6.2
Radjewski
AP Biology
Cellular Respiration
• Catabolism (break down) of organic molecules
within cells
• Key ways cells get energy
• 4 steps
1.
2.
3.
4.
Glycolysis
Formation of Acetyl CoA (pyruvate oxidation)
Krebs Cycle (Acetyl CoA oxidation)
Electron Transport/Chemiosmosis
• Occurs in a bunch of small steps to allow for
more energy to be made
Glycolysis
• Takes place in the cytosol in the cytoplasm
– All organisms have cytoplasm, so all organisms can
do glycolysis
• 10 steps
• Glucose is oxidized releasing stored energy
– To break down glucose, cells need to invest 2 ATP’s
(endergonic)
ATP is required
because
glucose has
covalent
bonds, which
are strong.
The phosphate
from the ATP’s
are basically
being added to
glucose in
these steps.
The 6
carbon
molecule is
broken in
half,
creating
two 3C
sugars.
Later steps are
exergonic and
release energy,
forming ATP and
NADH. ATP is
made through
substrate level
phosphorylation
Glycolysis Ins/Outs
• Requirements: 1 glucose, 2 ATP, 2 NAD+,4
ADP, 4 Pi
• Products: 2 Pyruvates, 4 ATP,2 NADH, 2 ADP, 2
Pi
• Net ATP Production is 2ATP
• In the presence of oxygen, further oxidation
can occur.
Formation of Acetyl CoA (Pyruvate
Oxidation)
• Takes place in the mitochondria matrix
• Pyruvate gets oxidized to a 2C acetate
molecule and CO2
• Then Acetate is bound to Coenzyme A (CoA),
forming acetyl coenzyme A or Acetyl CoA
» It is a carrier of acetyl groups
» Vitamin B
• Exergonic reaction (released NADH) and
decarboxylation occurred (release of CO2)
Formation of Acetyl CoA (Pyruvate
Oxidation)
• Requirements: pyruvate, NAD+, Coenzyme A
• Products: Acetyl CoA, NADH, CO2
• The main role of Acetyl CoA is to donate its
acetyl group to the 4C compound
oxaloacetate, forming a 6C compound, citrate
Krebs Cycle
• Citric Acid Cycle
• 8 steps
• 2C Acetyl CoA combines with 4C oxaloacetate to
form 6C citrate
• Citrate changes to its isomer isocitrate in step 2
(water was added and released)
• In step 3, isocitrate undergoes decarboxylation to
form 5C alpha-ketoglutarate.
– This releases CO2 and forms NADH
Krebs Cycle
• In step 4, alpha ketoglutarate undergoes
decarboxylation to form 4C succinyl CoA
– NADH is formed and CO2 is released
• In step 5, succinyl CoA loses it’s CoA to form
succinate
– This is a coupled reaction where GDP + Pi forms
GTP, which then transfer its high energy
phosphate to form ATP
Krebs Cycle
• In step 6, succinate undergoes
dehydrogenation to form fumarate
– This forms FADH2, which is similar to NADH
• In step 7, fumarate adds water forming malate
• In step 8, malate undergoes dehydrogenation
forming oxaloacetic acid (which started the
cycle!)
– NADH was made!
Krebs Cycle
• Requirements: Acetyl CoA, 3 NAD+, 1 GDP,
1Pi, FAD, Water, CoA, Oxaloacetate
• Products: 3 NADH, Water, 2 CO2, 1 ATP, FADH2
• So far, we only made 3 ATP (2 from glycolysis,
and 1 from Krebs) This isn’t a lot. How do we
make all the energy?
Electron Transport Chain
• Occurs on the cristae of the mitochondria
• NADH and FADH2 are oxidized and it is
exergonic
– The protons get pumped through proton channels
on the cristae and go through chemiosmosis
• Remember this creates a proton gradient and then they
go back through ATP synthase, driving the reaction to
create ATP from ADP and Pi
– The electrons pass through proteins and then add
to oxygen (with protons)
Oxidative Phosphorylation
• Requirements: NADH, FADH2, Oxygen
• Products: Yields a lot of ATP and H20
• For each NADH or FADH2, 2-3 ATP molecules
are formed