Vesicular Transport Pathways

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Questions and Answers

Which of the following best describes the central theme of vesicular transport?

  • The synthesis of ATP in the mitochondria.
  • The random movement of molecules within the cell.
  • The degradation of misfolded proteins in the endoplasmic reticulum.
  • The selective movement of molecules between different cellular compartments. (correct)

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

  • To remove the clathrin coat after vesicle formation.
  • To provide the mechanical force for vesicle budding.
  • To hydrolyze GTP and regulate the vesicle formation.
  • To select and bind specific cargo receptors for incorporation into the vesicle. (correct)

Sar1-GTP is essential for the formation of COPII-coated vesicles. What is the direct role of guanine nucleotide exchange factor (GEF) in this process?

  • GEF recruits cargo molecules into the forming vesicle.
  • GEF stimulates the GTPase activity of Sar1, leading to coat disassembly.
  • GEF directly binds to the ER membrane to initiate vesicle budding.
  • GEF facilitates the exchange of GDP for GTP on Sar1, activating it. (correct)

What quality checkpoint is used to determine when proteins can exit the endoplasmic reticulum (ER)?

<p>Proper folding and assembly of proteins. (B)</p> Signup and view all the answers

Which of the following best describes the function of NSF in vesicular transport?

<p>NSF disassembles SNARE complexes after membrane fusion. (D)</p> Signup and view all the answers

How does botulinum toxin interrupt vesicular targeting?

<p>By cleaving SNARE proteins, preventing vesicle fusion. (A)</p> Signup and view all the answers

What is the key difference between homotypic and heterotypic membrane fusion?

<p>Homotypic fusion involves vesicles from the same cellular compartment, while heterotypic fusion involves vesicles from different compartments. (A)</p> Signup and view all the answers

What is the primary purpose of the KDEL sequence in ER-resident proteins?

<p>To signal retrieval of proteins from the Golgi back to the ER. (B)</p> Signup and view all the answers

In which cellular location is the Golgi apparatus typically observed?

<p>Close to the nucleus. (B)</p> Signup and view all the answers

What is the function of protein glycosylation?

<p>To assist in protein folding, stability, and cell-cell recognition. (C)</p> Signup and view all the answers

How do hydrolases, destined for the lysosome, reach their target compartment?

<p>They are modified with M6P in the Golgi and then transported. (B)</p> Signup and view all the answers

Which of the following best describes lysosomal storage diseases?

<p>A group of genetic disorders resulting from deficiencies in specific lysosomal enzymes. (D)</p> Signup and view all the answers

What is the role of LDL receptors in endocytosis?

<p>To bind LDL particles and initiate their uptake into the cell. (D)</p> Signup and view all the answers

What happens to endocytosed receptors after they are internalized?

<p>They are recycled back to the plasma membrane, degraded in lysosomes, or transcytosed. (A)</p> Signup and view all the answers

What must occur before exocytosis can proceed?

<p>The vesicles must be properly targeted and docked at the plasma membrane. (C)</p> Signup and view all the answers

How does a plant vacuole differ functionally from a lysosome in animal cells?

<p>Plant vacuoles regulate cell turgor pressure and store nutrients, while lysosomes degrade cellular waste. (C)</p> Signup and view all the answers

Which of the following best describes the role of dynamin GTPase in clathrin-mediated endocytosis?

<p>Dynamin polymerizes around the neck of the budding vesicle and mediates its fission from the membrane. (A)</p> Signup and view all the answers

What is the implication of homotypic fusion occurring between vesicles coming off the ER?

<p>It contributes to the formation of the ER network. (C)</p> Signup and view all the answers

Which of the following is an example of a disease that results from LDL receptor malfunction?

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

What is the role of GlcNAc phosphotransferase in the context of lysosomal hydrolase targeting?

<p>It adds a GlcNAc-phosphate group to mannose residues on lysosomal hydrolases in the Golgi. (B)</p> Signup and view all the answers

Flashcards

Vesicular Transport

Movement of molecules within a cell via membrane-bound vesicles.

Major Vesicular Transport Pathways

Endocytic, biosynthetic/secretory, and retrieval pathways.

Clathrin-Coated Vesicle

Vesicles coated with clathrin; involved in transport from the trans-Golgi network and plasma membrane to endosomes.

Clathrin Vesicle Components

Triskelion: structural unit, Adaptor proteins: link clathrin, Dynamin GTPase: pinches off vesicle, Hsp70, Auxilin.

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COPII-Coated Vesicle

Vesicles coated with COPII proteins; mediate transport from the ER to the Golgi.

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COPII Vesicle Components

Sar1, GEF, Sec23, Sec24, Sec13, and Sec31.

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Vesicle Targeting

Proteins are marked with specific signals that interact with receptors in the target compartment.

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Key Targeting Proteins

v-SNARE: vesicle, t-SNARE: target, Rabs: GTPases, tethering protein, and NSF.

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Homotypic Fusion

Membrane fusion between identical compartments.

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Heterotypic Fusion

Membrane fusion between different compartments.

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Protein Transport

ER to the Golgi and from the Golgi apparatus back to ER.

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Golgi Apparatus

Organelle with cis- and trans- faces, processes and sorts proteins.

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Protein Glycosylation

Addition of a sugar molecule to a protein.

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Types of Glycosylation

N-linked: Added to asparagine; O-linked: Added to serine or threonine.

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Lysosome and Vacuole

Organelle that degrades cellular waste; plant vacuole stores water and nutrients.

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Lysosomal Targeting

Mannose-6-phosphate (M6P) directs hydrolases to lysosomes.

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Lysosomal Storage Diseases

Genetic diseases from missing lysosomal enzymes causing accumulation of undigested material.

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Endocytosis

Cell membranes engulfing external materials.

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Types of Endocytosis

Pinocytosis, Phagocytosis, Receptor-mediated endocytosis

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Secretory Pathways

Constitutive and Regulated Secretory Pathways.

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Study Notes

  • Central theme of vesicular transport is moving materials in and out of cells

Major Pathways of Vesicular Transport

  • Vesicular transport involves 3 major pathways

Clathrin-Coated Vesicles

  • Donor and target compartments are needed in their description
  • Triskelion, adaptor proteins, and cargo receptors are needed in functional descriptions
  • Dynamin GTPase, PIP phosphatase, Hsp70, and auxillin are also needed in functional descriptions

COPII-Coated Vesicles

  • Donor and target compartments are needed in its description
  • Sar1, GEF, Sec23, Sec24, Sec13, and Sec31 are needed in functional descriptions
  • Quality check point to determine when proteins exit the ER

COPI-Coated Vesicles

  • Donor and target compartments are needed

Vesicle Targeting

  • Vesicles are marked so they get to the proper target compartment
  • v-SNARE, t-SNARE, Rabs, tethering protein, and NSF are needed in functional descriptions
  • Botulism toxin interrupts vesicular targeting

Membrane Fusion

  • Heterotypic and homotypic membrane fusion are defined
  • Process of homotypic membrane fusion with results from vesicles coming off the ER is described

Protein Transport

  • Describes how proteins go from the ER to the Golgi apparatus and from the Golgi apparatus back to ER
  • States the signal retrieval and name for this type of transport

Golgi Apparatus

  • The cis- and trans- faces are described
  • States the 4 target compartments where vesicles coming from the Golgi apparatus may go
  • States where the Golgi apparatus may be observed

Protein Processing in the Golgi Apparatus

  • The protein processing that can occur in the Golgi apparatus is described
  • N-linked oligosaccharides are defined and lists 2 classes of N-linked oligosaccharides that may be added to proteins
  • O-linked oligosaccharides are defined
  • Some functions of protein glycosylation are described

Lysosomes and Plant Vacuoles

  • Gives functional descriptions of a lysosome and a plant vacuole
  • How the necessary proteins for lysosome function arrive at the lysosome is described using a hydrolase as an example
  • Describes the signals involved and the functional descriptions of M6P and GlcNac phosphotransferase

Lysosomal Storage Diseases

  • Gives a general description of a lysosomal storage disease and specific information on what functional enzyme is lacking in the specified lysosomal storage diseases

Endocytosis

  • Lists and completely describes the three types of endocytosis
  • Includes in description the proteins and vesicles that are involved Use LDL reception, uptake, and receptor recycling as an example
  • Describes the disease that results from LDL receptor malfunction

Endocytosed Receptors

  • Describes the 3 fates of endocytosed receptors

Secretory Pathways

  • Describes the two secretory pathways and what must occur before exocytosis can occur

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