MCB 2210 FALL 2021 PROBLEM SET 4 1. How are proteins imported into mitochondria and chloroplasts? a. Pre-translationally. b. Imported fully-formed and properly-folded across membrane of the appropriate organelle. c. Post-translationally. d. Post-transcriptionally. e. b and c are correct. 2. The N-terminal targeting sequence of mitochondrial-matrix proteins is ultimately removed by ____________ a. a chaperone b. a mitochondrial processing glycosidase c. mitochondrial processing lipase d. mitochondrial signal peptidase e. mitochondrial ATP synthase 3. How do the signal sequences of nuclear-encoded mitochondrial proteins targeting the inner mitochondrial membrane differ from those targeting the mitochondrial matrix? a. Inner mitochondrial membrane protein signals are all made of alanine. b. Inner mitochondrial membrane protein signals remain as part of the molecule. c. Inner mitochondrial membrane protein signals are internal rather than on the end. d. b and c e. Inner mitochondrial membrane protein signals contain adenine. 4. Which functions do molecular chaperones perform to help proteins that enter mitochondria? a. they keep polypeptides unfolded in the cytoplasm b. they help pull polypeptides into the mitochondrial matrix c. they help fold mitochondrial proteins once they reach the matrix d. they direct mitochondrial proteins to the outer mitochondrial membrane e. a, b and c 5. The outer mitochondrial membrane contains a protein import complex, the _________ that includes a(n) ________ and a protein-lined ________. a. TOM complex, receptor that recognizes and binds mitochondrial proteins, channel b. TIM complex, receptor that recognizes and binds mitochondrial proteins, channel c. TOM complex, receptor that recognizes and binds the outer mitochondrial membrane, channel d. TIM complex, receptor that recognizes and binds the outer mitochondrial membrane, channel e. importer, receptor that recognizes and binds mitochondrial proteins, channel6. Which helps power the movement of the mitochondrial targeting signal on a mitochondrial protein into the mitochondrial matrix? a. electric potential across the inner mitochondrial membrane acting on the positively charged targeting signal b. electric potential across the outer mitochondrial membrane acting on the positively charged targeting signal c. ATP d. GTP e. electric potential across the inner mitochondrial membrane acting on the negatively charged targeting signal 7. Put the following in the correct order: I. Protein is imported through the TIM complex II. Protein is imported through the TOM complex III. Fully-folded, mature protein is located in the mitochondrial matrix IV. Protein is folded by mitochondrial chaperone using ATP V. Import signal is recognized by receptor protein a. V, I, II, IV, III b. II, V, III, I, IV c. II, III, V, IV, I d. V, II, I, IV, III e. none of the above is correct. 8. Proteins that are destined for the thylakoid membrane or the thylakoid lumen must have _________. a. a thylakoid targeting domain b. a thylakoid lumen domain c. a transit peptide d. a stroma-targeting domain e. a and d 9. Compared to mitochondria, chloroplasts have an extra membrane-enclosed compartment called: a. Thylakoid b. Lumen c. Cytoplasm d. Stroma e. Nucleus10. If you took a gene that is normally present in the mitochondrial genome and codes for an enzyme that works in the matrix, and then inserted the gene into the nucleus of a cell, what would you expect the final destination of the protein to be? a. ER lumen b. Nucleus.! c. Secreted.! d. Mitochondrial matrix e. None of the above 11. If you took a gene for a protein which is normally found in the cytoplasm and added a mitochondrial targeting signal (N-terminal amphipathic helix) to it and expressed the gene in the cell, where would you expect the protein to end up a. ER lumen b. Nucleus c. Cytoplasm d. Secreted e. Mitochondrial matrix 12. If you engineered a nuclear-encoded gene for a mitochondrial matrix protein to contain an Asn-X-Ser glycosylation signal and a c-terminal peroxisomal targeting signal, and then inserted the gene into the nucleus of a cell, and examined the expressed protein, the protein could: a. Be glycosylated and found in the mitochondrial matrix. b. Be unglycosylated and in the cytoplasm. c. Be unglycosylated and exported from the cell. d. Be unglycosylated and found in the mitochondrial matrix. e. Be glycosylated and found in the peroxisome. 13. Which is FALSE: In order to target a protein to the lysosomes the protein needs to: a. Be made on ribosomes of the rough endoplasmic reticulum b. Have a net positive charge c. Have an Asn-X-Ser glycosylation sequence d. Be maintained in an unfolded state by chaperones until it reaches the lysosome e. b and d are false. 14. If a mitochondrial localization signal were added to a lysosomal protein so that the ER targeting signal sequence preceded the mitochondrial signal sequence (i.e. was at the 5’ end), where would the protein likely be found? a. Nucleus. b. Cytoplasm. c. Mitochondria. d. Lysosomes. e. None of the above are correct.15. Which is the FOURTH step of the five listed in lysosomal enzyme sorting? a. Co-translational addition of an oligosaccharide to the protein. b. Binding of Man-6-Phosphate to its receptor in the TGN. c. Removal of the man-6-phosphate signal d. Transport of the enzyme from the TGN e. Transport from the ER to the Golgi 16. PTS1- and PTS2-bearing matrix proteins utilize: a. a common cytosolic receptor. b. a common translocation machinery on the peroxisomal membrane. c. a common receptor on the nuclear pore that catalyzes entry into the nucleus via pore targeting sequences. d. a common receptor protein within the peroxisomal matrix that activates protein processing for PTS1- and PTS2-bearing proteins. 17. Compartments from different parts of the Golgi complex ranging from the cis-most to the trans-golgi network (TGN) display differences in enzymatic activity. Which item(s) below might be correct descriptions of those differences? a. They contain different enzymes that add different sugars to the ends of growing carbohydrate chains of glycoproteins. b. They contain different ribosomes. c. They contain different polynucleotides that add different sugars to the ends of growing carbohydrate chains of glycoproteins. d. They contain different enzymes that add different sugars to the ends of growing carbohydrate chains of polynucleotides. e. a and b 18.