycolysis than is needed for cell respiration)?
Fats
Converted to an stored as:
What if there is an over-flow of glucose (more glucose in the blood from glycolysis than is needed for cell respiration)?
Converted to an stored as:
glycogen

25. Anabolic Pathways Synthesize Key Molecules
Molecules found in carbohydrate metabolism are used to synthesize macromolecules such as RNA, DNA, glycogen or starch, amino acids, fatty acids, and other cell components.