Cellular Transport: Endocytosis and Exocytosis

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Questions and Answers

What is the role of mannose-6-phosphate in protein targeting to lysosomes?

It is an enzymatically active hydrolase
It acts as a signal patch for protein folding
It is involved in the sorting of proteins in the Golgi apparatus
It serves as a recognition signal for M-6-P receptors (correct)

What is the purpose of the acidic environment in late endosomes?

To promote protein synthesis
To release prohydrolases from M-6-P receptors (correct)
To activate prohydrolases
To facilitate vesicle fusion

In which organelle is the modification of the signal patch on a protein destined for a lysosome taking place?

Lysosomes
Golgi apparatus
Endoplasmic reticulum (correct)
Nucleus

What is the function of M-6-P receptors?

To recognize and bind to M-6-P tagged proteins (B) Signup and view all the answers

Where are the prohydrolases activated by cleavage and removal of phosphate groups?

Trans-Golgi network (D) Signup and view all the answers

What is the function of the TGN in the context of lysosomal enzyme trafficking?

To sort and package lysosomal enzymes into vesicles (D) Signup and view all the answers

What is the role of early and late endosomes in the context of lysosomal enzyme trafficking?

To receive and process vesicles from the Golgi apparatus (B) Signup and view all the answers

What happens to secretory vesicles after they receive a neural stimulus?

They fuse with the plasma membrane and discharge their contents. (A) Signup and view all the answers

What is the primary role of the Golgi apparatus in this process?

To package and modify proteins for secretion. (B) Signup and view all the answers

What is the function of Rab-GTPase in vesicular trafficking?

To facilitate the docking of vesicles with the target membrane. (B) Signup and view all the answers

What is the name given to secretory vesicles containing inactive precursor proteins?

Zymogen granules. (B) Signup and view all the answers

What causes a transient influx of Ca2+ into the cytoplasm after a neural stimulus?

The neural stimulus itself. (A) Signup and view all the answers

What is the result of the interaction between v-SNAREs and t-SNAREs?

The formation of the cis-SNARE complex. (C) Signup and view all the answers

What is the role of Ca2+ in this process?

To stimulate secretory vesicles to fuse with the plasma membrane. (C) Signup and view all the answers

What is the final step in the process of vesicular trafficking described?

The fusion of vesicles with the plasma membrane. (C) Signup and view all the answers

What is not directly involved in the process of vesicular trafficking described?

Autophagy. (C) Signup and view all the answers

What is the function of the Rab-GTPase activity in vesicular trafficking?

To tether the vesicle to the target membrane (A) Signup and view all the answers

Which protein family is responsible for target recognition in vesicular trafficking?

v-SNARE (B) Signup and view all the answers

What is the function of the NSF/α-SNAP protein complex in vesicular trafficking?

To recycle v-SNAREs in transport vesicles (C) Signup and view all the answers

What is the result of the tethering of the vesicle to the target membrane?

Beginning of the docking process (C) Signup and view all the answers

What is the function of the adaptin complex in vesicular trafficking?

To form a coated pit (B) Signup and view all the answers

What is the final step in the vesicular trafficking process?

Discharge of the cargo protein (C) Signup and view all the answers

What is the result of the interaction between the Rab-GTPase and tethering proteins?

Tethering of the vesicle to the target membrane (C) Signup and view all the answers

What is the primary function of COP-I coated vesicles?

Retrograde transport between Golgi cisternae (A) Signup and view all the answers

Which type of vesicle is formed as a result of receptor-mediated endocytosis?

Clathrin-coated vesicle (C) Signup and view all the answers

What is the primary function of exocytosis?

Transport of molecules out of the cell (B) Signup and view all the answers

What is the function of the constitutive pathway of exocytosis?

Continuously delivering substances to the plasma membrane (A) Signup and view all the answers

Where are newly synthesized proteins initially delivered to after post-translational modification?

COP-II coated vesicles (C) Signup and view all the answers

What is the function of COP-II coated vesicles?

Transport of newly synthesized proteins to the Golgi apparatus (D) Signup and view all the answers

What is the result of the fusion of a vesicle with a cytoplasmic organelle?

Release of molecules into the cytoplasm (B) Signup and view all the answers

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Study Notes

Vesicle Formation and Fusion

Lipid rafts with cargo receptors initiate vesicle formation
Clathrin coat assembly and adaptin complex formation occur, followed by budding of the fully assembled coated vesicle
The coated vesicle travels to its destination, where the clathrin coat is disassembled, and the vesicle is tethered to the target membrane by Rab-GTPase and tethering proteins
The docking process begins, involving the recruitment of tethering proteins and the formation of the cis-SNARE complex
Fusion of the vesicle with the target membrane occurs, discharging the cargo protein into the early endosomal compartment
v-SNAREs are recycled in the transport vesicles for use in another round of vesicle targeting

Endosomes and Lysosomes

Some endosomes communicate with the vesicular transport system of the rER, providing constant delivery of newly synthesized lysosomal enzymes (hydrolases)
Hydrolase synthesis occurs in the rER as an enzymatically inactive precursor (prohydrolase), which is then folded, glycosylated, and modified with a signal patch
The signal patch is recognized by M-6-P receptors, which are present in early and late endosomes, lysosomes, and the Golgi apparatus
The acidic environment of late endosomes causes the release of prohydrolases from the M-6-P receptors, which are then activated by cleavage and removal of phosphate groups

Early and Late Endosomes

Early endosomes are found in the peripheral cytoplasm and fuse with cytoplasmic organelles
Late endosomes are positioned near the Golgi apparatus and nucleus, and the acidic environment causes the release of prohydrolases

Exocytosis

Intracellular traffic of vesicles is achieved by the presence of specific proteins (COATOMERS) on their surface, such as COP-I, COP-II, and others
COP-II-coated vesicles deliver newly synthesized proteins to the Golgi apparatus
Retrograde transport occurs between Golgi cisternae, mediated by COP-I-coated vesicles
Two general pathways of exocytosis exist: constitutive and regulated pathways

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