Transcript Ch 9: E.T.C./ Oxidative Phosphorylation

Ch 9 (Part 3): E.T.C./
Oxidative
Phosphorylation
• So far, in glycolysis & the Krebs cycle, 1
glucose molecule has resulted in:
– 4 ATPs (2 from glycolysis, 2 from Krebs)
– 10 NADH (2 from gly., 2 from acetyl-CoA
step, 6 from Krebs Cycle)
– 2 FADH2 (from Krebs Cycle)
ELECTRON TRANSPORT
CHAIN (E.T.C.)
• a collection of molecules
embedded in the inner
membrane of mitochondrion
(folding of inner membrane
to form cristae)
• the groups along the chain alternate
between reduced & oxidized states as
they accept and donate electrons
• each successive group is more
electronegative than the group
before it, so the electrons are “pulled
downhill” towards OXYGEN (the final
electron carrier!)
• as molecular oxygen (O2) is reduced,
it also picks up H+ from the
environment to form water (H2O)
ATP Production of the E.T.C.
Typically, the ATP produced is as
follows:
1 NADH

3 ATP
1 FADH2 
2 ATP
(“exchange
rate”)
(FADH2 is “dropped off” at a lower
point in the E.T.C., so it generates
fewer ATPs)
• The E.T.C. does not make ATP directly –
it generates a proton gradient across
the mitochondrial membrane, which
stores potential energy that can be used
to phosphorylate ADP
• Some of the proteins in the e.t.c. pump
H+ against their gradient…this generates
a proton (H+) gradient called the
PROTON MOTIVE FORCE.
(outer matrix)
-protons then diffuse
back across the
membrane through
the ATP synthase
complex
which causes the
phosphorylation of
ADP to
form ATP!
H+
H+ H+
H+
H+
ADP + Pi
ATP
(inner matrix)
CHEMIOSMOSIS:
• the coupling of exergonic electron flow down an
E.T.C. to endergonic ATP production; the proton
gradient drives ATP synthesis as protons
diffuse back across the membrane
**accomplished by ATP synthase complex!
We Have an Animation!!
SUMMARY:
• most ENERGY flows in this sequence:
Glucose  NADH  e.t.c.  proton  ATP
motive
force
PROCESS
Glycolysis
ATP
produced
by subs.
Phos.
2 ATP
ox. of
pyruvate
to acetyl
CoA (LINK)
Krebs
cycle
2 ATP
Reduced
coenz.
2 NADH
ATP
produced by
oxid. phos.
(in the
E.T.C.)
TOTAL
4-6 ATP
6-8
2 NADH
6 ATP
6
6 NADH
2 FADH2
18 ATP
4 ATP
24
TOTAL
36-38!
Energy in organic compd.  NADH/FADH2  ETC
(oxidative phosphorylation)
• approximately 40% of energy in glucose
is converted to ATP
• the remaining energy is lost as heat
Alternative Metabolic
Pathways - Vocabulary:
• aerobic: existing in
presence of oxygen
• anaerobic: existing in
absence of oxygen
• fermentation =
anaerobic catabolism
of organic nutrients
Alcoholic Fermentation
Pyruvate + NADH  ethanol + CO2 + NAD+
• pyruvate is converted to ethanol
• NADH is oxidized to NAD+ (recycled)
• performed by yeast and some bacteria
Lactic Acid Fermentation
Pyruvate + NADH  lactic acid + NAD+
• pyruvate is reduced to lactic acid
• NADH is oxidized to NAD+ (recycling of NAD+)
• performed by some bacteria (producing cheese and
yogurt)
• performed by our muscle cells when oxygen is scarce
Fermentation differs from
cellular respiration in:
• method NADH is recycled back to NAD+
• in fermentation, the final electron
acceptor is pyruvate, not O2
• amount of total energy harvested (2
ATP from glycolysis instead of 36-38
using Kreb’s and ETC)
EXTRA VOCABULARY:
E. Coli
• Obligate anaerobes:
only grow in absence of
oxygen (e.g. Clostridium
botulinum)
• Obligate aerobes: only
grow in presence of
oxygen
Micrococcus luteus
• Facultative anaerobes: can grow in either
presence or absence of oxygen (e.g. yeast;
bacteria that make yogurt, cheese; our
muscle cells at the cellular level)
*pyruvate is a “fork” in
the metabolic road
which leads to 2
alternate catabolic
routes:
-if O2 is present: Krebs
and e.t.c.
-if no O2 is present:
Fermentation