Download p134

p134 #2, 3, 4, 5, 8, 10, 11, 13, 20, 22, 23
2. (a) Glycolysis occurs in the cytoplasm.
(b) Pyruvate oxidation and the Krebs cycle occur in the mitochondrial matrix.
(c) The electron transport chain and ATP synthesis occur in the inner mitochondrial
membrane.
3. (a) Ubiquinone (Q) is an electron carrier. As part of the electron transport chain, it
carries electrons from NADH dehydrogenase to cytochrome b-c1 complex within the
membrane.
(b) FADH2 is an electron carrier from the Krebs cycle that transfers its two electrons to
Q.
(c) Pyruvic acid is a product of glycolysis that enters the mitochondrial matrix to
undergo pyruvate oxidation and then enters the Krebs cycle.
(d) ATP synthase is an enzyme complex located in the inner mitochondrial membrane
that uses the proton motive force to generate ATP.
4. (a) Theoretically, NADH and FADH2 should generate three and two ATP molecules,
respectively.
(b) NADH passes its electrons to the first protein complex in the electron transport
chain, NADH hydrogenase. FADH2 transfers its electrons to the second protein in the
chain, ubiquinone (Q). The free energy released by the oxidation of FADH2 is used to
pump two protons into the intermembrane space, while NADH oxidation pumps out
three electrons. The result is that two ATP are formed per FADH2, and three ATP
molecules are formed per mitochondrial NADH.
5. (a) The net gain in ATP after one molecule of glucose undergoes cellular respiration
is 36 ATP.
(b) The net gain in ATP after one molecule of glucose undergoes alcoholic fermentation
is 2 ATP.
8. NAD+ accepts two electrons and one proton during glycolysis and the Krebs cycle.
10. (a) An electrochemical gradient is created by pumping ions into a space surrounded
by a membrane that is impermeable to ions. The gradient has two components: an
electrical component caused by a difference in charge across the membrane
and a chemical component caused by a difference in ion concentration.
(b) An electrochemical gradient is created during electron transport as the enzyme
complexes move protons from NADH and FADH2 into the intermembrane space. The
intermembrane space becomes an H+ reservoir because the membrane is almost
impermeable to protons. There is, therefore, a much higher concentration of protons in
the intermembrane space than in the matrix. Also, protons are consumed in the
mitochondrial matrix as oxygen accepts electrons and form water.
(c) The electrochemical gradient is used to power ATP synthesis by the enzyme
complex ATP synthase. The electrochemical gradient stores free energy and this energy
is referred to as proton-motive force (PMF). Protons move through ATP synthase in
response to the PMF, reducing the energy of the gradient. This energy drives the
synthesis of ATP from ADP and inorganic phosphate in the mitochondrial matrix.
11. Yeast cells produce ATP from glucose by alcoholic fermentation. NADH passes its
hydrogen atoms to acetylaldehyde, which is formed when a carbon dioxide molecule is
removed from pyruvate using pyruvate decarboxylase. This produces ATP, ethanol, and
carbon dioxide.
13. Muscle cells produce lactate from pyruvate when there is no oxygen available to
accept electrons from the cytochrome oxidase complex.
20. A: inner mitochondrial membrane
B: cristae
C: mitochondrial matrix
D: outer mitochondrial space
22. Metabolism in a heart undergoing a heart attack would switch from cellular
respiration to lactic acid fermentation because of the lack of oxygen, which would be
caused by a blocked coronary artery. However, lactic acid fermentation does not
provide enough energy to keep the heart beating at a life-sustaining rate.
23. It is essential that muscle cells continue to convert pyruvate to lactate or else the
muscle cells would cease to contract and the cells would die.