F214 RESPIRATION 4: CHEMIOSMOSIS AND OXIDATIVE
PHOSPHORYLATION
Complete the notes sheets below. Where you see a blank
(…………………..), decide which word/phrase is most appropriate.
So far, in the first 3 stages of aerobic respiration, …… molecules of reduced NAD
and …… molecules of reduced FAD have been produced. These molecules are
transported to the …………………… mitochondrial membrane, where INTERGRAL
MEMBRANE PROTEINS form 4 large TRANSMEMBRANE COMPLEXES.
In the ………………………………………………….., ………… atoms from NADH release all of
their energy to form …………….., and are finally combined with ……………………….. to
form water.
The diagram below shows a representation of the 4 transmembrane complexes
and the ATP synthase.
Intermembrane
space
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STEP 1
…………………… molecules bind to Complex I (also known as Coenzyme Q), and
release their H atoms as protons (…..) and electrons (…..). NADH returns to its
……………………. state and is transported back to the earlier stages of respiration. H+
ions go into solution in the matrix: some are pumped into the intermembrane
space.
Intermembrane
space
…………………… molecules bind to Complex 2 (Ubiquinone), releasing H+ ions and ejust like the NADH did in Complex 1. Not all H+ ions are pumped into the
intermembrane
space
yet:
these
remain
in
solution
in
the
…………………………………….. .
Intermembrane
space
Step 2
Electrons are passed along complexes I, II, III and IV sequentially. At complexes I,
III and IV, the e- give up some energy so that H+ ions can be pumped into the
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………………………………………. . This is NOT …………………………………………… because the
energy comes from the electrons and not from ATP. A PROTON GRADIENT forms
(which is also a ………… gradient).
Intermembrane
space
Step 3
At complex IV, protons combine with electrons and ………………… to form
………………… .
Intermembrane
space
Rearrange the following into the correct order:
2H2O
+

4H+
+
4e-
O2
………………………………………………………………………………………………………………………………
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***REMEMBER*** oxygen’s only involvement in respiration is as the final
electron acceptor, but without it the whole process stops.
Step IV
***CHEMIOSMOSIS-
the
movement
of
ions
down
their
…………………………………………. across a …………………………………………. . ***
H+ ions diffuse through channels associated with ATP………………………. enzyme,
spinning the globular head as they go, and driving the reaction between …………..
and inorganic phosphate. ………………… is produced. This process is called
***OXIDATIVE PHOSPHORYLATION***.
Intermembrane
space
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Evaluating evidence for chemiosmosis
Chemiosmosis is …………………………………………………………………………………………………….
………………………………………………………………………………………………………………………………
The theory was first proposed by Peter Mitchell in 1961, who won a Nobel prize
for chemistry. There is much evidence supporting the theory.
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Explain how each of the following provide evidence for chemiosmosis (HINT: for
some you may find using information in the picture above useful):
 Lower pH in intermembrane space than in mitochondrial matrix.
………………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………………
 More negative potential on the matrix side of the inner mitochondrial
matrix.
………………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………………
 No ATP is made in mitoblasts (mitochondria whose outer membranes have
been stripped off).
………………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………………
 No ATP is made if headpieces are removed from ATP synthase enzymes.
………………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………………
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 No ATP is made in the presence of oligomycin (an antibiotic which blocks
the flow of protons through the ion channel part of ATP synthase).
………………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………………
 Coenzymes in complexes I, III and IV can use energy from electron transfer
to pump H ions into the intermembrane space.
………………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………………
How much ATP?
It is estimated that each NADH can make 2.5 ATP’s and each FADH can make 1.5
ATP’s. Therefore, for each molecule of glucose, NADH should make …………..
molecules of ATP and FADH should make ….. molecules of ATP. The total yield
should be ……… molecules of ATP per molecule of glucose.
HOWEVER, this is seldom achieved:
 …………………………. leak across the mitochondrial membranes thus reducing
the PROTON MOTIVE FORCE.
 ATP is used to actively transport ………………………………. into the
mitochondria.
 ATP is used to bring hydrogen from NADH made in the cytoplasm during
………………………………….. into the …………………………………… .
Respiring lipids and proteins
1. Lipids
 Triglycerides can be broken down into ……………………………….. and
………………………….., both of which directly enter the Krebs cycle.
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 Fatty acids combine with CoA, and are converted to Acetyl groups. This
process requires energy from ATP. The Acetyl CoA is able to enter the
…………………………… .
 From a typical fatty acid, 50 molecules of acetyl might be produced,
ultimately yielding approximately 500 ATP molecules.
2. Proteins
 Deamination of excess amino acids produces …………………. from the
amine groups. The remainder of the amino acid molecule can be
converted into glycogen or fat which feed into either ………………….. or
the Krebs cycle.
 Some amino acids can enter the Krebs cycle directly.
Energy values of respiratory substrates
Link each substrate to its correct mean energy value (KJ.g-1)
Mean energy value (KJ.g-1)
Respiratory substrate
Carbohydrate
39.4
Protein
17.0
Lipid
15.8
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