Cellular respiration (Parts 2 and 3)
 In
general: Pyruvate (3-C molecule) enters
the mitochondrion, and enzymes oxidize it.
 Transition between Glycolysis and CAC:
Pyruvate is converted to acetyl CoA.

(CO2 is removed)
 Like
a furnace because of all the oxidizing!
 Output per molecule of pyruvate
(Remember: 2 per glucose) –
 3CO2 , 1 ATP, 1 FADH2 , 4 NADH … carry highenergy electrons to ETC
 1)
acetyl group on acetyl CoA combines
with oxaloacetate to form citrate
 2) water is removed then added to make
isocitrate (isomer of citrate)
 3)
CO2 is removed and the
compound is oxidized (NADH is
formed)
 4)
CO2 is removed and the compound is
oxidized and attached to CoA (NADH is
formed)
 5)
CoA is displaced by a phosphate that is
eventually transferred to ADP to make ATP
 6) H’s are transferred to FAD to form
FADH2
 7) water is added to break and form
bonds
 8) NAD+ is reduced to NADH by oxidizing
the substrate to reform oxaloacetate
CO2
ATP
 Now
we see how most ATP is made from
energy in food!
 The “taxis” that escort the electrons from
Glycolysis & CAC to the Electron Transport
Chain are NADH and FADH2.
 Electron Transport Chain:




Made of molecules (mostly proteins) embedded
in the inner membrane of the mitochondrion
Many folds (“cristae”) provide more surface area
Proteins become reduced when they receive
electrons, then oxidized when they pass on the
electrons to their more electronegative neighbor
Free energy decreases with each step
 1.
NADH (carrying electrons from food)
releases its electrons to a flavoprotein.
 2. The flavoprotein then passes the
electrons to an Iron-Sulfur protein.
 3. From there, the electrons are
transferred to ubiquinone (a mobile, nonprotein electron carrier).
 4.
Other protein carriers known as
cytochromes then pass the electrons on to
oxygen.
 5. Oxygen is VERY electronegative, so it
readily grabs the electrons as well as
hydrogen ions to form water.
 *Note: FADH2 adds its electrons at a lower
energy level, so it provides less energy for
ATP synthesis.

Permits H+ to move down its concentration
gradient.
 ATP
Synthase is a protein complex in the
mitochondrial inner membrane that uses an
ion gradient to make ATP.
 This gradient (or proton motive force) drives
H+ back across the membrane through ATP
synthase
 Chemiosmosis – the process in which energy
stored as a H+ gradient across a membrane
drives cellular work (i.e. – generates ATP)
 Electron transfers cause protons (H+) to be
pumped across the mitochondrial membrane
by some members of the ETC.
 ATP
synthase is composed of a rotor, a knob ,
a rod, a stator
 ATP
synthase’s rotor spins as H+ pass
through it, then the knob’s enzymes are
activated by conformational changes
 Total = 36-38 ATP produced from 1 glucose