The ribosomes of chloroplasts closely resemble bacterial ribosomes, while the origin of mitochondrial ribosomes is more difficult to trace. Extensive protein similarities, however, suggest that both organelles originated when a primitive eukaryotic cell entered into a stable endosymbiotic relationship with a bacterium. Although some of the genes of these former bacteria still function to make organelle proteins and RNA, most of them have been transferred into the nuclear genome, where they encode bacteria-like enzymes that are synthesized on cytosolic ribosomes and then imported into the organelle. The mitochondrial DNA replication and DNA repair processes are substantially less effective than the corresponding processes in the cell nucleus. Damage therefore accumulates in the genome of mitochondria over time; this damage may be a substantial contributor to the aging of cells and organisms, and it can cause serious diseases.
Which statements are true? Explain why or why not.
14–1 The three respiratory enzyme complexes in the mitochondrial inner membrane tend to associate with each other in ways that facilitate the correct transfer of electrons between appropriate complexes.
14–2 The number of c subunits in the rotor ring of ATP synthase defines how many protons need to pass through the turbine to make each molecule of ATP.
14–3 Mutations that are inherited according to Mendelian rules affect nuclear genes; mutations whose inheritance violates Mendelian rules are likely to affect organelle genes.
Discuss the following problems.
14–4 In the 1860s, Louis Pasteur noticed that when he added O2 to a culture of yeast growing anaerobically on glucose, the rate of glucose consumption declined dramatically. Explain the basis for this result, which is known as the Pasteur effect.
14–5 Heart muscle gets most of the ATP needed to power its continual contractions through oxidative phosphorylation. When oxidizing glucose to CO2, heart muscle consumes O2 at a rate of 10 μmol/min per g of tissue, in order to replace the ATP used in contraction and give a steady-state ATP concentration of 5 μmol/g of tissue. At this rate,
What structures are needed to form the barriers that separate and maintain the differentiated membrane domains in a single continuous membrane—as for the cristae and inner boundary membrane in mitochondria?
how does a eukaryotic cell regulate the many functions of mitochondria, including atp production?
What are the origins and evolutionary history of photosynthetic complexes? are there undiscovered types of photosynthesis present on Earth to help answer this question?
Why is the mutation rate so much higher in mitochondria than in the nucleus (and chloroplasts)? Could this high rate have been useful to the cell?
What mechanisms and pathways have been used during evolution to transfer genes from the mitochondrion to the nucleus?
how many seconds would it take the heart to consume an amount of ATP equal to its steady-state levels? (Complete oxidation of one molecule of glucose to CO2 yields 30 ATP, 26 of which are derived by oxidative phosphorylation using the 12 pairs of electrons captured in the electron carriers NADH and FADH2.) 14–6 Both H+ and Ca2+ are ions that move through the cytosol. Why is the movement of H+ ions so much faster than that of Ca2+ ions? How do you suppose the speed of these two ions would be affected by freezing the solution? Would you expect them to move faster or slower? Explain your answer.
14–7 If isolated mitochondria are incubated with a source of electrons such as succinate, but without oxygen, electrons enter the respiratory chain, reducing each of the electron carriers almost completely. When oxygen is then introduced, the carriers become oxidized at different rates (Figure Q14–1). How does this result allow you to order