Cellular Respiration:
Harvesting Energy from Glucose
Cellular respiration: Purpose
Exergonic and endergonic
reactions of metabolism…
Exergonic:
C6H12O6 + 6O2  6CO2 + 6H2O DG = -686 kcal/mole
Cellular respiration!
Provides the energy to run cell processes
Endergonic:
6CO2 + 6H2O  C6H12O6 + 6O2 DG = +686 kcal/mole
Photosynthesis!
Allows plants to make energy rich sugars from
energy poor molecules
Summary of Cellular Respiration
The 3 stages of cellular respiration…
1. Glycolysis:
• occurs in the
cytoplasm of the cell
• results in the partial
breakdown of glucose
•anaerobic – no oxygen
is used during glycolysis
Summary of Cellular Respiration
2. Krebs Cycle
• occurs in the
mitochondrial matrix
• aerobic – although O2
is not used directly in
this pathway, it will not
occur unless enough is
present in the cell.
• main catabolic
pathway of C.R.
Summary of Cellular Respiration
3. Electron Transport Chain
• occurs along the inner
mitochondrial membrane
(IMM)
• aerobic – O2 is used
during this pathway.
• the main ATP
producing pathway!
What happens during cellular
respiration?
The Big Picture!
1.The oxidation of food molecules (i.e. glucose)
• food is broken down via oxidation-reduction
reactions (Redox reactions).
Oxidation:
Stripping of high
energy electrons
(and H+ ions) from
food molecules.
Reduction:
Whenever a molecule is
oxidized, another molecule
picks up the electrons and
becomes reduced.
Just remember…
LEO says GER!!!!
lose
electrons
oxidation
gain
electrons reduction
The Big Picture (cont.)
2. Electrons stripped from food molecules are accepted by
electron carrier molecules (called NADH and FADH2).
• Food molecules are being oxidized, and the
electron carriers are being reduced.
• Electrons stripped from food molecules
have high potential energy.
They are in a
high energy
shell!
Electron Carriers (The Big
Picture cont.)
2 H+ + 2 high energy electrons
Electron carriers (The Big
Picture cont.)
The Big Picture (cont.)
3. Electron carriers take these high energy
electrons to the Electron Transport Chain.
Electrons are run down
an “electron slide”…
The energy released
from this “slide” is
used to make ATP…
At the end of the slide,
the electrons and H+ are
accepted by oxygen…
…and become WATER!
Reduced!
e- and H+
C6H12O6 + 6O2  6CO2 + 6H2O
Oxidized!
Glycolysis
ATP/NADH Ledger
- 2 ATP
The energy
investment
phase
carbons
Energy
coupling
ATP  ADP + P: exergonic
Glu  Glu-6-P :endergonic
Glycolysis
The energy
payoff phase
Redox reactions
Energy coupling
ATP/NADH Ledger
-2ATP
+2 NADH
+2ATP
Glycolysis
More energy
coupling
End-products of
glycolysis are 2
pyruvate molecules
ATP/NADH Ledger
-2ATP
+2ATP
+2ATP
+2 NADH
Summary of Glycolysis
Glucose activation: Energy Input
= 2 ATP
Energy Harvest
= 4 ATP + 2NADH
Final
Ledger
-2ATP
+2ATP
+2ATP
+2ATP
+2 NADH
What you need to know
• Final ledger for glycolysis
• Starting materials – one 6
carbon glucose molecule
• End products – two 3 carbon
pyruvate molecules
• Don’t worry about all the
intermediate molecules they
are just there to illustrate
what’s going on.
Pyruvic acid must be chemically groomed
to enter the Krebs cycle
• Each pyruvic acid molecule is broken down
to form CO2 and a two-carbon acetate
molecule that binds to coenzyme A. This
forms acetyl CoA, which enters the Krebs
cycle. 1 NADH is produced here.
Acetyl CoA
(acetate and
coenzyme A)
Pyruvic
acid
Figure 6.10
CO2
The Krebs cycle completes the oxidation of
glucose, creating many NADH and FADH2
molecules
• The Krebs
cycle is a
series of
reactions in
which
enzymes strip
away electrons
and H+ from
each acetyl
CoA molecule
Acetyl CoA
KREBS
CYCLE
Figure 6.11A
2
CO2
2 carbons enter cycle
Oxaloacetic
acid
1
Citric acid
CO2 leaves cycle
5
KREBS
CYCLE
2
Malic
acid
4
Alpha-ketoglutaric acid
3
CO2 leaves cycle
Succinic
acid
Step 1
Acetyl CoA stokes
the furnace
Figure 6.11B
Steps 2 and 3
NADH, ATP, , and CO2 are generated
during redox reactions.
Steps 4 and 5
Redox reactions generate FADH2
and NADH.
What you must know about the Krebs Cycle
• Each turn requires one molecule of acetyl CoA.
• Don’t forget there are 2 turns per glucose molecule
• Each turn generates:
– 3 NADH molecules
– 1 ATP
– 1 FADH2 molecule
– Almost all of the energy removed from pyruvate
molecules are carried by electron carrier molecules
NADH and FADH2
– Reaction intermediates (citric acid, oxaloacetate,
etc.) are required to keep the cycle going.
Electron Transport Chain
Electron carriers (NADH and FADH2) take these
high energy electrons to the Electron Transport
Chain.
Electrons are run down
an “electron slide”…
The energy released
from this “slide” is
used to make ATP…
At the end of the slide,
the electrons and H+ are
accepted by oxygen…
…and become WATER!
Electron Transport results in H+ ions being
concentrated in the intermembrane space
• Proton (H+)
gradient is built
up as a result of
NADH
(produced by
Krebs cycle
reactions)
feeding
electrons into
electron
transport
system.
ATP Synthase enzymes use a proton (H+)
gradient to put ADP and P together
forming 32 ATP
Energy yield from Aerobic
Cellular Respiration