INTRACELLULAR COMPARTMENTS AND TRANSPORTMembrane-Enclosed OrganellesProtein SortingVesicular TransportSecretory PathwayEndocytic PathwaysHow We Know: Tracking Protein and Vesicle TransportCHAPTER 15INTRACELLULAR COMPARTMENTS ANDTRANSPORT 2009 Garland Science PublishingMembrane-Enclosed Organelles15-1 Which of the following statements about the endoplasmic reticulum (ER) is false?(a) The ER is the major site for new membrane synthesis in the cell.(b) Proteins to be delivered to the ER lumen are synthesized on smooth ER.(c) Steroid hormones are synthesized on the smooth ER.(d) The ER membrane is contiguous with the outer nuclear membrane.15-2 Which of the following statements about membrane-enclosed organelles is true?(a) In a typical cell, the area of the endoplasmic reticulum membrane far exceeds the area of plasma membrane.(b) The nucleus is the only organelle that is surrounded by a double membrane.(c) Other than the nucleus, most organelles are small and thus, in a typical cell, only about 10% of a cell’s volume is occupied by membrane-enclosedorganelles; the other 90% of the cell volume is the cytosol.(d) The nucleus is the only organelle that contains DNA.15-3 Name the membrane-enclosed compartments in a eucaryotic cell where each of the functions listed below takes place.A. photosynthesisB. transcriptionC. oxidative phosphorylationD. modification of secreted proteinsE. steroid hormone synthesisF. degradation of worn-out organellesG. new membrane synthesisH. breakdown of lipids and toxic molecules15-4 Label the structures of the cell indicated by the lines in Figure Q15-4:Figure Q15-4A. nucleusB. free ribosomesC. rough endoplasmic reticulumD. Golgi apparatusE. cytosolF. endosomeG. plasma membraneH. lysosomeI. mitochondrion15-5 Which of the following organelles are not part of the endomembrane system?(a) Golgi apparatus(b) the nucleus(c) mitochondria(d) lysosomes15-6 You discover a fungus that contains a strange star-shaped organelle not found in any other eucaryotic cell you have seen. On further investigation you find the following.1. The organelle possesses a small genome in its interior.2. The organelle is surrounded by two membranes.3. Vesicles do not pinch off from the organelle membrane.4. The interior of the organelle contains proteins similar to those of many bacteria.5. The interior of the organelle contains ribosomes.How might this organelle have arisen?Protein Sorting15-7 For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below. Not all words or phrases will be used; use each word or phrase only once.Plasma membrane proteins are inserted into the membrane in the __________________. The address information for protein sortingin a eucaryotic cell is contained in the __________________ of theproteins. Proteins enter the nucleus in their __________________ form. Proteins that remain in the cytosol do not contain a __________________. Proteins are transported into the Golgi apparatus via __________________. The proteins transported into the endoplasmic reticulum by __________________ are in their __________________ form.amino acid sequence Golgi apparatus sorting signalendoplasmic reticulum plasma membrane transport vesiclesfolded protein translocators unfolded15-8 Where are proteins in the chloroplast synthesized?(a) in the cytosol(b) in the chloroplast(c) on the endoplasmic reticulum(d) in both the cytosol and the chloroplast15-9 What would happen in each of the following cases? Assume in each case that the protein involved is a soluble protein, not a membrane protein.A. You add a signal sequence (for the ER) to the N-terminal end of a normally cytosolic protein.B. You change the hydrophobic amino acids in an ER signal sequence into charged amino acids.C. You change the hydrophobic amino acids in an ER signal sequence into other, hydrophobic, amino acids.D. You move the N-terminal ER signal sequence to the C-terminal end of the protein.15-10 Which of the following statements is true?(a) The signal sequences on mitochondrial proteins are usually C-terminal.(b) Most mitochondrial proteins are not imported from the cytosol but are synthesized inside the mitochondria.(c) Chaperone proteins in the mitochondria facilitate the movement of proteins across the outer and inner mitochondrial membranes.(d) Mitochondrial proteins cross the membrane in their native, folded state.15-11 Most proteins destined to enter the endoplasmic reticulum(a) are transported across the membrane after their synthesis is complete.(b) are synthesized on free ribosomes in the cytosol.(c) begin to cross the membrane while still being synthesized.(d) remain within the endoplasmic reticulum.15-12 After isolating the rough endoplasmic reticulum from the rest of the cytoplasm, you purify the RNAs attached to it. Which of the following proteins do you expectthe RNA from the rough endoplasmic reticulum to encode?(a) soluble secreted proteins(b) ER membrane proteins(c) plasma membrane proteins(d) all of the above15-13 In which cellular location would you expect to find ribosomes translating mRNAs that encode ribosomal proteins?(a) the nucleus(b) on the rough ER(c) in the cytosol(d) in the lumen of the ER15-14 You are trying to identify the peroxisome-targeting sequence in the thiolase enzyme in yeast. The thiolase enzyme normally resides in the peroxisome and therefore must contain amino acid sequences that are used to target the enzyme forimport into the peroxisome. To identify the targeting sequences, you create a set ofhybrid genes that encode fusion proteins containing part of the thiolase protein fused to another protein, histidinol dehydrogenase (HDH). HDH is a cytosolic enzyme required for the synthesis of the amino acid histidine and cannot function if it is localized in the peroxisome. You genetically engineer a series of yeast cells to express these fusion proteins instead of their own versions of these enzymes. If the fusion proteins are imported into the peroxisome, the HDH portion of the protein cannot function and the yeast cells cannot grow on a medium lacking histidine. You obtain the results shown in Figure Q15-14.Figure Q15-14What region of the thiolase protein contains the peroxisomal targeting sequence? Explain your answer.15-15 What is the role of the nuclear localization sequence in a nuclear protein?(a) It is bound by cytoplasmic proteins that direct the nuclear protein to the nuclear pore.(b) It is a hydrophobic sequence