MODULE 16

Questions and Answers

What is a key step that distinguishes regulated exocytosis from constitutive exocytosis?

Bud formation from the trans-Golgi network (TGN)

Trafficking of vesicles to the plasma membrane

Vesicle fusion with the plasma membrane

Storage of molecules in vesicles until a signal is received (correct)

Which proteins are required for the formation of trans-SNARE complexes during vesicle fusion?

Natural killer cells and cytotoxic T cells

v-SNAREs and t-SNAREs (correct)

Rab GTPases and coat proteins

Perforin and granzymes

What initiates the degranulation process in granulocytes and mast cells?

Specific cargo collection by coated vesicles

Signal reception for regulated exocytosis

Ca²⁺ influx triggered by an action potential

Vesicle fusion with the plasma membrane (correct)

Which small GTPases are involved in the regulation of vesicle formation from the donor membrane?

Sar1 and Rab Signup and view all the answers

In polarized cells, what determines the selective delivery of molecules from the TGN to the plasma membrane?

The molecular composition of the plasma membrane domains Signup and view all the answers

What process involves bringing molecules and other substances into the cell?

Endocytosis Signup and view all the answers

Which of the following is NOT a step in the process of constitutive exocytosis?

Priming Signup and view all the answers

What type of vesicles mediates transport between the Golgi and plasma membrane?

Clathrin-coated vesicles Signup and view all the answers

What is a key feature of regulated exocytosis compared to constitutive exocytosis?

It involves a priming step. Signup and view all the answers

What initiates the recruitment of coat proteins to membranes for vesicle budding?

ARF1/SAR1 small GTPases Signup and view all the answers

What defines a polyprotein in the context of secretory vesicles?

A protein containing multiple amino acid sequences Signup and view all the answers

What is the primary role of adaptor proteins in the formation of coated vesicles?

To recognize cargo molecules Signup and view all the answers

In which part of the cell does the proteolysis of inactive precursors begin?

Trans-Golgi Network Signup and view all the answers

What role do ADP-ribosylation factor (ARF) GTPases play in vesicle transport?

Recruit coat proteins and lipid-modifying enzymes Signup and view all the answers

Which proteins are responsible for the interaction during the fusion of vesicles with target membranes?

SNAREs Signup and view all the answers

What is the primary function of dynamin during vesicle formation?

To assemble a ring that pinches off vesicles Signup and view all the answers

How are transport vesicles guided to their target membranes?

Through surface markers and SNARE interactions Signup and view all the answers

What happens to the coat of a vesicle after it is released from the donor membrane?

It is lost due to an uncoating ATPase Signup and view all the answers

What defines the polarized sorting of proteins in epithelial cells?

Signals recognized by coat proteins for specific membrane domains Signup and view all the answers

What initiates the fusion of secretory vesicles with target membranes?

A chemical messenger leading to intracellular signals Signup and view all the answers

Which feature distinguishes apical plasma membranes in polarized epithelial cells?

High levels of GPI-anchored proteins and glycosphingolipids Signup and view all the answers

What is the primary distinction in the function of exocytosis compared to endocytosis?

Exocytosis involves the release of molecules from the cell. Signup and view all the answers

Which step is unique to regulated exocytosis and not part of constitutive exocytosis?

Priming Signup and view all the answers

What is the role of coat proteins in vesicle formation?

They recognize cargo molecules and shape the membranes into buds. Signup and view all the answers

Which type of coat is specifically associated with retrograde transport between the ER and Golgi?

COPI-coated vesicles Signup and view all the answers

What is the initial destination of soluble proteins from the Golgi in unpolarized cells if they are not retained in the ER or Golgi?

Cell surface Signup and view all the answers

How do transport vesicles travel to the cell membrane?

On microtubules Signup and view all the answers

What triggers the release of vesicle contents into the extracellular space during exocytosis?

Cytosolic calcium ion influx Signup and view all the answers

What is the method by which vesicles bud off from the plasma membrane?

Dynamin ring formation Signup and view all the answers

What happens to the coat of a coated vesicle once it is formed and released?

It disassembles and is released into the cytosol. Signup and view all the answers

Which of the following best describes a polyprotein in the context of secretory vesicles?

A precursor synthesized as multiple copies of the same amino acid sequence. Signup and view all the answers

What triggers the release of cargo from secretory vesicles during exocytosis?

Ca²⁺ binding to sensors Signup and view all the answers

Which additional step is involved in regulated exocytosis compared to constitutive exocytosis?

Priming Signup and view all the answers

In polarized cells, what does the transport from the TGN selectively deliver?

Different sets of molecules to different membrane domains Signup and view all the answers

What type of cells utilize directed exocytosis to release perforin and granzymes?

Cytotoxic T cells and natural killer cells Signup and view all the answers

Which GTPase is involved in the docking and tethering process of vesicles?

Rab Signup and view all the answers

What regulates the formation of coated vesicles during vesicle budding?

Small GTPases Signup and view all the answers

What is the main purpose of degranulation in granulocytes and mast cells?

To release antimicrobial molecules Signup and view all the answers

What does the vesicle 'coat' do during vesicle budding?

Helps collect specific cargo Signup and view all the answers

What role do v-SNAREs and t-SNAREs play in vesicle transport?

They form trans-SNARE complexes for fusion Signup and view all the answers

What is a key characteristic of regulated exocytosis?

Storage of molecules until a signal is received Signup and view all the answers

What role do small GTPases such as ARF and Sar1 play in vesicle transport?

They regulate the recruitment of coat proteins and transport direction. Signup and view all the answers

Which component is responsible for the final pinching-off of a budding vesicle?

Dynamin Signup and view all the answers

What is the importance of SNARE proteins in the vesicular transport process?

They mediate the fusion of vesicles with target membranes. Signup and view all the answers

How do vesicles identify their target membranes during transport?

Via surface markers and receptor interactions. Signup and view all the answers

Which type of membrane proteins are enriched in the apical plasma membrane of polarized epithelial cells?

Glycosphingolipids and GPI-anchored proteins Signup and view all the answers

What signals the regulated exocytosis process in secretory vesicles?

The presence of specific hormone levels. Signup and view all the answers

Which type of vesicle is involved in the transport from the Golgi to the endoplasmic reticulum?

COPI vesicles Signup and view all the answers

What triggers the loss of the clathrin coat from a vesicle?

Action of uncoating ATPases. Signup and view all the answers

What describes the role of Rab GTPases in vesicular transport?

They aid in the tethering and docking of vesicles. Signup and view all the answers

What happens to the water molecules during the fusion of vesicles?

They are expelled, allowing membranes to merge. Signup and view all the answers

What is the primary function of Sar1 in vesicle transport?

Regulates anterograde transport of proteins from the ER Signup and view all the answers

Which type of proteins are responsible for recognizing sorting signals in polarized epithelial cells?

Coat proteins Signup and view all the answers

What mechanism allows for the fusion of vesicles with their target membranes?

SNARE proteins form trans-SNARE complexes Signup and view all the answers

Which enzyme is primarily responsible for the removal of the coat from vesicles after they bud off?

Uncoating ATPase Signup and view all the answers

Which process is triggered by a chemical messenger leading to the release of secretory vesicle cargo?

Regulated exocytosis Signup and view all the answers

What type of membrane proteins are primarily associated with lipid rafts in the apical plasma membrane?

GPI-anchored proteins Signup and view all the answers

Which GTPase is specifically involved in recruiting coat proteins during vesicle formation?

ARF GTPase Signup and view all the answers

During which stage of vesicle transport do microtubules facilitate movement towards target membranes?

Transport Signup and view all the answers

What role does dynamin play in the process of vesicle budding?

Pinches off the budding vesicle Signup and view all the answers

What is the significance of Rab effectors in vesicular transport?

They enable the targeting of vesicles to specific membranes Signup and view all the answers

How does Ca²⁺ play a role in the exocytosis process?

It facilitates vesicle fusion with the plasma membrane. Signup and view all the answers

What step is specific to regulated exocytosis that is not found in constitutive exocytosis?

Priming of molecules in vesicles. Signup and view all the answers

What is the function of Rab GTPases in vesicle transport?

They bind to specific effectors for docking and tethering. Signup and view all the answers

In polarized cells, how is the delivery of molecules from the TGN to the plasma membrane characterized?

Selective delivery to different membrane domains. Signup and view all the answers

What is the primary mechanism by which cytotoxic T cells kill infected cells?

Degranulation of antimicrobial substances. Signup and view all the answers

What is the main function of exocytosis in cellular processes?

Releasing molecules from the cell Signup and view all the answers

What initiates the fusion of secretory vesicles with their target membranes?

Binding of v-SNAREs and t-SNAREs. Signup and view all the answers

What outcome results from the priming step in regulated exocytosis?

Molecules are stored until an activation signal is received. Signup and view all the answers

Which of the following defines the 'priming' step in regulated exocytosis?

Preparation of the vesicle for immediate release Signup and view all the answers

What is the role of coat proteins in the vesicle budding process?

They help collect specific cargo for vesicle formation. Signup and view all the answers

What role do coat proteins play in the processes of vesicle budding?

They recognize and select cargo molecules. Signup and view all the answers

What describes the type of exocytosis that occurs in a continuous manner regardless of external signals?

Constitutive exocytosis. Signup and view all the answers

Which type of vesicle is specifically involved in the retrograde transport between the ER and Golgi?

COPI-coated vesicles Signup and view all the answers

In what order do the steps of exocytosis occur?

Trafficking, tethering, docking, priming, fusion Signup and view all the answers

Which molecules are commonly released by degranulation in immune cells?

Antimicrobial peptides and cytotoxic granules. Signup and view all the answers

What happens to the coat proteins after vesicle budding?

They are recycled back to the donor membrane. Signup and view all the answers

Which component is NOT typically involved in the formation of secretory vesicles?

Cytosolic ribosomes Signup and view all the answers

What is the purpose of the 'tethering' step in the exocytosis process?

To secure the vesicle in proximity to the membrane Signup and view all the answers

What distinguishes soluble proteins in unpolarized cells from those in polarized cells regarding their destination?

Unpolarized cells transport soluble proteins directly to the cell surface. Signup and view all the answers

Which class of proteins is primarily responsible for recruiting coat proteins during vesicle formation?

Arf1/Sar1 small GTPases Signup and view all the answers

Study Notes

Exocytosis vs. Endocytosis

Endocytosis facilitates the intake of molecules into cells, with vesicles budding from the plasma membrane.
Exocytosis involves the expulsion of molecules from cells through the fusion of vesicles with the plasma membrane.

Introduction to Exocytosis

Exocytosis transports molecules out of the cell by fusing vesicles, originating from intracellular organelles, with the plasma membrane.
Proteins travel from the trans-Golgi network (TGN) to either lysosomes, secretory vesicles, or directly to the cell surface.
Two pathways exist: constitutive pathway (continuous secretion) and regulated pathway (in specialized cells).

Steps of Exocytosis

Four steps for constitutive exocytosis; five for regulated exocytosis including:
- Trafficking: Vesicle transport on microtubules.
- Tethering: Initial contact between the vesicle and cell membrane.
- Docking: Attachment of vesicle to cell membrane.
- Priming: Unique to regulated exocytosis, preparing vesicle for fusion.
- Fusion: Complete merging of vesicle and cell membranes releasing contents.

Coated Vesicles

Vesicle budding is driven by protein coats that cycle on and off membranes.
Coats contain adaptor proteins for cargo recognition and cage proteins that form a lattice to gather complexes.
Coat proteins, such as clathrin, COPI, and COPII, facilitate transport between the Golgi, ER, and plasma membrane.

Formation of Secretory Vesicles

Hormones and enzymes often start as inactive precursors that are activated by proteolysis within vesicles.
Pre-pro-proteins have an ER signal peptide that is cleaved during synthesis in the rER.
Signaling molecules can consist of multiple copies of an amino acid sequence forming polyproteins.

Sorting Signals

In polarized epithelial cells, proteins are sorted in the TGN for specific plasma membrane domains.
Basolateral membrane proteins have unique signals recognized by coat proteins; apical membranes contain glycosphingolipids and GPI-anchored proteins.

Coat Assembly GTPases

ARF and Sar1 are small GTPases that recruit coat proteins and regulate vesicular transport.
Sar1 is crucial for COPII vesicle-mediated transport from ER to Golgi.
ARF1 plays a role in COPI-mediated transport back to the ER and in clathrin recruitment.

Pinching-off and Uncoating

Dynamin assembles into a ring around the neck of budding vesicles, facilitating membrane destabilization.
The clathrin coat is removed after vesicle release, aided by an uncoating ATPase.

Transport, Tethering, Docking

Vesicle movement is powered by kinesin/dynein and myosin motors.
Surface markers on vesicles allow recognition by target membranes, regulated by SNAREs and Rab GTPases.
Rab effectors mediate the tethering and docking process at target membranes.

Fusion

Docking allows proteins on both membrane bilayers to interact.
Successful fusion displaces water from the membrane surfaces, enabling merging.
Trans-SNARE complexes form when v-SNAREs and t-SNAREs interact, pulling membranes together and facilitating fusion.

Release of Secretory Vesicle Cargo

In regulated exocytosis, secretory vesicles require priming before cargo release, triggered by specific signals like hormonal influx.
At nerve terminals, action potentials cause Ca²⁺ influx, initiating vesicle fusion and content release.

Overview of Exocytosis

Exocytosis can be constitutive or regulated, with secretory proteins evolving during vesicle maturation.
Requires a sequence of steps: trafficking, tethering, docking, fusion, and, in regulated cases, priming.
Polarized cells ensure selective transport to specific plasma membrane domains, utilizing small GTPases for regulation.

Mechanisms to Kill Cancer Cells

Degranulation enables the release of cytotoxic molecules from secretory vesicles in immune cells.
Used by granulocytes, mast cells, natural killer (NK) cells, and cytotoxic T cells to eliminate pathogens and cancer cells.
Directed exocytosis facilitates the release of perforin and granzymes critical for targeting and destroying infected or cancerous cells.

Exocytosis vs. Endocytosis

Endocytosis facilitates the intake of molecules into cells, with vesicles budding from the plasma membrane.
Exocytosis involves the expulsion of molecules from cells through the fusion of vesicles with the plasma membrane.

Introduction to Exocytosis

Exocytosis transports molecules out of the cell by fusing vesicles, originating from intracellular organelles, with the plasma membrane.
Proteins travel from the trans-Golgi network (TGN) to either lysosomes, secretory vesicles, or directly to the cell surface.
Two pathways exist: constitutive pathway (continuous secretion) and regulated pathway (in specialized cells).

Steps of Exocytosis

Four steps for constitutive exocytosis; five for regulated exocytosis including:
- Trafficking: Vesicle transport on microtubules.
- Tethering: Initial contact between the vesicle and cell membrane.
- Docking: Attachment of vesicle to cell membrane.
- Priming: Unique to regulated exocytosis, preparing vesicle for fusion.
- Fusion: Complete merging of vesicle and cell membranes releasing contents.

Coated Vesicles

Vesicle budding is driven by protein coats that cycle on and off membranes.
Coats contain adaptor proteins for cargo recognition and cage proteins that form a lattice to gather complexes.
Coat proteins, such as clathrin, COPI, and COPII, facilitate transport between the Golgi, ER, and plasma membrane.

Formation of Secretory Vesicles

Hormones and enzymes often start as inactive precursors that are activated by proteolysis within vesicles.
Pre-pro-proteins have an ER signal peptide that is cleaved during synthesis in the rER.
Signaling molecules can consist of multiple copies of an amino acid sequence forming polyproteins.

Sorting Signals

In polarized epithelial cells, proteins are sorted in the TGN for specific plasma membrane domains.
Basolateral membrane proteins have unique signals recognized by coat proteins; apical membranes contain glycosphingolipids and GPI-anchored proteins.

Coat Assembly GTPases

ARF and Sar1 are small GTPases that recruit coat proteins and regulate vesicular transport.
Sar1 is crucial for COPII vesicle-mediated transport from ER to Golgi.
ARF1 plays a role in COPI-mediated transport back to the ER and in clathrin recruitment.

Pinching-off and Uncoating

Dynamin assembles into a ring around the neck of budding vesicles, facilitating membrane destabilization.
The clathrin coat is removed after vesicle release, aided by an uncoating ATPase.

Transport, Tethering, Docking

Vesicle movement is powered by kinesin/dynein and myosin motors.
Surface markers on vesicles allow recognition by target membranes, regulated by SNAREs and Rab GTPases.
Rab effectors mediate the tethering and docking process at target membranes.

Fusion

Docking allows proteins on both membrane bilayers to interact.
Successful fusion displaces water from the membrane surfaces, enabling merging.
Trans-SNARE complexes form when v-SNAREs and t-SNAREs interact, pulling membranes together and facilitating fusion.

Release of Secretory Vesicle Cargo

In regulated exocytosis, secretory vesicles require priming before cargo release, triggered by specific signals like hormonal influx.
At nerve terminals, action potentials cause Ca²⁺ influx, initiating vesicle fusion and content release.

Overview of Exocytosis

Exocytosis can be constitutive or regulated, with secretory proteins evolving during vesicle maturation.
Requires a sequence of steps: trafficking, tethering, docking, fusion, and, in regulated cases, priming.
Polarized cells ensure selective transport to specific plasma membrane domains, utilizing small GTPases for regulation.

Mechanisms to Kill Cancer Cells

Degranulation enables the release of cytotoxic molecules from secretory vesicles in immune cells.
Used by granulocytes, mast cells, natural killer (NK) cells, and cytotoxic T cells to eliminate pathogens and cancer cells.
Directed exocytosis facilitates the release of perforin and granzymes critical for targeting and destroying infected or cancerous cells.

Exocytosis vs. Endocytosis

Endocytosis facilitates the intake of molecules into cells, with vesicles budding from the plasma membrane.
Exocytosis involves the expulsion of molecules from cells through the fusion of vesicles with the plasma membrane.

Introduction to Exocytosis

Exocytosis transports molecules out of the cell by fusing vesicles, originating from intracellular organelles, with the plasma membrane.
Proteins travel from the trans-Golgi network (TGN) to either lysosomes, secretory vesicles, or directly to the cell surface.
Two pathways exist: constitutive pathway (continuous secretion) and regulated pathway (in specialized cells).

Steps of Exocytosis

Four steps for constitutive exocytosis; five for regulated exocytosis including:
- Trafficking: Vesicle transport on microtubules.
- Tethering: Initial contact between the vesicle and cell membrane.
- Docking: Attachment of vesicle to cell membrane.
- Priming: Unique to regulated exocytosis, preparing vesicle for fusion.
- Fusion: Complete merging of vesicle and cell membranes releasing contents.

Coated Vesicles

Vesicle budding is driven by protein coats that cycle on and off membranes.
Coats contain adaptor proteins for cargo recognition and cage proteins that form a lattice to gather complexes.
Coat proteins, such as clathrin, COPI, and COPII, facilitate transport between the Golgi, ER, and plasma membrane.

Formation of Secretory Vesicles

Hormones and enzymes often start as inactive precursors that are activated by proteolysis within vesicles.
Pre-pro-proteins have an ER signal peptide that is cleaved during synthesis in the rER.
Signaling molecules can consist of multiple copies of an amino acid sequence forming polyproteins.

Sorting Signals

In polarized epithelial cells, proteins are sorted in the TGN for specific plasma membrane domains.
Basolateral membrane proteins have unique signals recognized by coat proteins; apical membranes contain glycosphingolipids and GPI-anchored proteins.

Coat Assembly GTPases

ARF and Sar1 are small GTPases that recruit coat proteins and regulate vesicular transport.
Sar1 is crucial for COPII vesicle-mediated transport from ER to Golgi.
ARF1 plays a role in COPI-mediated transport back to the ER and in clathrin recruitment.

Pinching-off and Uncoating

Dynamin assembles into a ring around the neck of budding vesicles, facilitating membrane destabilization.
The clathrin coat is removed after vesicle release, aided by an uncoating ATPase.

Transport, Tethering, Docking

Vesicle movement is powered by kinesin/dynein and myosin motors.
Surface markers on vesicles allow recognition by target membranes, regulated by SNAREs and Rab GTPases.
Rab effectors mediate the tethering and docking process at target membranes.

Fusion

Docking allows proteins on both membrane bilayers to interact.
Successful fusion displaces water from the membrane surfaces, enabling merging.
Trans-SNARE complexes form when v-SNAREs and t-SNAREs interact, pulling membranes together and facilitating fusion.

Release of Secretory Vesicle Cargo

In regulated exocytosis, secretory vesicles require priming before cargo release, triggered by specific signals like hormonal influx.
At nerve terminals, action potentials cause Ca²⁺ influx, initiating vesicle fusion and content release.

Overview of Exocytosis

Exocytosis can be constitutive or regulated, with secretory proteins evolving during vesicle maturation.
Requires a sequence of steps: trafficking, tethering, docking, fusion, and, in regulated cases, priming.
Polarized cells ensure selective transport to specific plasma membrane domains, utilizing small GTPases for regulation.

Mechanisms to Kill Cancer Cells

Degranulation enables the release of cytotoxic molecules from secretory vesicles in immune cells.
Used by granulocytes, mast cells, natural killer (NK) cells, and cytotoxic T cells to eliminate pathogens and cancer cells.
Directed exocytosis facilitates the release of perforin and granzymes critical for targeting and destroying infected or cancerous cells.

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Description

Explore the mechanisms of exocytosis and endocytosis in this quiz from Module 16. Understand how these processes function in transporting molecules in and out of cells, including the role of vesicles and proteins involved. Test your knowledge on these essential cellular activities.