2. The 3 Stages
Stage 1 –
Glycolysis –
occurs in the
cytosol
Stage 2 – The
Citric Acid
Cycle (aka
Kreb’s Cycle)
– occurs in
the matrix of
the
mitochondria
Stage 3 – Oxidative
phosphorylation – the electron
transport chain and
chemiosmosis – occurs in the
cristae of the mitochondria
3. 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
5. 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
8. 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
10. 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+
11. Aerobic Glycolysis
• NAD+ gains a hydrogen and an electron
and becomes NADH
• NADH = an electron‑ carrier
• Energy from 1 NADH is enough to make 3
ATP
12. 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
13. Can you explain it?
• Where?
• What goes in?
• What is produced?
14. Formation of Acetyl CoA, the linking step
between 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
16. Can you explain it?
• Where?
• What goes in?
• What is produced?
17. 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
18. The Citric Acid Cycle
For each turn of the cycle, 2 carbons enter
on acetyl CoA, and 2 carbons leave as
CO2
19. 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
=
20. The Citric Acid Cycle Summary
• Each turn of the cycle produces 2 CO 2, 3
NADH, 1 FADH2, 1 ATP
• So for 1 molecule of glucose, it would be 4
CO2, 6 NADH, 2 FADH2, and 2 ATP
21. What do we have so far?
For each molecule of glucose take in:
•
•
•
•
2 pyruvate
2 water
glycolysis
2 ATP
2 NADH
conversion of
• 2 CO2
• 2 NADH
• 4 CO2
• 6 NADH
• 2 FADH2
• 2 ATP
pyruvate to
acetyl CoA
Citric acid
cycle
• TOTAL energy
yield so far:
• 4 ATP
• 10 NADH Powerful
electron
carriers that
• 2 FADH2
will shuttle
the
electrons to
the electron
transport
chain
22. 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
23. 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)
24.
25. 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
26.
27. The Electron Transport Chain
Summary
• No 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
30. 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
31.
32. Chemiosmosis
• So chemiosmosis = the energy from a
hydrogen ion gradient is used to drive
cellular work, such as the formation of
ATP from ADP
33. 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
34. 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
37. 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
38. 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
39. Cellular Respiration Summary
• Cellular Respiration is ~ 40% efficient at
storing energy from glucose in ATP
• Best efficiency on cars is 25%
