Molecular Cell Biology - Problem Drill 17: Intracellular Vesicular Traffic

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1 Molecular Cell Biology - Problem Drill 17: Intracellular Vesicular Traffic Question No. 1 of Which of the following statements about clathrin-coated vesicles is correct? Question #1 (A) There are 2 different types of protein coats used by cells: (A) Clathrincoated and (B) COPI-coated. (B) Clathrin-coated vesicles are made up of a clathrin protein coat, which contains 6 polypeptide chains, forming a triskelion. (C) Clathrin-coated vesicles are made up of a clathrin protein coat, which contains 6 different types of lipids, forming a triskelion. (D) Adaptin proteins help bind the clathrin coat to the membrane, as well as maintain the clathrin-coat throughout the life of the vesicle. There are 3 different types of protein coats used by cells: (A) Clathrin-coated, (B) COPI-coated and (C) COPII-coated vesicles. B. Correct! Clathrin-coated vesicles are made up of a clathrin protein coat, which contains 6 polypeptide chains, forming a triskelion. Clathrin-coated vesicles are made up of a clathrin protein coat, which contains 6 polypeptide chains, forming a triskelion. Adaptin proteins help bind the clathrin coat to the membrane, as well as incorporate various membrane proteins required for vesicle cargo trapping and vesicle targeting. There are 3 different types of protein coats used by cells: (A) Clathrin-coated, (B) COPI-coated and (C) COPII-coated vesicles. (A) Clathrin-coated vesicles are made up of a clathrin protein coat, which contains 6 polypeptide chains, forming a triskelion. Clathrin triskelions together form a framework, producing a coated pit. Adaptin proteins help bind the clathrin coat to the membrane, as well as incorporate various membrane proteins required for vesicle cargo trapping and vesicle targeting.

2 Question No. 2 of Clathrin-coated vesicle budding. Question #2 (A) Through GTP hydrolysis, dynamin works with other proteins to pinch-off the vesicle in such a way that the vesicle membrane is sealed; the original membrane is open to the cytosol. (B) After the vesicle is released from the membrane, the clathrin coat remains on the vesicle until docking at the target membrane is complete. (C) After the vesicle is released from the membrane, the clathrin coat is removed by a chaperone protein, hsp70 (D) The clathrin coat is removed passively (no energy required), leaving an uncoated vesicle for transport. Through GTP hydrolysis, dynamin works with other proteins to pinch-off the vesicle in such a way that both the original membrane and the vesicle itself are sealed. After the vesicle is released from the membrane, the clathrin coat is removed by a chaperone protein, hsp70. C. Correct! After the vesicle is released from the membrane, the clathrin coat is removed by a chaperone protein, hsp70. Using the energy released from the hydrolysis of ATP, the clathrin coat is removed, leaving an uncoated vesicle for transport. After the vesicle is released from the membrane, the clathrin coat is removed by a chaperone protein, hsp70. Using the energy released from the hydrolysis of ATP, the clathrin coat is removed, leaving an uncoated vesicle for transport. Dynamin is a protein that regulates the final budding and release of the vesicle. Through GTP hydrolysis, dynamin works with other proteins to pinch-off the vesicle in such a way that both the original membrane and the vesicle itself are sealed.

3 Question No. 3 of Which of the following statements about COPI and COPII coated vesicles is correct? Question #3 (A) COPI-coated vesicles transport cargo from the endoplasmic reticulum ER to the cis end of the golgi complex, called retrograde transport. (B) COPI-coated vesicles transport cargo from the cis end of the golgi complex to the endoplasmic reticulum (ER), called retrograde transport. (C) COPII-coated vesicles transport cargo from the endoplasmic reticulum to the golgi complex, called retrograde transport. (D) GTP hydrolysis drives the budding and release of the COPI but not the COPII coat from the vesicle. COPI-coated vesicles transport cargo from the cis end of the golgi complex to the endoplasmic reticulum (ER), called retrograde transport. B. Correct! COPI-coated vesicles transport cargo from the cis end of the golgi complex to the endoplasmic reticulum (ER), called retrograde transport. COPII-coated vesicles transport cargo from the endoplasmic reticulum to the golgi complex, called anterograde transport. GTP hydrolysis drives the budding and release of the COPI and the COPII coat from the vesicle. COPI-coated vesicles transport cargo from the cis end of the golgi complex to the endoplasmic reticulum (ER), called retrograde transport. Through the hydrolysis of GTP, COPI-coated vesicles bud and then the COPI proteins are removed. COPII-coated vesicles transport cargo from the endoplasmic reticulum to the golgi complex, called anterograde transport. Again, GTP hydrolysis drives the budding and release of the COPI coat from the vesicle. Both COPI and COPII are unique to vesicle transport between the ER/Golgi.

4 Question No. 4 of Which of the following statements about SNARE proteins is correct? Question #4 (A) When vesicles dock on the target membrane (if SNARE interaction is correct) the v-snare and t-snare form a complex, locking the membranes in place. (B) When vesicles dock on the target membrane SNARE proteins remove the clathrin coat from the vesicles, through the hydrolysis of GTP. (C) Once the vesicle is docked successfully; membrane fusion takes place immediately. (D) v-snare is present both on vesicle and organelle membranes. A. Correct! When vesicles dock on the target membrane (if SNARE interaction is correct) the v- SNARE and t-snare form a complex, locking the membranes in place. When vesicles dock on the target membrane (if SNARE interaction is correct) the v- SNARE and t-snare form a complex, locking the membranes in place. Once the vesicle is docked successfully, membrane fusion takes place, in response to the specific cellular signal. There are 2 varieties of SNAREs, v-snare in vesicle membranes and t-snare in the target membrane. Fusion of the vesicle and its target membrane is facilitated in part by SNARE proteins. SNARE (soluble NSF attachment receptor) proteins, target membrane recognition and fusion of the vesicles with the target membrane. There are 2 varieties of SNAREs, v-snare in vesicle membranes and t-snare in the target membrane. When vesicles dock on the target membrane (if SNARE interaction is correct) the v- SNARE and t-snare form a complex, locking the membranes in place. Once the vesicle is docked successfully, membrane fusion takes place, in response to the specific cellular signal.

5 Question No. 5 of Which of the following statements about Rab proteins is correct? Question #5 (A) Rab proteins are activated by the exchange of ATP for ADP. (B) Rab proteins (GTPases) are a large family of over 30 members; they exist on the membranes of the ER and are involved in vesicle docking. (C) Rab proteins (GTPases) are a large family of over 30 members; they exist on the membranes of all organelles and are involved in vesicle docking. (D) By interacting with lipids in the vesicle, they assist SNARE proteins with docking. Rab proteins are activated by the exchange of GTP for GDP. Rab proteins (GTPases) are a large family of over 30 members; they exist on the membranes of all organelles and are involved in vesicle docking. C. Correct! Rab proteins (GTPases) are a large family of over 30 members; they exist on the membranes of all organelles and are involved in vesicle docking. By interacting with rab effectors on the target membrane, they assist SNARE proteins with docking. Rab proteins (GTPases) are a large family of over 30 members; they exist on the membranes of all organelles and are involved in vesicle docking. Their specificity is due, in part, to their specific organelle localization. Rab proteins are activated by the exchange of GTP for GDP. By interacting with rab effectors on the target membrane, they assist SNARE proteins with docking. Once docking is complete, rab proteins hydrolyze GTP into GDP.

6 Question No. 6 of Which of the following statements about vesicle transport from the ER through the golgi apparatus is correct? Question #6 (A) Incoming vesicles with cargo from the ER enter the golgi at the trans face. (B) After budding from the ER, the vesicles join together at the trans face of the golgi apparatus, in a region called the vesicular tubular clusters (intermediary compartment). (C) After budding from the ER, the vesicles join together in a region called the vesicular tubular clusters (intermediary compartment). (D) When vesicles bud from the ER with ribosomes in the membrane, the ribosomes are recycled back to the ER in separate vesicles. Incoming vesicles with cargo from the ER enter the golgi at the cis face. After budding from the ER, the vesicles join together in a region called the vesicular tubular clusters (intermediary compartment). C. Correct! After budding from the ER, the vesicles join together in a region called the vesicular tubular clusters (intermediary compartment). Vesicles bud from special ER regions, called RE exit sites; these sites usually do not contain ribosomes. The golgi apparatus, or golgi complex, is a group of membrane bound sacs (cisternae), and is responsible for the addition and modification of oligosaccharides. Vesicles leave the golgi from the trans face and deliver proteins to the cell surface for secretion. Incoming vesicles with cargo from the ER enter the golgi at the cis face. Proteins that are targeted for the golgi complex are packaged into COPIIcoated vesicles. Vesicles bud from special ER regions, called RE exit sites; these sites usually do not contain ribosomes. Proteins with an ER exit signal are directed to COPII-coated vesicles. After budding from the ER, the vesicles join together in a region called the vesicular tubular clusters (intermediary compartment).

7 Question No. 7 of Which of the following statements about protein transport through the golgi apparatus is correct? Question #7 (A) Vesicle Transport- In this mode of transport, the proteins move in vesicles as well as free in the cytosol within each cisternae. (B) Vesicle Transport- In this mode of transport, the proteins move in vesicles and the resident proteins remain fixed within each cisternae. (C) Cisternal Maturation- In this mode, the cisternae mature and they, along with all their contents, move to the ER. (D) There are two possible methods for transporting proteins through the golgi apparatus: (A) Vesicle Transport and (B) Vesicle Budding. Vesicle Transport: In this mode of transport, the proteins move in vesicles and the resident proteins remain fixed within each cisternae. B. Correct! Vesicle Transport: In this mode of transport, the proteins move in vesicles and the resident proteins remain fixed within each cisternae. Cisternal Maturation: In this mode, the cisternae mature and they, along with all their contents, move through the golgi apparatus. There are two possible methods for transporting proteins through the golgi apparatus: (A) Vesicle Transport and (B) Cisternal Maturation. There are two possible methods for transporting proteins through the golgi apparatus: (A) Vesicle Transport and (B) Cisternal Maturation. Vesicle Transport: In this mode of transport, the proteins move in vesicles and the resident proteins remain fixed within each cisternae. (B) Cisternal Maturation: In this mode, the cisternae mature and they, along with all their contents, move through the golgi apparatus.

8 Question No. 8 of Which of the following statements about transport from the trans golgi network to lysosomes is correct? Question #8 (A) Inside the late endosome, the ph is approximately 6.0; this acidic environment begins the hydrolysis of the protein. (B) Inside the late endosome, the ph is 7.4 this normal environment protects the transported protein. (C) Lysosomes likely form from peroxisomes and then receive cargo from maturing late endosomes. (D) Lysosomes likely form from early endosomes. A. Correct! Inside the late endosome, the ph is approximately 6.0; this acidic environment begins the hydrolysis of the protein. Inside the late endosome, the ph is approximately 6.0; this acidic environment begins the hydrolysis of the protein. Lysosomes likely form from maturing late endosomes. Lysosomes likely form from maturing late endosomes. Lysosomes receive cargo from vesicles originating in the cell membrane and the golgi apparatus. Proteins are transported in vesicles from the trans golgi network to endosomes. Proteins delivered to the late endosome from the trans golgi network begin the process of digestion. Inside the late endosome, the ph is approximately 6.0; this acidic environment begins the hydrolysis of the protein. Lysosomes likely form from maturing late endosomes.

9 Question No. 9 of Which of the following statements about mannose 6-phosphate (M6P) is correct? Question #9 (A) Proteins that are destined to reside in the lysosome, such as lysosmal hydrolase, are tagged with a M6P. (B) Proteins that are destined to reside in early endosomes, such as lysosmal hydrolase, are tagged with a M6P. (C) The M6P is recognized and bound to a specific M6P-receptor, within the ER. (D) Once inside the late endosome, the M6P and its receptor are digested and destroyed in the acidic environment. A. Correct! Proteins that are destined to reside in the lysosome, such as lysosmal hydrolase, are tagged with a M6P. Proteins that are destined to reside in the lysosome, such as lysosmal hydrolase, are tagged with a M6P. The M6P is recognized and bound to a specific M6P-receptor, within the trans golgi network. Once inside the late endosome, the M6P and its receptor dissociate in the acidic environment. Mannose 6-phosphate (M6P) is a lysosomal sorting signal. Proteins that are destined to reside in the lysosome, such as lysosmal hydrolase, are tagged with a M6P. The M6P is recognized and bound to a specific M6P-receptor, within the trans golgi network. The M6P-receptor binds proteins with the M6P tag, and is incorporated into clathrincoated vesicles, ultimately destined for lysosomes. Once inside the late endosome, the M6P and its receptor dissociate in the acidic environment. The M6P-receptor is recycled back to the trans golgi network. The hydrolase moves on to reside in the lysosome.

10 Question No. 10 of Which of the following statements about exocytosis is correct? Question #10 (A) Cells utilize a specific mechanism for molecule secretion known as the Constitutive secretory pathway. (B) Cells utilize 2 specific mechanisms for molecule secretion: (A) Constitutive secretory pathway and (B) the Regulated secretory pathway. (C) Most proteins are secreted through the constitutive (default) pathway. This pathway operates continuously and requires an external signal for control. (D) In the regulated secretory pathway, the molecules are packaged into coated vesicles in the trans golgi network and are secreted immediately. Cells utilize 2 specific mechanisms for molecule secretion: (A) Constitutive secretory pathway and (B) the Regulated secretory pathway. B. Correct! Cells utilize 2 specific mechanisms for molecule secretion: (A) Constitutive secretory pathway and (B) the Regulated secretory pathway. Constitutive secretory pathway: most proteins are secreted through the constitutive (default) pathway. This pathway operates continuously and does not require an external signal for control. In the regulated secretory pathway, the molecules are packaged into coated vesicles in the trans golgi network and then require a specific neural or hormonal signal to be secreted. The golgi apparatus is the location where secreted molecules are packaged into specific vesicles and transported to the cell membrane. Cells utilize 2 specific mechanisms for molecule secretion: (A) Constitutive secretory pathway and (B) the Regulated secretory pathway. (A) Constitutive secretory pathway: most proteins are secreted through the constitutive (default) pathway. This pathway operates continuously and does not require an external signal for control. (B) Regulated secretory pathway: cells that are specialized for secreting molecules, such as insulin secreting cells, primarily use the regulated secretory pathway. The molecules are packaged into coated vesicles in the trans golgi network and then require a specific neural or hormonal signal to be secreted.