The document summarizes the three main stages of cellular respiration: glycolysis, the citric acid cycle, and oxidative phosphorylation. Glycolysis breaks down glucose into pyruvate and occurs in the cytosol. The pyruvate then enters the mitochondria and is converted into acetyl-CoA to feed into the citric acid cycle, which takes place in the mitochondrial matrix. During oxidative phosphorylation, electrons are passed through the electron transport chain located in the mitochondrial cristae, establishing a proton gradient that is used by ATP synthase to produce ATP through chemiosmosis. The overall process generates around 38 ATP molecules per glucose molecule.

1. The StagesThe Stages
of Cellularof Cellular
RespirationRespiration

2. Let’s put up the Glycolysis
Poster

3. Your Goal
• For each stage:
• Know what goes in
• Know what comes out

4. The 3 Stages
Stage 1 –
GlycolysisGlycolysis –
occurs in the
cytosol
Stage 2 – TheThe
Citric AcidCitric Acid
CycleCycle (aka
Kreb’s Cycle)
– occurs in
the matrix of
the
mitochondria
Stage 3 – OxidativeOxidative
phosphorylationphosphorylation – the electron
transport chain and
chemiosmosis – occurs in the
cristae of the mitochondria

5. Glycolysis
• Glyco = sugar
• Lysis = break
Glycolysis is the first step
This step occurs in the cytosol
In this step, 6-carbon glucose is broken apart
into two 3-carbon molecules called
pyruvate

6. Glycolysis
Actually a series of 10 reactions that occur
No oxygen is required
No CO2 is released

7. Glycolysis
• Step 1 - the endergonic, energy investment
phase
– glucose is take in to cytosol
– 2 ATP are used to “kick off” the reaction by
phosphorylating the glucose
– Once the 2 phosphate groups are attached at
either end, the glucose molecule is ready to be
split in ½

9. Go to your diagram

10. Glycolysis
• Step 2 – the exergonic, energy payoff phase
– The 3 carbon sugar is oxidized and NADH is formed
• 2 Pyruvate molecules are what remains from the original glucose

11. Go to
your
diagram

12. Glycolysis Summary
1 glucose  2 pyruvate + 2 water
2 ATP used + 4 ATP formed  net gain of 2
ATP
2NAD+
+ 4 e-
+ 4 H+
 2 NADH + 2 H+

13. Aerobic Glycolysis
• NAD+
gains a hydrogen and an electron
and becomes NADH
• NADH = anNADH = an electron carrier‑electron carrier‑
• Energy from 1 NADH is enough to make 3
ATP

14. Glycolysis Summary
• Glycolysis only released a
small amount of the
energy in glucose
• Lots of energy still in the
pyruvate molecules
• If O2 is available, the
pyruvate will enter the
mitochondria and aerobic
respiration will continue

15. Can you explain it?
• Where?
• What goes in?
• What is produced?

16. Let’s put up the formation of
Acetyl-CoA poster

17. Formation of Acetyl CoA, the linking stepFormation of Acetyl CoA, the linking step
between glycolysis and the citric acid cyclebetween glycolysis and the citric acid cycle
• Pyruvate enters the
mitochondria via
active transport
• One CO2 is broken off
of the pyruvate
• 2-carbon compound
that remains is
oxidized to form
acetate, and the
electron released is
used to form NADH
• Coenzyme A is attached to
the acetate by an unstable
bond to form acetyl CoA,
which will enter the citric acid
cycle

18. Go to
your
diagram

19. Can you explain it?
• Where?
• What goes in?
• What is produced?

20. Let’s put up the Citric Acid cycle
poster

21. The Citric Acid Cycle
• 8 steps
• Overall, from each molecule
of pyruvate:
– 3 CO2 released (1 from
conversion of pyruvate to
acetyl CoA, 2 from the citric
acid cycle)
– 4 NADH produced (1 from
conversion of pyruvate to
acetyl CoA, 3 from the citric
acid cycle)
– 1 FADH2 produced
– 1 ATP produced

22. The Citric Acid Cycle
For each turn of the cycle, 2 carbons enter
on acetyl CoA, and 2 carbons leave as
CO2

23. The Citric Acid Cycle
• The acetyl group of
acetyl CoA joins with
oxaloacetate to form
citrate (the ionized
form of citric acid)
• The next steps break
down citrate back to
oxaloacetate
+ =
Go to
your
diagram

24. The Citric Acid Cycle Summary
• Each turn of the cycle produces 2 CO2, 3
NADH, 1 FADH2, 1 ATP
• So for 1 molecule of glucose, it would be 4
CO2, 6 NADH, 2 FADH2, and 2 ATP

25. What do we have so far?
For each molecule of glucose take in:
• 2 pyruvate
• 2 water
• 2 ATP
• 2 NADH
• 2 CO2
• 2 NADH
• 4 CO2
• 6 NADH
• 2 FADH2
• 2 ATP
• TOTAL energy
yield so far:
• 4 ATP
• 10 NADH
• 2 FADH2
glycolysis
conversion of
pyruvate to
acetyl CoA
Citric acid
cycle
Powerful
electron
carriers that
will shuttle
the
electrons to
the electron
transport
chain

26. Oxidative Phosphorylation – the
electron transport chain and
chemiosmosis
• Occurs in the inner
membrane of the
mitochondria –Inner membrane
highly folded into
cristae to make
lots of surface
area for lots of
chemical
reactions

27. Let’s put up the ETC poster

28. The Electron Transport Chain
• Made up mostly of
proteins in the
mitochondrial membrane
• Electrons delivered to
the chain by NADH
(delivers electrons to
the top of the chain)
and FADH2 (delivers
electrons to a slightly
lower step on the
chain)

30. The Electron
Transport Chain
• Electrons are
shuttled down the
chain from one
electron carrier to
the next
• When the electron
carrier accepts
electrons, it is
reduced
• It then becomes
oxidized when it
passes those
electrons to its
neighbor lower down
the chain, which is
more electronegative
and has a greater
affinity for electrons

32. The Electron Transport Chain
Summary
• No ATPNo ATP produced directly
from the electron transport
chain
• It functions in controlling
the drop in free energy
when electrons “fall” from
glucose to oxygen
• The released energy is
then used to create ATP
through chemiosmosis

34. Let’s put up the Chemiosmosis
Poster

35. Chemiosmosis
• All throughout the inner membrane of the
mitochondria are proteins called ATP
synthase

36. Chemiosmosis
• H+ ions accumulate
during the electron
transport chain
• This creates an ion
gradient across the
membrane
• This ion gradient
provides the energy
to drive the formation
of ATP from ADP by
the enzyme ATP
synthase

38. Chemiosmosis
• So chemiosmosis = the energy from a
hydrogen ion gradient is used to drive
cellular work, such as the formation of
ATP from ADP

39. Chemiosmosis
• As hydrogen ions
flow down their
gradient through
the ATP synthase
protein, parts of the
protein spin,
creating energy
that
phosphorylates
ADP to make ATP

40. Chemiosmosis
• The hydrogen ion
gradient is
maintained by the
electron transport
chain
• The electron
transport chain uses
the energy released
from moving
electrons down the
chain to pump H+
across the
membrane
• This creates a proton-motive
force- potential energy stored
in the ion gradient
• The hydrogen ions then move
back down their gradient,
through the only door open to
them, ATP synthase

41. Very slow animationVery slow animation 
Go to
your
diagram

43. Cellular Respiration Summary
• 1 glucose molecule 
30 ATP by NADH
4 ATP by FADH2
2 ATP by Citric Acid
Cycle
2 ATP by Glycolysis
Total 38 ATP

44. Cellular Respiration Summary
But…36-38 ATP is the actual total
Slightly less because
1. Ratio of NADH to ATP not a whole number
2. ATP yield varies depending on electron carrier
(FADH used more in brain, NADH used more
in heart & liver)
3. Proton-motive force used to drive other
reactions besides formation of ATP (like pulling
in pyruvate

45. Cellular Respiration Summary
• Cellular Respiration is ~ 40% efficient at
storing energy from glucose in ATP
• Best efficiency on cars is 25%