Protein sorting and vesicle trafficking notes

Signal Peptide → Function?

A short amino acid sequence that directs the transport of a protein to its specific cellular destination.

True or False: All proteins are synthesized in the cytosol.

False. Some proteins are synthesized on ribosomes bound to the endoplasmic reticulum (ER) for secretion or membrane localization.

What directs proteins to the nucleus?

Nuclear localization signal (NLS) - a specific amino acid sequence recognized by transport proteins that facilitate passage through nuclear pores.

Compare constitutive and regulated secretion.

Constitutive secretion occurs continuously and unregulated. Regulated secretion occurs in response to specific signals, often involving stored vesicles.

What are chaperone proteins?

Proteins that assist in the correct folding and assembly of other proteins, preventing misfolding or aggregation.

Fill in the blank: The _____ mediates transport of proteins between organelles.

endoplasmic reticulum (ER)

What is receptor-mediated endocytosis?

A process where cells internalize molecules by the binding of these molecules to specific receptors, followed by membrane invagination.

Sorting Signals → Examples?

- Signal peptides - Lysosomal targeting signals - Golgi retention signals

What is the role of the Golgi apparatus?

To modify, sort, and package proteins received from the ER for delivery to their final destinations.

True or False: Proteins do not need signals for proper sorting.

False. Proteins require specific sorting signals to ensure they reach their correct cellular locations.

Cause → Effect: What happens without a signal peptide?

Proteins remain in the cytosol and do not reach their intended organelle, leading to functional deficiencies.

What is the function of the translocon?

A protein complex in the ER membrane that facilitates the translocation of nascent polypeptides into the ER lumen.

Compare soluble and membrane proteins.

Soluble proteins are secreted or localized in the cytosol, while membrane proteins are embedded in cellular membranes.

What role do vesicles play?

Vesicles transport proteins between different organelles, ensuring they reach their destinations for proper function.

Fill in the blank: Proteins destined for lysosomes require a _____ signal.

mannose-6-phosphate

What is the significance of post-translational modifications?

These modifications, such as phosphorylation or glycosylation, can influence protein sorting, stability, and activity within the cell.

Vesicle budding

The process where a vesicle forms from a membrane, driven by coat proteins and cytoskeletal elements.

Function of COPI

COPI coats vesicles involved in retrograde transport from the Golgi to the ER. - Recycles proteins - Maintains Golgi structure

True or False: Clathrin is involved in endocytosis.

True. Clathrin coats vesicles that transport materials into the cell through endocytosis.

Vesicle fusion mechanism

Involves SNARE proteins that promote vesicle and target membrane merging, allowing content release.

Role of Rabs in vesicle trafficking

Rabs are small GTPases that act as molecular markers for vesicles, ensuring correct targeting and fusion.

Question: What initiates vesicle formation?

A membrane curvature induced by coat proteins and the recruitment of cargo molecules.

Comparison: COPII vs COPI

COPII facilitates anterograde transport to the Golgi, while COPI handles retrograde transport to the ER.

Fill in the blank: SNARE proteins facilitate __________.

membrane fusion during vesicle trafficking.

Endocytosis vs Exocytosis

Endocytosis involves vesicles bringing substances into the cell; exocytosis is the opposite, exporting materials out.

Vesicle transport speed

Transport speeds vary; for example, axonal transport can reach up to 400 mm/day.

Role of the Golgi apparatus

The Golgi modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.

Bidirectional transport in neurons

Neurons utilize both anterograde and retrograde transport to maintain communication and cellular health.

Mechanism of receptor-mediated endocytosis

Specific receptors bind to ligands, triggering vesicle formation and internalization of the complex.

Function of clathrin-coated vesicles

These vesicles transport proteins and lipids from the plasma membrane to endosomes.

Question: What is the role of Arf proteins?

Arf proteins regulate vesicle formation and coat assembly for Golgi-derived vesicles.

Cause → Effect: Rab protein activation

Rab activation causes vesicle tethering and fusion with the target membrane, ensuring accurate delivery.