Vesicular Transport Overview
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Questions and Answers

What is the initial step in the formation of nanodomains for membrane identity?

  • Fusion of vesicles from the plasma membrane
  • Conversion of phosphatidylinositol to P3P
  • Rab-GTP binding with SNARE
  • Activation of Rab by GEF (correct)

How does the identity of early endosomes change as they mature?

  • By losing Rab 7 and acquiring Rab 5
  • By maintaining a consistent PIP level
  • By losing Rab 5 and acquiring Rab 7 (correct)
  • By increasing the number of SNARE proteins

What role does Rab-GTP play in the process described?

  • It promotes the action of endocytosis
  • It binds to motor proteins to transport vesicles (correct)
  • It is a cargo selection factor
  • It activates liposomes for fusion

What is the function of COPII in vesicle transport?

<p>To cover vesicles with a double coat and select cargo (D)</p> Signup and view all the answers

Which protein complex is crucial for the fusion of vesicles with membranes?

<p>PIPs and SNAREs (D)</p> Signup and view all the answers

What characterizes the late endosome in terms of Rab identity?

<p>It becomes positive for Rab 7 (B)</p> Signup and view all the answers

What event initiates the cascade for the formation of microdomains?

<p>The activation of Rab by GEF (B)</p> Signup and view all the answers

What is an outcome of the activation of Rab 5?

<p>Activates effectors necessary for early endosome function (A)</p> Signup and view all the answers

What is the primary role of the pump found in lysosomes?

<p>To import protons into the lysosome (D)</p> Signup and view all the answers

Which characteristic distinguishes regulated exocytosis from constitutive exocytosis?

<p>Regulated exocytosis requires a specific stimulus for vesicle fusion (C)</p> Signup and view all the answers

What is a necessary condition for calcium-dependent synaptic transmission?

<p>Depolarization of the membrane leading to calcium release (A)</p> Signup and view all the answers

In what scenario do vesicles need to fuse to increase the plasma membrane surface?

<p>During cell division to accommodate new cells (B)</p> Signup and view all the answers

What role do SNARE proteins play in exocytosis?

<p>They help attract vesicles to the target membrane for fusion (B)</p> Signup and view all the answers

What happens to calcium ions during membrane depolarization?

<p>They are released from storage compartments like the ER (B)</p> Signup and view all the answers

What is a key function of the actin-myosin cytoskeleton ring during cell division?

<p>To create tension for constriction that increases membrane surface (C)</p> Signup and view all the answers

Why is the pH of the endosome not as acidic as that of the lysosome?

<p>The endosome has a neutral pH of 6.5 (A)</p> Signup and view all the answers

What is the primary role of transcytosis in polarized cells?

<p>To maintain the specific distribution of proteins in different cell membrane domains. (D)</p> Signup and view all the answers

What initiates the process of vesicle fusion when there is a membrane break?

<p>Calcium-dependent fusion events involving lysosomes. (D)</p> Signup and view all the answers

Which of the following correctly describes the progression of early endosomes?

<p>They mature into multi-vesicular bodies before becoming late endosomes. (A)</p> Signup and view all the answers

What is the significance of the coat on vesicular membranes?

<p>It helps in the regulation of vesicular trafficking. (A)</p> Signup and view all the answers

During cellularisation, what happens to the membrane surface?

<p>The membrane surface increases to aid in wound repair. (A)</p> Signup and view all the answers

What role does GDI play in relation to GTPases?

<p>It helps maintain GTPases in inactive GDP state. (B)</p> Signup and view all the answers

Which of the following statements about Rab proteins is true?

<p>Different Rab proteins are localized to specific organelles. (A)</p> Signup and view all the answers

Which protein is primarily responsible for the transport of lysosomal enzymes from the Golgi to the lysosome?

<p>Clathrin (C)</p> Signup and view all the answers

What is the primary function of Ras molecules in cells?

<p>They regulate cell growth and gene transcription. (B)</p> Signup and view all the answers

What is the role of receptors in the context of membrane transport?

<p>To facilitate the internalization of specific ligands (C)</p> Signup and view all the answers

Which protein facilitates the conversion of GDP to GTP?

<p>GEF (B)</p> Signup and view all the answers

What function does dynamin serve in the vesicle formation process?

<p>It cuts the membrane for vesicle formation (D)</p> Signup and view all the answers

The triskelion structure is formed by which protein?

<p>Clathrin (A)</p> Signup and view all the answers

Which GTPase is known to converge on mTORC signaling?

<p>Rheb (B)</p> Signup and view all the answers

What is the primary role of SNARE proteins?

<p>To mediate membrane fusion. (C)</p> Signup and view all the answers

Which protein interacts with the actin during the endocytosis process?

<p>Light chain of clathrin (D)</p> Signup and view all the answers

What is the purpose of uncoating vesicles after formation?

<p>To expose cargo for fusion with target membranes (C)</p> Signup and view all the answers

Which of the following GTPases is not membrane-bound?

<p>Run (D)</p> Signup and view all the answers

What type of regulation is facilitated by coating proteins during endocytosis?

<p>Cargo selection and membrane deformation (A)</p> Signup and view all the answers

What characterizes the interaction between vSNARE and tSNARE?

<p>They recognize each other and bring membranes together. (A)</p> Signup and view all the answers

How do clathrin and adaptor protein AP2 collaborate during endocytosis?

<p>AP2 assists clathrin in cargo selection and membrane deformation (B)</p> Signup and view all the answers

What is the primary purpose of N-glycosylation in proteins?

<p>To act as a marker for the correct folding of the protein. (A)</p> Signup and view all the answers

Which modification occurs first in the process of glycosylation in the endoplasmic reticulum?

<p>Mannose-6-phosphate attachment. (D)</p> Signup and view all the answers

What indicates that a protein is still in the earlier stages of the Golgi apparatus?

<p>The protein is Endo H sensitive. (D)</p> Signup and view all the answers

During the glycosylation process, what happens to mannose and N-acetylglucosamine levels?

<p>Mannose is completely removed while N-acetylglucosamine is added. (D)</p> Signup and view all the answers

What type of bond is involved in O-glycosylation?

<p>A covalent bond with an exposed oxygen atom. (A)</p> Signup and view all the answers

What is the significance of using Endo H in experiments related to glycosylation?

<p>It helps distinguish between mature and immature glycoproteins. (B)</p> Signup and view all the answers

What process allows proteins to be directed either to lysosomes or the plasma membrane?

<p>Exocytosis with modifications in the Golgi. (D)</p> Signup and view all the answers

Which of the following best describes a characteristic of a protein that is Endo H insensitive?

<p>It indicates a higher maturity with more sialic acid. (B)</p> Signup and view all the answers

Flashcards

Rab GTPases

GTPases involved in membrane trafficking, defining membrane identity.

SNARE proteins

Proteins that facilitate membrane fusion by bringing membranes close together.

GTP and GDP

Nucleotides involved in energy transfer and signaling, converted by GAP and GEF.

GAP and GEF

Proteins that promote the exchange of GDP for GTP and vice versa.

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Ras superfamily

A group of GTPases, including Ras and Rab, critical for cellular functions.

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mTORC

A signaling complex impacted by Rheb, regulating cell growth and metabolism.

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Rho GTPases

Small GTPases that assist in cytoskeleton modification and cell shape.

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GDI protein

Protein that binds GDP-bound GTPases to keep them inactive in the cytosol.

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N-glycosylation

A type of glycosylation that attaches carbohydrates to asparagine residues in proteins, aiding in protein folding.

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O-glycosylation

A type of glycosylation where carbohydrates attach to the oxygen of another amino acid's lateral chain.

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Mannose-6-phosphate

A marker added to proteins in the ER that indicates they are lysosomal enzymes.

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Post-translational modification

Chemical changes made to proteins after translation, such as glycosylation events in the Golgi.

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Endo H sensitivity

Ability of a protein to be recognized by Endo H, indicating a high mannose content and early Golgi stage.

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Sialic acid

A carbohydrate added to proteins during the later maturation stages in the Golgi, indicating reduced mannose.

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Western blot analysis

A technique used to detect specific proteins, often assessing glycosylation status by its sensitivity to Endo H.

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Lysosomal enzymes

Proteins destined for the lysosome that undergo specific glycosylation in the Golgi for sorting.

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Lysosome acidity

Lysosomes are acidic due to ATP-dependent proton pumps that concentrate protons inside.

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Endosome pH

Endosomes have a pH less acidic than lysosomes, at around 6.5—closer to neutral than cytosol.

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Regulated exocytosis

Exocytosis can be regulated by stimuli or occur constitutively without stimulus.

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Synaptic transmission

A type of regulated exocytosis involving calcium-dependent fusion of synaptic vesicles with the membrane.

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Calcium dependency

Fusion of synaptic vesicles requires calcium, which is released during membrane depolarization.

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Membrane surface increase

Exocytosis can expand plasma membrane surface, crucial during cell division and phagocytosis.

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Phagocytosis

A process where vesicles fuse to the membrane to engulf pathogens and increase membrane surface.

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Transcytosis

A specialized form of exocytosis in polarized cells that allows the transport of substances from one membrane domain to another.

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Endocytosis

The process of internalizing materials from the plasma membrane into the cell.

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Exocytosis

The process by which cells expel materials through vesicles fusing with the plasma membrane.

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Vesicular trafficking

The regulated movement of vesicles that transport proteins and lipids within the cell.

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Endo-lysosomal trafficking

The process by which vesicles mature and fuse to form endosomes and lysosomes, facilitating cellular waste management.

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Nanodomains

Microdomains formed in membranes composed of PIP, SNARE, and Rab proteins.

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Rab Activation

The process where Rab is activated by a GEF and converted to GTP for signaling.

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GTP

The active form of Rab after being activated, necessary for its function.

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PIP

Phosphatidylinositol phosphates that play a role in cell signaling and membrane identity.

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Early Endosome

An initial vesicle formed by endocytosis, which can mature into late endosomes.

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Rab 5 to Rab 7 Transition

The switch where early endosomes lose Rab 5 identity and gain Rab 7 identity.

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COPII

A double coat protein complex that packages proteins for transport from the ER to Golgi.

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Coating Proteins

Proteins that help shape vesicles and select cargo for transport.

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Clathrin

A protein that coats vesicles and helps in their formation and cargo selection.

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Adaptor Protein (AP2)

Protein that assists Clathrin in cargo selection and membrane deformation.

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Dynamin

Protein required to cut the membrane and form vesicles.

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Uncoating of Vesicles

The process where vesicles lose their coating to reveal cargo once inside the cell.

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Study Notes

Vesicular Transport

  • Vesicular transport moves materials between topologically similar compartments, including from the plasma membrane in and out of the cell.
  • Topologically similar compartments are compatible for fusion during vesicle trafficking. Transport is regulated and directional.
  • Exocytic transport: Vesicles from the endoplasmic reticulum travel to the Golgi, then to the plasma membrane for release. Release requires a continuous stimulus for vesicle fusion. Exocytosis also occurs within the cell, from the trans-Golgi network to the early/late endosome and lysosomes.
  • Endocytic transport: Materials are ingested into endocytic vesicles from the plasma membrane and transported to the early endosome, then to multi-vesicular bodies, late endosome and lysosomes.
  • Retrieval transport: Recycles proteins and receptors via vesicles between the plasma membrane, early endosome, lysosome, and Golgi/ER.
  • Regulation: Vesicle trafficking is highly regulated; each vesicle has an identity (membrane coating) to target compartments. Phosphoinositides (PIPs), signal proteins, GTPs, and regulators of PI create nanodomains on the membrane for recognition. Vesicles move on cytoskeleton structures (microtubules). Proteins regulate and restore membrane identity during movement. Thousands of vesicles continuously move in cells.

Membrane Coating Proteins

  • Membrane coating proteins (COPI and COPII). COPI moves vesicles between Golgi cisternae; COPII moves vesicles from the ER to the Golgi.
  • Clathrin: Forms a triskelion structure, interacting with adaptor proteins (AP2), actin, and cargo to mediate endocytosis. Clathrin is important for clathrin dependent endocytosis and lysosome transport.
  • Coating protein formation and selection: Determines which cargo is transported.

Phosphoinositides (PIPs)

  • PIPs regulate membrane trafficking, modifying from PI to differing types.
  • PIP3 is a major signaling lipid in plasma membranes; regulates pathways downstream of tyrosine kinase receptors.
  • PI(4,5)P2 is important for endocytosis.

Vesicle Trafficking Regulators

  • GTPases (Rab, Arf, Ran, Miro): Proteins that regulate vesicle trafficking and interactions; involved in membrane identity.
  • Rab GTPases and SNARE proteins direct vesicles to their destinations.
  • Rab proteins specify membrane identity.

Transcytosis

  • Transport across cells, occurs in polarised cells with a barrier (tight junctions).
  • Materials may be transported from one side of the cell to the other via endocytosis and exocytosis events.

Membrane Fusion

  • Dynamin: Crucial in vesicle fission during endocytosis, and also constricts membrane resulting in vesicle budding.
  • SNARE proteins (t-SNARE, v-SNARE) mediate membrane fusion.

Endosomes and Lysosomes

  • Endosomes sort and direct materials.
  • Mannose-6-phosphate receptors target proteins to lysosomes.
  • Acidic pH of lysosomes aids in protein degradation.

Glycosylation

  • N-linked glycosylation, O-linked glycosylation
  • Glycosylation is critical for protein folding and targeting. Modification markers aid in protein transport.

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Molecular Cell Biology - Membrane Trafficking & Regulation PDF

Description

This quiz covers the concepts of vesicular transport, focusing on the movement of materials between compartments like the plasma membrane, Golgi, and lysosomes. It includes details on exocytic, endocytic, and retrieval transport processes, and highlights the regulation of vesicle trafficking. Test your understanding of these essential cellular mechanisms.

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