Download 8 Aerobic Respiration

AEROBIC
RESPIRATION
Chapter 8
AEROBIC RESPIRATION
 Aerobic respiration is the next step after Glycolysis if the cell can
obtain oxygen.
 We won’t need it until the last step…but we still need it.
 Remember that the final product of Glycolysis is pyruvate.
 Aerobic respiration takes place in the mitochondria
 The first step is an intermediate reaction to prepare the pyruvate for
the citric acid cycle
 (The intermediate step is only one step, and it’s not technically part
of Glycolysis OR aerobic respiration. It’s just a preparatory step.)
 The pyruvate gives off a carbon as CO2, donates a H to form NADH, and the
final molecule is an acetyl-CoA molecule
CITRIC ACID CYCLE
The citric acid cycle takes place in the matrix of the
mitochondria
**Remember: each step in aerobic respiration happens
TWICE—once for each PGAL formed in Glycolysis
Step 1
 Acetyl CoA (2-carbon molecule) bonds with an oxaloacetate (4-
carbon molecule) to form citric acid (6-carbon molecule)
CITRIC ACID CYCLE
Step 2
Citric acid gives off a CO2
 The molecule now contains 5-carbons
 CO2 is not needed by the cell, so it is expelled out into the blood
stream.
Citric acid donates a hydrogen to an NADH
Citric acid reforms to an alpha-ketoglutarate
CITRIC ACID CYCLE
Step 3
Alpha-ketogluterate gives off a CO2, a hydrogen for an
NADH, and a phosphate for ATP
The molecule then forms a succinate
 The molecule is now back to the 4-carbon molecule that the
cycle started with
CITRIC ACID CYCLE
Step 4
Succinate donates a hydrogen for an FADH2 molecule.
The succinate then rearranges to form a molecule of
fumerate
CITRIC ACID CYCLE
Step 5
The fumerate rearranges to form a molecule called
malate
CITRIC ACID CYCLE
Step 6
The malate donates a hydrogen to form NADH
The malate then reforms to the original
oxaloacetate molecule
The oxaloacetate begins the cycle over again.
CITRIC ACID CYCLE SUMMARY
Inputs…per cycle, (per glucose)
Acetyl CoA…1 (2)
Outputs
ATP… 1 (2)
FADH2…
1 (2)
CO2… 2 (4)
NADH…
3 (6)
ELECTRON CARRIERS
 A hydrogen is simply one proton and one electron. So, when a
“hydrogen” is donated, it is also appropriate to say an “electron” is
donated
 Electron carriers are molecules that transport a hydrogen from one
location to another
 Typically, the electron of the hydrogen will be used as a cofactor for an
enzyme
 NADH and FADH2 have been synthesized multiple times so far in
cellular respiration.
 All will finally be used in the electron transport chain as reactants
ELECTRON TRANSPORT CHAIN
The electron transport chain follows glycolysis and the citric
acid cycle.
 It is taking place at the same time as glycolysis and citric acid cycle,
but it uses the products of glycolysis and the citric acid cycle as
reactants
The ETC takes place in the inner membrane of the
mitochondria.
The ETC is powered thanks to the concept of diffusion and
equilibrium
 Important fact to remember: diffusion and osmosis naturally occur
in the universe, which means that these processes happen for free.
ELECTRON TRANSPORT CHAIN
 The ETC is a series of protein channels embedded in the cristae
(inner mitochondrial membrane).
 The NADH and FADH2 give off their electron, which powers each
protein channel in sequence.*
 The NAD+ and FAD+ then return to pick up another electron
 *REMEMBER: If we can’t do this step, then the cell has to do fermentation instead.
 These proteins move hydrogen atoms from inside the membrane to
outside the membrane, against the concentration gradient.
 The energy for this comes from the NADH and FADH2 electrons.
 The hydrogen that cross the membrane are already present. They never leave.
 This creates an unequal ratio of hydrogen atoms along the membrane
(more are outside than inside). The membrane is NOT in equilibrium
ATP SYNTHASE
The only way for the hydrogen atoms to get back across
the membrane (and reach equilibrium) is through a specific
channel enzyme called ATP synthase.
ATP synthase looks like an upside-down light bulb.
As the hydrogen atoms pass through the ATP synthase
from the outside of the membrane to the inside, they
provide kinetic energy to the enzyme.
With this energy, ATP synthase attaches phosphates to
ADP molecules in the “bulb” part, building an ATP
molecule.
ATP PRODUCTION
 Each molecule of NADH powers the ETC enough to build 3
molecules of ATP
 FADH gives a little less power and can build only 2 ATP
 This means the ETC can produce a total of 32-34 ATP per glucose
molecule.
 Add that to the four ATP already produced in glycolysis and the citric
acid cycle, you have a maximum-possible net gain of 36-38 ATP
molecules from 1 molecule of glucose.
 With fermentation: it’s two.
 To remove the electron from the ETC, the cell bonds it with a
molecule of oxygen and forms H2O
 This is why you need to breathe. This is what the oxygen is used
for.
ETC SUMMARY
Inputs (per molecule of glucose)
 10 NADH
 2 FADH2
 O2
Outputs
 28-30 ATP from NADH
 4 ATP from FADH2
 NAD+
 FAD+
 H2 O
CELL RESPIRATION SUMMARY
C6H12O6 + 6 O2  6 CO2 + 6 H2O + Energy
C6H12O6 : For glycolysis
6 O2 : To collect the electron in the ETC
6 CO2 : Given off in intermediate step and Citric Acid Cycle
6 H2O
: Given off in the ETC
Energy
: In the form of ATP