Unit 5: Mitochondria and Chloroplasts - Practice Quiz

1 Which organelle is commonly called the powerhouse of the cell?

2 What is the name of the highly folded inner membrane of a mitochondrion?

3 Which mitochondrial compartment contains enzymes for many stages of cellular respiration?

4 Where is the mitochondrial electron transport chain mainly located?

5 How is the mitochondrial genome usually described in animal cells?

6 Mitochondrial DNA is located primarily in which organelle?

7 Which type of molecule is encoded by some mitochondrial genes?

8 Most mitochondrial proteins are encoded by genes located in the:

9 What is a common feature of a mitochondrial targeting sequence?

10 Which protein complex first recognizes many nuclear-encoded mitochondrial proteins at the outer membrane?

11 Which complex helps move many precursor proteins across the mitochondrial inner membrane?

12 Many mitochondrial inner membrane proteins contain which type of sequence that can become a membrane anchor?

13 A mitochondrial targeting sequence that is cleaved after import is usually removed by a:

14 A protein with a signal that directs it to the mitochondrial matrix will cross which membrane?

15 Where are many mitochondrial outer membrane proteins inserted?

16 Which process takes place in chloroplasts?

17 What are stacks of thylakoids called?

18 Which chloroplast compartment surrounds the thylakoid stacks?

19 The chloroplast genome is usually found as which type of DNA molecule?

20 Most proteins found in chloroplasts are encoded by genes in the:

21 A mutation makes the inner mitochondrial membrane freely permeable to protons. Which process would be most directly impaired?

22 Why does the mitochondrial inner membrane contain many folds called cristae?

23 If a cell suddenly lacks oxygen, which mitochondrial event is most directly blocked first?

24 A mitochondrial disorder is transmitted from an affected mother to all of her children, but only her daughters pass it to the next generation. Which inheritance pattern best explains this result?

25 Why can mitochondrial mutations produce different disease severity among cells in the same person?

26 A mitochondrial gene encodes a protein that is an essential subunit of an electron transport complex. Which result is most likely if that gene is deleted?

27 A newly synthesized mitochondrial inner membrane protein has an N-terminal targeting sequence and a hydrophobic stop-transfer sequence. What is its likely import pathway?

28 A mutation prevents mitochondrial matrix ATP from powering import motors, but the inner membrane remains intact. Which class of protein import would be most affected?

29 A precursor protein lacks a cleavable N-terminal targeting sequence but contains multiple internal hydrophobic segments. Which pathway is most appropriate for its insertion into the mitochondrial inner membrane?

30 A mitochondrial precursor contains an N-terminal targeting sequence that is removed after import and then remains soluble in the matrix. Which feature most likely directs this final localization?

31 A protein is initially imported into the mitochondrial matrix but is later found in the intermembrane space. Which mechanism could produce this localization?

32 A mitochondrial outer-membrane protein has a hydrophobic segment near its extreme C terminus. Which targeting feature is most consistent with its localization?

33 A chloroplast is treated with a chemical that prevents proton accumulation inside the thylakoid lumen. Which process would decline most directly?

34 Why are grana connected by stroma lamellae in chloroplasts?

35 If the enzyme that fixes carbon dioxide is inhibited while the light reactions remain functional, which immediate change is expected?

36 A chloroplast gene is mutated in only some chloroplasts of a leaf cell. What could explain variable photosynthetic activity among cells derived from that tissue?

37 Which observation most strongly supports the endosymbiotic origin of chloroplasts?

38 A nuclear-encoded chloroplast stromal protein is synthesized in the cytosol with an N-terminal transit peptide. Which route does it most likely follow?

39 A chloroplast protein contains both a transit peptide for stromal entry and a second signal that directs it to the thylakoid membrane. What does this arrangement indicate?

40 A nuclear-encoded chloroplast protein lacks its transit peptide but is otherwise functional. Where would it most likely accumulate?

41 A mutation selectively reduces the proton conductance of the inner mitochondrial membrane without directly affecting electron transport. Which immediate change is most likely in intact mitochondria supplied with oxygen and respiratory substrates?

42 Why does the highly folded inner mitochondrial membrane support greater oxidative phosphorylation capacity than an equally sized smooth membrane?

43 A respiratory-chain inhibitor is added to cells, and ATP production decreases despite normal substrate uptake and an intact ATP synthase catalytic domain. Which observation best distinguishes inhibition of electron transport from direct inhibition of ATP synthase?

44 A pathogenic mitochondrial DNA mutation is heteroplasmic. A tissue crosses a functional threshold only after the mutant genome fraction becomes high. Which inheritance pattern is most consistent with this mechanism?

45 A mitochondrial gene is experimentally relocated to the nuclear genome. Which additional change is generally required for the encoded protein to remain functional in mitochondria?

46 Which feature most directly explains why mitochondrial DNA mutations can produce a mosaic pattern of respiratory deficiency within a single tissue?

47 A nuclear-encoded inner-membrane protein has an N-terminal presequence followed by a hydrophobic stop-transfer segment. A mutation blocks the TIM23 lateral-release mechanism but leaves translocation through the TOM complex intact. Where will the protein accumulate?

48 A polytopic inner-membrane protein lacks a cleavable presequence but contains multiple internal targeting signals. Which import route is most likely?

49 A mitochondrial precursor with a cleavable presequence is synthesized in the presence of a protonophore that collapses the inner-membrane electrochemical gradient but does not damage the outer membrane. Which result is expected?

50 A protein contains an N-terminal matrix-targeting presequence followed by a hydrophobic segment that acts as an internal stop-transfer sequence. Which final location is most likely?

51 A small intermembrane-space protein contains a bipartite targeting signal: an N-terminal mitochondrial presequence followed by a hydrophobic segment that is cleaved within the intermembrane space. Which pathway best explains its localization?

52 A tail-anchored mitochondrial outer-membrane protein has a C-terminal transmembrane helix and no cleavable presequence. Which targeting logic is most appropriate?

53 A mutation prevents cleavage of a matrix-targeting presequence but does not block translocation. What is the most direct consequence for the imported protein?

54 A chloroplast is illuminated while stromal ADP and phosphate are abundant, but a mutation prevents proton transfer from the thylakoid lumen to the stroma through ATP synthase. Which immediate combination is expected?

55 Why does the stacking of thylakoid membranes into grana require spatial organization of photosynthetic complexes rather than simply increasing membrane area?

56 A herbicide blocks electron transfer from photosystem II but leaves photosystem I and ATP synthase structurally intact. Which change is most directly expected under illumination?

57 A chloroplast genome mutation affects a photosynthetic subunit in only a subset of chloroplast DNA copies. Why can daughter cells differ markedly in photosynthetic competence after cell division?

58 A chloroplast gene is transferred to the nucleus during evolution. Which change most directly permits its product to function inside the chloroplast?

59 A nuclear-encoded thylakoid protein contains an N-terminal chloroplast transit peptide followed by a lumen-targeting signal peptide. Which sequence of events is most likely?

60 A chloroplast inner-envelope protein has an N-terminal transit peptide and a hydrophobic stop-transfer segment. If the stop-transfer segment is experimentally removed, what is the most likely consequence?